Accepted Again: Nick Voice's Testimony

Monday, February 23, 2009

Nick Voice's Testimony

This story will make you forget ALL your own troubles and wonder why we ever complain about anything..........that's what I thought after reading his story........

A TRULY AWESOME & Touching Testimony

My name is Nick Vujicic and I give God the Glory for how He has used my testimony to touch thousands of hearts around the world! I was born without limbs and doctors have no medical explanation for this birth "defect". As you can imagine, I was faced with many challenges and obstacles.

"Consider it pure joy, my Brothers, whenever you face trials of many kinds."

....To count our hurt, pain and struggle as nothing but pure joy? As my parents were Christians, and my Dad even a Pastor of our church, they knew that verse very well. However, on the morning of the 4th of December 1982 in Melbourne (Australia ), the last two words on the minds of my parents was "Praise God!". Their firstborn son had been born without limbs! There were no warnings or time to prepare themselves for it. The doctors we shocked and had no answers at all! There is still no medical reason why this had happened and Nick now has a Brother and Sister who were born just like any other baby.

The whole church mourned over my birth and my parents were absolutely devastated. Everyone asked, "if God is a God of Love, then why would God let something this bad happen to not just anyone, but dedicated Christians?" My Dad thought I wouldn't survive for very long, but tests proved that I was a healthy baby boy just with a few limbs missing.

Understandably, my parents had strong concern and evident fears of what kind of life I'd be able to lead. God provided them strength, wisdom and courage through those early years and soon after that I was old enough to go to school.
The law in Australiadidn't allow me to be integrated into a main-stream school because of my physical disability. God did miracles and gave my Mom the strength to fight for the law to be changed. I was one of the first disabled students to be integrated into a main-stream school.

I liked going to school, and just try to live life like everyone else, but it was in my early years of school where I encountered uncomfortable times of feeling rejected, weird and bullied because of my physical difference. It was very hard for me to get used to, but with the support of my parents, I started to develop attitudes and values which helped me overcome these challenging times. I knew that I was different but on the inside I was just like everyone else. There were many times when I felt so low that I wouldn't go to school just so I didn't have to face all the negative attention. I was encouraged by my parents to ignore them and to try start making friends by just talking with some kids. Soon the students realized that I was just like them, and starting there God kept on blessing me with new friends.

There were times when I felt depressed and angry because I couldn't change the way I was, or blame anyone for that matter. I went to Sunday School and learnt that God loves us all and that He cares for you. I understood that love to a point as a child, but I didn't understand that if God loved me why did He make me like this? Is it because I did something wrong? I thought I must have because out of all the kids at school, I'm the only weird one. I felt like I was a burden to those around me and the sooner I go, the better it'd be for everyone. I wanted to end my pain and end my life at a young age, but I am thankful once again, for my parents and family who were always there to comfort me and give me strength.

Due to my emotional struggles I had experienced with bullying, self esteem and loneliness, God has implanted a passion of sharing my story and experiences to help others cope with whatever challenge they have in their life and let God turn it into a blessing. To encourage and inspire others to live to their fullest potential and not let anything get in the way of accomplishing their hopes and dreams.
One of the first lessons that I have learnt was not to take things for granted.

"And we know that in all things God works for the best for those who love Him." That verse spoke to my heart and convicted me to the point where that I know that there is no such thing as luck, chance or coincidence that these "bad" things happen in our life.

I had complete peace knowing that God won't let anything happen to us in our life unless He has a good purpose for it all. I completely gave my life to Christ at the age of fifteen after reading John 9. Jesus said that the reason the man was born blind was "so that the works of God may be revealed through Him." I truly believed that God would heal me so I could be a great testimony of His Awesome Power. Later on I was given the wisdom to understand that if we pray for something, if it's God's will, it'll happen in His time. If it's not God's will for it to happen, then I know that He has something better.

I now see that Glory revealed as He is using me just the way I am and in ways others can't be used.
I am now twenty-threeyears old and have completed a Bachelor of Commerce majoring in Financial Planning and Accounting. I am also a motivational speaker and love to go out and share my story and testimony wherever opportunities become available. I have developed talks to relate to and encourage students through topics that challenge today's teenagers. I am also a speaker in the corporate sector.

I have a passion for reaching out to youth and keep myself available for whatever God wants me to do, and wherever He leads, I follow.

I have many dreams and goals that I have set to achieve in my life. I want to become the best witness I can be of God's Love and Hope , to become an international inspirational speaker and be used as a vessel in both Christian and non-Christian venues. I want to become financially independent by the age of 25, through real estate investments, to modify a car for me to drive and to be interviewed and share my story on the " Oprah Winfrey Show "! Writing several best-selling books has been one of my dreams and I hope to finish writing my first by the end of the year. It will be called "No Arms, No Legs, No Worries!"

I believe that if you have the desire and passion to do something, and if it's God's will, you will achieve it in good time. As humans, we continually put limits on ourselves for no reason at all! What's worse is putting limits on God who can do all things. We put God in a "box". The awesome thing about the Power of God, is that if we want to do something for God, instead of focusing on our capability, concentrate on our availability for we know that it is God through us and we can't do anything without Him. Once we make ourselves available for God's work, guess whose capabilities we rely on? God's!

May the Lord Bless you
In Christ,
Nick Vujicic

__________________________________________________________________________________________________________________________________

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More from Dr. Anne marie Helmenstine

Make Biodiesel - Instructions for Making Biodiesel from Vegetable Oil

Save Money Making Your Own Biodiesel
By Anne Marie Helmenstine, Ph.D., About.com

It's easy and cost-effective to make your own biodiesel.
Biodiesel Engine Biodiesel Plant How to Make Biodiesel Biodiesel Production Making Biodiesel

Biodiesel is a diesel fuel that is made by reacting vegetable oil (cooking oil) with other common chemicals. Biodiesel may be used in any diesel automotive engine in its pure form or blended with petroleum-based diesel. No modifications are required, and the result is a less-expensive, renewable, clean-burning fuel. Here's how to make biodiesel from fresh oil. You can also make biodiesel from waste cooking oil, but that is a little more involved, so let's start with the basics.

Materials for Making Biodiesel

· 1 liter of new vegetable oil (e.g, canola oil, corn oil, soybean oil)
· 3.5 grams (0.12 oz.) sodium hydroxide (also known as lye). Sodium hydroxide is used for some drain cleaners, such as Red Devil™ drain cleaner. The label should state that the product contains sodium hydroxide (not calcium hypochlorite, which is found in many other drain cleaners)

· 200 milliliters (6.8 fl. oz.) of methanol (methyl alcohol). Heet™ fuel treatment is methanol. Be sure the label says the product contains methanol (Isoheet™, for example, contains isopropyl alcohol and won't work).

· blender with a low speed option. The pitcher for the blender is to be used only for making biodiesel. You want to use one made from glass, not plastic, since the methanol you will use can react with plastic.

· digital scale [to accurately measure 3.5 grams (0.12 oz.)]

· glass container marked for 200 milliliters (6.8 fl. oz.). If you don't have a beaker, measure the volume using a measuring cup, pour it into a glass jar, then mark the fill-line on the outside of the jar.

· glass or plastic container that is marked for 1 liter (1.1 quart)

· wide mouth glass or plastic container that will hold at least 1.5 liters (2-quart pitcher works well)

· safety glasses, gloves, and probably an apron. You do not want to get sodium hydroxide or methanol on your skin, nor do you want to breathe the vapors from either chemical. Both chemicals are toxic. Please read the warning labels on the containers for these products! Methanol is readily absorbed through your skin, so do not get it on your hands. Sodium hydroxide is caustic and will give you a chemical burn. Prepare your biodiesel in a well-ventilated area. If you spill either chemical on your skin, rinse it off immediately with water.

Let's Make Biodiesel!

1. You want to prepare the biodiesel in a room-temperature (70° F) or warmer room since the chemical reaction will not proceed to completion if the temperature is too low.

2. If you haven't already, label all your containers as 'Toxic - Only Use for Making Biodiesel', since you don't want anyone drinking your supplies and you don't want to use the glassware for food again.

3. Pour 200 ml methanol (Heet) into the glass blender pitcher.

4. Turn the blender on its lowest setting and slowly add 3.5 g sodium hydroxide (lye). This reaction produces sodium methoxide, which must be used right away or else it loses its effectiveness. (Like sodium hydroxide, it can be stored away from air/moisture, but that might not be practical for a home setup.)

5. Mix the methanol and sodium hydroxide until the sodium hydroxide has completely dissolved (about 2 minutes), then add 1 liter of vegetable oil to this mixture.

6. Continue blending this mixture (on low speed) for 20-30 minutes.

7. Pour the mixture into a wide-mouth jar. You will see the liquid start to separate out into layers. The bottom layer will be glycerin. The top layer is the biodiesel.

8. Allow at least a couple of hours for the mixture to fully separate. You want to keep the top layer as your biodiesel fuel. If you like, you can keep the glycerin for other projects. You can either carefully pour off the biodiesel or use a pump or baster to pull the biodiesel off of the glycerin.

Using Biodiesel

Normally you can use pure biodiesel or a mixture of biodiesel and petroleum diesel as a fuel in any unmodified diesel engine. There are two situations in which you definitely should mix biodiesel with petroleum-based diesel.

· If you are going to be running the engine at a temperature lower than 55° F (13° C), you should mix biodiesel with petroleum diesel. A 50:50 mixture will work for cold weather. Pure biodiesel will thicken and cloud at 55° F, which could clog your fuel line and stop your engine. Pure petroleum diesel, in contrast, has a cloud point of -10° F (-24° C). The colder your conditions, the higher percentage of petroleum diesel you will want to use. Above 55° F you can use pure biodiesel without any problem. Both types of diesel return to normal as soon as the temperature warms above their cloud point.

· You will want to use a mixture of 20% biodiesel with 80% petroleum diesel (called B20) if your engine has natural rubber seals or hoses. Pure biodiesel can degrade natural rubber, though B20 tends not to cause problems. If you have an older engine (which is where natural rubber parts are found), you could replace the rubber with polymer parts and run pure biodiesel.

Biodiesel Stability & Shelf Life

You probably don't stop to think about it, but all fuels have a shelf life that depends on their chemical composition and storage conditions. The chemical stability of biodiesel depends on the oil from which it was derived. Biodiesel from oils that naturally contain the antioxidant tocopherol or vitamin E (e.g., rapeseed oil) remain usable longer than biodiesel from other types of vegetable oils. According to at least one source stability is noticeably diminished after 10 days and the fuel may be unusable after 2 months. Temperature also affects fuel stability in that excessive temperatures may denature the fuel.

What Is the Difference Between a Scientist and an Engineer?

By Anne Marie Helmenstine, Ph.D., About.com

Chemical engineers supervise the central pumping station at the Yukos Oil and Gas company in Nefteyugansk, Siberia.

Links

Chemical Software FreeMolecular Builder and Property Estimation Neural Networkwww.bestsystems.co.jp
Information SecurityYour Flexible Route To University! Sign Up At University of London Nowwww.LondonExternal.ac.uk
Virtual Chem LabFun Simulations & Guided Lessons Register & Get Next 6 Months Free.www.VirtLab.com

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Question: What Is the Difference Between a Scientist and an Engineer?

Scientist versus engineer... are they the same? Different? Here's a look at the definitions of scientist and engineer and the difference between a scientist and engineer.

Answer: A scientist is a person who has scientific training or who works in the sciences. An engineer is someone who is trained as an engineer. So, to my way of thinking, the practical difference lies in the educational degree and the description of the task being performed by the scientist or engineer. On a more philosophical level, scientists tend to explore the natural world and discover new knowledge about the universe and how it works.

Engineers apply that knowledge to solve practical problems, often with an eye toward optimizing cost, efficiency, or some other parameters.

There is considerable overlap between science and engineering, so you will find scientists who design and construct equipment and engineers who make important scientific discoveries. Information theory was founded by Claude Shannon, a theoretical engineer. Peter Debye won the Nobel Prize in Chemistry with a degree in electrical engineering and a doctorate in physics.

Do you feel there are important distinctions between scientists and engineers? You're invited to define the difference.

Why is Stainless Steel Stainless?

What It Is and How It Works!

By Anne Marie Helmenstine, Ph.D., About.com

What Is Stainless Steel and Why Is it Stainless?

In 1913, English metallurgist Harry Brearly, working on a project to improve rifle barrels, accidentally discovered that adding chromium to low carbon steel gives it stain resistance.

In addition to iron, carbon, and chromium, modern stainless steel may also contain other elements, such as nickel, niobium, molybdenum, and titanium. Nickel, molybdenum, niobium, and chromium enhance the corrosion resistance of stainless steel. It is the addition of a minimum of 12% chromium to the steel that makes it resist rust, or stain 'less' than other types of steel.

The chromium in the steel combines with oxygen in the atmosphere to form a thin, invisible layer of chrome-containing oxide, called the passive film. The sizes of chromium atoms and their oxides are similar, so they pack neatly together on the surface of the metal, forming a stable layer only a few atoms thick. If the metal is cut or scratched and the passive film is disrupted, more oxide will quickly form and recover the exposed surface, protecting it from oxidative corrosion. (Iron, on the other hand, rusts quickly because atomic iron is much smaller than its oxide, so the oxide forms a loose rather than tightly-packed layer and flakes away.)

The passive film requires oxygen to self-repair, so stainless steels have poor corrosion resistance in low-oxygen and poor circulation environments. In seawater, chlorides from the salt will attack and destroy the passive film more quickly than it can be repaired in a low oxygen environment.

Types of Stainless Steel

The three main types of stainless steels are austenitic, ferritic, and martensitic. These three types of steels are identified by their microstructure or predominant crystal phase.

Austenitic: Austenitic steels have austenite as their primary phase (face centered cubic crystal). These are alloys containing chromium and nickel (sometimes manganese and nitrogen), structured around the Type 302 composition of iron, 18% chromium, and 8% nickel. Austenitic steels are not hardenable by heat treatment.

The most familiar stainless steel is probably Type 304, sometimes called T304 or simply 304. Type 304 surgical stainless steel is an austenitic steel containing 18-20% chromium and 8-10% nickel.

Ferritic: Ferritic steels have ferrite (body centered cubic crystal) as their main phase. These steels contain iron and chromium, based on the Type 430 composition of 17% chromium. Ferritic steel is less ductile than austenitic steel and is not hardenable by heat treatment.

Martensitic: The characteristic orthorhombic martensite microstructure was first observed by German microscopist Adolf Martens around 1890. Martensitic steels are low carbon steels built around the Type 410 composition of iron, 12% chromium, and 0.12% carbon. They may be tempered and hardened. Martensite gives steel great hardness, but it also reduces its toughness and makes it brittle, so few steels are fully hardened.

There are also other grades of stainless steels, such as precipitation-hardened, duplex, and cast stainless steels. Stainless steel can be produced in a variety of finishes and textures and can be tinted over a broad spectrum of colors.

Suggested Reading

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w('New posts to the Chemistry forums:Nernst Equation Worked Problem Chemistry Help PLEASE!!!electrochemistry help please')

Acceptedagain, again and again...

I'm back with a new perception of the persistent love of God...

Welcome to acceptedagain. A blog that will talk to your heart, let you see yourself at another view.
The blog contains Top Christian Testimonies, Articles, Science,
Nature, Education,Psychology, Philosophy and many other topics.

Seeing myself falling many times, against the will of God, feeling the shame of sin, and unworthy, He still accepts me back to Himself for we are made righteous only through faith in Christ Jesus.
Most of all, I am aiming at creating a forum for spiritual encouragement from the Holy Bible, the only true and inspired word of God.
Acceptedagain will help you meet the man JESUS CHRIST of nazareth who will at your choice change your life and destine you to Eternal life.

He calls you NOW to open your heart for HIM so to get you saved!

Check it out!!!!!

About Malawi

Malawi is a small country located in the central eastern part of Africa. It shares borders with Tanzania to the north, Zambia to the left and Mozambique to the south and west. It was called Nyasaland when it was a Britsh colony.
Malawi has several languages but the most used one is 'chichewa' and the official language is English.
Other languages include Tumbuka, yao, Lomwe, Sena, Tonga and Ngonde ( There are actually more than 20) originating from different tribes.
Malawi is diveded into 3 major geographic regions, the north, central and south.

Malawi largely depends on farming to live. There are several beautiful fresh water lakes, rivers and streams. Lake malawi is the largest of them and is the 2nd largest in Africa from lake tanganyika of Tanzania.

There are several green swamps, mountains and valleys from which Scientists find advantage of research and study.
The scenery in malawi is very good.

Malawi has had 3 state presidents from 1964, a year it got her independence.

Dr. Hastings Kamauzu Banda(MD) of the Malawi congress party (MCP)rulled even through1993 when malawians chose to live in a multiparty democracy by referendum. In 1994, Dr. Bakili Muluzi (honorally) of the United democratic front (UDF)took office and rulled for 10 years (two tenures of 5 years each) and in 2004, Dr. Bingu wa Mutharika (PhD) formerly of the UDF but later revived his political prty, the Democratic Progressive party (DPP) took over power up to date. Malawi is holds its general elections on the 19th of may every five years and local polls a year later.

Malawi is currently minning Uranium in karonga district of the northern region. As of last few years, it has managed to donate food to other African countries and its GDP has improved.

It also has coal mines in rumphi, northern part of malawi.

The majority of malawians are christians.

Malawi is a peaciful country and is commonly known as 'the Warm heart of Africa'.

Visit Malawi!

From Library roof

Brains and much brains!

I personally don't like browsing through the Internet. I know it might be one of your interrests!
I would like to share with you alittle about the impact of what we feed our gry matter with. I mean the brain, my primary school science teacher used to put it that way.by the way, he has just retired from the service last two months!
The brain is a very delicate organ of an animal including you and me.It is able to store many Gigabytes of information capacity, you can't believe it. It is folded alot inorder to create a large surface area for the storage already mentioned. At one time, i was tempted to think that the computers that we use are more able than our human brains!How foolish I was to think that way! When a computer is commanded to delete information, it obeys at once humbly sending it to the recycle bin. I have for many times followed information in the recycle bin, deliting it and it confirms the action is done for good.
Far low a perfomance compared to your brain.my brain.
The brain is able to absorb anything you feed it with. It will never tell you that data is incompartible with location.It sends everything to its rightful location.You do not need to delete old data to create space.seen it? Should I say something about a student's brain?so tempting to do it now but pliz wait until I write a dedicated article on that,soon I hope.
Not without mentioning, you need to check what you want your brain to take out. be sure that everything you have ever seen, watched,heard,....is still in your brain.
I know you just can't like some of the data that you can retrieve from your brain.some sad, some shameful,some vitally important, on this one you long to review,don't you?so that you can finish your good report with relevance before you submit it to your boss, or you wanna pass exams just like that...PHA!
Many times when you get exposed to sensual stuff, your brain responds just as it should.But, are you able to control your brain?or it conrols your life. The brain is there for you to coordinate, centrally, all neural activities and not to control you.You need to be in comand of it.
I've talked about feeding your brain with bra..bra..bra...What do you feed your brain with? Man has a siniful nature and it is that nature that God always longs to deal with. As you browse through the Net,it is very likely that you will meet stuff that may lead you to sin.We cant live to avoid the internet.We need it.But the devil knows you need the net and he has put before you alot of snares so you, child of god should fall into.Some sites clearly warn you of the content you are about to view.If not, you need to go to settings of your PC and allow it to give pop up warnings.
If its in a cafe, I am sure all computers are set to warn you.
Your sinful nature then tells you to proceed and you obey it,the sinful nature!
Pschologists may choose to debate on this but I know it may just be a need in them to pass time.The psychology of any adolescent provides for an ability to make choices and the schema are very active to hold your fed in data.It is at your will to proceed.
The Holyspirit in you urges you NOT to proceed but you eventually CHOOSE to disobey Him.that's dangerous my friend.some sites even agrees with your conscious to say 'you are a fool to enter this site' and you shamelessly go on with sin.You do not want to see,listen or do any longer but you still do it.Now tell me who is controlling your life.if so its satan.Do you know that the devil has no mercy?and its him in control at that time that's why you do not have mercy again on your own soul.you come to a point that you don't care to die and go to hell.please, not you if you are in this.
I know readers to my blog may not like it but take not that God is talking to you right now.Soften your heart before you become used and entangled in sin.
In the bookm of romans chapter 7,paul has confidence in Christ Jesus as his deliverer from the sins that easily weighed him down.Look to jesus.
Make a deliberate choice to view sites that you know they will not compromise your purity.It's possible only if you are in christ.
The bible says do not be deceived,God cannot be mocked, everyman shall reap what they sow today.
Food for thought.Gabbage in-Gabbage out.
What you do is from the much embeded in your heart.Discuss this with your friend.Share what you learn rom articles on this blog with your friends.I need your feedback and most of all,Prayers to see god working even through this blog.
Jesus loves ya!

Material Science

Materials
Dr David Harrison
School of Education and HumanitiesAthrofa Addysg Uwch Gogledd Ddwyrain CymruNorth East Wales Institute of Higher EducationWrexham, NORTH WALES
Discussion topics.
What is a metal?
What makes metals immediately recognizable?
What are the properties of metals that make them such useful materials?
To what uses are metals put? - surprisingly diverse!
What simple experiments can be carried out in the primary classroom to distinguish metals from other materials?
INDEX:
Structure and Bonding
Conductivity
Lustre
Alloys
Smelting
Polymers and Plastics
Cotton and Linen
Wool, silk and hair
Nylon and Kevlar
Rubber
Glass
E-mail

No other materials have contributed to mankind's development over the centuries . . . except perhaps synthetic polymers in the twentieth century. The intimate connection of metals with human development is evident from many terms and phrases:
· the Bronze Age (circa 4000 BC onwards in Middle East),
· the Iron Age (circa 2000 BC onwards),
· a Golden Age,
· Edmund Ironside (Saxon king of England 1016),
· Copper, Tin, Silver, Golden and Platinum respectively for 9th, 10th, 25th, 50th and 70th wedding anniversaries,
· a leaden sky and leaden footsteps,
· nickel (US 5 cent coin),
· ". . . like a lead balloon.",
· tinny, cheap or thin sounding,
· a platinum blonde,
· Golden Oldies
· " . . . a steely glint in the eye.",
· gilt-edged stocks,
· chromium plated (meaning flashy),
· a silvery voice,
· a coppery tint,
· copper-bottomed (of good quality esp. pans),
· mercurial,
· " . . . that he might hear the pudding singing in the copper." (from "A Christmas Carol" by Charles Dickens),
· " . . . earth stood hard as iron . . ." (from the carol "In the Bleak Midwinter" by Christina Georgina Rossetti),
· iron fist in a velvet glove, etc.,
· as bold as brass,
· brassy (shameless)
· a brazen hussy,
· to be brassed off.
that reflect some of the important properties of metals -durability, lustre, strength, hardness etc. It is no coincidence that the cradle of the industrial revolution in Britain was the Ironbridge Gorge! (Definitely worth a school visit!)

Pure metals are elements that comprise more than 80 (75%) of the 110 or so chemical elements, including well known metals tin, copper, silver, iron, aluminium, sodium, mercury, uranium, etc., and some less well known, e.g., molybdenum, tungsten, iridium, cerium, praseodymium, etc., in fact most of the periodic table apart from the right hand corner and side. In addition to the pure elements there are many metallic alloys- mixture of metals (and some non-metals) with metallic properties, e.g., brass, bronze, steel, cupronickel, solder, type metal, ferrochrome, magnalium, Misch metal, etc.

Gold was the first metal to be exploited by mankind and has always been highly valued for its ease or working and its untarnished brilliant yellow metallic or "golden" lustre. As early as the 7th century BC it was used in coinage. Alchemists were obsessed with discovering "philosopher's stone" or "elixir" which would transmute base metals into gold and silver (and also prolong life indefinitely!). It is easy, with hindsight, to ridicule what alchemists did but through their quasi-mystical experimentation they laid some of the foundations of modern chemistry and physics.

Gold's long historical association with man arose because it is so very unreactive and occurs in nature as the uncombined or native metal (gold is more stable as the element than in compounds). Silver also occurs in nature uncombined and has also been used for many thousands of years. Copper very occasionally occurs as the pure element, though more often it is combined with other elements in copper ores, e.g., copper pyrites CuFeS2 cuprite Cu2O, malachite Cu2(OH)2(CO3) etc. However copper is quite unreactive and is very easily recovered from its ores and this ease of recovery led man to exploit it soon after fire was discovered. The unreactivity or noble nature of copper, silver and gold resulted in their widespread use in coinage for thousands of years and they are collectively known as the coinage metals. It is only in the twentieth century that the intrinsic worth of these metals in coinage has exceeded their face value and cheaper substitutes are used, e.g., cupronickel and aluminium alloys.

Gold has another remarkable property - it is the most malleable metal known. Gold can be hammered out into sheets of gold leaf no more than 1000 atoms thick, 1 cm3 can be hammered out to cover 3-4 m3 but more usually it is hammered out so that 1 cm3 covers 1 m2. Gold leaf is widely used in decoration and is hammered out between the exceptionally tenacious ox intestine membrane known as gold beaters' skin.

Gold is also the most ductile of metals and can been stretched or extruded into very fine wire without breaking. Lead and tin are amongst the least ductile of metals. The order of ductility of some familiar metals is gold > silver > platinum > iron > copper > palladium > aluminium > zinc > tin > lead. Malleability and ductility and other properties relating to the workability of metals are usually associated wtth the transition metals (those forming the central block of the familiar form of the periodic table).
Top of Page
STRUCTURE and BONDING
Most metals adopt one of three structural types based on different ways of packing the metal atoms. Two structures have the metal atoms arranged in a close packed way and differ only in the stacking of the layers of atoms. In the third common structural type the metal atoms are not close-packed - this structural type is adopted by metals with large atoms. For information the three types of packing are:
cubic close packed (ccp) or face centred cubic(fcc), e.g., copper, silver and gold,
hexagonal close packed (hcp), e.g., magnesium and zinc
body centred cubic (bcc), e.g., sodium, potassium and iron.

Not all metals adopt these structures, that of cobalt alternates between cubic and hexagonal close packed. Tin adopts two structures or allotropes depending on temperature. At room temperature white metallic tin is stable but on prolonged storage below 13oC white tin turns into grey tin, a very brittle semi-metallic form with a covalent giant structure like diamond. Napoleon's army that besieged Moscow wore trousers and tunics fastened with shiny white tin buttons that in the severe Russian winter turned into brittle grey tin (so called tin plague) which crumbled away - not very convenient when you want to keep warm, you could say that Napoleon's army were caught with their trousers down and if it was cold enough to freeze the balls off a brass monkey then pity the poor French soldiers . . . ! Tin plague was noticed by Aristotle (384-322 BC) and Plutarch (46-120 AD). In the severe European winter of 1850 the tin organ pipes of Zeit church in Germany were destroyed by the cold.

Whatever structure the metal adopts it is an array of metal cations and the valence electrons are free to move or are delocalized throughout the array. The metallic bond is the 3-dimensional electrostatic attraction of the all the metal cations for all the delocalized electrons which also serve to shield each cation from the repulsion of neighbouring cations.

If we regard metal atoms as being like ball bearings we can understand why metals are malleable and ductile (see later) and not brittle (unlike covalent and ionic giant structures). When subject to any distortion the metal atoms slide past each other and the mobile electrons rearrange to ensure cation-cation repulsions to not occur. When ionic compounds are subjected to distortion cation-cation and anion-anion repulsions between layers of ions cause brittle cleavage. When covalent giant structures are distorted covalent bonds are ruptured and the materials fractures unevenly - diamond may be hard but when hit with a hammer it will shatter!.
Top of Page
CONDUCTIVITY
Metals are noted also for their thermal and electrical conductivity (lack of electrical resistance). The high thermal conductivity makes metals cold to touch as they conduct the heat away from the fingers or hand. Metals warm up and cool down rapidly - the metal surface loses/gains heat to/from its surroundings which is internally conducted from/to the main body of the metal. However a shiny surface (see later for lustre) reflects much incident infrared (heat) radiation and shiny metallic surfaces are used for keeping heat in/out, e.g., the silvered surface in a vacuum flask and the shiny plastic survival bags used to protect against exposure/hypothermia, and the aluminium foil which prevents your Sunday joint from being burnt on the outside and raw in the middle. A matt metal surface heats up rapidly and also radiates heats more effectively than a shiny surface.

Thermal conductivities J cm-1 s-1 K-1
Silver 4.16
Copper 3.86
Gold 3.02
Aluminium 2.01
Iron 0.46
Mercury 0.07
Brick 0.0063
Water 0.0055
Wood 0.0013
thermal conductivity: silver > copper > gold > aluminium > magnesium > zinc > chromium > iron > tin > lead,
electrical conductivity: silver > copper > gold > aluminium > magnesium > zinc > iron > tin > chromium > lead.

Note the close similarity in the two series both properties are related to the structure of metals. When atoms absorb heat energy they vibrate (temperature is a measurement of molecular energy) and this vibration is passed from one atom to the next. In metals, because the metal atoms are often close packed together (with 12 or 14 close neighbours) the vibration or heating effect is passed rapidly through the metal from one atom to another. In covalent and ionic compounds the atoms are not close-packed (lower densities) and the heat energy is less easily transferred from atom to atom, also the thermal energy is used in covalent bond vibration in covalent compounds.

Passing a current through a metal causes it to heat up because electrons are constantly and randomly colliding with metal cations causing vibration. The lower the conductivity (or higher the resistance) or the more obstructed is the electronic motion then the more the metal heats up and the higher the resistance becomes leading to a further increase in the heating effect etc., thus an electric element on a fire or cooker does not glow red instantly as it takes time for the temperature and resistance to increase. The resistance of a tungsten filament bulb increases ten fold between room temperature and its operating temperature.

In a light bulb the wire filament becomes very hot (white hot) and is thus made of the metal tungsten because it has a very high melting point (3387oC). Tungsten is very reactive at this temperature so it is necessary to exclude oxygen from inside the bulb - however in a vacuum the tungsten filament would slowly evaporate so enough unreactive argon gas is placed in the bulb to ensure that evaporation is suppressed at the operating temperature.
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LUSTRE and TARNISH (CORROSION)
Another highly characteristic feature of gold and all metals is their metallic lustre which makes most metals instantly recognizable. The surface lustre of a metal is an essential feature of their use in decoration and ornamentation. Most metals have a characteristic silvery lustre but copper and gold have unique salmon-pink and yellow lustres respectively. With the exceptions of gold and platinum most metals are more or less tarnished. The tarnish may be of aesthetic beauty - the patina on antique bronze, the beautiful green on copper roofed buildings, etc. Sometimes tarnish is synonymous with corrosion, e.g., rust on iron and steel which is not only unsightly but is damaging and possibly dangerous, and the black tarnish on silver, mainly silver sulphide, that spoils the brilliant silvery white lustre which makes silver so attractive.
2Ag + H2S + 4O2 -> Ag2S(black) + H2O

The tarnish on most metals is a surface layer of oxide arising from the reaction of the metal with oxygen in the air. In the case of aluminium, a highly reactive metal, the surface oxide layer is very tenacious and renders aluminium quite inert to reaction.
4Al + 3O2 -> 2Al2O3

The oxide layer on aluminium can be artificially enhanced by anodizing (an electrolytic process) - anodized aluminium can be readily coloured and painted without the need of a primer. If the surface oxide layer of aluminium is removed the metal is much more reactive. Titanium jewellery with its iridescent lustre relies on a special surface tarnish for its decorative value.

When iron rusts the hydrated iron oxide that forms expands and constantly peels off the surface of the metal exposing more iron to atmospheric moisture and air.
4Fe + 3O2 + xH2O -> 2Fe2O3.xH2O(rust)

The degree to which, and rapidity with which a metal tarnishes or lustre is lost are clearly related to some extent to reactivity. The elements below are listed in order of decreasing lustre of metal after some exposure to air:
lustre: gold > silver > chromium > tin > copper > zinc > magnesium > aluminium > lead > iron.

Gold and silver as we have seen already are unreactive and very lustrous. Lead although quite unreactive is never very lustrous even when polished. Some highly reactive metals, e.g., sodium and potassium tarnish almost instantly on exposure to air but the untarnished surface can be briefly seen when a lump of the metal is cut with a knife.

Why are metals lustrous? Why do we see a perfect (but laterally inverted) image in a plane mirror (silvered glass)? The lustre is intimately related to the electronic structure of a metal. Every electron can absorb a specific quantum or packet of radiation to become excited and the quantum of radiation absorbed depends on the energy level of the electron. "Free" electrons often absorb quanta of visible light. In metals the outer electrons are essentially "free" electrons and their energy depends on their distance from a nucleus; as there are countless "free" electrons of almost every possible extranuclear distance and energy they can absorb all the visible light that falls on the metal surface thus:
metals are completely opaque, even the thinnest gold leaf is opaque.

However an excited electron re-emits the same absorbed quantum of radiation as it becomes de-excited and most of the radiation that is incident on a metal surface is expelled from the surface thus:
metals are highly reflective or lustrous.

How can we protect a reactive metal from corrosion or rusting? There are four common techniques:
painting or lacquering - the cheapest but least effective as maintenance is required. The body of a car has a hard paint exterior but if this is damaged rusting leads to blistering under the paint with all the tell-tale signs the motorist is familiar with - the interior of body panels is often treated with a soft-set paints or waxes that self seal when scratched. The Forth Rail Bridge and Blackpool Tower need constant year on year painting as they are both exposed to corrosive sea air. Decorative brass and copper items are often lacquered with a transparent varnish to prevent tarnishing.
alloying - slightly more expensive; small amounts of other metals and carbon can turn iron into a whole range of stainless steels suitable for a wide range of applications as well as cutlery!
electroplating - more expensive; most familiar is probably electroplated nickel silver (EPNS) as a cheaper alternative to silver cutlery and, rather less familiar since the 1980s, the chrome (chromium) plate trimmings on motor vehicles (bumpers, door handles, window frames, radiator grill).
galvanizing - an chemically cleaned iron object is briefly dipped in molten zinc (m.p. 420oC) and is coated with a thin layer of zinc. Inspection of a freshly galvanized object (dustbin, bucket, nail, wire netting) will reveal the obvious crystalline nature of the zinc coating. The zinc surface gradually oxidizes so the iron surface is double protected by a layer of zinc oxide and zinc. Even when scratched to reveal the iron surface rusting does not occur because an electrochemical effect, arising from the two metals in contact, ensures that it is the zinc that is preferentially oxidized. [The steel legs of off-shore oil rigs are protected from corrosion by a magnesium block attached by a conducting cable to the steel leg - electrochemistry ensures that the magnesium is preferentially oxidized whilst the steels remain unoxidized (reduced). The magnesium block must be periodically renewed.]
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ALLOYS
Alloys can be regarded as a solid solution of one metal in another. Bronze is a particularly important alloy of copper and tin. Like copper it is corrosion resistant but it is much harder and can be used in engineering - it is particularly useful in the manufacture of marine propellers where its corrosion resistance is paramount but it has the additional benefit of the copper being toxic to molluscs and barnacle growth is inhibited. Neither copper or tin are hard metals when pure so why is bronze much harder that either component?

The atoms in most metals are close packed together in layers and these layers stacked one upon another. When copper is squeezed or bent or beaten the layers of coppermatoms can easily slide over or past one another hence copper is malleable and ductile. The inclusion of about 15% of larger tin atoms disrupts the layers of copper atoms (makes the layers "rough") and prevents the layers sliding over one another. There is also a small amount of chemical bonding between the copper and the tin which adds to the strength.

Another important effect of alloying copper with tin is that bronze has a melting point much less than that of pure copper (1084oC) and much higher than pure tin (232oC).

mass % Cu
mass % Sn
M.P./oC
100
0
1084
90
10
1005
80
20
890
70
30
755
60
40
724
50
50
680
40
60
630
30
70
580
20
80
530
10
90
440
0
100
232

Solder is a low melting (about 180oC) alloy of mainly tin (50%) and lead (49.5%) with antimony (0.5%) used to join cleaned metal surfaces - a soldering flux helps by reducing any metal oxides adhering to the surfaces to be joined. It is not possible to solder metals like aluminium which have a very tenacious oxide surface.

Pewter comprises tin (80%) and lead (20%) and is used for decorative utensils and ornaments because it can be carved by hand or on a lathe.

Nichrome comprises nickel (60%), iron (20%) and chromium (20%) and can be repeatedly heated to redness and cooled without oxidation, embrittling or sagging and is used in heating elements.

Constantan comprises copper (60%) and nickel (40%) and has a resistance that does not change with temperature.

Iconel comprises nickel (76%), chromium (15%), iron (8%) and manganese (1%) and is very inert and widely used in food processing utensils.

Invar comprises iron (64%), nickel (35%) and carbon + manganese (1%) and has a very low expansivity when heated.

Wood's metal (m.p. 65oC) an alloy of bismuth (4 parts), lead (2 parts), tin (1 part) and cadmium (1 part) can be used as a heat exchange fluid and Wood's metal novelty teaspoons melted when stirring a cup of tea!

A 3% by mass beryllium alloy with copper is hard, does not spark when struck and finds application in oil refineries and other fires sensitive areas.

Many metals dissolve in liquid mercury to give solid alloys known as amalgams. An amalgam with silver and tin sets rapidly into a hard mass known as dental amalgam widely used as a tooth filling. Mercury does not amalgamate with iron and can be stored in iron flasks.

Chapter 11 (Industrial Alloys) of Bernard Moody's "Comparative Inorganic Chemistry" 3rd Edition, gives a very thorough review of the range of metallic alloys in use today.
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SMELTING - BRONZE & IRON AGES
Teacher Tip: opportunity here to develop cross-curricular ideas about materials, history, and geography.
The approximately 200oC drop in melting temperature with the formation of 20% tin bronze was probably crucial in mankind's Bronze Age development - an ordinary wood fire (approx. 950oC) will not melt pure copper but will melt bronze so that it could be cast into a variety of shapes. How was bronze discovered? Serendipity ensured that copper and tin ores often occur together, e.g., in Cornwall both copper ores and tin ore (cassiterite SnO2) occur together (the British Isles were once referred to as the Cassiterides) and accidental smelting of copper and tin ores must have occurred. Tin had been separately smelted at an earlier date but had been found to soft to be useful. For both copper and tin ores it is sufficient to heat them to a sufficiently high temperature in air to decompose them to the metal.
CuS + O2 -> Cu + SO2
2CuO -> Cu + O2
SnO2 -> Sn + O2

Another temperature quirk led to the Iron Age. Bronze Age man had discovered that charcoal fires (1150oC) were hotter than simple wood fires. However iron ores are not decomposed by heating in air alone and pure iron melts at 1535oC! But iron ores are reduced by carbon, actually by carbon monoxide, to iron metal at charcoal fire temperature and what is more a 4% by mass mixture of carbon and iron melts at 1150oC!
Fe2O3 + 3CO -> 2Fe + 3CO2
C + O2 -> CO2
C + CO2 -> 2CO

The same basic reactions in a modern blast furnace use iron ore and coke. A problem with cast iron from the Iron Age forge or pig iron from the blast furnace is that the presence of the carbon makes it brittle when cold. The carbon has a similar effect in iron as tin had in bronze - making it harder but the smaller carbon atoms give rise to weaknesses in the atomic arrangement where fracture can occur. However iron age man soon learned that by hammering the iron whilst still hot or forging gave a much stronger and workable product - the hammering squeezes out and exposes the carbon and sulphur other impurities where they oxidize in air. The hammering at the forge is not just to shape the product but also strengthen it to give wrought iron. It was essential that some carbon was retained or the iron became less hard and unable to keep a the sharp edge required for knives, scythes, swords, spears etc. Iron Age man also learned to temper or harden iron by plunging it hot into water or, better still, urine! Times change - the blacksmith and the smithy or forge were an essential feature of country-life until fifty years ago - their memory lingers on as in Acton Smithy on the old Chester Road out of Wrexham.
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POLYMERS & PLASTICS
Some useful Internet addresses:
All of these can be accessed from the NEWI Internet pages for Science for Education students links page
http://www.lbl.gov/MicroWorlds/Kevlar/KevlarIntro.html - an excellent MicroWorlds resource with many simple ideas, experiments, analogies, and demonstrations.
http://www.lexmark.com/ptc/book.html - an introduction to plastic by the Plastics Technology Center.
http://www.umr.edu/~wlf/ - polymer chemistry hypertext, an educational resource compiled by students, a bit heavy going.
http://www2.ncsu.edu/ncsu/pams/science_house/ctchem.html - not exactly polymers but some recipes for some gooey colloids that can be made in the kitchen including slime, silly putty, clear slime, glurch and cat’s meow??? Have fun!

Polymer - poly = many, mer = parts includes many natural and synthetic materials which can be further classified as organic or carbon based and inorganic or non-carbon based and can be regarded as being assembled from a simple repeating units held together by covalent bonds.

Natural Polymers
Organic: wool, linen, cotton, hemp, jute, wood, coal, spiders’ web, silk, starch, cellulose, proteins, latex rubber, chicle (chewing gum), etc.
Inorganic: sand, clay, asbestos, volcanic glass (obsidian), etc.

Synthetic Polymers
Organic: polyethene, polypropene, polyvinyl chloride, perspex, polycarbonate, poly vinyl acetate, teflon, neoprene rubber, etc.,
Inorganic: pottery, cement, concrete, silicones, etc.,
Although all the above are polymeric materials the term polymer usually refers to the synthetic organic polymers often referred to as plastics or synthetic fibres (or synthetics). Many are household names, e.g., nylon, terylene, teflon, rayon, acrylic, polyester, perspex, polystyrene, etc., and most are derived from natural petroleum.

All polymers are assembled from repeating units. The repeating unit may be derived from one or more monomers.

There are many ways of classifying these synthetic organic polymers as indicated below:
thermoplastic and thermosetting - the former soften and melt on heating and can be moulded, e.g., polyethene, the latter decompose on heating and must be shaped at manufacture, e.g., bakelite.
addition and condensation - the former are made from the simple addition of monomers, e.g., polyethene from the addition of ethene, the latter are usually synthesized from two different monomers with the elimination of biproduct, e.g., nylon 6-6 from hexandioyl chloride and 1,6-diaminohexane with elimination of HCl.
homopolymer and copolymer - the former are assembled from one repeating unit, e.g., propene in polypropene, the latter are based on two different repeat units, e.g., nylon.
atactic and isotactic (also syndiotactic) - the former has chemical groups attached to the polymer chain randomly on either side of the carbon chain, the latter has the chemical groups attached to the same side of the carbon chain, e.g., atactic and isotactic polypropene, syndiotactic polymers have the groups alternately on oppostite sides of the chain.
crystalline and amorphous - the latter are stronger and have the polymers chains stacked together in a more or less ordered form, e.g., high density polyethene (HDPE), the former are of lower strength and have the polymer chains randomly arranged because of branching or bulky side groups, e.g., low density polyethene (LDPE) or atactic polypropene.
linear (or straight chain), branched and cross-linked - the former have long chains of carbon atoms only, e.g., natural latex rubber, branched chain polymers as the name indicates are branched, cross-linked polymers have polymer chains joined together by other atoms, e.g., vulcanized rubber.
Teacher Tips
Use paper clips to act as monomers and these can be linked together to give chains, branched chains and cross-linked chains. Coloured paper clips could be used to model homo- and co-polymers.
Use uncooked spagetti to model a crystalline polymers -many sticks of spagetti lie side by side in an ordered fashion; cooked spagetti is a model for an amorphous polymer.
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The Structure of Polymers - Polythene
Polythene is a polymer formed by the polymerization of ethene. Its formula can be variously represented as CnH2n+2 (n = large integer 100 - 200 000) or CH3-(-CH2-)n-CH3 or -(-CH2-CH2-)-n etc., all of which amount to the same thing, that is long chains of CH2 groups though at the ends of the chains there must be CH3 groups to ensure that each carbon atom always forms four bonds. The value of n in the above formula is variable in polyethene from hundreds to hundreds of thousands and the average value of n is a measure of the average chain length - because of this variation polyethene is not, strictly speaking, a pure compound as the molecules are not all the same it is better to call it a mixture of hydrocarbons.

The simplest hydrocarbon is methane CH4 (n=1) which is familiar as natural gas; bottled heating and cooking "Calor" gas is propane CH3CH2CH3 (n=3); camping gas and lighter fuel is mainly butane CH3CH2CH2CH3 (n=4); petrol is mainly CH3CH2CH2CH2CH2CH2CH2CH3 or octane; paraffin wax for candles has on average twenty carbon atoms in a chain, i.e., typically C20H42; the waxes found in shoe polish and vaseline have upto 70 carbon atoms in the chain.

The chains are not straight chains but in fact zig-zag chains - the term straight refers to the fact that they are not branched! The zig-zag nature of the chain arises because when we look down a carbon-carbon bond the atoms attached to adjacent carbon atoms should always be "staggered" rather than "eclipsed" - this is known as the staggered conformation and is more stable.

Notice also that as the chain of carbon atoms gets longer the materials change from gases to volatile liquids to oils to waxes to solid plastics. The only bonds in these compounds are covalent bonds between the atoms in the molecule (C-C and C-H bonds which are strong) but there are no bonds between the molecules. So what is holding the molecules together? Why are all hydrocarbons not gases like methane?

There are very weak intermolecular forces called London or dispersion forces that give rise to van der Waals interactions between molecules. These forces of attraction between molecules arise because electrons in the covalent bonds are always in motion and at any instant a pair of electrons may not be equally shared between the two atoms of a covalent bond, i.e., there will be instantaneous bond polarization Cd +-Hd -. This bond polarization induces bond polarization in neighbouring molecules leading to very weak electrostatic attraction bewteen molecules. In methane however the van der Waals forces are to small to overcome the thermal motion of the molecules due to their kinetic energy at room temperature and methane is a gas. As the temperature is lowered and the thermal kinetic energy gets less then methane eventually liquefies and at very low temperatures freezes.

Although molecular size increases in longer hydrocarbon chains, the van der Waals forces do not increase and the thermal energy remains the same as for methane at a given temperature. But, because the molecules are heavier, the speed at which they move becomes less (kinetic energy is 1/2mv2 m = mass, v = speed) and are thus less likely to be able to escape from the weak van der Waals attraction of another molecule. Also longer molecules have more van der Waals contacts as shown below.

The lecture diagram showed sections of zig-zag polythene stacked together in a highly idealized manner. In practice polymer chains are never stacked as regularly as shown above for several reasons:
the polymer chains are very flexible and can be twisted into other orientations,
the chains tend to form loose spirals or coils,
the chains may be branched,
not all polymers are ordered or crystalline.

Low density polythene LDPE is obtained by polymerization of ethene at high pressure (1000 atmospheres) and high temperature (200° C) which leads to a waxy solid in which the polymers chains have irregular branches and cannot pack together in an ordered way shown above - there are still van der Waals attractions between the chains but these are of random orientation. The result is that LDPE is an open polymer of low density and little mechanical strength and rather a tangled mess at the molecular level.

Polythene can also be prepared catalytically by use of Ziegler-Natta catalysts at lower pressures (1-10 atmospheres) and temperatures (50-100° C). The catalyst is a metal compound and the polymerization occurs at the metal atom in a conveyor belt fashion which gives rise to a regular non-branched chain polymer which is highly ordered or crystalline with regular van der Waals attractions between chains and is known as high density polyethene HDPE. HDPE is tough and strong and the ordered structure means that it has higher density.

HDPE and LDPE can be distinguished by their transparency: LDPE is fairly transparent (sandwich bagsand bread bags) whereas HDPE is whitish and at best only translucent (supermarket carriers & plastic milk bottles).

Even in HDPE the ordering of the polymer chains is not complete - there are definite regions of the polymer where the chains are packed in an orderly fashion and these regions are called crystallites. The number of crystallites determines the crystallinity of the polymer. In between the crystallites are areas where the polymer chains are more randomly arranged. The crystallites act rather like the cross-links in a thermosetting polymer and by holding the polymer chains tightly together give HDPE the strength and toughness that are lacking in LDPE. Although van der Waals attractions are weak (5-20 kJ mol-1) when concentrated in an orderly fashion in the crystallites they can give a polymer strength.

Polythene is very familiar as the plastic of plastic carrier bags from supermarkets which are made of thin HDPE. The way HDPE is manufactured and its structure ensures that most the polymer chains are arranged so as to give the internal structure a fibrous nature or grain. As with any "grained" material the strength varies according to whether tension is applied across or with the grain, this can be demonstrated with a supermarket carrier bag.

Cut out two similar large squares (6" x 6") from a plastic carrier bag noting carefully which edges correspond to the top and bottom and side of the bag. Make a small cut in one edge of each square - the top edge of one square and the side edge of the other square.
Grasp each square in turn firmly with both hands and pull gently so as to tear each square starting at the small cut. Repeat the experiment several times to convince yourself (or not as the case may be) that the polymer does not tear as easily in both directions. As supermarkets bags become thinner, for reasons of economy, this experiment becomes less reliable but you should find that the bag tears more easily from top to bottom than from side to side. This is because the polymer chains are aligned from top to bottom and tearing in this direction or with the grain involves breaking mainly weak van der Waals attractions. Tearing from side to side or against the grain must involve breaking not only van der Waals attractions but some covalent bonds as well which requires more energy and is thus more difficult. The bags are made in this away because most of the strain is in the vertical direction which parallel to the grain and would tend to pull the bag apart perpendicular to the grain.
Next cut out a vertical strip from your bag. It should be about 1" or 2.5 cm and 6" or 15 cm long. Grab hold of each end of the strip and pull gently but steadily - observe and describe what happens and try to monitor changes in stress in the plastic as you increase the strain. If necessary repeat the experiment several times to ensure that it is reproduceable.
When you start to pull on the strip nothing happens at first except a little stretching but then as you increase the applied strain one or more "necks" form in the strip and as you continue to increase the strain the necks get longer as material appears to "flow" into the necks from the taut regions, either side of the neck, which get smaller. Eventually the neck grows to the whole length and the polymer becomes stiffer and ridged - it is difficult to stretch at this stage and eventually, as you increase the strain beyosd a certain point, the strip snaps.

We can explain what is observed by considering the changes on a molecular scale. The individual polymer chains are held together by van der Waals forces so that the chains are parallel within crystallites. However, although the chains are parallel, they are not straight but are randomly coiled. When tension is applied there is a tendency for the uncoiling to occur which results in a highly aligned molecular structure -this occurs as the "necks" are formed in the strip of plastic. The uncoiling and alignment continues until all the molecules are highly aligned and at this stage the strip has become noticeably more rigid and ridged reflecting the highly organized linear structure. The uncoiling and alignment can occur because van der Waals attractions are weak and easily broken and reformed. Eventually when enough strain is applied the highly aligned molecules slide past each other, overcoming the van der Waals attractions, and the polymer breaks.

The high level of strain required to break the polymer explains why it is so difficult to tear open a bag of frozen peas - you have to tug and pull very hard and then suddenly it rips open and you’ve got peas all over the kitchen floor! It is much easier to open the bag if the manufacturer provides a weakness or flaw into the packaging which allows you to concentrate your applied tension in one area.
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Change of State
A convenient way of identifying a pure solid organic compound is by the determination of its melting point, e.g., pure benzoic acid crystals C6H5COOH have a melting point of 122° C.
HDPE is an organic compound but differs from other organic compounds in two ways:
it is only partly crystalline or ordered unlike benzoic acid crystals which are almost perfectly ordered,
it is not a single compound but is a mixture of compounds of formula CnH2n+2 where n is large and variable, i.e., it is not a pure substance.
HDPE thus does not have a sharp melting point. When we heat it up slowly nothing happens for a while then there comes a temperature at which it starts to gradually change from a hard solid to a treacle like substance. The temperature at which this starts is known as the glass transition temperature, so called because glass behaves in a similar way - it starts to soften and flow but does not melt to a runny liquid.

Chewing gum, either based on natural chicle from the sapodilla tree or synthetic based on poly(vinyl acetate), is a relatively brittle material at room temperature - a stick of gum straight from the packet is not chewable. However most chewing gum has a glass transition temperature of around 25-30° C (pva gum 28° C) and in the mouth, temperature 37° C, it becomes the soft chewy material we are familiar with.
The glass transition temperature varies from polymer to polymer and depends on:
(i) the average chain length,
(ii) the rigidity of the polymer chains,
(iii) the strength and nature of interactions between chains,
(iv) the degree of crystallinity.

When polymers soften (we should not use the word melt) they do not become runny liquids - why not? Ice melts to become water! The reason is that when polymers soften each molecule cannot behave independently, like a small molecule, because they are all entangled and there are still van der Waals attractions, although these are random rather than ordered. To use the cooked spagetti analogy again, the softened polymer chains are like a tangled mass of cooked spagetti - try to move one string of spagetti on its own, it cannot be done! In a true liquid (a molten solid) each individual molecule can behave independently - this is not possible in a softened polymer. The glass transition temperature marks a boundary between little or no molecular movement (solid) and restricted molecular movement (treacle-like).

Cotton has a glass transition temperature of 225° C so cotton fabrics keep their shape because the cotton molecules cannot move at room temperature. Cotton is a carbohydrate polymer of glucose which contains lots of hydroxy groups, -OH, and these can hydrogen bond (another story for another lecture) to -OH groups in another polymer chain. The inter-chain hydrogen bonding is much stronger than van der Waals attractions in polyethene so cotton is a much tougher material than polyethene and can form strong fibres which can be formed into threads, which cannot be done for polyethene. The high glass transition temperature reflects the strength of the forces between the polymer chains.

However cotton absorbs water which, because it contains -OH groups, will also hydrogen bond to the polymer - one reason why undergarments are cotton rich is because they are absorbent. Water acts as a plasticizer or lubricant between the chains allowing them to move more freely and lowers the glass transition temperature to 20° C. Cotton shirts and blouses thus crease most where they absorb most moisture and are under most pressure - inside the elbows, under the arm pits, where they are tucked into trousers, etc. Where they are not subject moisture or pressure they remain quite flat and uncreased. The lubricating power of water is used when we use a steam iron to press our cotton shirts or blouses - the high temperature speeds up molecular motion and make the pressing process more rapid, it could be done at 20° C but it would be a very slow job!

PVC (polyvinyl chloride) is a rigid polymer that is difficult to process for most applications but we are all familiar with pvc in clingfilm, shower curtains, waterproof clothing, pvc wellies, synthetic upholstery and all these applications rely on substantial amounts (upto 50%) of plasticizers. The plasticizers in clingfilm had a bad press a few years ago when people worried about migration from the film to the food. A typical plasticizer is dibutyl phthalate - it is responsible for the oily film that condenses on the inside of the windscreen of a new car as it is released from the vinyl upholstery and dashboard and is also responsible for the smell of a new car. Of course when you have your new double-glazing installed you want only the best - UPVC frames - which should be strong and rigid and so are made from Unplasticized PVC.
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COTTON and LINEN
The nature of cotton was briefly discussed in the last lecture. Cotton and linen are both natural cellulose polymers based on glucose as the repeating unit. They both form strong fibres that can be woven into threads. Polyethene does not form strong fibres and cannot be woven into threads. This difference in behaviour can be explained by the different nature of the forces of intermolecular attraction between the polymer chains. In polyethene the only forces between the polymer chains are van der Waals attractions.

In polymers based on cellulose there are, in addition to van der Waals attractions (these are always present), hydrogen bonding interactions. Hydrogen bonds are about five times stronger than van der Waals attractions but only about one tenth of the strength of a covalent bond.
van der waals attraction 5-10 kJ mol-1
hydrogen bond 25-50 kJ mol-1
covalent bond 250-500 kJ mol-1

The hydrogen bond occurs between hydrogen atoms that are themselves attached to oxygen or nitrogen and oxygen or nitrogen atoms in another molecule. -OH groups are known as hydroxyl groups and N-H groups as amino groups or, in some cases, amido groups.

Hydrogen bonding arises because oxygen and nitrogen are very electronegative elements, i.e., they strongly attract electrons towards themselves in compounds, and as a result O-H and N-H bonds are very polar. The electrostatic force of attraction of the positive hydrogen end of an O-H or N-H bond for another electronegative oxygen or nitrogen atom in another molecule results in the hydrogen bond. Hydrogen bonds are about twice as long as a normal covalent bond, e.g., O-H or N-H typically 90 to 100 pm and O----H and N----H 180-200 pm [pm = picometre or 10-12 m].

Don’t try to remember the structure of cellulose! Just remember that it is a polymer of glucose, which is a carbohydrate, and has lots of hydroxyl groups -OH that can hydrogen bond to oxygen atoms in other polymer chains giving rise to strong intermolecular attractions leading to a strong polymer that can be woven into threads.
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WOOL, SILK and HAIR
Other natural fibres that contain hydrogen bonded polymer chains are wool and hair, examples of animal fibres. These are however a different sort of polymer as the repeating groups are amino acids and this sort of polymer is a protein which is a polyamide known as a polypeptide. The term polypeptide is reserved for polymers containing the amide link derived from amino acids.

As the lecture diagram showed, there is scope for hydrogen bonding between amido groups. There are, however, many different amino acids so the protein chains in animal fibres can have a variety of different repeating units made up of different combinations of amino acids. The different repeating units leads to different possibilities in the secondary structure of the animal fibre because of different hydrogen bonding possibilities not only between polymer chains but within the polymer chain. a -Keratin the protein of wool, human hair, nails and feathers has the individual polymer chains coiled into a right handed helix, or a -helix, held together by hydrogen bonds. The helical chains of wool and hair are then coiled about one another, held together by further hydrogen bonds, to form a superhelix which accounts for the thread-like nature of these proteins.

Another protein known as silk fibroin has different protein chains hydrogen-bonded together to give a puckered layer structure known as a b -pleated sheet. (The hydrogen bonding pattern is very similar to the pattern of van der Waals forces between zig-zag chains of polyethene.)

However in the case of wool or hair this is not the complete story. One of the amino acids that make up the protein of hair and wool is cysteine HSCH2C(NH2)CHCOOH. When two cysteine molecules in adjacent protein chains are close together they react together, or are oxidized, to give cystine which contains an S-S bond that holds the protein chains by covalent bonds, the protein or polymer chain is crosslinked.

The crosslinks that hold the chains together give a very durable fibre that retains its shape. The crosslinks survive stretching and wool is springy and when when pulled or stretched returns immediately to shape when released. The curliness in hair is due to the S-S bonds in cystine which hold the hair protein chains together. The S-S bonds can be removed by reducing agents. In the reduced form the hair can be brushed, combed, rollered and held into a new style. The hair can then be re-oxidized to form new S-S bonds which then retain the new style. This is the basis of the permanent wave or perm of the ladies’ hairdressers - and the process is responsible for some of the stranger odours found in those establishments! A sulphur crosslink is also found in vulcanized rubber (see below).
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SYNTHETIC POLYAMIDES - NYLON and KEVLAR
Synthetic polymers that contain the amide link are known as polyamides and have the same repeating units throughout unlike the natural proteins. Nylon and Kevlar are examples of polyamides. Like proteins the polymer chains are held together by hydrogen bonds but they do not have the complex hydrogen bonding within the chains that give rise to the complex spiral structure of some proteins. Nylon was discovered in 1935 by an American Wallace Carothers (1996-1937) who worked in the Research Division of the chemical company Du Pont - however despite his discovery he was obsessed with self-failure and committed suicide before the large scale manufacture of nylon (after New York and London) began in the U.S. during WW2.

Nylon 6-6 or nylon 66 is a condensation copolymer made from hexandioyl (adipyl) chlorideand 1,6-diaminohexane. In the laboratory last week you saw the preparation of nylon 68 in the nylon rope trick - this used octandioyl (sebacoyl) chloride as one of the monomers (two more carbon atoms in one of the monomers). In the reaction hydrogen chloride (hydrochloric acid gas) is formed or "condensed" from the reactants.

Another type of nylon called nylon 6 is a homopolymer made from only one monomer called caprolactam. Caprolactam, a ring amide, is heated with water to give a chain compound 6-aminohexanoicacid which on strong heating forms the condensation polymer (releasing water) nylon 6. In caprolactam the amide groups are formed intramolecularly to form rings whereas in nylon 6 the amide links are formed intermolecularly to give long chains.

In addition to van der Waals forces and hydrogen bonding in nylon there are dipole-dipole attractions between chains. These are electrostatic attractions between polar bonds that are similar to, but weaker than, hydrogen bonds. In addition to side to side bonding between chains by hydrogen bonding the additional attractions can give rise to bonds to other polymer chains above and below a polymer chain.

As a result of all three inter-chain attractions nylon is extremely strong and tough. Thin extruded nylon wires, like fishing line, can withstand surprisingly high tensional stress. Nylon can be used to prepare cogs for motors and gears because it is very hard wearing and abrasion resistant, it is lighter and more durable than metal cogs and requires less lubrication. Nylon, because it is so strong, can be spun into very fine threads suitable for weaving into cloth. In the 1960s there was a vogue for nylon shirts (BriNylon was the British product) -they were drip-dry and required little or no ironing but they did not keep their shape like cotton and were non-absorbent and "sweaty" to wear. Nylon shirts were however very hard wearing and did not shrink or stretch - one snag was that the cotton stitching wore out long before nylon material. What gave you street cred in 1960s would definitely make you a nerd today! Nylon curtains were a failure too, as nylon is degraded by ultra-violet light in sunlight.

Kevlar is another type of polyamide called an aramid (from aromatic amide) prepared from the reaction of 1,4-diaminobenzene and 1,4-benzenedicarboxylic acid. Any compound containing the ring of carbon atoms found in benzeneis said to be aromatic - the name arises because many simple benzene compounds have very characterisitic odours.

The benzene rings are planar and ensure that the polymer chain is almost flat. The flat nature of the Kevlar chains means that they hydrogen bond together to give sheets and these sheets are stacked one upon another and are held together by dipole-dipole attractions. The highly organized or crystalline nature of Kevlar has been demonstrated by a special form of X-ray microscopy called XANES and contributes to its enormous strength.

Kevlar cables are many times stronger than steel cables and much lighter and corrosion resistant and find application in marine engineering. Bullet proof vests, windsurfing sails that can stand 60 mph gales without tearing, skis, golf clubs, aircraft parts, gaskets and brake linings are all manufactured from Kevlar. The comparative strengths of some polymers is given below.
Kevlar 20-30 gram/denier
Rayon 1-2
Nylon 66 3-10
Nomex 4-5.5
Nomex is very similar to Kevlar but the amide groups are attached to the benzene rings in a different orientation.
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RUBBERS or ELASTOMERS
Natural rubber is a unique polymer and was exploited by South American Indians to make waterproof clothing and footwear long ago. Columbus in 1493 recorded that Indians played with a ball made from a tree gum ". . . which tho’ heavy would fly and bound better than those fill’d with Wind in Spain." [J. Chemical Education, 1990]. Rubber arrived in Europe in 1735 as "caoutchouc" from the Indian word "caa" (wood) and "o-chu" (to flow or weep). Joseph Priestley coined the word India Rubber in 1770 when he found that it erased pencil marks on paper better than using breadcrumbs. Charles de la Condamine observed that Amazon people poured rubber tree sap on their feet to make waterproof boots - instant wellies! He did not record whether they were also practised at instant birth control! In 1823 Charles Mackintosh made a rubber solution that enabled him to make a sandwich of rubber between two layers of cloth and made the first mackintoshes.

Rubber is derived from the sap or latex from the rubber tree Hevea braziliensis. The sap is a suspension of a natural polymer in water which, on on acidification, coagulates and is made into sheets of crêpe rubber, a tacky elastic waterproof material. Michael Faraday found that rubber was made up of C5H8 units or cis-isoprene units . Gutta percha is another natural polymer of trans-isoprene which differs in the arrangement of atoms about the double bond - it is hard and horn-like and was used to make golf balls.

The polymer chains in rubber, because of the shape of the repeat unit and its double bond, are strongly coiled and held as coils by van der Waals attractions. When pulled the coils straighten out to become extended chains and the rubber stretches. When the tension is removed the rubber chains return to their orginal coiled arrangement. The stretched coils do not form new van der Waals attractions, and hence retain their stretched shape, because the rubber polymer chains are not packed tightly together because of the side chain (CH3) attached to the double bond. Rubber is an example of an elastomer.

Natural rubber is a thermoplastic and in hot weather becomes soft and sticky and in cold weather hard and brittle. In 1839 the American Charles Goodyear made the accidental discovery that the addition of sulphur to natural made a much more useful polymer that was stable to heat and cold and no longer soluble in organic solvents but still rubbery. He had invented the process of vulcanization.

When natural rubber is heated with sulphur a reaction occurs between some of the double bonds in neighbouring rubber chains and the sulphur to give sulphur cross-links between the chains. This gives rise to changes Goodyear noticed. The more sulphur is added the greater degree of cross-linking occurs - elastic bands are soft and very stretchy and have only small amount of cross-linking. Tyres are made of extensively cross-linked rubber which is quite hard and bouncy rather than elastic. 1% cross-linking actually improves the elasticity of rubber as it prevents molecular slippage. The situation is very similar to that in wool described earlier.

Much rubber is now synthetic including neoprene, butyl rubber (pond and landfill linings), polybutadiene (modern golf balls) and SBR (Styrene Butadiene Rubber) for modern tyres, chloroprene (like ordinary rubber except CH3 group replaced by Cl) which has a greater resistance to oils, heat and oxygen, BUNA S or GRS which is a copolymer rubber of butadiene and styrene.

CONTACT LENSES
For many years contact lenses were made of glass which had to be individually ground, were "hard" on the cornea, and inflexible. About 50 years ago "perspex" contact lenses were introduced which was more easily machined than glass, was less prone to chip or break if accidentally dropped, and were physiologically harmless to the eye. However it was stil "hard" on the eye - what was wanted was a flexible contact lens.

Perspex is an addition polymer of methyl methacrylate or methyl2-methylpropenoate and is known as poly(methyl methacrylate) or PMMA. By replacing one of the methyl groups with an hydroxyethyl group to give 2-hydroxyethylmethacrylate a new polymer can be prepared which has all the desireable properties of PMMA but has some additional useful features. The presence of the hydroxyl group allows the polymer to absorb water by hydrogen bonding which lowers the glass transition temperature and it becomes a clear flexible gel - the absorbed water is a plasticizer. Water also effectively lubricates the contact surface between the cornea, the eyelid and the contact lens and the contact lenses are much less irritating.This new polymer is known as a hydrogel and finds application not only as a contact lens but also in lens replacement after cataract removal.
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POLY(ETHYLENE TEREPHTHALATE) (PET) or TERYLENE (POLYESTERS)
This polymer is the most notable example of a polyester which contains the ester linkage and is a condensation polymer made by elimination of water between molecules of 1,2-ethanediol (ethylene glycol - antifreeze) and terephthalic acid (benzene-1,4-dicarboxylic acid).
PET can be manufactured into a wide variety of different forms - as thin films it is the base of magnetic tape, as thicker film it is used for "boil-in-bag" food packaging, a thicker layer is used for soft-drink bottles and oven ready trays for convenience foods, and in the fibrous form it can be woven into polyester materials, e.g., TeryleneTM, CrimpleneTM or DacronTM.
A look at the structure of PET shows that there are no hydrogen atoms attached to the oxygen atoms so there is no possibility of hydrogen bonding between polymer chains. The inter-chain attractions in polyesters are of van der Waals and dipole-dipole nature between the C=O or carbonyl groups. Polyester is stronger than polyethene (van der Waals only) but less strong than nylon (van der Waals + hydrogen bonds + dipole-dipole).

BIOPOL
Biopol (ICI 1980s) is a polyester copolymer of 3-hydroxypentanoic acid and hydroxybutanoic acid that is slowly and harmlessly dissolved in the body so it is used in sutures (stitches). The interesting feature of this polymer is that it is produced by fermentation. A bacterium, Alcaligenes eutrophus, is cultured in a medium containing glucose, pentanoic acid etc. As the bacteria grow they manufacture the polymer to store as a food reserve (much as we store fat) and by the end of fermentation the dried bacteria may contain 70% or more by mass of the polymer. The polymer can be made from entirely natural sustainable materials (plant sugars) and is also biodegradeable as the ester bonds are slowly attacked by water (hydrolysed) and the products are gradually oxidized in the environment to carbon dioxide and water. In May 1997 the Cooperative Bank announced that its bank cards were to be made of Biopol to emphasise its credentials as the the U.K.’s "green" bank.

GLASS
Pliny the Elder recorded that Phoenician sailors came ashore and, not finding any local materials suitable for supporting their cooking pots above the sandy shore, used lumps of of trona (natural soda or sodium carbonate) that formed part of their ship’s cargo. As the trona was heated in the fire it combined with the sand to give a material that flowed. This story may not be entirely accurate but points to the fact that glass as a man-made material has a long history and some of the oldest dated Middle Eastern pieces are over 4000 years old; a deep blue charm is estimated to date from 7000 BC. Egyptians and Romans fashioned a wide range of intricate and coloured glass objects. A highly developed glass industry in Syria in 1500 BC. In medieval times the centre of the glass blowing expertise was Venice (1200-1600 AD).

The serendipitous preparation of glass by the Phoenician sailors is basically the same as that used today. A mixture of purified sand is heated with sodium and calcium carbonate together with some sodium sulphate. The gases evolved help to stir the mixture. The addition of calcium is necessary to make the glass insoluble in water - simple sodium glass is water soluble to give a very viscous liquid known as water-glass (used as an egg preservative in WW2). For those who like the chemistry:
Na2CO3 + SiO2 -> Na2SiO3 + CO2
CaCO3 + SiO2 -> CaSiO3 + CO2
Na2SO4 + SiO2 -> Na2SiO3 + SO3
Glass made as above is known as soda-glass. Replacement of sodium with some pstassium give a harder glass that is familiar as window and bottle glass. The molten glass is made by a continuous process and is floated on a bath of pure molten tin, with which it does not mix, and cooled to give flat smooth sheets. The scale of production is enormous - in 1939/40 a glass melting plant poured out a 51" wide sheet of glass without interruption for 600 days - each day 3.25 miles of glass poured from the plant which is 46,000 tons or 42,100,000 square feet!!!

Common glass is sodium (+ potassium) calcium metasilicate but by replacing the metal ions (Na,K,Ca) by other metal ions (Pb,Ba,Fe,Co) and by replacing the silicate (SiO3) with borate (BO3) or phosphate (PO3) a wide variety of different glasses can be made.

Write down what you consider to be the most important advantages and disadvantages of glass.
Let us look at some of the features you have listed. Hopefully you have placed transparency as one of the most important advantages of glass.

Transparency - the ability to transmit (conduct) visible light without distortion. What other common materials are transparent? most liquids and some plastics (perspex, polycarbonate). Note that coloured glass is transparent but only to selective wavelengths of light. What have many of these materials in common? They have non-ordered structures - they all have the "liquid" structure, i.e., molecules in close contact but free to move. Glass can be considered as a very viscous liquid. Does glass flow like a liquid? Yes it does! When stained glass windows at Chartres Cathedral were restored it was found that many pieces of glass were much thicker at the bottom than at the top because the 500 or 600 year old glass has flowed under the influence of gravity. Glass, like many polymers, does not melt - it softens into a treacly liquid above the glass transition temperature (see polymer notes).

Any of you who use a dishwasher may have noticed that glass items that are regularly washed in a dishwasher become cloudy or, in extremes case, opaque. This devitrification occurs because certain components of dishwasher detergents chemically scour the glass surface and induce the growth of tiny crystals which continue to grow (much like clear honey eventually crystallizes) and render the glass opaque. The devitrification extends into the glass and cannot be removed by polishing.

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Structure and Bonding
The structure of glass can be regarded as a mixture of an ionic compound (containing cations and anions) and a covalent polymer(containing long branched chain molecules). The basic structure comprises long branched polysilicate chains that are sometimes known as network formers. The chains are tangled and branched and even when molten the chains are not free to move and molten glass is viscous. The silicon atoms can be, partly or wholly replaced by, e.g., boron in borosilicate glass or PyrexTM or phosphorus in crown glass (optical glass). The lecture diagram showed a tiny fragment of a polysilicate chain. Each silicon is covalently bonded to four oxygen atoms and each oxygen can either form two covalent bonds to silicon OR forms one covalent bond and carries a negative charge.

In order to balance the accumulated negative charge on the silicate chains there are metal cations that randomly occupy suitably sized cavities in the silicate network. The bonding between the cations and the chain anions is ionic.

When simple glass is subject to stress - dropped on to a hard surface or hit with a hammer - it shatters readily because it is brittle. This brittle nature arises, in part, from the ionic nature of glass - ionic compounds are usually brittle, e.g., a large crystal of rock salt will shatter is struck with a hammer. However the way in which glass breaks is different to that of ionic compounds. Ionic compounds contain highly regular arrays of ions and split or cleave cleanly between layers or rows of ions - ionic compounds display good cleavage. Glass does not cleave - it fractures - or breaks randomly to give curved (conchoidal) surfaces with sharp edges. The random fracture arises, in part, because of the lack of order on the molecular scale.

Why does glass sometimes shatter when heated suddenly? There are three properties of soda-glass that lead it to shatter:
expands significantly when heated,
is a poor conductor of heat,
the structure contains voids.
When hot water is poured into a cold glass vessel the inner wall of the glass in contact with the hot water expands. However because glass is a poor conductor of heat the outer walls remain cool and do not expand but remain in contact with the expanded inner surface. The temperature difference thus sets up strain in the glass which may lead to cracking or shattering. Thin walled tumblers are much less likely to crack as a result of thermal stress than are thick walled tumblers. The expansion of glass is concentrated around voids in the structure of glass. An article manufactured out of thick glass needs careful annealing (heat treatment) and slow cooling to remove strain - the 20 ton glass mirror used to manufacture the 200" reflecting mirror of the Mount Palomar telescope required one year’s cooling!

PyrexTM or borosilicate glass contains about 12% boric oxide replacing some silicate and contains much less sodium and more aluminium. The resultant glass contains more branching and cross-links and fewer voids, expands very little when heated, is not subject to the thermal stresses of common glass and is widely used for oven-to-table ware. More sophisticated glasses can be used to manufacture pans that can be placed directly onto a gas flame or red hot electric cooker ring.

Ultra low expansion glass VycorTM is made by moulding a vessel from glass and then leaching out the metal oxide with strong acid to leave only the silica network. The vessel is then baked at high temperature wherupon it fuses and shrinks to give a translucent glass resembling quartz that can be plunged from red-heat into ice-cold water without shattering.

Glass can also easily shatter as a result of impact and in many situtations this is highly undesireable. Car windscreens are regularly hit by flying grit and insects - a cockchafer beetle hitting a windscreen at 40 mph packs quite a punch! It is essential that a windscreen such be able to withstand such impacts and, if it does fail, that it does so safely. The glass windscreen is carefully annealed or tempered during manufacture to strengthen it and also incorporates a polymer interleaving which prevents the glass shards from dispersing if the windscreen shatters. The dis-benefit is that if the windscreen shatters whilst the car is in motion the driver cannot see a thing through the crazed glass until he/she is able to break a hole in the windscreen.

Specially toughened glass AmourplateTM and HerculiteTM are used in the construction industry (glass doors etc.) and are manufacture to shape, then heated to softening point and chilled suddenly to leave the surface of the glass under a good deal of compressive tension - such glass is four or more times stronger than ordinary glass but cannnot be machined further. Glass can also be reinforced with steel mesh to give security glass (burglar proof).

What colour is ordinary glass? Look through a section of the base of a milk bottle and you’ll see that it is perceptibly green. The old ink-bottle, shown to you in the lecture, is more distinctly green. The green colour is due to ferrous Fe2+ ions in the glass which come from impurities in the sand - mainly iron oxide (Fe3+)(O2-)3 (rust). The Fe3+ ions are reduced to Fe2+ during the manufacture of the glass. However by using purified sand the green colour is usually not a problem. An alternative is to add oxidizing manganic ions Mn4+ (MnO2 or pyrolusite) during manufacture which oxidize green Fe2+ to almost colourless Fe3+ (the black MnO2 is reduced to almost colourless Mn2+).

However for certain applications, e.g., optical fibres, the glass must be absolutely transparent (100% transmittance or light or zero absorbance). Fibre optic cables transmit information as light pulses rather than electic pulses. Optical fibres are usually double glass with an outer sheath of lower refractive index which prevents light escaping out of the fibre. The high purity optical glass is drawn out into fine fibres (5-100 µm diameter) which are then packed into bundles of several thousand. The bundles are strong but retain the flexibility of individual fibres. Such a bundle of fibres can transmit 30 000 times more information than an equivalent diameter copper communications cable as well as being cheaper and lighter. Fibre optic technology has contributed to the communications revolution and a fibre optic cable link Europe with the States and three cables link Japan with the States. An undersea fibre optic cable will (or may already) connect the U.K. with Japan. Fibre optics are also used in endoscopes for internal bodily examination and, in conjunction with lasers, in controversial key-hole surgery.

For other purposes many other different sorts of glass may be required. These are just a few other types of glass:
lead crytstal (or flint glass) - by the addition of lead oxide gives a brilliant glass of high refractive index that can be easily cut and polished is obtained,
crown glass - 0% silicon 5% boron 57% phosphorus used in lenses and other optical applications, barium flint glass is used in bifocal lenses,
amber glass - for protection of light sensitive liquids (drugs, chemicals) contains Fe3+ and S2- which make the glass dark brown, also green glass for wine (Fe2+ rich glass),
cobalt blue glass - contains Co2+ and was formerly used for poisons and by chemists in flame tests to mask the yellow colour of sodium ion which is a common contaminant,
white opaque glass - is made by the addition of calcium fluoride (CaF2 fluorspar) or stannic oxide (SnO2) to the glass and is used in the food and drink packaging industry,
nuclear storage glass - molten glass is an excellent solvent for metal oxides which are accommodated in the voids in the structure; metallic nuclear waste (caesium, cobalt, strontium etc.) is converted into oxides and dissolved in molten glass (vitrification) to give a relatively inert shiny black glass which is stored in sealed steel containers underground in geologically sound areas (nimby!),
one-way glass, heat/light reflecting glasses, low transmission, and insulating glasses are designer glasses manufactured to meet a wide range of security and construction purposes,
optically variable or photochromic glass is used in spectacles and car windows in sunny climates and is borosilicate glass containing silver and copper compounds - the silver ions are photochemically reduced by copper ions to silver metal in strong sunlight causing the glass to darken, when the light fades the reverse reaction occurs and the glasses becomes light again.
low light Cu+ + Ag+ -> Cu2+ + Ag strong light

Fibre glass is coarsely spun conventional glass and is widely used in insulation and the manufacture of fireproof cloth (replacing dangerous asbestos) in safety curtains and fire blankets. Mixed with resins, glass fibre forms light rigid materials for construction of boats, skis, canoes etc. Glass fibre filter papers are used by chemists to filter corrosive solutions.
Also available - Introduction to Ceramics, written by Greg Geiger of The American Ceramic Society - Click here
Please send comments, suggestions on this paper to:
Dr David Harrison(harrisond@newi.ac.uk)
or: Dr Clive Buckley(Buckleyc@newi.ac.uk)

Soul Searching

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Your soul has desired so much today......and your body done alot.
did you consider that your body is the temple of the Holy Spirit?
Come on, face it.
Your life will be demanded of you at a time you do not expect or Christ may appear any time.
Have you accepted Him as personal Lord and Savior today?
Don't delay coz later may be too late.

Please do so now.
Search your soul.
Is what you do a reflection of GOD?
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Monday, February 23, 2009

Nick Voice's Testimony

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Chancellor college Library,hot hot hot in a hot summer

From Library roof

Nice view

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Likoma Island

Ching'aning'ani

Lake Malawi

Malawi

Brains and much brains!

Material Science

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