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Chemistry: Ceramics and Glass

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About this Lesson

  • Type: Video Tutorial
  • Length: 14:38
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 157 MB
  • Posted: 07/14/2009

This lesson is part of the following series:

Chemistry: Full Course (303 lessons, $198.00)
Chemistry: Condensed Phases: Liquids and Solids (15 lessons, $25.74)
Chemistry: Ceramics (2 lessons, $3.96)

This lesson was selected from a broader, comprehensive course, Chemistry, taught by Professor Harman, Professor Yee, and Professor Sammakia. This course and others are available from Thinkwell, Inc. The full course can be found at http://www.thinkwell.com/student/product/chemistry. The full course covers atoms, molecules and ions, stoichiometry, reactions in aqueous solutions, gases, thermochemistry, Modern Atomic Theory, electron configurations, periodicity, chemical bonding, molecular geometry, bonding theory, oxidation-reduction reactions, condensed phases, solution properties, kinetics, acids and bases, organic reactions, thermodynamics, nuclear chemistry, metals, nonmetals, biochemistry, organic chemistry, and more.

Dean Harman is a professor of chemistry at the University of Virginia, where he has been honored with several teaching awards. He heads Harman Research Group, which specializes in the novel organic transformations made possible by electron-rich metal centers such as Os(II), RE(I), AND W(0). He holds a Ph.D. from Stanford University.

Gordon Yee is an associate professor of chemistry at Virginia Tech in Blacksburg, VA. He received his Ph.D. from Stanford University and completed postdoctoral work at DuPont. A widely published author, Professor Yee studies molecule-based magnetism.

Tarek Sammakia is a Professor of Chemistry at the University of Colorado at Boulder where he teaches organic chemistry to undergraduate and graduate students. He received his Ph.D. from Yale University and carried out postdoctoral research at Harvard University. He has received several national awards for his work in synthetic and mechanistic organic chemistry.

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Thinkwell
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This is a fork. Forks are made out of metal. This is a bowl. It's made out of something called a ceramic. Now the definition of a ceramic is a little "iffy." Basically everything that isn't a fork. I mean it's all things that are made out of inorganic compounds but they are not metallic. Sort of an operational definition. Not, this is a ceramic bowl. It's probably made out of china porcelain and I will have more to say about that in a second. I'd show you the inside but it contained day old nachos and it's sort of yucky, so...
Anyway, here's the idea. We can define a ceramic by just some operational words. Typically, they are crystalline but in fact they can be amorphous as well and I'll talk about that. They're typically insulating but they can be conductive as well and, in fact, some are super conducting and I'll talk about that later on. But, it is certainly true that they are generally stable at high temperature and so, if you think about things that they might be useful for, they are useful for things that have to deal with high temperatures. The tiles on the underside of the space shuttle, for instance, are ceramic tiles and they basically insulate the bottom of the space shuttle from all of the heat that arises from the friction when the space shuttle reenters the atmosphere. They are also typically hard and brittle and that can be both good and bad. If you have something that's hard, that might be a good thing if you want to have an abrasive, but they are brittle, meaning that if you accidentally hit it with a hammer or something like that, it's not going to go with the flow and just dent a little bit. It could just get totally destroyed.
Now, let me give you some examples. Glass, window glass, glass for making dishes, that's a ceramic, that's a silicate ceramic (and I'll talk about more of that later on). Catalyst support - I've shown you the inside of a catalytic converter and the palladium and platinum is deposited on a catalyst support because you don't want to waist a lot of platinum and palladium, only those atoms that are on the surface are going to do anything and so, what you have is a support that is able to withstand the high temperatures on the inside of a catalytic converter, but just holds everything together, and then on top of this catalyst support, you put the active metal, the palladium or platinum. Abrasives - if you go and get a piece of sandpaper, for instance, very often it will be silicon carbide or carborundum and it is a hard material. It's brittle, it's good for sanding things. And finally, coming back to our bowl of day old nachos, clay pottery is made out of a ceramic typically something like kaolinite, which is an aluminum silicate, and what happens in the reaction is that you fire it, so you make it into what you want and then you fire it and what happens is it changes into two other oxides, mullite, which is aluminate silicate and silica, and driving off water in the gas state. And the reason why a piece of ceramic is hard is because the mullite forms fibers that get woven into or essentially woven into the silica backbone and so that's what gives it the structure. But, other examples are things like cement. Again, a ceramic is sort of like, you know it when you see it. It's not a fork. It's not a metal. It could be conductive, but it isn't a metal. I'd show you the reactions for cement, but they're just lots and lots of reactions and they're really complicated.
Let's focus on one ceramic that you're all familiar with, which is glass. And glass actually has a broader term to chemists than just things that you make bottles and windows out of. A glass is anything that's amorphous. So, we have crystalline solids and then the opposite of a crystalline solid is a glass, or a amorphous solid. Now, what glass for this kind of glass is, is a quartz glass, or silica glass. This is actually not quartz glass or silica glass, this is based on quartz glass. The simplest way to make glass is to take silicon dioxide, take some quartz, and you heat it to a liquid, and this of course takes thousands of degrees, a couple of thousand degrees. And then if you cool it rapidly, you get it to come out not as a crystal - it started out as a crystalline solid - but it comes out as an amorphous solid. And the reason is when you cool it down rapidly, it doesn't have time to get organized in its absolute most perfect situation, which is what it is when it's a crystal, so you know, you have dangling bonds and you have bonds where the bond angles aren't exactly quite right, and so it's not regularly periodically ordered the way a crystalline solid is, and that's what we call a glass. But, in fact, plastics are also glasses. Plastics are chains of organic molecules. Plastic are not ceramics, because they are organic, not inorganic, but they are glasses because they aren't ordered in a crystalline lattice.
People don't actually do much with silica glass; at least it's not the common glass that you're familiar with. What you're familiar with is soda lime glass, and soda lime glass comes from taking silica and adding bits of sodium oxide and calcium oxide. Calcium oxide is lime and sodium oxide is sodium salt, hence the name soda, like in sodium bicarbonate and sodium carbonate and that sort of thing. If we then add additional transition metal oxides, we can give it color, things like cobalt glass. This is, I'm pretty sure, an example of cobalt glass, in which you've added some cobalt oxide to make it blue.
Now, your Mom and Dad probably have some leaded crystal and leaded crystal is silicon dioxide that has potassium oxide and some lead oxide in it. And what the lead oxide does is it increases the index of refraction. It makes it more dense so leaded crystal seems heavy for the same size object but it also increases the index of refraction and based on the physics, that's what allows the light to bounce around on the inside of the glass, which makes it all shiny and sparkly and gives it nice colors. Diamond for instance, which is not a glass, but diamond has a really index of refraction which is why diamonds are really sparkly. Now, clearly there is a misnomer here, because we're saying that this is a glass and so leaded crystal doesn't mean that its crystalline because it's not crystalline. It's still a glass; it's just sort of unfortunate that it goes by the name leaded crystal.
And, finally, the last kind of glass I'd like to talk about is borosilicate glass, in which you take silica and you add some sodium oxide and aluminum oxide and diboron trioxide and borasilicate glass goes by the name Pyrex and Kimax. It tolerates high temperatures better. If you take a piece of window glass and you heat it up really hot, you may have actually done this with a drinking glass. If you heat it up really hot, and then cool it down really fast, sometimes it will shatter. And that's because glass typically has a fairly large coefficient of thermal expansion. So, it gets larger when you heat it up and then when you cool it down really fast, it has to shrink really fast and that introduces stresses which cause the thing to shatter. Remember, ceramics are brittle and glasses are brittle. The coefficient of thermal expansion on borosilicate glass is smaller and so you can actually cook in it and you don't run as great a risk of having it shatter and break into a million pieces
Finally the most interesting ceramic that's been in the news, maybe not so much now, but certainly when I was in graduate school about ten years ago, and I had the pleasure and the honor of working in this field, is that in 1989, I believe, but certainly in that time range, a superconducting ceramic oxide was discovered. You'll remember from my operational definition of ceramics, most ceramics are insulating. They do not conduct electricity. Well, this compound not only conducts electricity, but if you cool it down to below about 93 Kelvin, it conducts electricity with zero resistance. Not only a little bit of resistance; remember good metals, things like copper and silver and gold conduct electricity, meaning that they have small resistance. Well, this stuff, when you cool it down to below 93 Kelvin, actually conducts with zero resistance. And that's why we call it a superconductor. Up until that point, the highest temperature superconductor that had ever been discovered, was a niobium alloy and it had a T[C], or a temperature below which it was superconducting on the order of 23 Kelvins or something like that. And it was generally believed that it wasn't going to get any higher. I actually was one of the people who thought we could do better and so I was working on materials, not this particular material, but working on high T[C] superconducting and looking for materials that might superconduct at higher temperature. Now, this particular compound, which goes by the name of yttrium barium copper oxide, has the formula YBaCuO, where x is a small number on the order of a tenth or something like that. And it has the structure, which is called the defect perovskite and if you take a look in the graphic, you'll see what a defect perovskite is. Well, it's defective because perovskite is calcium titanium oxide and perovskite is a cubic structure in which there are titaniums in the cube corners, oxygen along the cube edges and then a calcium in the middle. And see if you can see why this is a defect perovskite. First of all, the yttrium and the bariums share the calcium site, so the yttrium and the bariums combined form one. So, we have three of them here, but it's 3 is to 1, and then the copper sits on the titanium site, so that's 3 is to 1, and so there should have been 9 oxygens instead of three oxygens, right? So these two guys go on the calcium site, these three coppers go on the titanium site and then the oxygens would go on the oxygen site, and since it's 3 to 3 to whatever, it should have been 9. So there are a bunch of oxygens missing, and that turns out to be important in the structure.
So, why is this all interesting? Well, if you have a superconductor, you can do two things that are really cool. First of all, you can make a kick-ass magnet because what an electromagnet is, is it's current flowing through a wire. And you can run a lot of current through a superconductor and because it has no resistance, you can run the current through and it doesn't get hot and so you don't have to worry so much about keeping it cold. If you run a lot of current through copper, eventually you'll just melt it. Whereas, if you run current through a superconductor, since there's no resistance, it doesn't get hot. So that's one thing.
And then the other thing is, you can just transmit huge amounts of power without losses. So when we run electricity right now through a wire, like a high-tension wires that you see on the poles, those wires get a little bit hot as a result of the fact that they have resistance. And we lose a lot of heat to the environment and we lose voltage as a result of having to run electricity through conventional wires. And so if we could just distribute electricity through super conducting wires, we would not waste that energy. We wouldn't waste it as heat that's given off to the environment. So, being able to find materials that superconduct is really important. Now, the problem is you have to cool them down. Before, you had to use liquid helium and liquid helium is expensive. The analogy is always that liquid helium costs about as much as champagne, whereas liquid nitrogen, which boils at 77 Kelvin, is more like the cost of beer. And so, clearly, the big breakthrough is the fact that we now have superconductors that superconduct above the temperature of liquid nitrogen, so we can use liquid nitrogen to cool them and that make sit a lot cheaper. And, in fact, the critical temperature has been pushed up into the neighborhood of 150 Kelvin. It evolves a little bit year by year, and I think the last number I saw was in the neighborhood of 150 Kelvin.
Anyway, here's another billion-dollar challenge for you. Because, scientists don't really understand how this all works. And if you could understand how it works, you can make a better one, you could write your own ticket. Open up your billion-dollar company; be richer than Bill Gates. Because, again, the applications are waiting for the material. Sometimes, when you have a new material, you have to wait for the application. Now what we have are applications for ceramics. Another application for ceramics is high temperature, so people are talking about making engine blocks out of ceramics, for airplanes and stuff like that. Again, here we have an application that's just waiting for the right material, room temperature superconductivity, so we don't have to deal with liquid helium, we don't have to deal with liquid nitrogen, and we're not going to lose any more energy to the universe by just heating up electrical wire. So, billion dollar challenge for you.
Condensed Phases: Liquids and Solids
Ceramics
Ceramics and Glass Page [2 of 3]

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