MSE_F2017_01

Whatever one you like, yeah. You know, you shouldn't, I mean, it doesn't count as two modules to watch the same module twice in two different semesters, right. Once I do them they're archived, and one of the reasons for doing that is sometimes the videotape doesn't work because we don't have any videographer, or sound didn't work or something, and then we can always substitute one from a year before or something, okay. But frankly, if you're not being quizzed on it, who cares if you missed a class, right? You should have gotten sick and you've missed a class, right. Is every class critical? No. Is any class critical? Well, hopefully if you're supposed to get the grade you have to learn something.

I remember, I have sat through probably ten different faculty meetings over the last forty years where the faculty are talking about the students' curriculum and how they need to learn X, you know, we can't omit this topic from the curriculum because they can't graduate without knowing such-and-such. And I point out that, well, you know, the average grade on the quiz is about sixty percent, so obviously there's forty percent they don't know, so must not be important to know a hundred percent of everything. And in fact it's not, the whole purpose of education is not to — actually, have a quote from Robert Hutchins. You might know who Robert Hutchins was. Anyway, he was the president of the University of Chicago after World War Two, and he wrote the great books of the rest, or assembled the great books of the Western world. But he wrote books about education and he was a philosopher on education, and he said the mind is not a receptacle, information is not education, education is what you remember after everything you've learned has been forgotten. Okay, so one of the reasons I teach in stories or parables is because the only thing I remember from my education is the stories, okay. I don't remember the equations, I just remember the stories they told, right.

Anyway, so it's about time. If other people come in that's fine, but if our two videographers — one of these is going to be videotaped for MITx. So today I'm going to talk about introduction to structural materials, as the introduction to this twelve hours of lectures for the course, but also for some modules or mini-modules that will be done for the MITx program. So there have been many ways that people have classified materials over hundreds or even thousands of years. One is to think about — one way of classifying them is to think about either structural materials or functional materials. Those are two very broad classifications, but if I do that, it turns out it's important to recognize structural materials are used in very large quantities.

In fact, there are four structural materials we'll learn about that are actually used in a billion tons a year, okay. In fact, I have an example of each one of them right here. [Tom produces samples.] One is stone, okay. Stone is used at 53 billion tons a year, and if you think about that, if you sell stone for only twenty dollars a ton — it might be worth $40 a ton — but that's a hundred-billion-dollar business worldwide. But it also tends to be sort of a local business, because you can't afford at $20 a ton to be transporting the stone very far, okay.

Another material, actually the second largest use of structural material, is concrete. And this happens to be a piece of concrete siding for a house, which is actually a fairly new material in the last ten or fifteen years. Concrete's not new, the Romans used it, but it's only in recent years that we started making siding for houses. We used to use wood for the side of houses and the ants and termites would eat it, but then we started using plastic and it deteriorated in the sun after ten years or fifteen years or twenty years. Concrete, we know from the Romans, if you make it properly will last for thousands of years. And it turns out we use over 4 billion tons a year of concrete. Of course that's not completely fair because a lot of the concrete that we use already has stone in it, it's actually a composite.

The next largest is engineered wood product. And of course we've been using wood products for structural houses and bridges and railroad ties and things for thousands of years, but one of the problems with wood is nature doesn't always grow the trees in a nice uniform way with homogeneous properties. So now we basically glue these things together into an engineered product and we don't have to have such big trees. We actually will probably talk at some point about — the one of the first energy crises of 400 years ago was the fact that they were tearing down all the big trees in England, and they discovered the new world, and one of the first things they did was come over to the new world and start an ironworks right here in Saugus, Massachusetts, because we had big trees, okay. So far as that goes, but we'll talk about that.

And the fourth member of the billion-ton-per-year club is basically steel. And so this is the closest thing I have to an I-beam, but I-beams we build bridges and buildings and whatnot. [Tom holds up a steel test plate.] This is a piece of steel from a nuclear submarine hull, or actually test plate for a nuclear submarine. And steel is about 1.6 billion tons a year, but at about $500 a ton it is the closest thing to a trillion-dollar-a-year economy, okay. So it turns out the first — actually, the person who was richest, the richest person in the world to date that we know of, was Andrew Carnegie. He was richer than Bill Gates and Warren Buffett and all these other people in constant dollars, okay. And he made his money off steel. And in fact, this department at MIT was known as the metallurgy department. Metallurgy didn't start until the 1880s, and steel was the thing that built railroads, and it still is one of the primary structural materials, but not the most common.

Okay, now we have — so we have structural materials, we also have functional materials, okay. And if we look at functional materials, not that we're going to spend a lot of time on those, but you know about single-crystal silicon, okay. [Tom holds up a silicon crystal.] This is a piece of silicon single crystal that's been fractured, but these things are grown in sixteen-inch diameter and sliced, and they make wafers out of them, make semiconductors out of them. This is a piece of polycrystalline silicon that is solidified over several weeks very slowly, not to make single crystals but to make very coarse-grained polycrystals, and this is basically for solar cells. This one's been sawed up with diamond saws. This one is still a single crystal.

This is a piece of functional material, it's sapphire, and it's grown the same way. You heat it up to 2,000 degrees centigrade, you melt it, you slowly cool it in the furnace, you make something — we call it a boule of sapphire, it's about the size of a big football, okay. It takes about a month to solidify and you get very big grains. [Tom passes the sapphire around.] I can pass this one around, you'll be able to see some of the grains in here. For these two polycrystalline materials we slowly cool them to try to get large grain size because of their functionality. This one we want a single crystal.

We have some single crystals that are structural materials. [Tom holds up a turbine blade.] This is a turbine blade, and this is actually a single crystal because we need the mechanical properties — we don't want the grain boundaries. Actually we don't want the grain boundaries in any of these, but we go to large grains to get the fine grain size, okay. This particular single crystal has been cut into — when they solidify it at 2,400 degrees Fahrenheit they actually create these internal cooling passages, and then they laser or electron-beam drill holes in here for cooling channels. Each one of these is worth about $4,000, and every disk on the turbine has about close to a hundred. So if you want to know why the engine costs five or ten million dollars, you got a million dollars in one disk with the blades, okay.

Now there are cases where you'd like to have a fine-grained material for strength, and here's an example of that. [Tom holds up a copper sample.] This is copper, it's actually copper with just a little bit of silver in it, only two-tenths of a percent or a tenth of a percent to strengthen it, but it had very large grain size. And I was asked one time — I was given all of 48 hours to go to New York where they were making this, and they were going to draw it into wire for the Northeast extension. If you've taken Amtrak and the Acela train between New Haven and Boston, they were putting in the trolley wire. This is the overhead conductor that basically carries the electric current. You need the copper for wear resistance, corrosion resistance, electrical conductivity, but it also has to be a structural material, it has to be strong to be able to be strung along a couple hundred miles.

Turns out I was given 48 hours to accept or reject six million dollars worth of this copper. I rejected it, and then they had a big fight over it. Turns out what we ended up using — and in fact this is ultrafine grain as opposed to this coarse grain. This was the casting that they wanted to use, but someone else came up — a big copper company — with an ultrafine-grain product which has tremendous ductility and strength. And in fact that was the big fight, it had too much elongation, okay. How can you have too much elongation for a structural material? So this is actually a tensile specimen and you can see the ductility of the copper.

So those are some examples of things that you can look at, of different structural materials. Structural materials are used in extremely large volumes, usually measured in tons, whereas things like the sapphire is actually the substrate for an LED light, okay. The gallium nitride that's put on there is actually put onto a sapphire substrate, and so they take these great big boules of large-grain material, slice them up into very small things, and use them in gram quantities in an LED.

There are structural materials that are not used in tonnage quantities, such as diamond. [Tom holds up a diamond pad conditioner.] This is what's called a diamond pad conditioner. It's nothing more than a steel pad with diamond raised in the surface, and when you're making semiconductors you have to use the diamond to polish the semiconductor so that you can lay on another twenty layers of different things, okay. So this is a structural material. Diamond is one of the few structural materials that has very high cost but very low volumes, as opposed to stone, which is used in very high volumes at very low cost. So here's a pad conditioner of diamond. Diamond is a very important structural material because it's the hardest material, strongest material known, and it can work any other material. That silicon photocell, this rectangular — that little square cube — or it's not a cube anyway, rectangular parallelepiped I guess — of the silicon was cut with diamond, okay.

Now what's the next material? The next material in line after the billion-ton-per-year club — you can take all the plastics in the world, lump them together, and you only get 300 million tons a year, okay. [Tom holds up a plastic pipe section.] So this is a piece of polyethylene pipe. It's got yellow stripes on it because they're going to make it into gas pipe. It has the advantage it doesn't corrode, okay, whereas the steel pipe they used for eighty years is corroding all the time and creating problems.

And we can talk about some of these other structural materials, but structural materials have important properties. They can be strong, usually. They can be ductile — this is a piece of plastic that I can bend into a horseshoe and will not break. Plastics also — different materials can be brittle, okay. And we can pass these around and you can look at the brittle fracture versus the non-brittle fracture in these things.

So one of the things that's important in structural materials is the tensile strength, or the force necessary to fracture it for a given cross-sectional area. But the other thing we learned about fifty years, sixty years ago after World War Two, is we should also be very concerned about toughness of the material. And it turns out you can illustrate toughness with just a simple sheet of paper. [Tom picks up a sheet of paper.] Now a tensile test measures the force of fracture, a toughness test measures the energy of fracture, and that's the difference between the two. For nearly — well actually, going back to Galileo was one of the first people who ever showed a picture of a tensile test of the material, okay. But we learned about the energy of fracture back in the 1920s, and we never really paid too much attention to it because the guy who'd studied it was studying glass. But then in World War Two we had a problem with ships breaking in two in the middle of the North Atlantic, a couple of Liberty ships, and we'll talk about it later. But we learned afterwards that you need to have good energy of fracture, you can't have something that's brittle, doesn't absorb energy.

So the difference — what we learned about fracture mechanics — I can take a perfect material like a piece of paper like this and I can pull on it with several pounds of force, but if I put an imperfection in it, if I put a little notch, it takes ounces, not pounds. So that's a measure of toughness. And if something is brittle, if you put it back together the two halves meet. It's like breaking a coffee cup, you can glue it back together with Krazy Glue because all the pieces fit. But if you take a ductile material and you pull it apart, they don't go back together, okay, because they stretched and deformed before they did it.

So there's lots of properties of these structural materials. Tensile strength, which is the force of fracture. Toughness, which is the energy of fracture. Creep strength, which is high-temperature fracture that occurs over long periods of time. Corrosion — many of our structural materials are metals, and one of the Achilles heels of most metals is they corrode. There are other properties such as aesthetics. I happen to like — if you go in my office, I like wood, I have cherry bookcases, I have a cherry desk, I have cherry chairs, okay. So it's a structural material. I could have steel tubes, okay, or steel sheet for filing cabinets or desk or chairs, but, you know, some people like aesthetics of different materials. There are fatigue properties — you take a paper clip and bend it back and forth, cycle it, and you can have problems that it will eventually fail.

Functional materials have other properties than mechanical properties they have to worry about: chemical or magnetic or electrical or optical or thermal. And some of these have some pretty amazing properties, and people would say that over the last fifty years they've been tremendous advances in the functional materials because of how many chips you can put on a semiconductor, or the strength of magnets. [Tom holds up a magnet.] These are neodymium-iron-boron magnets, and I can pass it around. They have little plastic spacers — if you put them together without the plastic spacer it's not easy to get them apart. And we'll talk a little bit later about the rare-earth magnets and their strengths and whatnot. So these functional materials are not the primary things that we're going to talk about, but I will use some examples as we get into things.

Another topic that we're going to cover is the fact that we cannot just engineer materials like we want anymore. In the old days you want to build a house, and you build that out of straw, you build it out of wood, you build it out of brick — and you can tell the story of the three little pigs, right, about which one had better properties for their materials. But today you're going to have neighbors who are going to tell you what you can build your house out of, okay. And there's a paper that I'd asked you to read called the age of socio-engineering. If you want to be an engineer today, you don't just worry about structural materials. Norm Augustine was an engineer at Martin Marietta, later became chairman of Martin Marietta, he became president of the National Academy of Engineering, he was asked to be science advisor to the president, was smart enough to turn it down. But in any case, he's a Princeton grad but he is on the MIT corporation. But he talks about the age of structural materials, the mechanical age, the electrical age, the information age, and now today — he gave this talk twenty-five years ago — the socio-engineering age, where you are going to have to look at different externalities.

In economics, externalities are things that the cost of a material or process or a policy will impose a cost or benefit that affects someone who did not choose to incur that cost or benefit, okay. That's the definition of an externality in economics, okay. So you can have people who are making something and they're polluting the atmosphere, and so you see the smokestacks there. You can have someone who chooses to smoke in a public facility, and everyone else gets to smoke with them, okay. But we've changed this — age of socio-engineering, you now have to go outside to smoke, okay, because people decided that you have no right to make us breathe your smoke.

Now there are lots of externalities. There are political externalities. I passed around those neodymium-iron-boron magnets, and rare-earth metals are used in a wide variety of things. They're not really that rare. They're called rare earth because they were not — they're in the middle of the periodic table and they were not that easy to extract because they have very strong affinity for oxygen. And in fact scandium has the strongest affinity of any metal for oxygen, and scandium, because of its great affinity for oxygen, currently costs about $2,000 a pound and is not used as a structural material. But it could be used at about a tenth or two-tenths of a percent in the next generation of aluminum alloys for aircraft. Problem is, you put a tenth of a percent or two-tenths of a percent scandium at $2,000 a pound into an aluminum alloy and you just doubled the price of the aluminum alloy. The scandium is — even though it's a one-thousandth or one five-hundredth the volume of the aluminum alloy, that amount of scandium is equal to the rest of the alloy.

So there's a challenge there, can we get the scandium from the oxide. These rare earths are not really that rare, but it turns out 97% of the rare earths over the last twenty-five years have gone to be manufactured in China. Why? China has 36 percent of all the rare-earth reserves, they have 130 million tons. That's not very rare, okay. We have almost as many reserves in the United States of rare earths, but it turns out China is willing to manufacture the rare earths, and we for political environmental reasons have let them do it. Well, they took over 90 percent, 97 percent of the market, and then they shocked the world in 2010 by essentially cutting off rare-earth supplies to Japan. And so all of a sudden Sumitomo and Hitachi and all these people make electronic components that require rare earths, okay.

The motors can be reduced in size by about a factor of five or ten. Well, if you're making a motor with rare earths in it and all of a sudden you can't get rare earths, you can't just all of a sudden make bigger motors and put it in the same car, okay, it doesn't fit, okay. So this was a major shock, and everyone else had given up on producing rare earths. Well, why are they given up on producing rare earths? Well, if you look at what it looks like to make rare earths in China, you can see why we exported the technology. It's filthy, it's dirty, it's environmentally unclean, and we would just as soon export our filthy dirty processes to a third-world country. Now I don't think China would like to be known as a third-world country, but in fact they were willing to do it.

And so it was tremendous shock, and because of that all kinds of people wanted to start investing in rare-earth technology. We weren't going to let the Chinese hold a gun to our head again, because it wasn't just Japan, okay, because companies in the United States were buying these things from Hitachi and Toshiba and others in Japan. But China really shocked the world economy by refusing to sell their rare earths to Japan. So all of a sudden there were bills in Congress and there were incentives to open up the old rare-earth mines and processing facilities, and there were all kinds of academics who started trying to think of a clean way to make rare earths. And after a few years — well, first of all, after about a year or so the Chinese under pressure, but also they had achieved their objectives, started selling rare earths again to the Japanese. But no one wanted to have the gun pointed at their head again, and so now China no longer has a stranglehold.

And what I've learned over my career is it takes about five years — the, I remember in 1973 there was the Arab — the first Arab oil embargo, and I remember sitting in the gas lines. People would sit for two hours to be able to purchase a tank of gas, you couldn't drive your car without gas. And Saudi Arabian and other Middle Eastern countries basically said we're not going to sell you oil. And so the government started creating a Strategic Petroleum Reserve, companies like utilities that were burning oil to generate electricity decided they were going to be able to use two different energy sources, they'd be able to flip a switch and go from oil to gas to coal or vice versa. So in 1978, five years later, when the Arabs tried the same thing, it was much less effective. People had learned their lesson not to put all your eggs in one basket, okay, which was the oil basket, and they diversified their energy portfolio, okay. So it takes five to ten years to recover from a supply disruption, and China no longer has that stranglehold on rare-earth materials.

Another economic externality is the Environmental Protection Agency. In 1980 decided to do something about cleaning up sites, okay. And I remember in 1996 or so I was asked to go to a Pennzoil facility in Oil City, Pennsylvania, and basically a welder had been welding on a tank, and the tank blew up, threw the welder across the river, killed her, and caused a lot of damage. And I remember going to that facility and looking at it, and this tank had been built in 1922. It was old riveted steel, they didn't even know how to weld in 1922. This facility had been built in the 1890s, okay, and here in 1996, a hundred years later, it was still operating. And they had different economics in the old days, and I'll show you a picture of some of that in a second. But basically I looked at it, and in the tank farm, where they have the big tanks, storing facilities and stuff, they had crushed stone around the tanks. If you went down one foot you would strike oil. They had been spilling oil for so long, a hundred years, that the ground was just nothing but oil underneath the stone. And these were relatively small tanks because in the 1920s we didn't use great big tanks like we do today out of welded construction and stuff.

And I thought, how could Pennzoil, a major oil company, still run this facility? And the second day I was there, I thought about it that night and I realized they had to run it, because they couldn't shut it down. If they shut it down it would become an EPA Superfund site, the government would force them to come in and pay hundreds of millions of dollars to clean it up. It was cheaper to keep it open even though it was not economical to keep it open, than it was to pay the cost of shutting it down because of the regulations of the Environmental Protection Agency. Well it turns out, since then, now it's over twenty years later, this particular oil refinery has been closed because it got to be uneconomical, and now they have decided to pay the hundreds of millions of dollars to start cleaning it up.

But in fact if you looked at the environment in Oil City, it's just down the river from Titusville, Pennsylvania, where in 1857 or whatever, Edwin Drake discovered oil, okay. And it turns out, do you know how they transported the oil from Titusville to Oil City? They just floated it on the river, okay, and they'd skim it off at the other end. So the rules have changed. Some of you look a little surprised, okay, well I bet you are surprised, okay, because today if you see an oil sheen on the water, you know they're going to bring out all the environmentalists and people will start having a fit. Well in Oil City they just skim it off, because that was part of work, okay. So the environmental rules have changed over the years, and this lower picture is actually from I think one of the oil slicks from the BP Horizon leak and things like that.

But we tolerated a lot of different things in the old days. And in fact there are companies today that have serious problems because of what they call legacy costs. The steel companies produce millions of tons of steel and have for a hundred years or more than a hundred years, and they used to take their slag and other things and just make landfills. Well that was acceptable when they did it, but it's not acceptable today. And so one of the reasons USX cannot make very much money in the steel business is because they have these legacy costs. And a lot of the companies go out of business because they can't afford the legacy costs of cleaning up what was legal fifty years before, okay. So you have to kind of look at not just what the costs are of doing business today, but what the costs are in the future as well.

Anybody have any questions on any of those economic and environmental externalities? There are other types of externalities. There are social externalities, and the example I give here is conflict diamonds. Back twenty-five years ago, a lot of the diamonds are mined in Angola or the Democratic Republic of the Congo. They're also mined in the Soviet Union, in South Africa and stuff. But it turns out they were having a civil war in Angola for about forty or fifty years, and in order to pay for the civil war they pressed a lot of the workers, or the populace — the rebels, just like they did in Colombia, in other places. The rebels in order to finance their war against the government in Colombia, they basically sold drugs to the United States. In Angola, they basically forced the people to run the diamond mines, and they would take the money from them, sell the diamonds on the open market. And you weren't supposed to be able to do that, we supposedly had an embargo on conflict diamonds. But, you know, it's pretty hard to tell the difference between a conflict diamond and a non-conflict diamond. There are actually some ways, but you have to kind of do some destructive testing on the diamond, and that's not very economical. So there's lots of problems with that.

Actually let me jump ahead to another externality. Where's the one — here we go. This is — since I just talked about embargo, so we can talk about embargoes. Right now they're talking about putting stiffer embargoes on North Korea, right. Embargoes don't usually work, okay, so far as that goes. So you got to get everybody to agree to it, and what's in the paper today, and the paper today is the Soviet — the China is worried about the North Koreans, and is actually considering whether to cut off the energy, which means you're going to turn that into a Stone-Age country. If you cut off the energy supplies to North Korea, it's not far from being Stone-Age for the population right now. But if they have nothing to heat their homes for the winter, people will really be not only starving but freezing. But who said they're not going to cooperate? The Soviet — Russian Union — Putin says he's going to keep shipping oil to North Korea, okay.

So embargoes don't usually work, but it turns out forty or fifty years ago they had a civil war in Rhodesia, and it turns out Rhodesia has the world's best chromium ore. And it is so good, so much better than anyone else's, anyone can tell if it came from Rhodesia because no one has anything this good anywhere else in the world. And so they put an embargo because they were having this civil war and it was the same type of thing, and you were not supposed to be able to use Rhodesian chromite. Well it turns out, so you'd buy your chromium ore from somewhere else, but it turns out where did they get it from? They got it from Rhodesia, okay, and they were just passing it through. And you could tell when they got to the steel mill they knew this was Rhodesian chromium ore, but you know, according to the paperwork it came from another country, okay. So most people will find a way around embargoes, and they rarely work.

So let me go back to some other externalities. Anybody have any questions about externalities right now? We can look at, again, some things that used to be forbidden — that are no longer — used to be permitted that are no longer permitted. And we just had a big hullabaloo last summer about the lead in the drinking water in Flint, Michigan, right. Well, and everybody — actually Mark, can't remember his name — is a professor at Virginia Tech, who I know won an award because he was one of the whistleblowers, okay. Well he was the whistleblower because what they found is yes, the water in Michigan was above the EPA requirement level for lead. Today it probably would have been within the level fifteen years ago, but whenever they learn to analyze for lead in water more precisely, the EPA drops the level to the new level that they can monitor. And they say we don't want any lead in the water. All those mothers who say their children are not doing well in schools because they have lead poisoning, well I don't think it really is lead poisoning, I think some of those kids just have bad genetics, okay. But nonetheless, lead will hurt — won't hurt children — will hurt children.

And if you actually look at how much lead we've used over the centuries, so they were using lead and refining it into the lead metal back 5,000 years ago, and the Romans used it, had lead mines and used it for coinage and other things. And then the British used to use it, and we used to use it. In fact, when I bought my house forty years ago it had the lead pipe in the basement, okay, and they used to put all the water through the lead pipes. Now people get all upset about having lead solder in the copper pipes. Well, you know, I think it was 1978 or so they outlawed lead in solder for copper pipes, and now by law if you read your water bill every year they have to send you something telling you what the lead content is in the water that you've been drinking, okay.

But let me tell you that a lot of people have been drinking water that has ten or a hundred times as much lead as the EPA allows. And it wasn't lead, it was actually arsenic, but I remember they built a gold mine in Alaska, and the environmentalists said you cannot release any water from your — you're going to have river water coming in, you're going to process the gold, and you must be below something like one part per million of arsenic in the water. Well the interesting thing is, the river coming in had seven parts per million arsenic. So they had to lower the arsenic and put the clean water back into the river that had seven ppm, okay. That was the natural level of lead [arsenic] in that water. So there are environmental problems, but a lot of these things and requirements don't make a lot of sense, okay. But they are real socio-engineering problems.

So, if you look at this — this is on a log scale — this shows that the amount of lead, they used to mine about 10,000 tons a year back in the time of the Romans, and it dropped, and we were up to a million, a hundred times as much. And why are we using it? We still use it in lead-acid batteries. There is no substitute for a lead-acid battery. If you look at — people were doing all kinds of things on battery technology in 1925. A company in Japan named Toyota that made sewing machines — they had never made a car, but they are the successor — the car company is the successor — offered a twenty-five-million-dollar prize for someone who could come up with a replacement for the lead-acid battery, which was used in sewing machines back then, okay. Twenty-five million dollars in 1925 was a lot of money, but in any case no one has come up with that replacement for the lead-acid battery as far as that goes.

Other things in lead poisoning, where does it come from? Well, lead from the soil, lead-painted toys, lead-soldered cans — I don't know how people are eating out of the trash can but they may — lead-glazed pottery, okay. Pewter — the old pewter people used to eat off of. Now we use Britannia metal which is a tin-bismuth alloy, but it used to be lead-tin, okay, was pewter, okay, or actually had other things in it. Peeling lead paint, okay. I used to always wonder, why are these kids eating paint? I never ate paint as a kid. Does anyone know why children eat lead paint? Lead oxide is sweet, okay. But we have found other replacements for it. What did we use most of the lead oxide — we use lead oxide in paint. We use tremendous amount of lead oxide, not because it was sweet, but because it has a very high index of refraction and it makes white walls white, and even colored walls it gives them a better sheen.

So what do we use today to replace the lead oxide? We use titanium dioxide, which has a higher refractive index than diamond, okay. So if you want to really have a nice diamond ring that really sparkles, you should make it out of titanium dioxide, which is actually too soft — it's not hard. So actually diamonds are better because they don't wear out. But zirconium dioxide is like titanium dioxide, and it's also hard, and so zircon — we're not — zircons are a little bit different than pure zirconia, but pure zirconium oxide is actually a better replacement for diamond for jewelry than diamond. However, you know, we could grow artificial diamonds, but DeBeers has taught us all that it has to be a real natural diamond, and you have to have those people suffering in Angola in order to — but DeBeers is the star.

Mercury, okay. Mercury has been used for thousands of years. It was an interesting material. When I was an undergraduate student, if you broke a mercury thermometer in the lab you just kind of swept it up and threw it in the trash. Now we have these mercury spill kits which basically — you put some sulfur on it and it forms mercury sulfide to lower the vapor pressure, okay. But, I mean, we'd just play with mercury, take some gold ring and put a mercury on it and you could destroy it and make it brittle with liquid-metal embrittlement. One of the problems now is fluorescent light bulbs. We've replaced them now with LEDs, but the fluorescent light bulbs were taking over for the incandescent light bulbs because they use less energy. But they also had to use some mercury to start, you needed to vaporize, get a metallic vapor that was conductive, and mercury was basically the only thing that worked well. Now we're using less compact fluorescents, okay.

Anybody have any questions on some of these externalities? There's lots of externalities. Another environmental externality, it turns out for metallurgy, it turns out we know from the stability of the oxides that any oxide in the world can be reduced with carbon. Turns out the thermodynamic stability of burning carbon and oxygen together, or carbon in air with oxygen, you'll generate carbon monoxide. And as you go to higher and higher temperatures, the stability of the carbon monoxide becomes greater and greater, it gets more negative — that's the free energy of formation, carbon monoxide becomes more and more stable. Whereas the reduction of the oxide to form the metal goes the other way, and so these lines cross at some point if you go to high enough temperatures. And in fact the way we make steel in a blast furnace is we get up to 1700 degrees centigrade, and there should be — maybe there's not on this one — the iron oxide line — oh there's the iron oxide line. Iron oxide, anything above about 400 degrees if everything was pure, but in fact we get better reaction kinetics at 1700, off here where there's a big free energy difference between carbon monoxide and iron.

But the problem is that carbon dioxide is going to go into the atmosphere and cause global warming. So what people are trying to do is come up with non-carbon ways, carbon-free ways to make metals. Most of our metals have been made traditionally with carbon because of this diagram, but in fact we're spending lots of time — Professor Sadoway in this department has made a career out of using an electrochemistry rather than carbon to make metals.

Maybe the last one for today, so maybe I'll do two. Let's see — oh here's a military externality. It turns out one of the major causes of World War Two — bringing the United States into World War Two — was the fact that we were trying to — we didn't like some of the things the Japanese were doing. They went into Manchuria, they murdered ten million people, okay, in Manchuria. We didn't think that was nice. There were other things they were doing. And we cut off their source of iron and steel scrap. They didn't have a big economy that was generating old metal parts. We did, we had the world's largest economy, and we generated more iron and steel scrap, we still do, than just about anybody in the world. I don't know if China — China probably hasn't surpassed us, but they might surpass us in a few years. But when we cut off the iron and steel scrap to Japan, we were basically like cutting off the oil to North Korea today, okay. And so you can argue the Japanese had no choice and they bombed Pearl Harbor, because they were basically going to starve without the iron and steel scrap. And we cut it off without thinking of what we were doing to them and whether they would get desperate enough to attack us, okay.

And the last one I'll do is cultural externality. Gold. This is the amount of world gold production over time, and you can see we have had tremendous increase in the amount of gold that we produce in the world. This data is from the US Geological Survey so it's probably pretty good. What is the inherent value of gold as a product? Very low. There are very few things that you must have gold and cannot use something else that's much less expensive. Gold is primarily cultural, for jewelry. And where is most of the world's gold? Turns out half of the world's gold that we have mined since the beginning of time is in India. If you go look on Google and it says gold reserves, the United States has the most gold reserves, but that's a small fraction, okay. However, a million — billions of dollars, tens of billions of dollars that we have in gold is almost nothing to what is around the arms and necks of people from India.

And here's a picture of a guy — anybody know who this guy is or was? He's wearing a $250,000 gold shirt. He's a very wealthy Indian and he decided that he wanted to have a gold shirt, so he had this $250,000 shirt made for him. He became very famous because of that, and someone murdered him because of it, okay. So what — so moral is, don't go buying $250,000 gold shirts without spending some money on your bodyguards, okay.

Any questions? So tomorrow we will have Simone Belmar [Sami Belmaaziz?] start his lecture. He will do something on Monday and I will be back on Tuesday to finish up talking about externalities and regulatory externalities, and go into other things. But the point of today is there's lots of other factors that go into selecting materials other than just engineering, okay. And you will find that lots of other people have an opinion on what you should use for material, okay. So you see it.