§1. Opening: Lester Thurow and the way things are said [00:13]
We had a problem with the second videotape this semester, so we just inserted the second class from last semester. It's got to be somewhat close, but since I don't really work from an exact outline, I never know what I'm going to say until I get to class. Not that I didn't think about what I might say, but I never know until I get in the flow of it. It's no big deal, you're not being quizzed, so who cares? If you missed a class you would have missed a class and you wouldn't have even had a videotape to watch. Essentially we all missed class that day, except for the ones that were here. Anybody who watches it on video some other time will get a slightly different version, which is why it's better to come to class. I can't lecture to an empty room. I get the adrenaline going and start getting into it.
About 1988 I took the senior executives program over at the Sloan School, and Lester Thurow was lecturing. In 1988 he used to get $30,000 a lecture. Not at MIT, but if you went to talk to some board of directors or some conference, he would charge thirty thousand dollars. He was a very engaging speaker. The first time I ever heard him, I was there with 49 other people from the senior executives program — fairly senior people in industry, I was the only academic in the room — and we were all just enthralled with what he had to say. The second time he came, everyone else was just enthralled again. But I was sitting there analyzing — I was the engineer — analyzing why everybody was so interested in what he says. At the end I realized it wasn't anything that he said that I didn't already know. It's the way he said it.
I later got to know Lester Thurow. He became the dean of the Sloan School of Management in 1988. I remember him giving a talk over at the Marriott hotel to a bunch of people. He never used PowerPoint. He had a little three-by-five card and just scrawled a few words on it, and that was his notes for his whole talk. And he gets thirty thousand dollars. It was the way he said things.
For example, he was lamenting the fact that this business school up the river would tend to hire away some of the top faculty from the Sloan School because they had all this money. And he said, "But fortunately they tend to hire our extinct volcanoes." That metaphor of extinct volcanoes does not require any explanation. You know exactly what he means. I know he was talking about Robert Merton, who is the father of derivatives along with Black and Scholes. Merton was the graduate student, I think. Black passed away, but a few years later, in the 1990s or maybe early 2000s, Merton won the Nobel Prize for derivatives. And of course in 2008 the whole world economy fell apart because of derivatives. Not because the theory was wrong, but because people were abusing it. Hard to believe that someone would abuse something that had to do with money, right? I could give you another economics lesson on derivatives, but it's not worth it.
§2. Energy content, productivity, and the six elements [05:32]
The themes for Friday, which was mostly a recitation, were that the cost of structural materials is closely related to the energy content, and that has changed over particularly the last twenty or thirty years from where it used to be the cost of labor. To make a ton of steel 400 years ago was about 6,000 person-hours. Obviously most of that was labor content. 220 years ago, ninety-seven percent of the workforce were farmers. They needed food to eat, and it took ninety-seven percent of the populace to grow enough food to feed the people. Only three percent of the people were doing all the manufacturing and other things, and that's why productivity and manufacturing growth was slow. Then you had the Industrial Revolution in the 18th century, and then all of a sudden in the 20th century we've had tremendous productivity growth.
When I was working in 1975 for Bethlehem Steel Corporation, half the cost of a ton of steel was labor and half was energy. Today it's about ninety-five percent energy, and labor cost is down to twenty minutes per ton. Even if you're paying someone eighty dollars an hour for a steel worker in the United States, and paying them fifteen dollars in some other part of the world, which would be a handsome wage in another part of the world, you're only talking about five to thirty dollars per ton. That's only about ten percent of the cost, or five percent of the cost of the material. The energy cost is the dominant thing because productivity has just taken over the last 150 years. Labor is not the major cost driver for materials now.
The other thing I showed you was, when we talk about structural materials, there's only six elements in the periodic table to break the billion-pound-per-year margin. This should be 10 to the 12th — that's 10 to the 9th tons per year. We can forget the factor of two when we're talking orders of magnitude, so 10 billion tons per year. The only six things are carbon, aluminum, silicon, magnesium, calcium, and iron that are used in those quantities. It turns out — we talked about availability in the earth's crust — that most of those are in fairly high supply or availability. Silicon is number two after oxygen, and we certainly use a billion tons of oxygen when we use all that stone and other stuff. Aluminum, not as metallic aluminum but as stone. Iron is the only metal on here that we use in the metallic state. Calcium is stone, magnesium is limestone. Carbon is actually fairly low availability in the crust — coal — and that's not really a structural material, but we do use carbon as wood, probably into this billion-tons-per-year regime. Carbon's low, but it's sort of concentrated on the very top surface, in terms of wood. You don't dig for wood.
So availability and cost are two of the most important things in material selection. This little plot I've shown you — I'm giving you a handout on the paper that I wrote on material selection. It's Jack Westwood's plot, but in fact the usage is proportional to the cost of the material in dollars per pound versus tons per year. There is a correlation with some scatter, in this order of magnitude or two scatter, but around seven orders of magnitude.
§3. Value of weight saved: cars, aircraft, spacecraft [10:14]
Over the life of a vehicle, the value of a pound of weight saved is two dollars for automobiles, two hundred for commercial aircraft, and twenty thousand for spacecraft. So it really depends on what industry you're in. If you're talking about shipping, or you're talking about nuclear reactors, they're going to be made out of steel, and I'm going to show you why. If you're talking about aerospace — this is the V-22 Osprey in the experimental version, a tilt-rotor helicopter — this could not have been made without composites. It's made out of carbon fiber composites for the fuselage, the wings, everything. It's the first aircraft, back in the 1990s, ever designed with a hundred percent composite structure. Why? Because helicopters are not very efficient — you have to have a lot of energy to lift a little bit of weight, and the only way to make this thing light enough was composites. You could have made it out of aluminum; it would have been too heavy, never would have flown, wouldn't have had any payload. As it is, you can drive a Humvee into it. You can carry something like 24 Marines in full regalia with their weapons.
And this is the X-33 space plane. When you're going to twenty thousand dollars a pound for material into space — it always cost about ten thousand dollars a pound to get a pound of useful material into space. In the early 1970s, NASA had a goal to drop that to a thousand dollars a pound, and so they designed the space shuttle. The goal of the space shuttle was to drop the cost to about a thousand dollars a pound of useful material into orbit. So whenever you read about these things — any Course 16 folks in here? — they say, "Oh, we're going to colonize the moon, and we can send all the rich people to the moon." The only people who can afford ten thousand dollars a pound — it's going to cost $1.8 million to send an average person, just to get them there without their clothes or anything else. So there's a little problem with this "we're going to colonize Mars." It's because you haven't looked at the cost of these things.
The X-33 space plane was going to hopefully do what the space shuttle never did. The space shuttle never dropped the price from ten thousand dollars a pound to a thousand dollars a pound, because all the operational problems ended up costing more like forty thousand dollars a pound on the shuttle. It increased the price by a factor of four. Now you've got these private companies that are taking over from NASA to put things into orbit, or the Soviets, where economics is a whole other dimension with different rules. But the X-33 space plane was supposed to be the successor to the space shuttle. It was going to fly on water, H2O — two hydrogen tanks and one oxygen tank; the oxygen tank was going to be aluminum. I've passed around a piece of one of these two tanks. It was a $1.3 billion program to build this half-size model. This really didn't have any payload or cargo space. This was just to prove they could build it. The whole thing was an interesting structural problem.
These struts had to take the thrust — those were titanium and Inconel and very heavy metals because they had the strength. The outside skin was actually part of the structure. In fact these tanks were part of the structure. You had to have multi-functional use of these materials in order to make things light enough. And it still cost $50 million to build one tank and $15 million to build the other. They only weighed about two thousand or twenty-four hundred pounds. Pretty light, but fifty million dollars — you figure out it's twelve thousand dollars a pound as fabricated. That's one of the problems with composites. They work for military aerospace, they work for aerospace, and they actually work for automobiles. What automobiles?
[Student suggests Tesla.] Tesla — which is a hundred-thousand-dollar vehicle, and they had to do it because it has all these heavy batteries. What did someone else say? Formula One — fancy race cars, Indianapolis racers which cost about a million dollars, fancy composites. Another place of fancy composites is America's Cup yachts. Not every ship is made out of steel. The America's Cup yachts are made out of fancy composites. They don't care about the cost because these are billionaires trying to rub some other billionaire's nose in it at the country club, saying "I beat you in the America's Cup."
When you get to one of my classes — I can't remember which one — I bring in a part of America's Cup. A graduate of Mechanical Engineering over here runs a company down in Connecticut, makes specialty hardware for fancy yachts. He brought me a broken little hydraulic cylinder. They use 7,500 psi hydraulics on the America's Cup yachts. Even on the V-22 Osprey they went to 3,000 psi hydraulic systems to run the controls, which was a big jump from the typical 1,500 or so psi. The higher the pressure, the lighter the weight. If you run a system at higher pressure, it can be thinner, smaller diameter tubes, and lighter weight overall. Well, they go to 7,500 psi, and if you have a fracture in one of those things, you've got hydraulic fluid that could come out and just cut some person — cut their arm off. Take a high-pressure washer at 3,000 psi — you can slice your finger off. Don't run your finger through the high-pressure jet. But at 7,500 you could kill one of those people.
He brought me this thing and it had failed, it had split. No one got killed but they were worried about the safety. He explained to me: for America's Cup yachts, if the thing doesn't fail every now and then, you made it too heavy as a designer. A different philosophy. You should be shaving it down and making it thinner and thinner until it fails on a regular basis. These are fairly expensive yachts in that you usually are expecting parts to fail and you just replace them, because it doesn't have to last very long. America's Cup has to last for a few hundreds of hours before you trash it and go on to the next America's Cup. There's only one other component that I know — well, there are five things in nuclear weapons that have to last for a fraction of a second before they're no longer useful. But the engine on a cruise missile only has to last for about two hours. They make it out of carbon composites, and they can keep it from oxidizing away at high temperatures, but it won't last for 10 hours because it will oxidize away in 10 hours. It only has to operate for two hours, because then you're going to blow it up.
§4. Sprague's law, Williams's law, and the cost fraction [18:33]
In selection of materials, it depends on the value of the material and what its cost is going to be. There's a guy, Bob Sprague, who's retired for 15 or 20 years now from General Electric Aircraft Engines, and Bob had a lot of great quotes. Here's one of them — he was head of materials at General Electric Aircraft Engines: whenever you first hear about the properties of a new material, write it down, because those are the best properties the material will ever possess. Materials scientists are always developing some wonderful new material. And Jim Williams, who was a professor at Carnegie Mellon, titanium expert, went on to be dean at Ohio State. Jim replaced Bob Sprague at General Electric. His corollary — this is actually his slide, he gave it to me because we were both talking at a conference once and he heard me quote Bob Sprague and he wanted me to start quoting his corollary — whenever you hear the price of a new material, write it down, because it'll be the lowest price you will ever hear. People want to develop new materials, always touting wonderful properties and wonderful cost, but in fact over time you find it's not so great.
One of the things that I've looked at over the years is, what is the material cost as a fraction of the whole product cost. [Tom holds up his laser pointer.] I paid 200 bucks for this blue pillar [laser] pointer — maybe $120. I don't know what it weighs, a few ounces, but we're talking $500 a pound. This is well beyond automobiles into the aerospace regime of product cost. But it's a functional material — it's got a little laser. I don't think the holder is all that valuable, but in any case.
For an automobile or an aircraft, typical material cost is about ten percent of the overall product cost. I gave you this paper on materials for 21st-century defense needs where I quoted this. Obviously in functional materials like semiconductors or spacecraft, it's maybe only one percent. Materials cost is nothing compared to the overall twenty thousand a pound to get something into space. However, pipelines — I just wrote this in the other day because I just learned in the past month — the big transmission towers for the 345-kilovolt electricity lines sell for about $1.30 a pound out of galvanized steel. And that's about thirty percent — pipelines and transmission towers, the steel is about thirty percent of the cost. Sinking the poles into the ground and transporting them and everything else is the other seventy percent. For pipelines, most of the cost is transporting the pipe, welding it and burying it in the ground, coating it for corrosion resistance before you bury it. Pipelines and transmission towers have probably the highest material cost as a fraction of the total installed cost. Automobiles and aircraft are only about ten percent. So you buy a car for $25,000; it's got about $2,500 worth of material in it. Actually probably a little bit less in terms of the amount of steel or aluminum or plastic. Because the value of a pound saved in an automobile is only about two dollars a pound.
This is out of Ashby's first edition. I think I mentioned Ashby before. If I'd figured out earlier I probably would have made this a textbook for the course. This is Michael Ashby's third edition of Engineering Materials. If I start looking at the cost of materials: diamonds at about a billion dollars a ton in 1980, boron-epoxy composites at 330 thousand dollars a ton, cobalt alloys — these things are getting almost too pricey even to make spacecraft out of. Titanium alloys, yeah, you can make spacecraft out of that. Nickel alloys, stainless steels. These are the materials that you can build airplanes out of, at $200 a ton. And what can you make automobiles out of? Well, you can't quite make them out of plastic, but silicon carbide, plywood, low-alloy steel, mild steel, cast iron, concrete, coal, or cement. So we're sort of limited. You can put aluminum in here, but aluminum is actually up here. You can make a very expensive vehicle out of aluminum, but if I want to make a $20,000 or $25,000 Ford Taurus, you don't make it out of aluminum. This aluminum sheet is $2,200 — if it's only ten percent of the value, you've got to take these numbers and divide by ten, for the material cost that you're going to pay for it, because the other ninety percent is going to be fabrication, inspection, G&A. You know what G&A is? It's general administrative — that's all the overhead. The account is usually called G&A for general and administrative. Got to pay the boss something.
This is out of Ashby in the second edition, and here's the relative price. If mild steel is at a relative price of a hundred dollars, cast iron is cheaper, then ingot iron, softwoods, concrete, fuel oil, cement, and coal. When you start looking at these things you realize that for automobiles, ships, pressure vessels like nuclear reactors, big heavy structural materials — there's a limited number of materials that you can use. That's kind of an 80,000-foot view, looking at what costs two dollars a pound saved, or two hundred a pound saved, over the life of a vehicle.
§5. Density, sprung weight, and the blisk [25:00]
It also depends where the material goes. Here's a slide I put together years ago: if a product moves, low density is an advantage. For equal volumes one will pay for the less dense material. Here's a curve I calculated in my head. If the density is seven, which is steel — which is one of the Achilles heels of steel, it's a heavy material — you're only willing to pay less than twenty dollars a pound for that material in some application. If it's aluminum you could be willing to pay two and a half times as much, on a density basis. We often talk about specific properties, which is the property divided by the density.
What are the examples of paying more if something moves? Anybody know what the sprung weight is on a car? They call it the sprung weight in the business. It's everything that's on the axle — the wheels, the brakes, the axle itself. It's got springs that connect it to the rest of the vehicle. Why do you have the springs? Because the roads are bumpy. You want a nice smooth ride for the passengers, the body, the seats. That's all unsprung weight — the springs have already been used to smooth out the ride. But you hit a pothole — a lot of those in the Boston area. That's the sprung weight. The wheels move faster because they're going around in circles. Actually do they move faster than the vehicle? They move the rate of the vehicle, but the part inside, smaller radius, moves less fast. In any case, the brakes are on the wheels, and if you could make the brake calipers lighter, then you would be able to save weight on the axles and the springs and everything else. The sprung weight is moving and is taking more harsh environment than the unsprung weight, and therefore you can save weight in other parts of the overall design.
A better example that I like to use is turbine discs in aircraft. The Air Force has spent billions of dollars trying to make a blisk — a bladed disc. You know what a turbine engine looks like, and what the disc looks like with turbine blades sticking off around it. It sort of looks like a sun from elementary school painted yellow. They attach the blades — which are this fancy material that can't be welded generally — with what they call a Christmas tree structure. This flange and all this weight, this is actually probably half the weight or more of the blade. If I could weld the blade directly to the disc, I could get rid of this big heavy flange on the end of the disc. These discs, depending on the engine, could be traveling at 18,000 rpm, or maybe only two or three thousand depending on the size of the engine. If you can get rid of this big heavy rim, you can lighten the whole thing. The Air Force estimates you can get twenty pounds out of a single disc. There might be three or four discs in the engine, two engines, maybe four engines on an aircraft, so you could save a couple hundred pounds off the engines in a military aircraft.
I keep saying commercial aircraft is $200 a pound. Studies of military aircraft show that a thousand dollars a pound is the bogey for a military aircraft. You can either carry more fuel to get more distance, or you can carry more payload to kill more people, on a military aircraft. It's worth about a thousand dollars a pound over the life of the vehicle. If I can take twenty pounds off a disc, I can take 200 pounds off the engines, which means I can take 2,000 pounds off the wings and the rest of the structure which have to hold those engines. This collateral weight savings — if I'm taking it off the highest speed part of the aircraft, that's moving the fastest — I can get all kinds of follow-on savings. That's true in automobiles, it's true in most moving vehicle structures. You have to see how fast the part that's moving is, and you'd be willing to pay significantly more, up to ten times more, for something that has to move very fast, to save weight.
So 25 years ago they tried to use aluminum calipers for the brakes on cars. You know, you've got disc brakes. They don't try to use aluminum for the disc in the disc brake — that's made out of cast iron, for reasons that have to do with the wear resistance and frictional properties of cast iron. They wanted to make just the brake pad housing — the housing was made out of ductile iron. If they could make that out of aluminum they could take 15 or 20 pounds off the sprung weight of the vehicle, which is worth more than two dollars a pound — it might be worth ten or twenty dollars a pound. Well, they tried, and the problem was, brakes heat up if you use them really hard. Some of these aluminum alloys aren't much good above 200 degrees Fahrenheit — they start to creep. If your brakes start to creep, they call that fade. That means if you slam your brakes on hard two or three times, or you're coming down from Berthoud Pass on Interstate 80 [70], heading from Salt Lake into Denver — anybody know that area? Colorado, big long downward slope. Got lots of turn-offs for the trucks because they go rolling off the mountain — probably lose 20 trucks a year just going over the edge. The guy just opens the door and jumps out and lets his car go down the mountain, and they have these ramps where they can slow down. The Eisenhower Tunnel — you've got like 20 miles of just coming down the Rocky Mountains at about six percent grade. If your brakes fade, then they no longer are braking. Not a good thing. So aluminum brakes didn't work. Although they've developed new ones — it took them 25 years — I've read that some of the newer cars have aluminum brake housings. Because of the creep problem, they had to overcome that, and it took them a couple of decades to figure out what the right alloy would be.
The Air Force would love to make a blisk and they still have big programs to do it. The only aircraft that I know that actually has a cast integral disc and blade — and I'd like to get one — is an M250 Detroit Diesel Allison, which is now Rolls Royce. They make like 10,000 or 20,000 of these engines; they go in helicopters and small business jets. Very high volume engine. It's a cast technology, everything is cast. It's not as fancy as these single-crystal blades. It's a 30-year-old engine, but they do use blisk technology.
§6. Ships, aluminum, and the Visby [33:36]
So that's another important point. The faster something goes, the more you're going to pay to use it. We don't care about nuclear reactors — hopefully they don't go very fast at all, and when they do go fast we don't want to be around them. Ships don't go very fast, except now the Navy is interested in higher speed ships for the littoral battlefield. The littoral battlefield is anything within about 100 miles of the coast. Because of terrorism and stuff, they don't need the same number of great big aircraft carriers and nuclear submarines that are pretty slow and ponderous. They want some ship that can go at 60 miles an hour and go catch those pirates off Somalia. So they have to go to aluminum ships. There are all kinds of problems — even though we know how to use aluminum in a lot of applications and we've been using it for ships, when we start putting it in these bigger ships we start running into problems.
The Swedes about twenty years ago scooped the rest of the world by building an all-composite frigate called the Visby. Anybody ever heard of the Visby? It was an all-composite corvette. A corvette is smaller than a frigate. We make frigates — a destroyer is sort of a big ship, but now we've got such high-technology weapons that a destroyer probably has the firepower of an old battleship or more nowadays. So we don't build battleships, they're expensive, they're big, they're just a perfect target. We started building destroyers 25 years ago. Today we build mostly frigates because frigates are small, like small destroyers, half the size of a destroyer. A corvette's even smaller. The Israeli Navy uses lots of corvettes. It's bigger than a PT boat from World War II, but it's not a very big ship. The Swedes built the Visby out of all composites. They wanted to prove they had the technology to build the world's best ship. All the other countries thought, oh, they scooped us. Until they found out that the modulus of all those plastics — the stiffness — was such that the sea-keeping ability, when you go out there in those rough North Sea conditions, the Visby just would flex. So the Visby had a lifetime of about three years before it had so many cracks.
It's fine as long as it stays in port. Admiral Grace Hopper said, a ship is safe when it stays in port, but that's not what ships are for. Anybody know who Grace Hopper was? She was an admiral; I think she may have been the first woman admiral. She invented COBOL [Cobalt], which was a business computer language in the 1960s. She rose to be an admiral, and she was sort of kept around until she was about 85 or 90, because she was just a very accomplished person, and Congress had to pass some laws so the Navy couldn't force her to retire. But she said, a ship in harbor is safe, but that's not what ships are for. They built the Visby out of composites — sort of a disaster. People would like to make lightweight things, but there are certain material properties that are critical to a number of designs, and when you select materials you've got to think about some of those things, which not everybody does. Any questions?
[Student asks about aluminum.] There wouldn't be a problem with aluminum — it's just, the lighter you can be, the faster you can go in that ship. The Visby, when it was going all out on a nice smooth lake or smooth ocean, could go probably 20 or 30 percent faster than an all-aluminum ship of similar size.
[Student follow-up.] The problem with the larger boats made of aluminum is cracking, fabrication, fatigue cracking. They don't have the experience. It's not really a problem that they didn't have when they first started building steel ships, but there's a learning curve of how to do the design. The way you design for aluminum is not the same way you design for steel in terms of welded construction and fatigue cracking. Whenever you go to use a new material there's always a learning curve. When Audi went to build all-aluminum [lunar] automobiles, even though they had been built for J.P. Morgan back in the 1930s — he could afford to have his cars repaired — but when they went to high-volume production, they started running into lots of problems they never realized they would have. Then you work your way around and learn to design around those things.
[Student asks about the USN Zumwalt.] The Zumwalt — I don't really know that much about it. Have they built one? It's going to be a two-billion-dollar ship — three and a half billion, yeah, okay, so they're not going to build very many. This is one of the problems in the military just in general — they want to have all the bells and whistles. It's sort of like the town I live in. We have the oldest public swimming pool in the nation — it's the Underwood pool. Underwood was a professor at MIT, he lived in Belmont, and he had a nice little estate right near the center of town. He was an MIT professor; he was with Prescott, and he and Prescott perfected canning. You ever had Underwood deviled ham? It's like pure fat. Underwood deviled ham was down in Dedham, but he lived in Belmont. When he died he gave his property to the town. We have a 100-year-old swimming pool, they decided it's not good enough. All my neighbors say, oh, we're going to get a new swimming pool, it has to have this and has to have that. This is just like the admirals — the Zumwalt has to have this and has to have that, and you end up with a technology package that no one can afford. We're going to end up with a pool that no one can afford, except they will just tax me. That's my feeling on some of these things.
The Zumwalt is designed to wipe out major capital ships of other nations. Now, what other nations have major capital ships that we need to wipe out? You ever thought about that? The U.S. Navy has more capital ships than all the other navies in the world combined. We have more than fifty percent of all the capital ships in the world. Who else has aircraft carriers? The French have two or three aircraft carriers. The Russians just bought an aircraft carrier from the French. Very few people have these fifteen-billion-dollar aircraft carriers. An aircraft carrier is not a warship; it's basically an instrument of intimidation in peacetime. You set an aircraft carrier off someone's coast and you just have enough to destroy their nation and they know it. You can intimidate people, and if you send two carriers, that means you're really serious.
Remember the tsunami in Indonesia. There's a great quote about some Frenchman complaining about those stupid Americans. There was this tsunami and people were starving, and what did the Americans do? They sent an aircraft carrier. He was at some cocktail party at some State Department function, mocking the Americans. What are they going to do to help these people? And some American diplomat says, well, a modern U.S. aircraft carrier has two fully equipped hospitals. It has two dozen helicopters. It can generate enough fresh water out of sea water for twenty thousand people a day. There are five thousand people on the ship, so they have a little excess capacity when they're not running full steam, by desalination plants. And he goes on and on about all the things that an aircraft carrier can do, and if you park it off the coast some places have been decimated, you can bring hospitals, water, helicopters as aid. And he says, the United States has fifteen aircraft carriers — how many does France have? And the guy kind of crawled into his hole. So an aircraft carrier is an instrument of diplomacy and intimidation. If we ever start having to use aircraft carriers for a real all-out war against the Soviets or the Chinese, then we've got bigger problems.
What the Navy needs is a lot of lighter ships. The Zumwalt is a perfect ship for 1980; it's not the perfect ship for 2010. But Zumwalt was a great admiral.
§7. Density demonstration and beryllium copper [43:50]
[Tom passes around metal bars.] You can pass that around. This is aluminum — you can feel the weight. This is magnesium — it's forty percent lighter than aluminum. This is zinc, almost the same density as steel. So you can compare the three materials. I didn't have a one-inch, 12-inch-long steel bar. I don't remember what the density of zinc is — I meant to look it up. [Tom locates the periodic table.] If I look at the periodic table, density of iron is 7.8, density of zinc is 7.2. So steel is heavier than that bar of zinc. If you want to feel the difference between steel and aluminum, it's almost the same as zinc and aluminum.
[Student asks about zinc uses.] You can die-cast cheap metal parts — zinc die-cast parts. It used to be that the handles in automobiles were zinc die-cast; now a lot of times they're plastic. A lot of die-cast components, small little parts — in the old days, IBM had a huge business in die-casting zinc parts for typewriters and computer printers. The biggest use of zinc is in protecting steel from corrosion. Corkscrews — the cheap ones are cast, basically cheap castings. They also make pennies out of zinc; it's got copper on the outside, but it's zinc. The real Achilles heel of zinc is its corrosion. Actually that's one benefit — if you use it as an anode it'll protect almost any other metal except magnesium. Magnesium is the only more electroactive element than zinc if you look at the galvanic series. So zinc protects anything from corrosion except magnesium. It's relatively cheap, but it doesn't have great strength. If you've got handles on the car or a corkscrew, most people don't have enough strength to break a corkscrew housing.
Let's take beryllium. If you go look in the Ashby handbook on price and availability, you'll find beryllium is off the charts — a couple hundred thousand or a hundred thousand dollars a ton. I wanted to get a piece of beryllium, and to buy a one-inch disc, 0.015 inch thick, they wanted to charge me a thousand dollars. Mike Tarkanian knows a member of the department who works for Chase Brass and Copper [Brush], and we were going to try to get a chunk of beryllium. It's actually about the same density as that magnesium that she's got in her hand. It's not that much lighter, but it has higher-temperature capability. It's got a low coefficient of thermal expansion, so when you're building a space telescope where you can't have big differences in thermal expansion — you've got the sun heating things to 150 degrees centigrade in the day, and at night it's down to minus 200 centigrade — you don't want to have a lot of thermal expansion. Beryllium is a wonderful material. My other possibility was, I bought a beryllium copper wrench. [Tom holds up the wrench.] This only cost $120. I could have bought this wrench out of steel with chromium or zinc plating for all of twenty bucks. But I could buy beryllium copper. Beryllium is used as an alloying element to harden it. This is just as hard as a steel wrench; it will not wear out. Why would someone pay $120 for a beryllium copper wrench?
Nope, it's not lighter — you can pass it around, it's actually a little bit more dense because copper is heavier. [Student suggests beryllium toxicity.] If you breathe beryllium — if you get beryllium powder in your lungs — ten percent of the population have a genetic predisposition to berylliosis, and you will get berylliosis and you will soon die because you will grow these big nodules in your lungs and you will just slowly suffocate to death over several weeks. The first berylliosis case ever discovered was at MIT, right after World War II, right up there where the BayBank or the little kiosk is in the parking lot, the border of Mass Ave and Vassar. There was a building there once, and during World War II in the Manhattan Project they were machining beryllium, which is a nice new material. Several of the people there got berylliosis and died, and so they learned about berylliosis. It is a very toxic material in any form — oxide, metallic — but you have to breathe it into your lungs to have the problem.
[Student suggests thermal conductivity / spark resistance.] Yes, it has high thermal conductivity. They use them in mines, because you cannot draw a spark. If that was steel, I could take two pieces of steel and hit them together, get a spark, and if I'm working down the mine — kaboom — because there's plenty of methane in the air potentially. I can go and buy a full set of tools at Sears or Home Depot for four hundred dollars. I can buy the same thing if I go to Brillco online, which is where I bought that wrench, for $120, and I could have gotten any tool you could imagine. They're all proportionate — I could have bought an entire set for $4,500. Someday when I feel like it, I may buy that full set of beryllium copper tools. That's if you're working in a mine underground, or any type of potentially explosive environment. You can bang the tools together and you will not get sparks because of the high thermal conductivity. I take two pieces of steel and hit them together, and the friction will raise the temperature to a thousand degrees, I can send off a little chip of metal and it will be glowing red, and it will ignite flammable gases in the environment. I could bang two pieces of beryllium copper together until the cows come home and I will never get a spark because of the high thermal conductivity — the frictional heating's probably not moving more than a couple hundred degrees. So if you're a Boy Scout or Girl Scout, don't take a beryllium copper tool to start fires — it won't work.
§8. Competition among materials: water-conveyance pipe [51:11]
I told you about competition among materials and I want to start that today. I showed you the competition among plastic beverage containers and aluminum — they actually had steel soda cans 25 or 30 years ago when I lived in Japan, because the Japanese government, there's an externality — didn't want to support the aluminum industry. They didn't have a domestic aluminum industry. They did have a domestic steel industry, so they had steel cans. But they corrode a lot easier than aluminum.
Conveying water over the ages — what was the first material people used to convey water? They may have had to go down to the stream, and if they had a bucket made out of clay, a clay pot — or maybe they just scooped it up with their cupped hand. But after that, if they wanted to convey it, what might they have done? They could have used animal skins. I was actually thinking of soil. They might dig a hole and make a trough — except it leaks through. So what did they use next? They probably would have lined it with wood, because they had lots of wood, it was easy to work. After that they might use stone, then concrete. The Roman aqueducts were concrete. Then in the 18th and 19th centuries they were using lead pipe.
My house was built in the 1930s, so it's 85 years old now. When I first moved in, there was one lead pipe left in the house — it was above the laundry sink in the basement, and I had it taken out. They built the house in the 1930s and they had lead pipes in part of the house. They didn't always have it for the drinking water, but by the time I got there in the 1970s, most of it had been replaced with copper pipe. Copper pipe didn't really come into its own until after World War II as a building material. They still use galvanized pipe — zinc-coated pipe — in many parts of the Midwest, if they have the right water chemistry. You can put galvanized pipe in your home to convey water; it's a zinc-coated pipe inside and outside, and it will last for 40 or 50 years using New England soft water, where you have a pH of rainwater of 5.5 — the water that comes from the utility is probably pH 9, and it might last well.
So they went to copper pipes, but that is not necessarily the best material. Copper and brass, actually pretty good, but it's expensive. So people have gone to plastic pipe — I'll pass this around later. This is PEX, polyethylene X. P-E-X, and the X means cross-linked. Remember Charles Goodyear — you don't remember him; he died before you were born, before I was born. He cross-linked rubber with sulfur. He had these long polymer chains — polyethylene has long polymer chains — and he found that if you added sulfur compounds to the latex rubber, you could get a hard rubber from a soft latex. Vulcanization, yes — it's called vulcanization, Charles Goodyear.
They learned to do this with PEX plastic tubing in an economical way about thirty years ago — to cross-link polyethylene. This stuff is stiffer than most polyethylene you might look at. In fact, I have a piece of polyethylene here. This is pretty flexible; this is nowhere near as flexible, even though it is tubular. PEX-a is electron-beam cross-linked, and we can talk about that tomorrow — why use electron beam to cross-link something. PEX-b is chemically cross-linked — they actually put a chemical in to break some of the chemical bonds, and they get cross-linking between the chains, and it makes a very stiff, rigid plastic that can take 100 psi. Most PEX is rated for about 200 psi pressure, which is much more than you need for conveying water in a home. So much of the water in homes is now plastic.
From lead pipe of 300 years ago, to galvanized pipe of a hundred years ago, to copper pipe of 60 or 70 years ago, to plastic pipe for the last 20 years — tremendous change in the materials we used. From clay pipe and concrete aqueducts that we used for thousands of years. I'm going to give you another example tomorrow of what we've done for gas piping. Just to give you a hint, anybody know the first gas piping in the streets of Boston, what material they used? Wood. Yep. I'll tell you that story tomorrow. Thanks.