§1. Energy content and the productivity revolution [00:08]
Student: What influences the price of materials like platinum or copper? Is there a trend there?
Today, it's ninety-five percent energy. Thirty years ago it might have been fifty percent.
It's still mostly energy, because you still have to move a lot of dirt. Productivity in mining has just exploded in the last thirty years. We used to have people with shovels in their hands. Now you have great big earth-moving trucks — the back of a dump truck will take a two-story house.
We're now in a stage where we're seeing productivity growth in the last fifty years that matches what we saw during the industrial revolution in the 19th century. We're in a productivity revolution in terms of manufacturing — really in the last thirty-five or forty years. Everything has sort of flip-flopped because of that.
Platinum is still mostly the energy. The ore is so rarefied — there's so much entropy in it, it's so dispersed — that in order to concentrate it, it takes a tremendous amount of energy. It's not a lot of labor hours anymore. In the old days people had to do it by hand. Take 1849 in the San Francisco gold rush — people were sitting there with little pans, panning for gold. That was a lot of labor content. It wasn't a lot of energy content. You could say labor is almost energy, but by energy I mean the equivalent oil — barrels of oil, trillions of cubic feet of natural gas, coal, whatever. Now we are using energy. The per capita use of energy has just exploded in the last thirty or forty years.
We've reduced the labor content of virtually every material. It's not just steel and aluminum — it's platinum, gold, titanium, you name it. It's still digging it out of the ground and the energy to refine it, get rid of the oxygen and the sulfur, turn it to a metallic state. That's not true of platinum and gold because they can be found almost in a metallic state in nature, but they're so rarefied. So it still is energy content.
It's a tremendous displacement that I've seen in my lifetime. For steel, when I started working it was fifty percent labor; now it's about five percent.
In the 1980s the steel industry had like a four percent annual productivity growth rate, which was double the manufacturing growth rate in the United States. The service industry growth rate was zero — there was no productivity gain in services. In the decade of the eighties the mining industry was like seven percent. Mining was way ahead of everything else in the world.
When you start doing that — seven percent productivity over ten or twenty years, or even five percent over twenty years — you get a twenty-fold improvement. You take something that was fifty percent labor and all of a sudden you've dropped it to one-tenth as much. That occurred in the 1980s and 1990s, and it's created tremendous displacements in all the metals industries.
They were all in this great lethargy in the 1980s and 90s, and Wall Street thought, oh, metals are passé. Ned Thomas, who was department head here, had the same mentality as all the business school idiots — that less employment means the industry's dying. Well, if you could produce everything that everybody wanted in a huge quantity with one person, wouldn't that make a wonderful industry, as opposed to a bad industry? Isn't productivity good? In the long run it is good. In the long run it also causes tremendous displacement of employment and heartache.
In the 1950s and 60s, if you got a job in a company you could stay there for thirty or thirty-five years and retire from that company. That doesn't happen anymore because of the productivity gains in manufacturing — and because computer technology and information technology make you a dinosaur within ten years. You'd better go into management, because you won't know how to do anything useful within five or ten years unless you somehow manage to keep up with the technology. In the old days your grandparents could start with a company and retire from that company. Very few people can do that today. You've got to be continuously reinventing yourself in terms of your capabilities.
§2. Aside: university productivity and how to teach calculus [06:29]
Except college professors, I mean — we just teach. We just get up and expound. So universities have not changed much in 400 years, and our productivity is about the same as 400 years ago, in terms of the number of students we interact with. But that's going to change too, because of videotaping and things like that.
Think about it: if you're going to teach a calculus course, how many students in the country need to take freshman or sophomore calculus every year? It's a huge number. Not everybody wants to be a science or math major, but math is sort of fundamental. There are probably only half a dozen really good calculus teachers. So why do we have a thousand, or two thousand, or three thousand people lecturing calculus classes, some of whom don't even know what they're talking about?
Student: Haven't you had teachers who didn't know what they were talking about?
I've had it. One of the advantages at MIT is you have fewer of those. Most of the faculty at MIT actually have a clue.
I reviewed a thermodynamics book from another university a number of years ago. The publisher sends it out — it's a textbook someone had written. They defined energy as a property that never changes. Really? What they meant is energy is conserved. But to say it never changes — the whole study of thermodynamics is how energy changes from one form to another. This was an undergraduate textbook in materials, and they defined energy as something that never changes. And they defined entropy as something that always increases. Wait a second — if I refine something, I might increase the entropy in the universe, but I decreased the entropy by purifying that material. Something that was impure before had lots of entropy, and now it has less entropy. It depends on what I'm talking about. There's a concept of a system in there.
And then they had a chapter five or six that was obviously one of their student's doctoral thesis. Why are you going to put that into an undergraduate textbook? It was completely out of place, didn't fit with anything. It was also totally irrelevant, and I didn't bother to check if it was right or not. So I panned the book, but it's been published anyway. Why should you teach something that's wrong that has to be unlearned later? It's okay to simplify things — thermodynamics for graduate students is not the same as thermodynamics for undergraduates — but you shouldn't teach things that are wrong that have to be unlearned later.
So I'm of the philosophy that there are only certain people who really know how to teach certain things. We really ought to have something like — I've never even looked into University of Phoenix, but the idea of it — you have courses that can be taken by thousands of people, the lecture is a very effective lecture, and then you basically go and do recitations.
You know why that idea will never fly? I've been pushing it for twenty-five years around here, and it falls on deaf ears. Because if you have only the best people lecturing, what happens to all the other professors? They become TAs. And what does that do to their pride? How many senior faculty at MIT would like to be told that you're going to TA this course that's going to be lectured by this guy from Stanford, because he's the best lecturer?
Not everyone's a Don Sadoway, but Don Sadoway can lecture better than anybody else in this department. He has a natural gift. Bill Gates told the board of directors of Microsoft that they should watch Don Sadoway's lectures on chemistry. Why is he doing that? I don't know. He likes lectures on chemistry. And he's now funding Don Sadoway's startup company. These interesting externalities.
So did I answer that question? In a sense it would be better if someone like Michael Ashby lectured on material selection, and Tom Eagar just came in and gave a recitation every week, and answered your questions. I'd rather answer questions than lecture. You could probably read the book and get the general idea. But then you ought to be able to get the insights from someone who has some real expertise. That doesn't sit with faculty pride, so it's a non-starter — until someone figures out a way for the best lecturers to give the lectures, and other people just to be the servants. Not everyone can be the master teacher.
§3. Coal, productivity, and the global externalities of pollution [12:13]
Student: Yesterday we saw that coal is in pretty short supply in the Earth's crust, but its cost per ton is pretty low.
Right, because it's actually concentrated. That's where the forests were — the coal is located where they had forests. The Amazon — if we didn't cut it down and burn it today — 500 million years from now, the Amazon, or any other jungle, would end up being a tremendous coal reserve. Because what is coal other than organics that got buried by geological processes and, under heat and pressure, got cooked into coal?
There are all kinds. You start with lignite, which is basically — or peat bogs — pretty close to a plant. Then you go to lignite, sub-bituminous, bituminous, and anthracite. Anthracite was under the highest pressures and highest temperatures for the longest period of time — that's the little piece of coal I passed around. Burns really clean because all the volatiles are gone. Lignite is still fifty percent water, and it's got lots of volatiles in it. As you go down the chain to higher cooking pressures and temperatures, you get cleaner coal. And then we take some of that coal and turn it into coke inside an oven, and that makes it even stronger and cleaner burning — except we're burning off all those bad things. That's what coke ovens give off that the EPA doesn't like, and that's why we let other people in other parts of the world produce the coke. We ship our pollution to other parts of the world, where people would rather eat than have clean air.
We actually have the luxury of being able to do both, because we are more productive than anybody else. This is all part of Maslow's hierarchy of needs. We're near the top of that economic pyramid, so we can afford to be self-righteous and environmentally sound. We ship all our pollution and lung disease abroad.
§4. The magnesium anode and the steel hot water tank [14:51]
One of the students came up afterwards last time — I passed this magnesium around — and asked, what's that little dot in the middle of it? [Tom holds up the magnesium bar.] If you pass this around, it turns out it's a piece of steel. I bought these last spring when I was teaching this course on the side — wanted something more touchy-feely, so people can feel the density of something light like magnesium. I couldn't afford to buy a one-inch diameter, twelve-inch-long bar of beryllium, which is actually about the same density.
I bought it off the web, and it was cheap and convenient. Just like this bar of zinc — the bar of zinc is just a piece of cast zinc. I can tell it's cast because of the surface texture; they just cast it in the mold. That magnesium piece is actually a magnesium anode. I didn't know that until the student came up and asked me about it.
The primary use of zinc is as anodes, because magnesium and zinc are top of the galvanic series. They are the most anodic of any materials. Magnesium has significantly higher anodic potential and will corrode more easily than even zinc, at least from the thermodynamic potential point of view. Magnesium, zinc, and aluminum are all high-energy. But magnesium's the best.
Every steel hot water tank in the world has a magnesium anode in it. Because the Achilles heel of steel is that it corrodes. If I want to use steel to contain water, I have to do something to protect it. I can glass-line it — that's what they do. They take steel tanks and use a glass they've developed that has roughly the same coefficient of thermal expansion as steel. They spray it on as a glass frit inside the steel tank, then heat it up. The glass melts against the steel, cool it back down, and you've glass-lined the steel tank.
The problem is, every now and then there'll be one little spot where the glass didn't flow, because of surface tension or some contamination. So an American company has exported the fabrication of these steel water tanks to maquiladoras in Juarez, across the border from El Paso. In other parts of the world you can't ship hot water tanks very far, but you can ship them from Mexico because that's not too far from the market in the United States.
They haven't put the bottom of the tank on yet, and they have a bunch of Mexican women — women are more diligent at piece work — stick their head in there with a flashlight and look for the gaps in the glass. They have a little epoxy and put it on there to repair it. That doesn't always work, so they stick in the designer stick of magnesium electrode in there. It has a steel wire, because if the magnesium completely corroded away you wouldn't have any electrical circuit left. So you have a steel wire, and they extrude the magnesium around the steel wire, plug that in, stick it down in your hot water tank.
If you have a steel hot water tank and you look at the manual — no one ever reads the manual — it will tell you to unscrew the electrode on the top of the tank and inspect it every year. Go ask a plumber if he knows about that. Most plumbers say, what? No one ever inspects the magnesium anode. Usually the holidays in the coating are small enough that the anode covers them. But every now and then there'll be one about half a centimeter in diameter, and all the corrosion gets concentrated right there. Within two or three years you can blow a hole right through that tank. That creates floods. I've probably put one or two children through college that way, looking at these tanks and saying, ah, corroded.
The interesting thing about that magnesium — it is some of the purest magnesium in the world. I don't remember the statistics, but most of the magnesium in the world is used to alloy with aluminum. There are a number of aluminum alloys with about five percent magnesium. A lot of aluminum is made — it's second only to steel in metals. The next most use of magnesium is in making ductile iron. You put a little bit of magnesium into cast iron and it greatly improves the mechanical properties by changing the carbon flakes to spherical carbon. It's called ductile iron, and you get ten times the ductility. The third largest use of magnesium — maybe larger than ductile iron — is in anodes for water tanks.
[Tom checks the sample.] Oops, this is neodymium — I was in a rush this morning — but it actually looks almost the same. It turns out the specification for the magnesium in that anode is less than seven parts per million nickel. Because if you had a nickel precipitate, it would become cathodic, and the magnesium anode would just eat away itself. It won't protect the steel — it'll protect the nickel, the impurity within it, because there's a shorter electrical circuit path. So it's a very high-quality magnesium. Very low nickel. Virgin material, no remelted alloy recycling.
That's a long aside on why there's steel wire in the middle of that thing. Because that's the easiest way to buy one-inch magnesium rod. Who else wants a one-by-one-inch magnesium rod? Sort of useless.
§5. Magnesium's Achilles heels, and the Alcoa–Dow cartel [21:44]
Magnesium has several Achilles heels. The U.S. Department of Energy has been spending probably a hundred million dollars a year since their inception forty or fifty years ago, because they're going to put magnesium in automobiles. Steel is too heavy, aluminum is lighter, but magnesium is even better. They started putting more magnesium in cars — there might be twenty pounds of magnesium in an average automobile today. Where does it go? It used to be more — they used to make mag wheels of real magnesium. Now what they call mag wheels are usually made out of aluminum.
Because mag wheels have to go through all that road salt in the northern climates, and they corrode. Where is the most magnesium found in the world? In the ocean, because magnesium chloride is extremely soluble. There aren't a lot of mineral deposits of magnesium. The only ones are things like the Great Salt Lake — which is just a dried-up ocean. So that's where you get magnesium, from dried-up oceans. It's cheaper than refining it from the ocean itself. But magnesium chloride is so soluble that you have to get it from those sources.
So you don't like magnesium anywhere it's exposed. You can't even use it for deck lids — that's what they do for aluminum on automobiles. They make the rear hatch door or the hood lid out of aluminum, bolt it onto the rest of the steel structure, paint it, and aluminum's got good corrosion resistance — it's just fine. You don't do that with magnesium, because even just a little bit of atmospheric corrosion underneath, and the paint starts flaking off after four or five years. Not with aluminum. Aluminum's got better corrosion resistance than steel. It's rusty steel causing the paint to flake off on automobiles.
What they've done is they've now used galvanized steel and then painted it, and it'll last seven or eight or ten years. But thirty years ago, this was one of the biggest problems they had when they decided they didn't want to sell disposable cars anymore. When I was your age they sold disposable cars. You had to buy new cars every three or four years. This was actually a plan of General Motors in Detroit. No one wanted a car that lasted more than four or five years. They came out with a new model every year, and they were basically disposable. Then the energy crisis of '73 hit, and all of a sudden they wanted cars that lasted five years, then seven years, and by the 1980s they were shooting for ten years. But they couldn't do it because the steel rusted. It's the Achilles heel of steel.
What did they do? They started putting zinc on there. For ten years I had research out of Detroit on welding of galvanized steel, because it was a new material. Not new in most industries, but in automotive — painting, welding, everything — they had to learn all kinds of new things.
There were people here — I won't mention faculty members' names — who have been promoting magnesium for many years. Joel Clark's first doctoral student looked at the fact that there was a cartel between Alcoa and Dow Chemical after World War II. This was not what I intended to lecture on today, by the way.
After World War II — there had been a tremendous growth in the aluminum industry. [Tom produces a book.] Here it is — From Monopoly to Competition: The Transformation of Alcoa, 1888 to 1986, written by a professor at Columbia Business School. This is a comparison of primary aluminum production in thousands of metric tons. 25,000 tons in the United Kingdom in 1939. Germany actually had more than the United States in 1939 — they were in the war. By 1943, the United States had grown more than five and a half fold. By 1944 they were starting to wind down, they could tell they were winning the war. The United States rose way above everyone else. So Alcoa became huge during World War II. This is one of the major transformations.
The next chapter is the great antitrust case. It started in 1911 — the Justice Department started looking at Alcoa in 1911. As I mentioned, Andrew W. Mellon and his aluminum Pierce-Arrow. It goes on for seventy or eighty pages. So George Kenney, who was Joel Clark's first doctoral student around 1976, basically looked at sales and prices, and could prove that Alcoa, probably Alcan, and Dow Chemical had all agreed after World War II — when the Justice Department was really investigating them and making Alcoa spin off all kinds of things — that Dow Chemical would control the world's magnesium business after World War II, and Alcoa would control the aluminum business, and Alcoa would stay out of the magnesium business.
They had the technology to go into it, but they never did. Why wouldn't they, if five percent of a lot of their alloys was magnesium? Because they were letting Dow control the magnesium business. This was a cartel — all in the wonderful United States where we don't believe in such things. George had an excellent thesis that really proved it.
In any case, there are people saying, oh, we're going to put more magnesium in automobiles. But where do we put it? Under the dashboard, because we don't want any atmospheric corrosion near it. We also don't want it where people see it starting to corrode. Go look under the dashboard of a ten-year-old car, take off the plastic, and you're going to see corroded magnesium. It's still probably fine for holding the wires and the radio in place, and it will last the life of the vehicle. But magnesium's big Achilles heel is that it corrodes.
No one's ever solved that problem, except for the people who use it as a corroding material — using it as an anode. The U.S. Navy had an interesting application once. They developed a magnesium-carbon composite, and people said, oh, this would be wonderful — lightweight carbon, lightweight magnesium, we'll be able to use this all kinds of places. Ron Latanision, a professor here a number of years ago, said that when you tried to polish that metal metallographically, if you used a water-based polishing solution, it would corrode faster than you could polish. You had to use diamond oil-based polishing solutions.
§6. Aluminum's protective oxide and the chloride problem [29:50]
Student: [inaudible question about aluminum vs. magnesium corrosion]
Right, because aluminum has a very protective oxide skin. Magnesium has an oxide skin, but if there are any chlorides around, it's toast. Aluminum doesn't like chlorides either, but it's still pretty good. In fact aluminum has excellent corrosion resistance. We do make ships out of it — small ships and boats — and they go through saltwater and last longer than steel. Aluminum oxide is the key. If you use the right aluminum alloy — there are some aluminum alloys that just go to pot, the higher-strength ones — but we make aircraft out of it, and they're certainly out in the air and get rained on.
Magnesium oxide is more stable, but when it forms with a chloride it pits, it delaminates, it just corrodes. It prefers the chloride. Magnesium chloride is much more stable than aluminum chloride. Aluminum chloride isn't really that stable. In fact, if you react aluminum chloride with water, it generates hydrogen — it creates HCl and aluminum oxide. I learned this when my oldest son was doing a high school chemistry project. I brought back all the chlorides I could think of, and he was going to look at their solubility. I was sitting at the kitchen table and put a little bit of aluminum chloride in water, and there was a little fire — generated hydrogen. I didn't realize it was that reactive.
Aluminum chloride isn't anywhere near as stable as magnesium chloride. It has to do with the relative stability of chlorides and oxides. Pure aluminum has wonderful atmospheric and water corrosion resistance. One of the companies founded by Alcoa was Wear-Ever, the pots and pans — that's relatively pure aluminum. You start putting copper and other things in aluminum — just like the nickel in the magnesium — and you create your own little concentration cell, anode and cathode. Copper alloys are not happy in salt water. Aluminum-magnesium alloys are actually very good in seawater, so the 5000-series aluminum alloys are good.
If you look at the Metals Handbook, the section on aluminum corrosion is much thicker than the one on steel corrosion. Because aluminum corrosion is a lot more complex. But aluminum has excellent corrosion resistance. We use it for ships, cars; we build sewage treatment plants out of aluminum, because the steel will corrode in thirty or forty years. That aluminum will be there a hundred years from now — not because it's lightweight in that case, but because it has excellent aqueous corrosion resistance, if you use the right alloys. Use the wrong alloys, you're toast. But the right alloys, it's great.
§7. Aloha Airlines and corrosion fatigue [32:55]
Student: [inaudible question about commercial aircraft lifetimes]
I don't know if that's true. I do know that the typical lifetime of a commercial jetliner is about a hundred thousand hours. That time is primarily due to fatigue. They've been flying around for a hundred thousand hours, they have fatigue cracks, and they have so many that you don't want to keep chasing them. Some are getting big enough that you don't want to be flying over an ocean, because you could be swimming.
Does anybody remember the Aloha Airlines disaster? Not just a hole — the whole top two-thirds came off. A commercial airliner is actually called a ship, like an airship. It has a keel beam, just like a boat. You start with this great big aluminum beam at the bottom of the aircraft and build up from there. You build a structure, sort of like a backbone with a rib cage — lying on your back with your backbone on the table and the rib cage coming around — and you put an aluminum skin around it.
I always say that the U.S. Navy, among the services, is the corrosion leader, because they're surrounded by saltwater. Aloha Airlines was the corrosion leader because they were always flying over saltwater. What happened with Aloha is they also have short flights. You don't fly five hundred miles in Hawaii very often, unless you're circling a lot. Their flights were averaging forty-five minutes, and the fatigue stress cycles were like forty-five minutes on average. Because it's pressurization of the cabin, depressurization — ground-air-ground cycles, takeoff-landing cycles.
They were flying between islands and the whole top came off. You could see the seats, and people were strapped in. Only one person died — a stewardess who was walking down the aisle, she wasn't in a seatbelt. They landed. The first time I ever saw it, in the 1980s, I saw a picture and thought, how did that thing stay together? Because it's got a keel beam in the bottom. Most of the structural strength is that keel beam. What they found is it was corrosion fatigue.
So what you're saying is probably true. It's fatigue, and corrosion fatigue is worse over the ocean. If you're over saltwater as opposed to always over land with a commercial airliner, you will have less corrosion. But I don't have the data, and I haven't read it. So that's why I said I don't know.
And that whole story about "I don't know" — in 1985 I walked into my lab, and we had a little whiteboard, and two of my doctoral students were doing something on the board. I came in and said, what are you doing? They said, oh, we're looking at such-and-such, and we were wondering — and they asked me some question. I said, well, I don't know, but — and I started giving an answer, and they started breaking out laughing. I said, what are you laughing about? They said, you always give an answer. We ask you a question, you always say "I don't know," and then you proceed to give us the answer. Well, it's not that I'm giving them the answer — I'm a professor, I'm supposed to be teaching you how to think through a problem.
I handed out the World Trade Center paper. I spent three hours putting that paper together. I've had more comments on that than all the other several hundred publications combined. I wrote it because I was tired of hearing all this stuff that I knew was false, but I really didn't know anything about the World Trade Center. But I did know some basic physics and chemistry. What can you say about something when you know nothing at all about a subject? You can go back to your freshman physics and chemistry and start saying, what do I know? I knew about flames and thermodynamics and flame temperatures and various things, and that's what I wrote about. It still stands today. I just got a nice letter from some lady this weekend who was reading it because of 9/11. She thanked me for writing it. I wrote it because I'd done less work on that than anything else I'd ever worked on. But I wrote it in a way that people could understand, and on a subject people cared about, as opposed to my research — no one cares about my research. It's too specific, too narrow. People want to know about bigger, broader things, which is what I lecture about.
§8. Voltage, bond energy, and the limits of materials [38:31]
Student: [inaudible question about fuel cells]
In a fuel cell you're trying to corrode things. You're trying to recombine and uncombine things. In batteries and fuel cells, the reason they're using these materials is because you want a decent voltage.
If you look at the thermodynamics of some of these things, the breakdown voltage of H₂O in an electrochemical sense is about 1.1 volts. It doesn't take very much voltage to separate hydrogen and oxygen. You probably did that in high school chemistry — you could light a splint and blow up the hydrogen, and put a glowing splint into the pure oxygen and it bursts into flames. You can do that with a dry-cell battery if you want. It doesn't take much voltage.
For Al₂O₃, or magnesium oxide, which are two of the more stable oxides, you can decompose those at less than two volts, probably less than one and a half. So some of the most stable compounds we have — two volts is an eternity for these bonds. That was going to be part of my lecture today: primary bonds and secondary bonds.
A typical primary bond energy, from your freshman chemistry — one to three electron volts. All I need is a couple of volts and many things will decompose, electrically.
Going back to your question — corrosion in fuel cells. If I'm going to try to make a battery, one of the reasons I use lithium is — if you look at the electrochemical potential, which you learn in high school chemistry — if I want to get the biggest electrochemical difference on the periodic table, I'm going to go from this corner up here to that corner down there. Except no one uses astatine, or polonium, or tellurium — they're toxic — or iodine. They tend to use lithium with something on the other side, maybe chlorine. You want to go all the way across the periodic table to get the biggest voltages.
If you have voltages between calcium and silicon, there's almost no voltage at all — a few tenths of a volt. So you don't want to have a bunch of cells stacked up to get a hundred or 120 volts. You want to have only fifty cells to get a hundred volts. That's why they're using these very reactive metals — because you want the voltage.
That's one of the problems with Don Sadoway's company — Ambri now. There are probably only one or two elements on the periodic table that will work for his cell. Most of them give you two or three tenths of a volt, and your losses in the resistivity of the copper wires bringing the current in — you can lose half a volt. If you're only generating three-tenths of a volt and you lose half a volt, it's not a very good power generator. You really need something on the order of a volt or two. A carbon-manganese dry cell — a double-A battery — that's one and a half volts. That's about the most you can get, because even the most stable compounds only take a couple of volts to break down.
I once consulted for a division of Johnson [Ethicon, J&J], and they make medical instruments for all kinds of surgery. At the time, one of the big things was electrocauterization. Someone's doing an operation, they cut through an artery, and they want to cauterize that wound — essentially weld that blood vessel back together. Hey, it's a welding problem.
They would take a tool with two insulated halves — basically like tweezers — that would grab the blood vessel and apply a hundred volts to it. A hundred volts DC, locally. It would dry out the protein in the blood vessel, and you basically weld it together with the protein and cauterize it.
They said, we've tried everything for our tips. They started with stainless steel, and the tips were pitting — terrible pitting on the anode, because that's where the corrosion occurs. The cathode was cathodically protected, no corrosion. They said, we need a better material. I said, what voltage are you using? They said a hundred volts. I said, forget it. They said, isn't there something we could use? I said, you could try platinum, but it only gives you about two volts. You could try titanium — it has a pitting resistance of about five volts because it has a very stable oxide skin. But there's nothing any better.
There are limits to the properties of materials, and it has to do with the strength of the bonds. In the case of a fuel cell or a battery, we're trying to use the most reactive things to get the most voltage. When we don't want corrosion, or we don't want a lot of voltage, we use things that don't have a lot of potential on the galvanic series.
§9. Conveying water: lead, copper, terne plate, and galvanized steel [45:06]
Last time, we said material cost is only about ten percent of the total product cost. Sorry for all you Course 3 folks, but the material cost is only about ten percent of the total product cost. All you mechanical engineers in manufacturing — you've got the ninety percent. Actually you don't — the management folks have about thirty percent. But you've got the inspection and the fabrication and all those other things. The big costs are in making the product and shaping and forming it. Materials folks can get involved in that if they want.
The faster something moves, the greater the value of being lightweight and using magnesium and aluminum. That's why you get people in the Department of Energy saying, oh, we're going to use magnesium. They have no clue why they want to use magnesium or how they're going to use it. They're just going to throw a hundred million dollars at it every year because a bunch of people say, oh, magnesium is nice and lightweight. Well, thank you very much, but there are a few other properties I'm interested in. Density is not the only property that makes a product.
I talked about conveying water. In the old days, you might just dig a groove in the ground and line it with wood and send the water. Eventually, in the 16th century, they started using lead pipes — maybe even the Romans used some lead pipes, I don't know. It's a nice soft metal, easy to form, excellent corrosion resistance. It'll last for a hundred years.
The roof of Kresge Auditorium is lined in lead. Cheaper than copper, has atmospheric corrosion resistance, will last forever.
In the old days, the gas tank in automobiles was made out of steel. But steel has lousy corrosion resistance, and if there's anything you don't want leaking out of your automobile, it's gasoline — tends to start fires. So they had terne-coated plate. Terne plate is almost impossible to find today. I don't even know if there's any steel company still making it. It's lead-coated steel. You wouldn't use zinc-coated steel, because in ten years that zinc is going to be completely consumed.
The lead forms a protective lead carbonate on the surface. First it forms lead oxide, then the lead oxide reacts with CO₂ in the air and forms lead carbonate. That's actually one of the reasons galvanized zinc in the atmosphere is pretty good too. It first forms zinc oxide, then zinc hydroxide — almost immediately, because there's moisture in there. But then over about a year, the CO₂ in the air reacts with that zinc hydroxide and forms zinc carbonate. The zinc carbonate is really what gives you good corrosion protection. The zinc is still protective underneath, but you've got this protective surface oxide of zinc carbonate.
Just like aluminum has good corrosion resistance because it has a very stable aluminum oxide skin. Titanium is even better than aluminum because it has a very protective titanium oxide skin. Stainless steel is better than regular steel because it has a protective chromium oxide skin. Some oxides are protective and some aren't — it's a question of how good. The best is tantalum. If you look at my lectures on corrosion, which isn't part of this course, tantalum is better than gold in terms of corrosion resistance.
Student: [inaudible question about timescale of zinc carbonate formation]
It takes about a year, because there are only about 300 ppm CO₂ in the air. If we have more global warming, it'll form faster.
§10. The galvanized handrail Eagle Scout project [49:13]
Student: [inaudible follow-up]
That's an interesting question. The answer is, I don't know — so now I'll answer the question having said I don't know.
When my oldest son was doing his Eagle Scout project, our church had some outdoor light posts and guard handrails for some of the steps outside the building. It was a brand-new building in 1986 or so, and all the paint was flaking off. Because someone had galvanized the steel and then painted it right away.
One of the things I've since learned is that if you hot-dip galvanize your steel, you have to paint it within a few hours, before the zinc hydroxide is really formed. Because if you get zinc hydroxide under there, the paint will not adhere. There are some ASTM specs on all this.
They had painted it, and within a year — brand-new building — the paint started flaking off in big chunks. A square inch and bigger. So this became my son's Eagle Scout project. I was researching it, and we could have the scouts come one Saturday and scrape all the paint — I had sandblasters and everything. That's what scouts love to work on. Give them a chainsaw, give them an axe, they'll use it. Power tools — they like tools.
So I had them sandblasting and scraping. And I've never found this again, but somewhere I'd found that if you paint it with acetic acid — which is just vinegar — so I got some acetic acid from lab supplies and we diluted about fifty percent. It was nice and smelly, but it was all outdoors. Nothing better than a scout with a paintbrush — he can swab it around wherever he wants. Acetic acid, if it gets on your clothes, it's not a big deal. It's not like sulfuric that's going to dissolve your clothes.
So they put the acetic acid on as a pre-treatment. I don't know if we formed a zinc acetate — I'm sure we probably did. Then we painted it. It's now thirty years since Matthew did his Eagle Scout project, and they repainted some of these things, but not because any paint was flaking off. You can see where it's worn down to the zinc in thirty years on a handrail. The paint stays on, because you have the right chemistry at the interface.
I haven't done Auger or X-ray photoelectron spectroscopy — I haven't cut out a sample to see if I've got zinc carbonate or zinc acetate there. But I think it's zinc acetate. So you can do some things. Either that or we just wasted a couple of gallons of acetic acid — no big deal — but the scouts had fun. Give a scout a paintbrush and send them outdoors where they can't do any damage, and they couldn't even damage their clothes.
I have a trailer that we use for campouts. About every ten years I buy the Rust-Oleum and the paint, and I tell the scoutmaster, okay, the scouts using this trailer have to paint it with Rust-Oleum. It's outdoors. We don't care if they spill the green paint on the asphalt — it's just paint. They love it. Twelve-year-old boys spraying paint all over or spilling it all over — who cares?
§11. Pipe materials: from galvanized to copper to PEX [53:01]
So we got to galvanized pipe, because people learned lead was toxic. They went to galvanized before World War II, and you still had to replace it every twenty or thirty years. Still used in the Midwest, where in some waters it'll last for forty or fifty years. Then they went to copper and brass — much more expensive but can last forever.
I just had some — probably terne plate — I had some flats on some windows. My bedroom in my house is eighty-five years old. They had some that was just steel, been there for about eighty-five years. Just a year ago it was starting to show a little rust. I think it was probably terne plate. Back in 1930, during the Depression, you could buy all the terne plate you wanted — steel with a thin layer of lead to protect it.
For five thousand dollars they were going to replace it for me, and they were going to put in plastic. Well, you know what I think of plastic in UV rays from the sun — I don't trust it. So I had to put in copper. Don't tell anyone in my neighborhood, because some night someone will come by and rip the copper off. But copper has excellent corrosion resistance. The price went from five thousand to nine thousand dollars to replace this flat part of the roof with copper instead of plastic. Not cheap, but it has very good atmospheric corrosion resistance.
Then, trying to save money, they went to PEX tubing — this stuff. [Tom holds up a sample of PEX.] They basically had to cross-link it. PEX-A is electron-beam cross-linked.
Why do you need to go to electron beams to cross-link? It turns out they do the same thing when they're making sandpaper. Sandpaper is this paper, and they put some glue on it and put some sand on that, and they want to glue the sand to the paper. There's no adhesive that sets up fast enough when they're running this paper through the machine at about fifty miles an hour. It'll still be wet by the time you want to coil it.
So they run the paper and the sand through an electron beam, and the electron beam has enough energy to break the primary bonds in the adhesive, and cause the adhesive to cross-link and set up within fractions of a second. So they can run it real fast. People have been using electron-beam cross-linking for dozens of years.
Someone said, let's do that with polyethylene — we'll use an electron beam to cross-link it. They came up with PEX-A about twenty-five years ago. Some other people couldn't fight that patent, so they came up with a chemical cross-linking. That's not the easiest thing to do, because polyethylene is just carbon and hydrogen. It's got the same formula as paraffin wax. Paraffin wax is a shorter chain — polyethylene is a longer chain hydrocarbon. Just a carbon backbone with a bunch of hydrogens.
Tests show both of them will last well over a hundred years in corrosion. There are some other issues people have run into, but it works extremely well.
You couldn't do it with ultraviolet light alone — well, you could potentially. Ultraviolet light will break down primary bonds. As I told you, primary bonds are one to three electron volts. If I'm trying to break the bonds on the carbon backbone of polyethylene, I can't do it with something that has only a few tenths of an electron volt.
From your high school chemistry — or maybe freshman chemistry — energy is equal to h-nu, Planck's constant times frequency. From my 3.091 forty-some years ago, that's equal to 12,400 over the wavelength in angstroms, which equals 1.24 over the wavelength in micrometers.
Ultraviolet is anything below 0.310 micrometers, so the energy of ultraviolet is about four electron volts. Ultraviolet will break down primary bonds. Ultraviolet gives you a sunburn because it breaks down the primary bonds in your skin. You can go out in the sun, and if you have something to protect you — transition lenses or something — you won't get sunburned, if there's no ultraviolet in the light spectrum. But there is ultraviolet in the sun, so you break primary bonds.
Dr. Bellmore will be here tomorrow and Thursday, and I'll be here Monday.