SMS_F2013_12

Um, so I looked over those of you that had topics. There's still a few that haven't picked a topic. And I think I just talked to the two of you that I had some questions about your topics being a little broad. If you have some more questions about that, I'd be happy to sit down with you individually and kind of flesh things out.

I will probably over the next couple of days put together a schedule, a tentative schedule of what days we're going to do it and who's going to present and things like that, and what day. And again, you're welcome to come to all of them. I'd like you to come to half, but I'm not going to require that you come to all six or seven days of presentations unless you want to. You're welcome to. You may find that they're more interesting than the lectures. I find they're more interesting than the lectures. I've heard the lectures before. Uh, yes.

Uh, it's going to be towards the end of October, beginning of November, and it'll be spread out over a couple of weeks, okay. And I might try to pick different days, like some Tuesdays and some Mondays, because some people have scheduling things. Although we're, I think we solved most of the scheduling problems with the 8, 8:30, 9:30 slot. But in any case, so we were talking about aluminum. Any other questions? Okay.

We were talking about aluminum and I just want to finish up a little bit with, give you some idea of the scale of aluminum production and compare it and contrast it with steel, which is forty times the scale in terms of amount of material made. But also I want to talk about some of the corrosion or fatigue problems. Anybody know what this is a picture of?

Aloha Airlines, okay. This was twenty-five years ago now. Uh, it was a while ago, but this was, I think, a 737, and it was fl— basically flying on chartered, not chartered, but on scheduled flights between islands in Hawaii. And it never went, except for being flown out to Hawaii, it was always just doing these twenty-minute flights from island to island, okay. Uh, and so as a result it had like a hundred thousand cycles, or sixty thousand cycles, in about half the time of a regular aircraft, because its flights were an average of twenty minutes or thirty minutes as opposed to forty-five minutes or an hour, because the islands are so close together.

It turns out the fuselage of an aircraft, a pressurized aircraft, is a pressure vessel. You've got higher pressure inside than you do outside. It might be eight tenths of an atmosphere, so it's like being in Denver at a higher altitude. But outside it might be four tenths of an atmosphere. I don't remember what it is at forty thousand fi— feet, but it's, there's a pressure differential. And so you actually have to build this thing as a pressure vessel, and every cycle there, we call GAG cycles, ground-air-ground, taking off and landing, you pressurize it and depressurize it. That's a fatigue cycle. So this thing had forty-some thousand cycles and finally it just let go at all the rivet holes and the whole top came off. Only one person died. There was a stewardess who was not sitting down and seat-belted in. The people who were sitting in a seat and had seat belts didn't get pulled out. She got pulled out and perished, but the thing landed. Yes?

Okay, yeah. Yeah. This was, as I remember, this was around 60,000 cycles, but it was like 40,000 hours or something. It was a lot fewer hours. And this is what happens in corrosion or fatigue. The, uh, whoever's the leader is going to be the first one who fails. I'm going to give you another example, but this happens to be a fatigue failure. It was partly corrosion fatigue, as far as that goes.

I was amazed until I started, stopped to think about it, there really is a keel beam down here. I always thought if you lost over half your pressure vessel the whole thing would just crack up, but in fact it's got this great big I-beam down here made out of aluminum. And so, you know, it was just sort of a pressure vessel canopy, if you will, so far as that goes. But so aluminum has, we have to worry about some of the, some, we have to worry about some of the, um, lifetime problems.

Another example I have here is this washer, which it's got a gray edge which means it came from a Seahawk helicopter. [Tom holds up a washer and a steel nut.] This is a steel nut that goes on top of it. And the holes don't line up because it's designed — instead of having a cotter pin or something, you put the washer on and you put the nut on and you tighten it to the proper torque, and there's one more hole in one of these than in the other, and so there'll always be one that lines up and you put a screw through it to keep it in place rather than a lock nut or a lock wire or washer or something. And this essentially holds the tail rotor of a Blackhawk helicopter or a Seahawk helicopter. And like I say, one's an Army part, one's a Navy part. I don't have a lot of these, but in fact what had happened is, this particular alloy was 60-61, which I told you was the workhorse aluminum alloy yesterday.

And it was supposed to be 6061-T6 heat treatment, which is solutionized and artificially aged. And it was supposed to be a 51, means they would take the bar and they'd stretch it one percent to relieve residual stresses. This is made from like a three inch bar and machined into a washer. And when they bought it from Alcoa or whomever, they would, when they make the bar they would heat treat it to the T6 condition. But in aluminum, because of the good thermal conductivity, the quenching process introduces residual stresses, and the 5-1 is a way to relieve residual stresses.

Now this tensile relief of residual stresses by mechanical means is common in a lot of aluminum alloys. I mean they will take whole plates at the Davenport, Iowa world's largest rolling mill — is not for steel, it's for aluminum. And in Davenport, Iowa they have this kind of twelve foot wide, about, I've only been there once, but anyway, about twelve foot wide rolls with four foot diameter steel rolls to roll the world's largest steel plates. And what do we use the world's largest steel plates for? The world's largest aircraft wings, okay. All the aircraft wings, you know, for Boeing and, uh, not necessarily for Airbus, they may get theirs from somewhere else, but anyway, for Boeing, or when McDonnell Douglas was in business, they all came out of the Alcoa Davenport works.

And there are residual stresses, and they will take these huge plates that are four inches thick, and that, I've been to the room where they have these big hydraulic expanders, and they just grab the plates, which might be thirty feet long or something, and they just pull them one to three percent in plastic strain to relieve the residual stresses from heat treatment. And that's because the residual stresses from heat treatment can lead to stress corrosion cracking, which is exactly what happened to the washer. Actually was on an Army helicopter, Sikorsky Blackhawk, but it cracked. They lost the tail rotor. It wouldn't spin because it no longer had the tension on it it's supposed to have holding it together, and it's just sort of freewheeling, and the helicopter starts spinning around and crashed and killed a bunch of soldiers in Arkansas.

So anyway, they started looking around, saying, well, why did this happen? And it turns out, so of course he says, oh, we shouldn't have been using the T6 heat treatment, we should have been using the T-73 heat treatment. And T-73 is a heat treatment, this is aged for optimum strength, this is actually over-aged. You go past the peak strength and you get about ten percent lower strength. If you look at the tempering curves for aluminum, they'll kind of go like this. This is time versus temperature. And if you actually, this is optimum age, that's T6, and T73 is a temper that's just passed by about ten percent, but the toughness like doubles, okay. And the stress corrosion cracking resistance increases by about a factor of two on stress, which is like a factor of ten on life in terms of corrosion fatigue.

So they had actually had this problem in a different helicopter, not the Blackhawk or the Seahawk — it's a Navy, or it's the Jayhawk if it's the air, for the Coast Guard, or I can't remember where the Air Force, it's all, they make the same helicopter, basically the same helicopter for all the different services, but they have their own name for it. There's also another form of the Blackhawk which is called the Presidential helicopter, and if you go down to Sikorsky, that where they make that version, is in a super secure area. It has all kinds of super-secret stuff on it, and communications gear and stuff.

Well, it turns out the washer is exactly the same. And what had happened is, they investigate this failure that killed a few people in Arkansas, and they said, oh, this other helicopter group had seen this problem and they had switched from T6 to T73 to get rid, to double the strength of stress corrosion cracking in the aluminum alloy by going to the over-age condition. And so, of course he said, oh well, we better order some new washers of T-73 that won't stress corrosion crack, because they started looking and they found these things sitting on the shelf in Navy supply depots with cracks, explosion [stress-corrosion] cracks in them, never been put in service, just the residual stresses from the original manufacturer.

We measured them — that's why it's got a little cut in it, but we put some strain gauges, actually we didn't take strain gauges, we just measured the distance between these flats before and after cutting, and then calculated, estimated the residual stresses is eight ksi. Turns out five ksi is a stress corrosion cracking, uh, limit. So this was, the residual stresses were enough to crack this thing on the shelf without ever putting it in service. The Navy saw it first. Why? Because the Navy is the corrosion leader in the military. They put everything they've got and surrounded by salt water, okay. And so the Navy will crack things first.

Anyway, the Navy had seen some, the Blackhawk design team kind of went and found out from this other design team, oh yeah, we switched those over to T73. So they order 1500 of them, fifteen-month lead time. In the meantime, the helicopter goes down in Arkansas, okay. But unfortunately it wasn't the Presidential helicopter. Although it depends on whether you're a Democrat or Republican at the time, okay.

Aluminum in general has very good corrosion resistance, as pure aluminum. That picture of the Aloha Airlines, the outside skin is a clad aluminum. They, for sixty, seventy years we've been making roll-bonded aluminum, where you take a heat-treatable aluminum plate, 2024 typically — in fact when I had those, that FAA manual, the old MIL Handbook 5, I opened it up, it was 2014 Alclad. They call it aluminum clad. It's aluminum-clad aluminum. And I'll tell you, explain what this is in a second.

Um, and they've been using it for seventy years. They basically roll a pure aluminum, 1100 aluminum, and roll it into about one inch thick plate. They take an ingot of like 2014 or 2024 heat-treatable alloy. They roll-bond the one, that one inch thick pure aluminum on the surface of the heat-treatable aluminum. The pure aluminum has no copper, so it doesn't set up a little galvanic cells that can lead to corrosion between the aluminum and the copper precipitates. So the 1100 aluminum is fantastic in corrosion resistance. We use it for things like cookware in the kitchen, okay. Not much strength, but if all you're doing is lining the bottom of a pan to give it good thermal conductivity, and it's a stainless steel pan, you just want good thermal conductivity, but you want good corrosion resistance, you don't want it to pit and things like that, you use pure aluminum.

Well, that's what they started doing with the skin of aircraft. Were very expensive, so they learned to roll bond a very thin layer. So if you had, end up rolling this big ingot that had clad surfaces of aluminum, you might roll it down to sixteenth of an inch thick, and it have one or two thousandths of pure aluminum on the surface — called Alclad aluminum, clad aluminum.

A couple of years ago, a guy in Spokane, Washington whose father had invented, father and uncle had invented the process or the machinery for casting essentially all the aluminum in the world, developed a process to jointly cast one aluminum alloy next to another aluminum alloy. And so instead of roll bonding this, they could continue, they could cast continuously. And this would be the 1100 aluminum, this would be the alloy aluminum over here, etched a little different color, and this is actually a casting fusion line where they cast it in shape. And so they no longer had to roll bond and made clad type of aluminum sheet much cheaper. And that's kind of coming to the market and bringing aluminum into lots of things like kitchen appliances and other things where it didn't have as — kitchen appliances being like stoves and refrigerators and stuff, where it didn't have as big a market, because you can now have a corrosion-resistant surface with a high-strength core. Essentially it's a composite that they grew from the melt, so they reduced the price of this compot— aluminum composite dramatically, and that was about five or seven years ago that came on the market. Um, nope.

It's a continuous casting process and they pour the molten aluminum in here, one alloy, and they pour the other aluminum in here. And it turns out for aluminum it works that the two of them just fuse together. This is actually a fairly broad fusion line, okay. Let it focus there a little bit. I mean, you can see it's a millimeter wide, and if you got it in there, you'd see a fair amount of mixing, okay. But they just cast together. And now it's the whole aluminum casting process, called direct chill. You start off with a water-cooled copper plate about the size of a desk, which is going to be the size of your ingot, and some water-cooled copper molds, and the bottom of that mold will withdraw, and you basically just pour aluminum, it freezes on the bottom and freezes on the soft, water-cooled sides. It's called DC casting, direct chill casting of aluminum. And you withdraw that thing and you make an ingot that's twenty, forty feet long by five or six feet wide by two feet high.

But now you can make it with one or two clad layers, or actually you can have up to, well, they've done up to double layers of cladding. You may want to have a brazed alloy in there, okay. And it's not always you want corrosion resistance. Sometimes you want a brazed alloy. All the aluminum that goes into automotive radiators is a brazed. And so there's a tremendous volume of radiator sheet, so far as that goes.

In any case, you've got to worry about some of the corrosion resistance of aluminum. Since one of you is interested in sailing, I brought one of my America's Cup projects. [Tom produces a fractured hydraulic cylinder.] I don't know if you can see it much anymore. It was always hard to see. Um, I never have etched it. Anyway, this is a fractured hydraulic cylinder from Amer— America's Cup, okay. The fracture origin is right here, but over time it's hard to see it unless I put it in a microscope. It's right there, okay.

Um, but the America's Cup is sort of interesting. In most cases we don't want things to fail, and we don't want them to fail for a long period of time. The America's Cup doesn't last that long, and they say their philosophy — I've talked to one of the guys who used to be, graduate of mechanical engineering here at MIT, who makes components like this and he brought this to me once. He's down in Connecticut, has a company called Navtec, and they make high-end marine equipment, hydraulic cylinders and things like that. So that makes one-of-a-kind special purpose things for people like the America's Cup.

Um, but stainless steel turnbuckles and aluminum cylinders. This is a 7,500 psi hydraulic system for raising and lowering the sails. And 7,500 psi, if you know anything about hydraulics, pretty high pressure, okay. The Blackhawk helicopter went to 3,000 psi hydraulics to save weight, but they didn't go anywhere close to 7,500. So they're not, the V-22 Osprey went to 3,000. Typical hydraulic might be 1,500 or 2,000 in most equipment. But when you get really weight-critical, they will go to, rather than steel hydraulic cylinders, they'll go to aluminum, and they'll make them so thin that they expect them to fail. In fact, what he told me is, if they don't fail, then you're not, you're making them too heavy, in the America's Cup trade, okay.

You don't want them to fail, you want it to last as long as a race, but they don't care. I mean, they're spending a hundred million dollars on these, uh, vessels, and you know, you've got a multi-multi-billionaire who once had bragging rights at the yacht club, okay, that he, you know, funded the America's Cup, and so he doesn't care if it fails and he has to spend another five thousand dollars for a silly little hydraulic cylinder. But you do want them to fail safely, okay. And the problem was, these things were exploding when they failed. And it was a little stress corrosion fatigue crack starting from the outside. And he brought me this thing and wanted to know, what do we do about it?

Well, it turns out, I think it was 7075-T6 — sure, I have my notes here from the letter he sent me originally. Yeah, with 7075, which is an aluminum-zinc alloy. So erase that and put in 7075. And it was stress corrosion cracking. They had gone to T6. I don't think they had the 5-1 heat treatment in there necessarily, the stretching. But in fact, uh, the solution to his problem was — it was only that, was like only an eighth of an inch thick — to go from three millimeters thick to four millimeters thick, to increase the wall a little bit. Because we're going to get less strength, but we could double our fracture toughness, or our corrosion, stress corrosion cracking threshold.

And with that we made it into a leak-before-break. So when the crack went all the way through it would just spray out a little stream of oil and people get all oily, but they wouldn't get shrapnel going through them, okay. So you don't mind being as oily, because you got slickers on anyway. So, but you expect them to fail. And if they don't, if your hardware doesn't fail on a regular basis in the America's Cup, you've made it too heavy. A little different philosophy, okay. So actually one of the only industries I know where you design things so they're right on the edge of failure.

But anyway, what else do I have on aluminum? Maybe, oh, maybe that's most of it. I guess to give you a feel for what we do in aluminum, it's the heat-treatable alloys with their copper and their magnesium and their zinc, that's what gives them their strength by precipitation hardening. But it also decreases the corrosion resistance, okay. I taught you about scandium on baseball bats to increase the, or decrease the grain size.

When we look at trying to get both toughness and strength — and I'm going to put up here, this is the old ratio analysis diagram that I put up before, earlier in the semester. This is the one for steel, and this was developed out of the Liberty ships at the Naval Research Laboratory in the 50s and 60s. And it plots the toughness versus the tensile strength or yield strength of the material, and this is called the technological limit. At low strength steel you can get very high toughness. As you go to higher and higher yield strengths up to 300 ksi, your toughness goes down and your critical flaw size gets smaller and smaller. That's what these lines here, critical section thickness, is two and a half inches. So you can build a pressure vessel out of anywhere, a steel with properties anywhere along this line, and it could be two and a half inches thick and it would leak before it breaks. You don't want a brittle fracture where it shatters like glass and sends shrapnel all around in a pressure vessel or a submarine, which is also a externally pressurized pressure vessel. But you get down here to 300 ksi steels and your critical flaw size is a tenth of an inch, okay.

It turns out you'd like to have a ratio of toughness to yield strength, uh, K squared over sigma, of two and a half is kind of the difference between your plastic deformation region and your plane strain region. If you want to be in the elastic plastic region, which is where we can usually afford to design structures, you've got to have a fracture toughness squared over stress of two and a half, okay. Well, it turns out, here's the, actually it's fracture toughness over yield strength, so this two and a half is kind of the ratio that we'd like to have. This is for aluminum. It has one-fifth of fracture toughness. It has about one-seventh the strength unless you go way out here, and it still has only one-third the strength. The critical flaw size, when you start getting into baseball bats or aluminum-lithium alloys, you've got critical flaw sizes, they're getting down to a tenth or two tenths of an inch, okay. Type of critical flaw size, critical depth of surface crack in inches, okay, depending on different ratios of these things.

But without going through all that, so that's the ratio analysis diagram, and here's titanium, but I'm going to go back to the Ashby plot and just talk a little bit about structural materials in general. If this is the Ashby toughness versus strength, and for mechanical structural material, we're interested in toughness and strength as the two measures. Remember, strength is the force, toughness is the energy of fracture. If I have yield before fracture, it's going to deform before it shatters. If I have fracture before yield, I've got a brittle material that just shatters. It's going to be like a hand grenade and send shrapnel all around.

If I'm looking at this K1c over sigma-f constant of two and a half, it has this slope. There's another criteria for safe design of K squared over sigma — we won't worry about that one right now. But if here are the K1's — oh actually, we won't worry about it — K1c squared over sigma of pi sigma squared, okay. So this is the K1c over sigma. And that's actually that is kind of the dimensionless number for the fundamental equation of fracture mechanics. But this two and a half, this little log scale on these dashed lines down here, this two and a half, I put a blue line in here. So this is the material elastic plastic, we'd like to design. This is brittle material. We got to be careful when we start using these types of materials on that side of the diagram.

Well, let's look and see what we've got. Steel's overlap. Nickel out, overlap, actually nickel is mostly on that side. Titanium overlaps. All of your composites — graphite reinforced, carbon fiber reinforced, Kevlar reinforced. Aluminum alloys overlap, copper alloys, magnesium out once, overlapping, okay. That's of the metals. If we look at woods, this is parallel with the grain — that's how we usually use a two-by-four. Perpendicular to the grain, it's a brittle material. You would never put wood in that direction, okay, if you're trying to do a structural material. So wood is actually an anisotropic composite material.

This two and a half line splits right — here are your ceramics, you know, rocks, pottery, most of your ceramics over here. Even your high-performance ceramics and glasses are down here. So if we really look at structural materials, it's on this side of the line that we're usually working, okay. But we still have to be careful, because this blue line cuts through most of these things, most of these materials. Well, this alloy's great and this alloy's lousy, and it's the same base system. Yes, is that the question? No? Okay, sorry. No, you can twirl your pen, uh, okay, um, I just didn't know if you're raising your hand.

In any case, I'm trying to bring it back to why we spent so much time talking about certain types of materials. So I'm pretty much done with aluminum, and I was going to go into magnesium, which I probably will. Remember tomorrow we've got a guest lecturer, Adam Powell, will be coming to talk about the company that he and Professor Paul — both of them used to be faculty members in this department in chemical metallurgy.

But anyway, periodic table. I will finish up on Friday. We have gone through — cross out iron, we've sort of done aluminum, we're going to do magnesium in a little bit. Uh, but as structural materials, we have not gotten very far, right, according to the periodic table. However, you can sort of cross out everything. Among the alkali earths, hydrogen is not much of a structural material unless you're down at less than twenty degrees Kelvin. Uh, lithium, these things are all too soft. I mean, you may not want to push on them with your finger because they will react with the moisture in your skin and cause sodium hydroxide and cause a burn, okay. But they're very soft materials, inherently soft.

Francium, we can't even isolate it. The only time we've ever discovered it is we can see it in the spectra of some, as an impurity in some other things. So it's sort of almost a non-existent material on Earth. It does exist on Earth, but only as an impurity in other things. We don't, there's, you can't go buy a lump of francium, okay. Cesium, well, we'd use cesium for a few functional material things. Rubidium, shoot, we put that, it concentrates in tobacco stocks, and they use tobacco stocks to make welding electrodes because they like the rubidium. Anything here is an easy electron donor, so we like to put sodium and potassium and rubidium and lithium into welding electrodes fluxes, okay. But they're not structural materials.

And this column, well, beryllium is a structural material. So let's talk about beryllium real quick. Um, what's, if you look at, if you went back to Ashby's book and look at the price of beryllium, I haven't gone to look at it, but it's probably several hundred thousand dollars a ton. First of all, you get a lot of it per ton. It's very light element. If you ever picked up a piece of beryllium, which I'm sure most of you haven't, it's like picking up a piece of paper, it's so light, okay. It has a very high melting point. I can't, well, actually it should be on here. Melting point of beryllium is 16— it's 1560 centigrade. So it melts at a higher temperature than steel.

It's used for, at $400,000 a ton or whatever it costs, spacecraft. That's the only structural application, but it's used all the time in spacecraft because it is so light. And it's a very rigid material, it's relatively rigid. It has a fantastic strength-to-density, a specific, uh, density or specific strength ratio. It's just way off the chart if you looked at one of these Ashby charts. But it's very expensive. Why is it expensive? Anybody know what the problem with beryllium is? Toxic. If you get any beryllium, pure beryllium powder, any compound, in your lungs, and you were part of ten percent of the population that has a genetic predisposition to berylliosis, you will get nodules forming in your lungs that just start consuming your lungs, and you slowly die of suffocation. But the ninety percent of people, it's not a problem.

This was discovered right up here on the corner of Mass Ave, okay. Not where we have Building 35, but just on the corner of the other side of the railroad tracks. I believe that's where it is. It could have been on this side of the railroad tracks where the little bank kiosk is in the parking lot. But MIT, during the Manhattan Project in World War II, was working on beryllium for some nuclear warheads. It was sort of a new material. And there's some faculty members here working on the metallurgy of beryllium, and they had a little machine shop over there and they were machining beryllium parts. And towards the end of World War II, beginning of just after the war, when they were working on nuclear materials, all of a sudden a few of the machinists started dying of this lung disease, and they tracked it down and found out it was berylliosis, which had never been discovered before because it was a new material.

But they showed, through whatever, contaminating rats — it wasn't until years later I learned that, or they learned, and then I had to learn, that there's apparently a genetic predisposition. I think one of the students in my, in the class did a little presentation on berylliosis once, and that may have been where I found out it was only ten percent of the population get it. But people are just deathly afraid of using beryllium. I remember I was cleaning out an old lab, Professor Grant's lab, where I had someone else cleaning out when I was department head, it's right around the corner from headquarters. And young Professor, actually Professor Shu's, professor at Northwestern, but he was a young professor here. He came in, he was in a fit because he found a bottle of beryllium powder. And I went and I said, David, it had been sitting there since 1946 or whatever. Uh, I said, it's got a cap on it. He says it's dusty. I said, yeah, but that's dust from the air. I mean, it's had the cap on it for twenty years. This has been a lot. Anyway, so, you know, I went and picked it up, you know, it's in the jar. I'm not going to dust it and throw it in the air and find out if I've got that genetic predisposition.

But people are deathly afraid of beryllium. Um, I mean it's sort of beyond what they ought to be afraid of. It has to be in a powder form, can be beryllium chloride, beryllium oxide, beryllium metal, gets inside your lungs and you're part of that ten percent of the population, you've got serious problems. So it's toxic, but it's also expensive to manufacture, in part because it's toxic, so they have to have all these controls so the people manufacturing don't get berylliosis. That's one of the reasons it's expensive.

But it has one application which I keep on thinking how to buy one of these tools and bring in. It's called non-sparking tools. You can take copper alloys and you can give them 180 or 200 ksi strength by a precipitation heat treatment by copper beryllium. So you can make a copper, two or three percent beryllium alloy, heat-treat it, and end up with a copper alloy that's as strong as some of your strongest steels, okay. And they use it in mines for non-sparking equipment. If you're in a mine, you've seen steel shovels or other tools get a spark when you hit them, right? It's not a good thing in a mine full of methane, okay. You could have a ka-boom, okay.

So in mines they actually use high thermal conductivity tools — which copper is a high thermal conductivity material, and you make beryllium copper, you get a hard tool that's non-sparking. You can go with titanium, really copper-beryllium alloy hammers, and you can bang them against a copper-beryllium nail or, you know, uh, pick or something, and it won't spark. You can do it all day long. There's just enough heat transfer that when the frictional heating goes in there, it carries the heat away faster than the ability to generate temperatures sufficient to cause sparking. That's not true in steel. And you'd love to do it in aluminum because it'd be cheaper than copper beryllium. But aluminum just, it's got good thermal conductivity, but you can't get 200 ksi strength in aluminum.

In any case, so that's beryllium. We just covered beryllium, okay, check that one off. So let's go down the periodic table here, but I'm going to skip magnesium for just a second. Calcium — we've actually talked about that. How do we talk about it? It's used in larger quantities than steel. It's called Portland cement, okay. I gave you the formula. You take calcium carbonate, called limestone — all these little, sea critters gave their lives and deposited themselves at the bottom of the ocean over millions of years, and earthquakes and stuff brought them to the top, and we go mine it, turn it into powders, spread it on our lawns to get rid of the acid rain. But we also can take it, put it in a kiln and drive off at a thousand degrees centigrade the CO2 and end up with calcium oxide, also known as burnt lime, okay. And then you take that, you mix it with water and you get calcium hydroxide.

Now it's not always calcium, pure calcium limestone. Some of those little critters had magnesium in them. It might be, I think dolomite is fifty percent calcium with fifty percent magnesium carbonate. And so some of your Portland cement is a calcium-magnesium alloy. But we actually do use calcium as a structural material, and it's called Portland cement. It's used in a larger quantity than iron, so we've covered that, okay.

Magnesium — well, let me finish up these. Strontium and barium start to get very soft. Radium is actually, some of that forms is radium's radioactive in it. Some of it's got a fair number of radioactive species. Yeah, they also used to drink it back in the 1920s. Have you ever heard about that? Uh, when radioactivity was sort of new, people thought they'd make these radium cocktails and they thought that by drinking it, it would make them feel better, sort of like five-hour energy, okay. But it was very expensive. And then people found, the longer they drank it, they started having other effects, and they decided maybe — it was expensive, but there's one guy who was very wealthy, and he, to his dying day, would drink a glass of radium every day. And it turns out his dying day didn't take too many months, because his bones started decalcifying and he started turning into just sort of like an amoeba and stuff, you know, no structure. So maybe we call this an anti-structural material. But anyway, this is in the 1920s, so these things don't really count.

But magnesium, okay, magnesium does count for something, okay. Let's talk about magnesium a little bit. Magnesium, let's talk about the quantities of magnesium that are used in the world. So here's shipments of magnesium from '83 to '88. It doesn't really matter too much, they didn't change dramatically. The 28,000 tons, metric tons, was used for die castings, gravity, and then 37,000 tons for gravity and wrought products. Wrought — I mean only seven thousand of the thirty-seven thousand is wrought products. Wrought meaning sheet or wrought or something. Someone was talking to someone, they wanted to use magnesium, or they wanted to deform magnesium, and I said it's not easy. Well, this is an example. It's not easy. To heat it up, you have to do it warm. It's a hexagonal close-packed metal. Can be made into sheet, but you have to really know what you're doing, okay.

Mostly we use this, that's structural, non-structural. Magnesium is used to make the 6000 series or 7000 series aluminum alloys. In fact, about half of all the magnesium made goes into alloying for aluminum, okay. Desulfurization, that goes into steel, to get the sulfur out, okay, and just form manganese sulfide. Nodular iron — you can make cast iron and you can change the graphite morphology and call it ductile iron. So that's actually a growing market segment. You can see it growing fairly dramatically up until '80, well even beyond '87.

Metal reduction — we want to, magnesium so reactive, you can make magnesium metal and then you can react it with some chloride or fluoride of something else, like tantalum chloride, you could make tantalum metal, okay, out of magnesium metal and tantalum chloride. And they in fact do that. All your tantalum capacitive, capacitors are made by magnesium reduction of tantalum chloride or tantalum fluoride. So metal reduction, chemical uses of magnesium.

Electrochemicals — if you own a hot water heater, or your parents own a hot water heater, it has probably has a magnesium anode, okay, going down the center of it, a sacrificial electrochemical anode. That will corrode just like zinc on galvanized steel becomes the anode that corrodes and cathodically protects the steel in a hot water tank. To correct, to protect the copper, the brass, the steel, anything you've got that the water is coming in contact with in the hot water tank, use magnesium as a sacrificial anode. Yes? They use aluminum, yeah.

Magnesium is better. The problem with aluminum, if you have certain ions in your water, the aluminum can form a passive scale on the surface, and all of a sudden the aluminum becomes non-anodic, becomes cathodic. Aluminum is sometimes called amphim—, amphoteric, which means it can switch its polarity in the galvanic series. So aluminum, in proper conditioned waters, is fine as an anode material, but magnesium is better, because if you look at the galvanic series, all the way over here, the most reactive is magnesium, and all the way over here the least reactive is graphite. And it's like an extra half volt you get out of magnesium compared to zinc. I mean, magnesium has really got, it's really the most electroactive of our common, you know, sacrificial anodes.

And one structural, actually two structural applications. The US Navy out in Port Hueneme, California, where they have a diving school, they developed about thirty or forty years ago — people were interested, I mentioned these aluminum silicon carbide composites. People around 1980 were, or 70s and 80s, were very interested in these ceramic-metal composites. And so the Navy was trying to make lightweight magnesium composites that had silicon carbide or graphite or whatever in them. And I remember Professor Latanision, who worked on corrosion here, he was working on some of these things, and he found that if he tried to polish them to make a metallographic sample, they would corrode faster than he could polish. So they had to polish them in an oil rather than a water system, because you got graphite and you got magnesium, and those are the two far ends on the galvanic series. It would corrode so fast.

But the Navy said, ah, it corrodes fast, we will use that property of rapid corrosion of this composite. And they found two uses. One was, you could take this alloy, this composite, and in a plastic bag, down the divers could take it down, and when they're doing salvage operations, one of the things you sometimes do is build a great big balloon and then fill it with gas to lift the salvage to the surface. Just a great big bubble. Well, they didn't have to pump gas down, you know, a couple hundred feet. They could just break open this thing and it would corrode and generate hydrogen gas. You just had to be careful when it got to the surface that you somehow attached it before and dissipated the hydrogen before you blew it up. But anyway, it was, they used it as a salvage material. The other thing, it would corrode so fast that when divers were diving in cold water, they could strap it in these plastic things, and if they got cold they could just pierce the plastic and it would corrode and generate enough heat to keep them warm, okay.

So, okay, but you have to understand one of the Achilles heels of — they only made 200,000 tons in 1983, they were making 250,000 tons in 1988, a quarter million tons. Well, aluminum's like forty million tons, right? And steel's a billion tons, okay. So yes, magnesium is one of our structural materials. It has several Achilles heels. One is the fact that it corrodes. It's a great corroding material. Actually the Navy called these super-corroding alloys, okay. Um, but it has other problems.

In addition to corrosion, one problem is that it will burn if you get to certain temperatures. And if you want to see this, you go to New York City, you go to one of the poor areas of town where they torch cars on this part on the sidewalk to get the insurance money, okay. Your car's a junker but it's got mag wheels, okay. Uh, so you torch it. And the magnesium, you know, throw some gasoline on a car and on some magnesium, and the fire will get hot enough, magnesium will ignite, and you get a really hot fire. At that point burns at about 4000 degrees. Magnesium is used in flares, it's used in fireworks in powdered form, and gives bright white lights, okay. So it burns, because it's so reactive.

It also, you develop residual stresses, so you try to weld it, and the humidity in the air will almost crack it right behind the weld. I mean, not quite that fast, but you come back two days later after having fusion welded magnesium alloys, if you haven't stress-relieved it, just the humidity in the air will cause stress corrosion cracking, okay. So that's why most things are castings, because castings don't have residual stresses. And most of the magnesium that goes on automobiles used to be in the wheels, and they would just paint those for corrosion resistance. But now it's kind of going underneath the dashboard in places like that, very specialized applications.

It does come into play in some things like the Blackhawk helicopter. I mean, here's an old article about the Blackhawk helicopter and the use of high-performance magnesium. The US government is constantly spending tens of millions of dollars every year to try to develop a magnesium, low-cost magnesium market, because they say, oh, we can build lightweight automobiles. Well, you can't roll sheet very easily, and they sort of make automobiles out of sheet. You can make castings, but I have yet to figure out why they do all this. Uh, tomorrow when Adam Powell comes in, he will tell you that one of the first things they did was, with his technology, was to make magnesium because they could get several million dollars from the US government to make low-cost magnesium.

Cost about twice as much as aluminum. In terms of energy costs, it really shouldn't cost any more. There's a guy, Joel Clark's first doctoral student here in the mid-70s, did a thesis on the magnesium business and the cost of magnesium. And he didn't say it as directly in his thesis because he could have been sued, probably, but his basic conclusion was that after World War II, Dow Chemical, which has sort of a monopoly on magnesium production — of this 250,000 tons, they may make 200,000 tons, they got a near monopoly on this stuff — they, according to Dr. Kenney, it appears that you can track the price from 1946 all the way up to 1975, and the magnesium and aluminum prices tracked perfectly with one another. And you can do statistics and correlation coefficients. There is no economic reason for that to be true other than an illegal cartel. Okay, but Americans don't do that, okay. So obviously it's not true, right.