Rod Macleod brought up the subject of the Bloodhound SSC project. The subject was new to me, but there is an excellent entry in Wikipedia about it that explains what the project is about (building a supersonic car) and speaks to why it is being done, how, and what is hoped to be gained.
While thinking about the Bloodhound project, a lot of interesting memories came to mind. In the course of developing coatings, I have had the pleasure of meeting and working with many top-notch scientists and engineers. As a group, they sometimes get the reputation for being dull and rather boring; they’re just not the ones that you expect to be the life of the party. I think that this reputation is unfortunate and undeserved. But, I also think that this reputation is understandable when you consider how focused these people are. Their attention is tightly focused on their work. They don’t just plot-up their data and call it a day. They study their data, memorize it, agonize over it and reflect on it. Obviously, this is not something that everyone does or can do or would choose to do if they could. It takes a certain passion. To an outsider, one who did not understand what they were going through, or one who was not similarly afflicted, their demeanor could come off as distant, detached and disinterested.
Actually, I have found that, as a generality, these people are very approachable, especially after regular office hours when the hubbub of the day’s activities have subsided and the quiet of the evening has set in. Then, in that setting, you can have some very interesting conversations and, if you are so inclined, you can learn some very interesting things. In the space of 40 minutes or maybe a few hours, you can learn more than you could have learned in your whole career. And, it’s not things that you could ever learn from a text book; it’s much better than that. They tell you about their frustrations and the challenges that they are up against. If they have a complaint, their complaint is usually directed toward the basic cussedness of nature. Nature has a way of staying a few steps ahead of us and is always more complex than we had hoped. Text books don’t reflect this and the popular view of science is that science provides all the answers. It doesn’t. The best science can usually do is to provide some of the questions, a few at a time.
That’s one of the things that make the Bloodhound SSC project so interesting. What the scientists and engineers are doing here is that they are putting something to a test. What they are putting to the test is not the Bloodhound craft itself or even their knowledge and understanding of the underlying science and technology. What they are putting to the test is their curiosity and their ability to learn.
So, what does all of this have to do with being a coating developer? Quite a lot, actually. Rod limited his question to the outer surfaces of the Bloodhound craft. On something that complex, the outer surfaces, well – please forgive me, they hardly scratch the surface of the potential for coating applications. Wherever you have a surface, an interface between two media, you have a potential application for coatings, especially if one of the media is abrasive, erosive, corrosive, or chemically or energetically aggressive. The Bloodhound craft is loaded with these, but I think that, for the most part, that these surfaces are well characterized and provided for. Those surfaces really don’t worry me. There is the matter of the bespoke hybrid rocket engine. That’s not something I know much about. A number of my co-workers worked on the NASA shuttle engines right up until their recent retirement. They will know much more than I do.
The thing that captures my attention about this project is the wheels. The wheels are to be made of aluminum. Now, aluminum is inherently a soft, ductile, malleable material with a very low specific gravity and a fairly high specific strength. When we say that a material is soft, we are referring to how it responds to pressing a hard indenter into it. It is a standard test. The way that this test works is that you place a hard indenter on the surface of the material that you would like to test. Then, you apply some pressure. What happens is that the hard indenter sinks into the softer material that you are testing. When you remove that pressure, there is some rebound. The surface of the softer material tends to return back to its original shape. That sounds all well and good, but if you carefully examine the test point under a microscope you will see something very interesting. Provided that you applied enough pressure while making your test, you will find a mark on the surface of the softer material and you can use the size of that mark to determine some rather fundamental properties of the material you are testing. This test is actually a rather common quality control test, and it is used in many industries. (What happens, you ask, if the hardness of the indenter and the material you are testing are equal or very close. Ah, well, you would have to ask. But we don’t have time for that right now.)
The thing is, aluminum is inherently very soft. If you push something into it, it tends to leave a mark. As the Bloodhound craft travels over the 12 mile test track, it is going to encounter a lot of very hard materials, and they will leave a mark. Actually, I don’t think trying to coat the wheels is a good idea. No coating would adhere or last at those speeds. No. The thing that I think should be done is to coat the test track to hold down the dust and to ensure that the hardness of the material that the wheels roll over is less than the hardness of the aluminum wheels.
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