字幕列表 影片播放 列印英文字幕 this episode has been brought to you by the great courses. Plus, today I'm going to tell you some more about malignant and wires and show you some amazing micro graphs pictures, the lights of which I've never seen before. So let me remind some of you that we did an experiment or Neil did an experiment where he put a high current through a piece of militant and wire piece of horizontal MMA Lipton wire on dhe. Amazingly, at the end, we got blobs of material all the way along the wire separated very regularly on dhe. The first thing we had to do was to see whether this experiment could be repeated. So we did the experiment two or three times again, and each time we got the same result. Now, when we did it the first stone, I suggested that what was happening was that we were forming a liquid on the surface. On the surface, tension was separating the liquid into little droplets. In fact, these droplets have a technical name which I learned by looking at some papers. They called Adam to Lloyd's ah, last video in which we showed you these under Lloyd's got people very excited. And quite a number of viewers suggested in the comments that we should try heating the where in a vertical position, because then if a liquid was being formed, it would run down. So when somebody proposes a test like that, you've got to try it and you were right. Instead of getting regular blobs, what happened was the liquid formed and ran down. We got a big globe at the bottom and the tiny one where the wire had burned through. Nothing is big full up down there. Lead over there. It looked as if the regular under Lloyd's was starting to form, but then it didn't happen, and the liquid ran down and form one big blob at the bottom on Dhe. The wire then broke, and there was a small blow up left at the end of the broken wire. So I was really pleased because it confirmed my suggestion that there was liquid. But that raises quite a different problem, which is why should they be liquid? But the clue came when Neil took one of these wires toe a nanotechnology center on DDE. There, they can use electron microscope to take images off the under Lloyd's or the surface of the Andrew Lloyd. What came back was absolutely amazing. One of the pictures, my favorite one, looks like an underwater coral reef, particularly the feature in the middle has almost perfect threefold symmetry and with things coming off its 120 degrees apart. I showed this to my colleague Andrei, who said, Something almost does a throwaway remark which helped to solve the whole problem. He said, Could it be oxide rather than metal? So then I began thinking, When you heat the buyer, you would expect it to melt in the middle because the outside can lose heat so the senator should be hotter. But we were heating it in air, so perhaps the surface of the metal was burning and forming oxide. Then, of course, it would be hotter on the outside because of the chemical reaction. So I looked at the melting point of MMA Lipton, um, oxides. Both the oxides belived, um, dioxide and the lib Dems. Try oxide have melting points that are nearly 1000 degrees lower than that of Melinda metal. So what that means is, if you, from oxide, it could melt way below the temperature of which the metal would melt so the metal would be so late and the liquid bit on top. The other thing is that the density of the oxide is about half that of the density of the metal. So if you form the oxide, you will get a bigger volume of liquid than the volume of the metal that you burn. So you get more liquid than you might expect just from melting. And because the Micrografx showed that it was all frothy, it's probably gone even lower density, which is why they suddenly appear so big. It turns out that droplets forming and regular space are quite a well known phenomenon. You see it in all sorts of circumstances. If you take a tap, force it for the Americans on DDE, start water going quite fast and then gradually turn it off. You'll suddenly find the stream of liquid will break up into Siri's of droplets on dhe. This is just the same effect as we're seeing here with the wire. Then, of course, what we have to do is the test. Is it malignant oxide? So with our new samples, near went back to the Manor Technology Center, where, as well as taking the pictures, they can do an elemental analysis on the electron microscope so you can look different areas of the surface. Hi. Come in. Well, all right. What we got? And lo and behold, where there was one of these blobs, the surface had oxygen in it as well as my Lipton. Um, but where there were no blobs, there was very little oxygen, Not none, but very much less so. The theory look really quite good. But when you have a theory, you need to test your theory or your hypothesis with the prediction. So I predicted that if we heated the wire on the vacuum when there's nowhere so the malignant couldn't burn, we shouldn't get the under Lloyd's. So Neil got one of his sophisticated vacuum chambers with a window and we started heating the wire, and we got amazingly bright light sort of super light bulb. It's super bright. I'm tearing everything down on the camera. I think it was impressed. He's gone to go and get the device so we can measure the current. The y got hotter and hotter and hotter, but not a trace. of under Lloyd. And then, when everything had cooled down the wire instead of being black, would shining like you would expect the metal. So not only did it so the oxygen was needed to form the Andy Lloyd's, but it also showed that oxygen was attacking the surface and making oxide layers. So just heating adapt drove off whatever mark there was on the surface and left a really nice clean piece of MMA, Lipton and wear. Also, where Neal opened the chamber, there was clearly a very thin film that had evaporated, and you could tell it was thin because it had a rainbow of colors. And you get these colors by diffraction of light by very thin films. Because it went to such a high temperature that MMA libbed unum was evaporating. It didn't have to boil because the pressure was low, but some of the Taliban and paper was coming off and it hit the cold surface and condensed. The important message is that this experiment, which began really, is a fun experiment with a piece of MMA. Lipton, um, has not only made us think and understand something about heating wears an air that we hadn't really thought about before, but it has given us these amazing pictures, and my favorite one is free to download in the description below. So we've been going deep with Emma lived in, um, wire. But if you want to go deeper into the topics you love, why not check out today's episode, sponsor the great courses? 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