1 00:00:16,649 --> 00:00:19,953 Today, we're going to just start by talking about what glass is 2 00:00:19,953 --> 00:00:21,254 and what its properties are. 3 00:00:24,057 --> 00:00:26,626 But before we do, this came in-- 4 00:00:26,626 --> 00:00:29,295 we've been talking about defects, OK. 5 00:00:29,295 --> 00:00:35,101 And vacancies, point defects, and then on Wednesday, 6 00:00:35,101 --> 00:00:36,236 we did line defects. 7 00:00:36,236 --> 00:00:37,003 Remember those? 8 00:00:37,003 --> 00:00:40,607 Right, and they create these planes that come in. 9 00:00:40,607 --> 00:00:42,709 They're slip planes that allow atoms 10 00:00:42,709 --> 00:00:47,514 to slide across each other that allows you to plasticly deform 11 00:00:47,514 --> 00:00:49,249 a material. 12 00:00:49,249 --> 00:00:54,621 And so OK, but with regards to vacancies, I got this by email. 13 00:00:54,621 --> 00:00:56,856 I'm at the Heathrow Airport in London, 14 00:00:56,856 --> 00:01:00,260 and even this aerial sculpture has vacancy point defects 15 00:01:00,260 --> 00:01:01,327 in its pattern. 16 00:01:01,327 --> 00:01:01,928 Look at that. 17 00:01:01,928 --> 00:01:03,163 There you go. 18 00:01:03,163 --> 00:01:04,431 And there you go. 19 00:01:04,431 --> 00:01:07,033 This is a beautiful thing, right? 20 00:01:07,033 --> 00:01:07,834 Thank you, Sophia. 21 00:01:10,503 --> 00:01:14,174 And notice that she's looking at it with her periodic table, 22 00:01:14,174 --> 00:01:16,209 of course, right. 23 00:01:16,209 --> 00:01:18,411 That's a no-brainer. 24 00:01:18,411 --> 00:01:22,715 But even such structures can't escape the fact 25 00:01:22,715 --> 00:01:25,718 that you always have vacancies. 26 00:01:25,718 --> 00:01:26,386 That was cool. 27 00:01:26,386 --> 00:01:27,554 OK, now where were we? 28 00:01:27,554 --> 00:01:30,056 Right, so we're going to talk about glass. 29 00:01:30,056 --> 00:01:32,826 Now, this is glass, and I'll start 30 00:01:32,826 --> 00:01:34,561 with just how cool glass is. 31 00:01:34,561 --> 00:01:36,763 But this is also not just-- 32 00:01:36,763 --> 00:01:39,566 this isn't all that glass is. 33 00:01:39,566 --> 00:01:42,035 And I want to make sure we get that 34 00:01:42,035 --> 00:01:43,169 by the end of this lecture. 35 00:01:43,169 --> 00:01:45,738 This is not the only thing that glass means. 36 00:01:45,738 --> 00:01:46,940 But this is what we think of. 37 00:01:46,940 --> 00:01:49,776 So here's a really cool video. 38 00:01:49,776 --> 00:01:50,810 OK. 39 00:01:50,810 --> 00:01:53,346 No and yes. 40 00:01:53,346 --> 00:01:54,013 [VIDEO PLAYBACK] 41 00:01:54,013 --> 00:01:54,646 There they are. 42 00:01:54,646 --> 00:01:58,283 Look at that molten [INAUDIBLE] and it's-- 43 00:01:58,283 --> 00:01:59,452 oh, he just added something. 44 00:01:59,452 --> 00:02:00,753 We'll talk about that. 45 00:02:00,753 --> 00:02:01,888 Oh, and now he's mixing it. 46 00:02:01,888 --> 00:02:05,358 - Table man carefully mixes this glass [INAUDIBLE].. 47 00:02:09,362 --> 00:02:11,397 Once the glass is blended to his specifications-- 48 00:02:11,397 --> 00:02:12,165 OK, there it is. 49 00:02:12,165 --> 00:02:13,533 Is it a liquid? 50 00:02:13,533 --> 00:02:14,501 Is it a solid? 51 00:02:14,501 --> 00:02:17,103 - [INAUDIBLE] 52 00:02:17,103 --> 00:02:20,707 And then he just puts it through a little roller. 53 00:02:20,707 --> 00:02:23,176 - That will mash that glass flat [INAUDIBLE] 54 00:02:23,176 --> 00:02:27,447 Mash it flat, and there is your piece of glass. 55 00:02:27,447 --> 00:02:28,848 OK, and we'll see another one. 56 00:02:28,848 --> 00:02:32,218 I'll show you another video of a larger scale-- 57 00:02:32,218 --> 00:02:33,286 don't keep going. 58 00:02:33,286 --> 00:02:33,853 [END PLAYBACK] 59 00:02:33,853 --> 00:02:34,721 OK. 60 00:02:34,721 --> 00:02:36,789 So what was it that they were just mixing? 61 00:02:36,789 --> 00:02:40,093 Why does it have the properties that it has? 62 00:02:40,093 --> 00:02:41,895 Why can they just take this thing 63 00:02:41,895 --> 00:02:43,897 that's not really liquid and not really 64 00:02:43,897 --> 00:02:47,500 solid, it's some viscous thing, and roll it through, 65 00:02:47,500 --> 00:02:50,336 and then it comes into this really beautiful sheet 66 00:02:50,336 --> 00:02:53,239 that we all call glass? 67 00:02:53,239 --> 00:02:56,910 And it all has to do with what I showed you before, 68 00:02:56,910 --> 00:02:58,311 and what we've been talking about, 69 00:02:58,311 --> 00:03:02,315 which is order or disorder. 70 00:03:02,315 --> 00:03:03,783 And so we did this already. 71 00:03:03,783 --> 00:03:07,187 We covered, OK, a solid that which is dimensionally stable. 72 00:03:07,187 --> 00:03:08,154 That's cool. 73 00:03:08,154 --> 00:03:15,228 Classification, oh ordered, regular, long-range order, BCC, 74 00:03:15,228 --> 00:03:16,696 FCC. 75 00:03:16,696 --> 00:03:17,597 All right. 76 00:03:17,597 --> 00:03:18,698 OK, long-range. 77 00:03:18,698 --> 00:03:21,301 Remember, we said it just keeps going and going and going. 78 00:03:21,301 --> 00:03:23,670 And then we say, well, it may be once in a while, 79 00:03:23,670 --> 00:03:28,508 once every 1,000, 10,000, 100,000, there's a vacancy. 80 00:03:28,508 --> 00:03:30,176 OK, so we started messing with it. 81 00:03:30,176 --> 00:03:33,780 But it still had this long range-- gesundheit-- order. 82 00:03:33,780 --> 00:03:35,648 And so they were called crystalline, 83 00:03:35,648 --> 00:03:39,185 crystalline with defects, maybe, but still crystalline. 84 00:03:39,185 --> 00:03:41,187 That is not what glass is. 85 00:03:41,187 --> 00:03:43,856 Glass is disordered. 86 00:03:43,856 --> 00:03:47,060 And so that is the topic of today and next Wednesday. 87 00:03:47,060 --> 00:03:50,597 What happens when you go from an ordered structure, 88 00:03:50,597 --> 00:03:53,933 like this, oh maybe it's got some-- 89 00:03:53,933 --> 00:03:57,036 oh these are 2D defects, right, the whole things 90 00:03:57,036 --> 00:03:58,638 are kind of-- so it's poly crystalline, 91 00:03:58,638 --> 00:04:00,106 but it's still kind of crystalline, 92 00:04:00,106 --> 00:04:03,443 and it's very ordered, to totally disordered. 93 00:04:03,443 --> 00:04:03,943 All right. 94 00:04:03,943 --> 00:04:09,449 And so a disordered solid looks random, certainly 95 00:04:09,449 --> 00:04:11,351 over long range. 96 00:04:11,351 --> 00:04:14,020 There might be short range order. 97 00:04:14,020 --> 00:04:16,656 There might be some short range order, but over a long range, 98 00:04:16,656 --> 00:04:18,625 it's going to be disordered. 99 00:04:18,625 --> 00:04:19,826 It's going to look random. 100 00:04:19,826 --> 00:04:23,796 This is called amorphous as opposed to crystalline. 101 00:04:23,796 --> 00:04:27,934 This is also called glass. 102 00:04:27,934 --> 00:04:29,369 This is also called glass. 103 00:04:29,369 --> 00:04:32,972 So one of the first things we've got, this is really important, 104 00:04:32,972 --> 00:04:37,076 glass is not just the window, or the thing on your phone 105 00:04:37,076 --> 00:04:38,778 that keeps cracking. 106 00:04:38,778 --> 00:04:39,712 No. 107 00:04:39,712 --> 00:04:44,584 Glass is equal to an amorphous solid. 108 00:04:49,522 --> 00:04:52,158 Well, so it's bigger. 109 00:04:52,158 --> 00:04:53,693 It's broader. 110 00:04:53,693 --> 00:04:54,761 It's bolder. 111 00:04:54,761 --> 00:04:58,064 You can have glass metal, metallic glass. 112 00:04:58,064 --> 00:05:00,133 It's a thing. 113 00:05:00,133 --> 00:05:05,104 Any solid that doesn't have long range order that's amorphous 114 00:05:05,104 --> 00:05:06,506 is a glass. 115 00:05:06,506 --> 00:05:07,974 OK. 116 00:05:07,974 --> 00:05:14,280 Now in this class we will use SiO2 as-- 117 00:05:14,280 --> 00:05:16,115 so what we're going to do is we're 118 00:05:16,115 --> 00:05:19,185 going to talk about glass with an example. 119 00:05:19,185 --> 00:05:22,488 We will use the kind that winds up 120 00:05:22,488 --> 00:05:24,657 being in the windshield of your car 121 00:05:24,657 --> 00:05:26,959 or in the window of your house and on your phone. 122 00:05:26,959 --> 00:05:29,095 And that is called quartz. 123 00:05:29,095 --> 00:05:30,463 So the chemistry that we're going 124 00:05:30,463 --> 00:05:39,672 to use is quartz, or SiO2 OK, and what we're 125 00:05:39,672 --> 00:05:43,576 going to talk about is how processing effects 126 00:05:43,576 --> 00:05:45,211 that chemistry, affects the-- 127 00:05:45,211 --> 00:05:47,213 sorry, the solid that forms. 128 00:05:47,213 --> 00:05:48,348 So processing. 129 00:05:48,348 --> 00:05:52,151 And there is lots of processing parameters 130 00:05:52,151 --> 00:05:53,486 and we can talk about. 131 00:05:53,486 --> 00:05:57,256 What I want to focus on today is the cooling, 132 00:05:57,256 --> 00:05:58,891 the cooling rate in particular. 133 00:05:58,891 --> 00:06:01,761 So that's going to be the focus today. 134 00:06:01,761 --> 00:06:03,663 We'll talk about the chemistry. 135 00:06:03,663 --> 00:06:04,997 We'll talk about the processing. 136 00:06:04,997 --> 00:06:06,399 And we'll talk about how those go 137 00:06:06,399 --> 00:06:08,835 back and forth to create glass. 138 00:06:11,504 --> 00:06:14,207 Now, OK, what am I starting with? 139 00:06:14,207 --> 00:06:17,276 I'm starting with a crystal. 140 00:06:17,276 --> 00:06:19,612 This is quartz. 141 00:06:19,612 --> 00:06:20,947 This is how you see quartz. 142 00:06:20,947 --> 00:06:24,784 Now, quartz is this beautiful, beautiful crystal. 143 00:06:24,784 --> 00:06:26,119 And it is ordered. 144 00:06:26,119 --> 00:06:28,054 That's why I'm saying the word crystal. 145 00:06:28,054 --> 00:06:29,889 I'm not saying the word glass. 146 00:06:29,889 --> 00:06:30,390 All right. 147 00:06:30,390 --> 00:06:32,492 This is an ordered solid. 148 00:06:32,492 --> 00:06:33,493 It's not cubic. 149 00:06:33,493 --> 00:06:35,261 So it's not one of the ones we've learned. 150 00:06:35,261 --> 00:06:38,998 But it's still periodically repeating. 151 00:06:38,998 --> 00:06:39,532 All right. 152 00:06:39,532 --> 00:06:40,500 And so it's a crystal. 153 00:06:40,500 --> 00:06:41,601 It's got long range order. 154 00:06:41,601 --> 00:06:42,568 It's called quartz. 155 00:06:42,568 --> 00:06:45,738 It's SiO2 So I'm going to hand this out 156 00:06:45,738 --> 00:06:47,607 so you can just see it. 157 00:06:47,607 --> 00:06:50,176 And that's what I want to start, I want to talk about, 158 00:06:50,176 --> 00:06:53,880 is that crystal, OK, because that's 159 00:06:53,880 --> 00:06:59,652 what we're going to be messing up and creating short-range. 160 00:06:59,652 --> 00:07:03,122 We're going to go from long-range to short-range. 161 00:07:03,122 --> 00:07:04,157 OK, so what is it? 162 00:07:04,157 --> 00:07:06,292 Well, let's see. 163 00:07:06,292 --> 00:07:08,428 In this class, how do we think about chemistry? 164 00:07:08,428 --> 00:07:11,364 Well you can think about it now in different ways. 165 00:07:11,364 --> 00:07:13,399 Let's pick Lewis. 166 00:07:13,399 --> 00:07:14,434 All right, OK. 167 00:07:14,434 --> 00:07:21,007 So I say, OK, I got silicon, silicon, silicon, 168 00:07:21,007 --> 00:07:25,311 if I think about silicon as it's Lewis, 169 00:07:25,311 --> 00:07:28,448 you know, dots, then it's got four. 170 00:07:28,448 --> 00:07:34,053 It's got four valence electrons ready to bond. 171 00:07:34,053 --> 00:07:37,089 You can see that now if I have oxygen, what does oxygen 172 00:07:37,089 --> 00:07:37,590 look like? 173 00:07:37,590 --> 00:07:40,393 So oxygen has six. 174 00:07:40,393 --> 00:07:42,328 I'm going to put those like that. 175 00:07:42,328 --> 00:07:44,130 So oxygen has six. 176 00:07:44,130 --> 00:07:46,265 Maybe it's got a couple lone pairs, 177 00:07:46,265 --> 00:07:49,969 which has six valence electrons, not four. 178 00:07:49,969 --> 00:07:52,705 Now so if I had-- 179 00:07:52,705 --> 00:07:55,508 so when you look at this, you think, you know, 180 00:07:55,508 --> 00:08:00,713 silicon looks like it wants four bonds when you look at it. 181 00:08:00,713 --> 00:08:03,483 And in fact, we know that the crystal in silicon 182 00:08:03,483 --> 00:08:06,052 as we've talked about-- gesundheit-- 183 00:08:06,052 --> 00:08:08,554 is tetrahedral because of this. 184 00:08:08,554 --> 00:08:09,555 Right, it's tetrahedral. 185 00:08:09,555 --> 00:08:14,060 Remember, it's a two atom basis FCC lattice which is 186 00:08:14,060 --> 00:08:16,562 is diamond. 187 00:08:16,562 --> 00:08:18,764 But what if I just look at it with oxygen, 188 00:08:18,764 --> 00:08:21,000 come at this with oxygen and say, well, you know, 189 00:08:21,000 --> 00:08:23,469 I want to have four bonds. 190 00:08:23,469 --> 00:08:27,240 One way to do that would be to add four oxygens. 191 00:08:27,240 --> 00:08:28,274 So what if I did this? 192 00:08:28,274 --> 00:08:32,010 What if I did silicon and oxygen, 193 00:08:32,010 --> 00:08:37,283 and I did plus 4 times the oxygen. 194 00:08:37,283 --> 00:08:39,352 Well, then you could see, what could you do? 195 00:08:39,352 --> 00:08:45,424 You could do this, OK, and this and this and this. 196 00:08:45,424 --> 00:08:48,361 But now, OK, the oxygens, how would they be left? 197 00:08:48,361 --> 00:08:49,829 They'd be left like this. 198 00:08:49,829 --> 00:08:56,969 And you'll see why I'm focusing on this SiO4 group in a minute. 199 00:08:56,969 --> 00:08:58,271 That's what I got. 200 00:08:58,271 --> 00:09:02,008 Now, OK, if I go back in and I put my Lewis cap on, 201 00:09:02,008 --> 00:09:05,845 silicon is very happy it's obeying octet, 202 00:09:05,845 --> 00:09:08,581 but the oxygens aren't quite there. 203 00:09:08,581 --> 00:09:13,386 So they need one more electron, one more electron. 204 00:09:13,386 --> 00:09:16,656 I'm going to make it a little bolder because I've added it. 205 00:09:16,656 --> 00:09:17,156 All right. 206 00:09:17,156 --> 00:09:19,458 So I've added an electron to each of those. 207 00:09:19,458 --> 00:09:24,196 So if I had SiO4, and I added 4-- 208 00:09:24,196 --> 00:09:30,403 if I had SiO4, and I added four electrons to it, 209 00:09:30,403 --> 00:09:33,372 I get a really nice stable Lewis structure. 210 00:09:33,372 --> 00:09:34,340 Right. 211 00:09:34,340 --> 00:09:36,242 That's called a silicate. 212 00:09:36,242 --> 00:09:37,376 That's a silicate group. 213 00:09:41,013 --> 00:09:41,948 SiO4. 214 00:09:41,948 --> 00:09:44,150 And I need those four electrons, as you 215 00:09:44,150 --> 00:09:46,786 can see just from looking at the simple dot diagram. 216 00:09:46,786 --> 00:09:49,689 I need those four electrons to make it happy. 217 00:09:49,689 --> 00:09:50,856 OK. 218 00:09:50,856 --> 00:09:52,825 By the way, just speaking of naming, OK, 219 00:09:52,825 --> 00:09:58,064 so let's see silicate, right silica, SiO2, 220 00:09:58,064 --> 00:10:01,601 we can talk about, so what we do is when we have oxide, silicon 221 00:10:01,601 --> 00:10:05,104 oxide, just in terms of naming, you know, 222 00:10:05,104 --> 00:10:10,543 like if you have an oxide, often, you kind of add an a, 223 00:10:10,543 --> 00:10:16,882 right, so like silicon went from SiO2, we call it silica. 224 00:10:22,455 --> 00:10:27,560 So in Al2O3, let's see, Al2O3 is also an oxide, right? 225 00:10:27,560 --> 00:10:29,295 And so we called that-- this is something 226 00:10:29,295 --> 00:10:32,531 we've already done, alumina. 227 00:10:32,531 --> 00:10:37,003 All right, and so on, except for sometimes. 228 00:10:37,003 --> 00:10:40,072 And so sometimes, like for example, 229 00:10:40,072 --> 00:10:47,246 if you do calcium oxide, well, that's called lime. 230 00:10:47,246 --> 00:10:51,017 It's called lime, calcium oxide. 231 00:10:51,017 --> 00:10:52,318 Well, what about sodium? 232 00:10:52,318 --> 00:10:55,388 Well, sodium, if you do sodium, you're 233 00:10:55,388 --> 00:10:58,924 going to need it I'm assuming the oxygen might 234 00:10:58,924 --> 00:11:00,660 break off and become to-- 235 00:11:00,660 --> 00:11:02,595 so you've got to think about the charge again. 236 00:11:02,595 --> 00:11:06,966 So Na20 would be the one that works there. 237 00:11:06,966 --> 00:11:10,703 All right, and this is sodium oxide. 238 00:11:10,703 --> 00:11:16,909 But see, sodium oxide, but sometimes, 239 00:11:16,909 --> 00:11:20,446 it's called soda, because-- 240 00:11:20,446 --> 00:11:26,118 and this is an extra step, because soda comes from calcium 241 00:11:26,118 --> 00:11:26,952 from-- 242 00:11:26,952 --> 00:11:31,590 let's see, Na2O from-- 243 00:11:31,590 --> 00:11:32,391 how do you make it? 244 00:11:32,391 --> 00:11:42,101 You make it from Na2CO3, which is actually what is soda? 245 00:11:42,101 --> 00:11:44,270 Sodium carbonate. 246 00:11:44,270 --> 00:11:50,476 But because we make Na2O, that oxide from something 247 00:11:50,476 --> 00:11:54,447 that we call soda, sometimes people just call in Na2O soda, 248 00:11:54,447 --> 00:11:55,681 it's not. 249 00:11:55,681 --> 00:11:56,782 But sometimes you see that. 250 00:11:56,782 --> 00:11:59,251 So I just want to kind of make you aware some of these names. 251 00:11:59,251 --> 00:12:00,352 Why am I writing it there? 252 00:12:00,352 --> 00:12:02,121 We're coming back to that. 253 00:12:02,121 --> 00:12:04,156 We're going to use those later. 254 00:12:04,156 --> 00:12:06,358 That's partly why I want them to be on the board, 255 00:12:06,358 --> 00:12:08,828 and also tell you about the names. 256 00:12:08,828 --> 00:12:11,163 So Na2O is sodium oxide. 257 00:12:11,163 --> 00:12:14,834 But it's made from sodium carbonate, which is soda. 258 00:12:14,834 --> 00:12:16,001 OK. 259 00:12:16,001 --> 00:12:16,502 All right. 260 00:12:16,502 --> 00:12:18,604 Now, OK, now, here's the thing. 261 00:12:18,604 --> 00:12:22,108 That's an isolated molecule. 262 00:12:22,108 --> 00:12:23,776 Look at what I'm passing around here. 263 00:12:23,776 --> 00:12:27,480 Oh, I wanted to tell you about the window. 264 00:12:27,480 --> 00:12:29,515 I almost forgot. 265 00:12:29,515 --> 00:12:32,685 In this class, in this class, we don't 266 00:12:32,685 --> 00:12:36,188 go around saying that windows are thicker on the bottom, 267 00:12:36,188 --> 00:12:40,359 than on the top, because glass flows like a liquid. 268 00:12:40,359 --> 00:12:41,460 No. 269 00:12:41,460 --> 00:12:43,395 That is not true. 270 00:12:43,395 --> 00:12:44,497 That is not true. 271 00:12:44,497 --> 00:12:45,965 That may be true down the street. 272 00:12:45,965 --> 00:12:48,834 That is not true here. 273 00:12:48,834 --> 00:12:50,603 We do the calculation. 274 00:12:50,603 --> 00:12:57,943 Glass is not a liquid, not once it's cooled down into a solid. 275 00:12:57,943 --> 00:12:58,844 It's a solid. 276 00:12:58,844 --> 00:13:03,349 If you do the calculation, and it's a centimeter thick, 277 00:13:03,349 --> 00:13:07,853 a window pane, for that piece of glass, 278 00:13:07,853 --> 00:13:10,523 under normal diffusion and temperature conditions 279 00:13:10,523 --> 00:13:12,558 for that piece of glass at the bottom 280 00:13:12,558 --> 00:13:15,561 to become thicker by one nanometer 281 00:13:15,561 --> 00:13:18,297 would take 10 billion years. 282 00:13:18,297 --> 00:13:19,665 OK. 283 00:13:19,665 --> 00:13:24,603 So no, it's not flowing under its own weight in a window. 284 00:13:24,603 --> 00:13:25,538 What happened? 285 00:13:25,538 --> 00:13:27,573 What happened is people didn't know 286 00:13:27,573 --> 00:13:30,709 how to make glass uniformly way back when, 287 00:13:30,709 --> 00:13:35,748 and so they came out un-uniform, non uniform. 288 00:13:35,748 --> 00:13:36,915 What's easier? 289 00:13:36,915 --> 00:13:38,884 To install it with the heavier side 290 00:13:38,884 --> 00:13:42,087 up or the heavier side down? 291 00:13:42,087 --> 00:13:45,257 It's easier to install it if it's heavier on the bottom. 292 00:13:45,257 --> 00:13:47,493 Class doesn't flow. 293 00:13:47,493 --> 00:13:48,160 OK. 294 00:13:48,160 --> 00:13:48,661 All right. 295 00:13:48,661 --> 00:13:51,297 I wanted to get that done early. 296 00:13:51,297 --> 00:13:52,331 Yeah. 297 00:13:52,331 --> 00:13:53,632 Oh, here we go. 298 00:13:53,632 --> 00:13:56,235 OK, so this is quartz. 299 00:13:56,235 --> 00:13:58,971 This is crystalline silica. 300 00:13:58,971 --> 00:14:04,977 This is groups of SiO2, not SiO4. 301 00:14:04,977 --> 00:14:08,214 This was how we made a molecule happy. 302 00:14:08,214 --> 00:14:15,487 But watch what happens now when I go from that picture to SiO2. 303 00:14:15,487 --> 00:14:17,857 So now, I've got these-- 304 00:14:17,857 --> 00:14:21,093 let's suppose I've got these molecules of-- and I'm just 305 00:14:21,093 --> 00:14:25,931 going to not draw it 3D, but I'm going to draw it 2D, and OK, 306 00:14:25,931 --> 00:14:26,432 there's-- 307 00:14:26,432 --> 00:14:28,567 gesundheit-- there's all these charges there. 308 00:14:28,567 --> 00:14:31,337 So now these are these molecules, 309 00:14:31,337 --> 00:14:33,038 these silicate groups. 310 00:14:33,038 --> 00:14:35,207 And they're kind of happy, and they're on their own. 311 00:14:35,207 --> 00:14:38,611 But now look what happens here. 312 00:14:38,611 --> 00:14:42,848 See, those two oxygen, what if instead of each of these 313 00:14:42,848 --> 00:14:46,051 being separate, they came together? 314 00:14:46,051 --> 00:14:46,719 All right. 315 00:14:46,719 --> 00:14:48,454 Well, you can see that-- 316 00:14:48,454 --> 00:14:53,325 you see, if they shared the same oxygen here, 317 00:14:53,325 --> 00:14:55,661 if they shared the same oxygen here, 318 00:14:55,661 --> 00:14:58,697 then that oxygen is actually now Lewis 319 00:14:58,697 --> 00:15:01,700 happy without the extra charge. 320 00:15:04,637 --> 00:15:14,246 So this oxygen, this bridge, oxygen, 321 00:15:14,246 --> 00:15:25,190 doesn't need that extra electron to be happy. 322 00:15:25,190 --> 00:15:26,392 What does to be happy mean? 323 00:15:26,392 --> 00:15:28,627 Well, we know what that means. 324 00:15:28,627 --> 00:15:31,430 And if we're talking about Lewis and speaking in those terms, 325 00:15:31,430 --> 00:15:32,965 it means you've got your octet. 326 00:15:32,965 --> 00:15:33,899 All right. 327 00:15:33,899 --> 00:15:35,501 So now the bridge oxygen-- 328 00:15:35,501 --> 00:15:37,803 oh, but that is what I'm passing around. 329 00:15:37,803 --> 00:15:40,205 That is what quartz is. 330 00:15:40,205 --> 00:15:42,908 It's all the oxygen is happy without needing 331 00:15:42,908 --> 00:15:45,277 the extra charge, because they are all bridged. 332 00:15:48,180 --> 00:15:49,281 So that's what we've done. 333 00:15:49,281 --> 00:15:53,152 We've made silica by thinking about it 334 00:15:53,152 --> 00:15:57,656 in terms of these silicate groups, OK, 335 00:15:57,656 --> 00:15:59,591 and just bridging them all together. 336 00:15:59,591 --> 00:16:00,859 And I can't draw it. 337 00:16:00,859 --> 00:16:03,262 But you have it there, and 3D models 338 00:16:03,262 --> 00:16:05,931 are the easiest way to see it. 339 00:16:05,931 --> 00:16:10,869 And they all act as bridges between silicate groups. 340 00:16:10,869 --> 00:16:11,637 OK. 341 00:16:11,637 --> 00:16:12,805 So why am I-- 342 00:16:12,805 --> 00:16:14,807 why do I keep this silicate group? 343 00:16:14,807 --> 00:16:16,909 So a lot of times if you look up the structure, 344 00:16:16,909 --> 00:16:18,277 and this is the 3D structure, you 345 00:16:18,277 --> 00:16:21,780 see every single oxygen is a bridge. 346 00:16:21,780 --> 00:16:24,650 Every single oxygen is a bridge. 347 00:16:24,650 --> 00:16:26,685 And it's nice to think about it in terms 348 00:16:26,685 --> 00:16:28,053 of the silicate groups. 349 00:16:28,053 --> 00:16:28,554 Why? 350 00:16:28,554 --> 00:16:31,123 Why did I start with that? 351 00:16:31,123 --> 00:16:35,527 I started with that because these groups are very strong. 352 00:16:35,527 --> 00:16:38,063 They stay together. 353 00:16:38,063 --> 00:16:41,567 And they kind of act as building blocks for the glass 354 00:16:41,567 --> 00:16:42,968 and for the quartz. 355 00:16:42,968 --> 00:16:45,604 And you now know those are two different things, 356 00:16:45,604 --> 00:16:49,742 quartz is silicate groups ordered in a crystal. 357 00:16:49,742 --> 00:16:51,844 Glass is what we're going to get to. 358 00:16:51,844 --> 00:16:54,580 It's when they're disordered. 359 00:16:54,580 --> 00:16:55,247 OK. 360 00:16:55,247 --> 00:16:56,281 And why is that? 361 00:16:56,281 --> 00:17:00,152 Well, because these oxygen, you see the silica, the tetrahedron 362 00:17:00,152 --> 00:17:03,255 with the silicon atom and those oxygens is pretty robust. 363 00:17:03,255 --> 00:17:05,223 But the bond between the oxygens is-- well, 364 00:17:05,223 --> 00:17:08,426 there's a whole lot of rotation that can happen here. 365 00:17:08,426 --> 00:17:10,396 You see that? 366 00:17:10,396 --> 00:17:12,964 That thing can rotate around. 367 00:17:12,964 --> 00:17:14,665 So that's a good way to picture this. 368 00:17:14,665 --> 00:17:16,801 That's a good way to picture quartz 369 00:17:16,801 --> 00:17:19,771 is these silicate groups that are bonded together 370 00:17:19,771 --> 00:17:21,740 through these bridge oxygens, but they 371 00:17:21,740 --> 00:17:25,077 have a lot of rotational and distortion 372 00:17:25,077 --> 00:17:31,250 relative one with respect to one another, that is possible. 373 00:17:31,250 --> 00:17:35,621 So I take those silicate groups, OK. 374 00:17:35,621 --> 00:17:38,924 Here they are up top, and I bring them together, 375 00:17:38,924 --> 00:17:40,526 and I make a perfect crystal. 376 00:17:40,526 --> 00:17:41,960 That is what's being passed around. 377 00:17:41,960 --> 00:17:44,930 But look, because there's so much possibility 378 00:17:44,930 --> 00:17:48,867 for rotation and distortion, maybe that didn't happen. 379 00:17:48,867 --> 00:17:51,537 Maybe as they start to form or they find each other, 380 00:17:51,537 --> 00:17:56,442 and they start bridging, maybe they didn't quite make it. 381 00:17:56,442 --> 00:18:00,212 And you can imagine these things are kind of bulky groups 382 00:18:00,212 --> 00:18:02,448 coming together and twisting around. 383 00:18:02,448 --> 00:18:06,752 You missed the mark, it might be hard to get back. 384 00:18:06,752 --> 00:18:10,856 So how does one happen over the other? 385 00:18:10,856 --> 00:18:12,357 All right, that's the crystal. 386 00:18:12,357 --> 00:18:15,794 That's the not crystal, the glass. 387 00:18:15,794 --> 00:18:17,629 And it depends on a couple of things. 388 00:18:17,629 --> 00:18:19,364 And that's what I want to talk about next. 389 00:18:19,364 --> 00:18:22,901 It depends on the temperature and the cooling. 390 00:18:22,901 --> 00:18:25,404 Depends on the temperature and the cooling. 391 00:18:25,404 --> 00:18:27,272 So how does temperature come in? 392 00:18:27,272 --> 00:18:30,809 So temperature comes in because temperature 393 00:18:30,809 --> 00:18:32,478 makes everything vibrate. 394 00:18:32,478 --> 00:18:32,978 Right. 395 00:18:32,978 --> 00:18:37,783 It gives these atoms and these groups kinetic energy. 396 00:18:37,783 --> 00:18:38,283 OK. 397 00:18:38,283 --> 00:18:39,284 So let's look at that. 398 00:18:39,284 --> 00:18:46,091 So if we were to plot, for example, temperature 399 00:18:46,091 --> 00:18:50,229 versus the volume per mole, so this is, 400 00:18:50,229 --> 00:18:55,601 you know, for a given number of these atoms, much volume 401 00:18:55,601 --> 00:18:56,168 do they take? 402 00:18:56,168 --> 00:18:59,438 Well, you can imagine that that is actually related 403 00:18:59,438 --> 00:19:01,440 to how much energy they have. 404 00:19:01,440 --> 00:19:01,940 All right. 405 00:19:01,940 --> 00:19:05,611 So like if I had like a crystal, you know, 406 00:19:05,611 --> 00:19:07,646 maybe I'll start it here. 407 00:19:07,646 --> 00:19:10,215 And if I have a crystal, you know, 408 00:19:10,215 --> 00:19:12,151 and I increase the temperature a little bit, 409 00:19:12,151 --> 00:19:14,720 maybe they're going to move more. 410 00:19:14,720 --> 00:19:17,756 And as they move more, they need more room. 411 00:19:20,159 --> 00:19:21,827 And this is just a simple-- you can just 412 00:19:21,827 --> 00:19:25,063 think of like a simple atom, connected 413 00:19:25,063 --> 00:19:27,399 to another on a spring. 414 00:19:27,399 --> 00:19:32,938 And more kinetic energy, more temperature, it goes further. 415 00:19:32,938 --> 00:19:35,007 And now you're all thinking, well, wait a second, 416 00:19:35,007 --> 00:19:37,943 doesn't it go in as far as it goes out? 417 00:19:37,943 --> 00:19:39,344 Why? 418 00:19:39,344 --> 00:19:41,980 Does it need more volume? 419 00:19:41,980 --> 00:19:46,485 Well, that is because of what we have already talked about, 420 00:19:46,485 --> 00:19:53,425 which is this energy curve between two atoms, or two 421 00:19:53,425 --> 00:19:54,760 silicate groups. 422 00:19:54,760 --> 00:19:57,896 This potential energy curve that plots 423 00:19:57,896 --> 00:20:00,165 the energy between those two groups 424 00:20:00,165 --> 00:20:02,834 and, say, the distance between them, 425 00:20:02,834 --> 00:20:06,171 has something very important about it, 426 00:20:06,171 --> 00:20:07,639 has something very important. 427 00:20:07,639 --> 00:20:08,607 This is the spring. 428 00:20:08,607 --> 00:20:14,846 OK, so I'm in there, and I'm at T equals 0 here. 429 00:20:14,846 --> 00:20:17,449 That would be like T equals 0. 430 00:20:17,449 --> 00:20:20,085 The absolute ground state, the place 431 00:20:20,085 --> 00:20:22,387 where everything is just in its minimum energy, 432 00:20:22,387 --> 00:20:25,457 but now I start making things move. 433 00:20:25,457 --> 00:20:27,559 All right, I put kinetic energy into it, 434 00:20:27,559 --> 00:20:31,463 I increase the temperature, what happens? 435 00:20:31,463 --> 00:20:33,332 The energy goes up. 436 00:20:33,332 --> 00:20:35,567 But look, it doesn't go up. 437 00:20:35,567 --> 00:20:36,602 It goes like this. 438 00:20:36,602 --> 00:20:39,938 The average-- I'm a little bit higher in energy, 439 00:20:39,938 --> 00:20:42,074 right, I'm a little bit higher in energy. 440 00:20:42,074 --> 00:20:43,976 So where I am is there, on average. 441 00:20:43,976 --> 00:20:47,145 Now I'm a little bit higher in energy, and so where I am 442 00:20:47,145 --> 00:20:50,549 is there, and now I'm a little bit higher, and where I am 443 00:20:50,549 --> 00:20:51,049 is there. 444 00:20:51,049 --> 00:20:55,420 This is what happens to the average. 445 00:20:55,420 --> 00:20:57,456 That's why solids expand. 446 00:21:00,392 --> 00:21:04,263 It's because of the asymmetry in this potential energy 447 00:21:04,263 --> 00:21:07,266 curve, which we have already talked about. 448 00:21:07,266 --> 00:21:09,268 It's because of the asymmetry. 449 00:21:09,268 --> 00:21:10,135 You see. 450 00:21:10,135 --> 00:21:14,973 This is going out differently than this goes up. 451 00:21:14,973 --> 00:21:17,576 That's why you have thermal expansion. 452 00:21:17,576 --> 00:21:18,277 All right. 453 00:21:18,277 --> 00:21:20,812 Things are vibrating. 454 00:21:20,812 --> 00:21:23,749 But more often than not, they're going to be farther apart. 455 00:21:23,749 --> 00:21:25,050 And so this happens. 456 00:21:25,050 --> 00:21:25,984 And so this happens. 457 00:21:25,984 --> 00:21:28,520 So we've just understood this from an atomic-- 458 00:21:28,520 --> 00:21:30,756 so this would be like if I had a crystal, 459 00:21:30,756 --> 00:21:34,960 and I'm going to save three letters and write xtal. 460 00:21:34,960 --> 00:21:37,362 That's so efficient. 461 00:21:37,362 --> 00:21:39,498 And then I keep going. 462 00:21:39,498 --> 00:21:41,166 And by the way, the slope of this 463 00:21:41,166 --> 00:21:47,839 is called slope is called the thermal expansion coefficient. 464 00:21:47,839 --> 00:21:53,412 Thermal expansion. 465 00:21:53,412 --> 00:21:56,982 That is the definition of the thermal expansion coefficient. 466 00:21:59,685 --> 00:22:00,886 Sometimes we use alpha. 467 00:22:03,488 --> 00:22:05,023 That's the slope of this line. 468 00:22:05,023 --> 00:22:07,492 It's the volume per mole divided by-- 469 00:22:07,492 --> 00:22:09,394 over the temperature, the change in the volume 470 00:22:09,394 --> 00:22:10,629 or the change in temperature. 471 00:22:10,629 --> 00:22:13,065 It's the thermal expansion coefficient of the material. 472 00:22:13,065 --> 00:22:16,635 OK, so I'm adding temperature, and I'm expanding 473 00:22:16,635 --> 00:22:19,404 and I'm expanding and then I get to this point. 474 00:22:19,404 --> 00:22:21,340 I get to this point. 475 00:22:21,340 --> 00:22:27,212 This point here is where everything changes. 476 00:22:27,212 --> 00:22:29,147 Everything changes. 477 00:22:29,147 --> 00:22:32,851 That's the melting point of the solid. 478 00:22:32,851 --> 00:22:34,186 That's the melting point. 479 00:22:34,186 --> 00:22:38,690 Now at the melting point, as we know, 480 00:22:38,690 --> 00:22:41,927 the whole thing goes through a transition. 481 00:22:41,927 --> 00:22:46,465 It goes through a phase transition. 482 00:22:46,465 --> 00:22:47,499 And it becomes a liquid. 483 00:22:50,035 --> 00:22:52,537 And the thermal expansion of the liquid 484 00:22:52,537 --> 00:22:55,674 is different than the solid, because those, now, 485 00:22:55,674 --> 00:23:00,412 you think about those molecules are not rigidly 486 00:23:00,412 --> 00:23:02,681 bonded to each other anymore. 487 00:23:02,681 --> 00:23:05,317 They're more weakly bonded, and they're moving around 488 00:23:05,317 --> 00:23:07,886 with a lot of kinetic energy. 489 00:23:07,886 --> 00:23:09,588 And so when they get more kinetic energy, 490 00:23:09,588 --> 00:23:11,289 they can expand even more. 491 00:23:11,289 --> 00:23:13,024 That's why those slopes are different. 492 00:23:15,694 --> 00:23:18,764 But as we know, there's also a big volume change. 493 00:23:18,764 --> 00:23:21,700 There's a sudden volume change. 494 00:23:21,700 --> 00:23:25,036 In going from a solid to a liquid, 495 00:23:25,036 --> 00:23:27,773 there's a sudden volume change. 496 00:23:27,773 --> 00:23:31,510 And it would be the same thing if I went back the other way. 497 00:23:31,510 --> 00:23:34,446 Right, I'm cooling it down and cooling it down, 498 00:23:34,446 --> 00:23:38,617 and all of a sudden, I get to the solidification temperature 499 00:23:38,617 --> 00:23:43,755 of the material, and I become a crystal. 500 00:23:43,755 --> 00:23:46,558 Except when I don't. 501 00:23:46,558 --> 00:23:48,760 Except when I don't. 502 00:23:48,760 --> 00:23:52,731 And when I don't, that's when I become a glass. 503 00:23:52,731 --> 00:23:54,433 And that's what we have to talk about now 504 00:23:54,433 --> 00:23:58,336 is, how do we go from this very simple picture of being 505 00:23:58,336 --> 00:23:59,471 a glass-- 506 00:23:59,471 --> 00:24:02,808 being a liquid or being a solid, a crystalline solid, 507 00:24:02,808 --> 00:24:07,479 how do we go from that to being a glass? 508 00:24:07,479 --> 00:24:10,782 And to explain this, to start, I want 509 00:24:10,782 --> 00:24:13,552 to show you something really cool that can happen. 510 00:24:13,552 --> 00:24:15,654 That actually wasn't an intentional pun. 511 00:24:15,654 --> 00:24:19,825 But it has to do with cooling, and it's really cool, 512 00:24:19,825 --> 00:24:23,862 because sometimes, if you cool a liquid down, 513 00:24:23,862 --> 00:24:26,398 it doesn't solidify right there. 514 00:24:26,398 --> 00:24:27,833 Then that's called super cooling. 515 00:24:27,833 --> 00:24:30,502 So you can actually cool the liquid down like that, 516 00:24:30,502 --> 00:24:31,770 and have it stay a liquid. 517 00:24:34,406 --> 00:24:36,274 That's called super cooling. 518 00:24:36,274 --> 00:24:43,348 By the way, so this is called super cooling. 519 00:24:43,348 --> 00:24:46,818 By the way, you can do that with water. 520 00:24:46,818 --> 00:24:49,354 And so I want to show you like one of the coolest things 521 00:24:49,354 --> 00:24:50,489 you could do tonight. 522 00:24:50,489 --> 00:24:51,623 It's a Friday night. 523 00:24:51,623 --> 00:24:53,425 You're going to have guests over, 524 00:24:53,425 --> 00:24:55,760 or you'll be out at that same restaurant that 525 00:24:55,760 --> 00:24:57,829 knows about you, because you asked them 526 00:24:57,829 --> 00:25:02,934 already all about the candle and the oxygen. 527 00:25:02,934 --> 00:25:04,803 And you always come with your periodic table, 528 00:25:04,803 --> 00:25:07,472 and this time, you sit down and you say I don't want water. 529 00:25:07,472 --> 00:25:08,874 Do you want sparkling or regular? 530 00:25:08,874 --> 00:25:10,976 I want super cooled. 531 00:25:10,976 --> 00:25:12,577 This is what you're going to get. 532 00:25:12,577 --> 00:25:13,879 This is what they'll bring you. 533 00:25:13,879 --> 00:25:14,379 They should. 534 00:25:14,379 --> 00:25:18,483 If it's a good restaurant, this is what they would bring you. 535 00:25:18,483 --> 00:25:21,920 You know, so here's who is supercooled water being poured. 536 00:25:24,623 --> 00:25:27,092 This is what you should see in your glass. 537 00:25:27,092 --> 00:25:34,733 Now, that is a liquid that is stable, for now, 538 00:25:34,733 --> 00:25:38,904 below its melting point, below its solidification point. 539 00:25:38,904 --> 00:25:43,408 So what happens is as soon as it hits the glass, 540 00:25:43,408 --> 00:25:48,113 it's like, whoa, wait a second, I am supposed to be a crystal, 541 00:25:48,113 --> 00:25:50,215 and it immediately solidifies. 542 00:25:50,215 --> 00:25:53,518 All right, so it immediately went like this. 543 00:25:53,518 --> 00:25:56,121 Now, by the way, it's not that hard to make supercooled water. 544 00:25:56,121 --> 00:25:59,624 If anybody's interested, I'd be happy to tell you how to do it. 545 00:25:59,624 --> 00:26:01,660 You can't just put bottles in a freezer. 546 00:26:01,660 --> 00:26:02,727 That won't work. 547 00:26:02,727 --> 00:26:06,197 But it's not that hard to do. 548 00:26:06,197 --> 00:26:13,038 Now, OK, back and forth, melting point, 549 00:26:13,038 --> 00:26:16,341 supercooled-- oh, it's playing again. 550 00:26:16,341 --> 00:26:17,509 And it starts freezing. 551 00:26:17,509 --> 00:26:20,712 You can also take a bottle of supercooled water 552 00:26:20,712 --> 00:26:21,613 and just go like this. 553 00:26:21,613 --> 00:26:23,782 It's liquid inside and just tap it, 554 00:26:23,782 --> 00:26:25,884 and the whole thing freezes instantly. 555 00:26:25,884 --> 00:26:27,185 It's really cool. 556 00:26:27,185 --> 00:26:28,820 It's really cool. 557 00:26:28,820 --> 00:26:29,321 OK. 558 00:26:35,627 --> 00:26:36,661 OK. 559 00:26:36,661 --> 00:26:41,333 Now, why am I talking about this? 560 00:26:41,333 --> 00:26:49,307 Because you can super cool and go down. 561 00:26:49,307 --> 00:26:52,477 You could go below that transition point 562 00:26:52,477 --> 00:26:55,213 and go and go down, like I just did there 563 00:26:55,213 --> 00:27:02,087 and become a crystal right away, but you could also not. 564 00:27:02,087 --> 00:27:06,992 You could also become a solid, so you could become a crystal, 565 00:27:06,992 --> 00:27:09,227 or you could also become a solid. 566 00:27:09,227 --> 00:27:12,430 And I'm going to need another plot to do this. 567 00:27:12,430 --> 00:27:15,033 And you could become a solid right where you were. 568 00:27:15,033 --> 00:27:18,870 You might not go down to the crystal curve, 569 00:27:18,870 --> 00:27:21,773 but you might start a new curve. 570 00:27:21,773 --> 00:27:25,243 And that will be a glass. 571 00:27:25,243 --> 00:27:27,846 And so we're going to draw this again and show you a glass, 572 00:27:27,846 --> 00:27:32,350 but this is what we need is this framework to understand 573 00:27:32,350 --> 00:27:33,184 when a glass forms. 574 00:27:33,184 --> 00:27:35,553 So this was our picture, crystalline, crystalline, 575 00:27:35,553 --> 00:27:38,690 glass, amorphous equals glass. 576 00:27:38,690 --> 00:27:40,659 When does it form? 577 00:27:40,659 --> 00:27:42,327 Now I think the best-- 578 00:27:42,327 --> 00:27:43,795 I'll show you that one in a second. 579 00:27:43,795 --> 00:27:46,264 I think the best way to think about it 580 00:27:46,264 --> 00:27:49,601 is let's draw the plot again, and I 581 00:27:49,601 --> 00:27:51,102 think the best way to think about it 582 00:27:51,102 --> 00:28:00,245 is an analogy that has been used before, and let's see-- 583 00:28:00,245 --> 00:28:02,947 and this is temperature. 584 00:28:02,947 --> 00:28:07,519 This is volume per mole. 585 00:28:07,519 --> 00:28:10,789 By the way, that could be energy, or enthalpy. 586 00:28:10,789 --> 00:28:14,759 Yeah, because as the atoms aren't packed in as well, 587 00:28:14,759 --> 00:28:17,262 we know this, right, as they're not packed in as well, 588 00:28:17,262 --> 00:28:20,565 they're also going to be higher in energy. 589 00:28:20,565 --> 00:28:22,267 Right, the bonding won't be as strong. 590 00:28:24,769 --> 00:28:27,505 But I think that one of the best analogies to think about 591 00:28:27,505 --> 00:28:30,508 is so I'm coming in as a liquid, so I'm now a liquid. 592 00:28:33,278 --> 00:28:39,484 And here's my melting point for the crystal, for the crystal. 593 00:28:39,484 --> 00:28:41,853 But I went past it. 594 00:28:41,853 --> 00:28:45,490 And I went past it, and now, instead of-- 595 00:28:45,490 --> 00:28:47,525 I'm just going to draw this out here. 596 00:28:47,525 --> 00:28:48,359 There's the crystal. 597 00:28:50,962 --> 00:28:57,902 Instead of going down to become a crystal, suddenly 598 00:28:57,902 --> 00:29:00,772 or super cooling, and then becoming a crystal, 599 00:29:00,772 --> 00:29:06,411 no, I super cool, and then I just become a solid. 600 00:29:06,411 --> 00:29:09,447 And then I just become a solid. 601 00:29:09,447 --> 00:29:10,415 OK. 602 00:29:10,415 --> 00:29:13,518 Now that-- this is a glass. 603 00:29:16,154 --> 00:29:19,457 You know that it's a solid. 604 00:29:19,457 --> 00:29:22,393 It's got the same slope as the crystal. 605 00:29:22,393 --> 00:29:23,895 The thermal expansion of this thing 606 00:29:23,895 --> 00:29:26,131 is the same as the crystal or very similar. 607 00:29:29,234 --> 00:29:32,837 So that's enough to tell you this is a solid, right? 608 00:29:32,837 --> 00:29:34,973 It should be a good indicator. 609 00:29:34,973 --> 00:29:39,310 It should have been a nice straight line just for now. 610 00:29:39,310 --> 00:29:40,278 OK. 611 00:29:40,278 --> 00:29:45,049 Yeah, but it didn't get-- 612 00:29:45,049 --> 00:29:49,254 those silicate blocks didn't find the lattice. 613 00:29:49,254 --> 00:29:51,289 They didn't find the lattice. 614 00:29:51,289 --> 00:29:54,459 As you're cool-- here, they've got all this freedom. 615 00:29:54,459 --> 00:29:57,629 I mean, they're a liquid, silicate, happy. 616 00:29:57,629 --> 00:29:59,197 Maybe it's an even higher temperature, 617 00:29:59,197 --> 00:30:01,633 and the silicons are even dissociated from the oxygen. 618 00:30:01,633 --> 00:30:03,802 Let's just assume they're in these silicate groups, 619 00:30:03,802 --> 00:30:09,007 and they're floating around in a liquid, and I start cooling it. 620 00:30:09,007 --> 00:30:11,042 I think one of the best analogies that I've heard 621 00:30:11,042 --> 00:30:13,912 is that of musical chairs. 622 00:30:13,912 --> 00:30:16,314 How many of you have played musical chairs? 623 00:30:16,314 --> 00:30:18,349 OK, you've got to fix this tonight. 624 00:30:18,349 --> 00:30:20,151 For those of you who didn't raise your hand, 625 00:30:20,151 --> 00:30:23,354 that's going on the menu tonight, 626 00:30:23,354 --> 00:30:26,825 because it's a really fun game. 627 00:30:26,825 --> 00:30:28,459 With supercooled water, of course. 628 00:30:31,196 --> 00:30:34,799 You line up some chairs, and you get around in a group 629 00:30:34,799 --> 00:30:38,369 and you walk around it as the music plays 630 00:30:38,369 --> 00:30:44,108 and then the music stops and everybody has to find a chair, 631 00:30:44,108 --> 00:30:46,311 but there's a chair missing. 632 00:30:46,311 --> 00:30:49,848 So you've got to go fast, or you might not get to a chair. 633 00:30:53,952 --> 00:30:58,489 Well, you see the silicate, let's put it below here, 634 00:30:58,489 --> 00:31:00,058 the silicates are you. 635 00:31:00,058 --> 00:31:02,360 You are the silicates. 636 00:31:02,360 --> 00:31:06,464 People equals silicate. 637 00:31:09,701 --> 00:31:18,276 And the chair equal lattice sites. 638 00:31:22,313 --> 00:31:23,915 And now you can really feel it. 639 00:31:23,915 --> 00:31:27,218 You can really feel it, because the speed around the chairs. 640 00:31:27,218 --> 00:31:29,220 How fast are you moving? 641 00:31:29,220 --> 00:31:29,988 Right. 642 00:31:29,988 --> 00:31:37,662 So the speed, well, if it's speed around the chair, 643 00:31:37,662 --> 00:31:45,570 OK, if that's fast, then it's, you know, high mobility, 644 00:31:45,570 --> 00:31:48,640 so let's see, speed around chair, let's do this. 645 00:31:48,640 --> 00:31:58,049 High mobility, maybe you'd find, you know, find 646 00:31:58,049 --> 00:32:08,026 lattice sites easier, or faster, at least, but see, 647 00:32:08,026 --> 00:32:12,263 if you have a high 1 over mobility-- 648 00:32:12,263 --> 00:32:14,632 by the way, that's also viscosity, 649 00:32:14,632 --> 00:32:18,336 if you have a high 1 over mobility. 650 00:32:18,336 --> 00:32:21,306 So if you have a high viscosity, [INAUDIBLE].. 651 00:32:26,377 --> 00:32:32,550 High 1 over mobility, high viscosity, then it's slow. 652 00:32:32,550 --> 00:32:36,721 And that's how you have a higher chance of forming glass. 653 00:32:36,721 --> 00:32:43,294 So I'm going to talk about what would make a glass form. 654 00:32:43,294 --> 00:32:45,897 If you're just walking around slowly, 655 00:32:45,897 --> 00:32:47,865 like this, everyone else is running, 656 00:32:47,865 --> 00:32:49,934 but maybe you're all walking slowly, 657 00:32:49,934 --> 00:32:54,005 and now the music stops, and I'm like, yeah, I'll take my time, 658 00:32:54,005 --> 00:32:58,242 it's going to be hard to get to the open lattice site. 659 00:32:58,242 --> 00:33:00,178 I might just get stuck. 660 00:33:00,178 --> 00:33:01,045 OK, so what else? 661 00:33:01,045 --> 00:33:03,614 Well, OK, so how about the arrangement? 662 00:33:03,614 --> 00:33:12,523 So the chair arrangement, that has 663 00:33:12,523 --> 00:33:14,726 to do with the crystal complexity. 664 00:33:18,696 --> 00:33:21,232 And you can imagine that if the chairs are arranged 665 00:33:21,232 --> 00:33:23,534 in a straight line, and you're going around the chairs, 666 00:33:23,534 --> 00:33:26,037 and it's is kind of an easy loop, 667 00:33:26,037 --> 00:33:29,807 right, now I don't have to concentrate too much 668 00:33:29,807 --> 00:33:32,076 on where I'm going, and it's kind of-- there's nothing 669 00:33:32,076 --> 00:33:34,178 really blocking me, I hope, but what 670 00:33:34,178 --> 00:33:38,850 if those chairs were arranged in a really complicated way. 671 00:33:38,850 --> 00:33:42,120 So how hard is it to get around these chairs? 672 00:33:42,120 --> 00:33:43,654 How hard is it to find them? 673 00:33:43,654 --> 00:33:46,190 How complex is the lattice? 674 00:33:46,190 --> 00:33:50,728 And you can imagine that it is higher. 675 00:33:50,728 --> 00:33:54,065 So let's see. 676 00:33:54,065 --> 00:33:55,600 More-- I'll just draw an arrow. 677 00:33:55,600 --> 00:33:58,603 Higher would lead to glass. 678 00:33:58,603 --> 00:34:00,471 OK, so it fits. 679 00:34:00,471 --> 00:34:04,942 Higher complexity of the lattice. 680 00:34:04,942 --> 00:34:07,045 It might be harder to find the lattice 681 00:34:07,045 --> 00:34:09,514 sites in this musical chairs. 682 00:34:09,514 --> 00:34:12,050 OK, one more, and I'll put it here, 683 00:34:12,050 --> 00:34:14,118 so that it's close by, because I've 684 00:34:14,118 --> 00:34:15,553 got no more room on that board. 685 00:34:18,356 --> 00:34:21,292 The third one is how fast you stop the music. 686 00:34:21,292 --> 00:34:28,498 So this would be like 1, 2, and then 3. 687 00:34:28,498 --> 00:34:31,601 How fast do we stop music? 688 00:34:35,106 --> 00:34:35,706 OK. 689 00:34:35,706 --> 00:34:41,112 So you can imagine if I, you know, if I slowly 690 00:34:41,112 --> 00:34:44,282 were playing musical chairs, and I am walking around, 691 00:34:44,282 --> 00:34:48,753 and I slowly fade the music, all right, 692 00:34:48,753 --> 00:34:50,420 well, then you got lots of time. 693 00:34:50,420 --> 00:34:53,491 You got lots of time, but what if I just stop it. 694 00:34:53,491 --> 00:34:56,393 Now, everybody's scrambling. 695 00:34:56,393 --> 00:34:59,330 So how fast do you stop the music is the cooling rate. 696 00:35:03,201 --> 00:35:06,003 It's how quickly you cool this material. 697 00:35:06,003 --> 00:35:07,405 It's how fast you stop the music, 698 00:35:07,405 --> 00:35:12,777 and you can imagine that if it's faster, faster, 699 00:35:12,777 --> 00:35:15,580 you are more likely to form a glass. 700 00:35:19,083 --> 00:35:20,551 You're more likely to form a glass, 701 00:35:20,551 --> 00:35:23,855 and so we go back to our picture. 702 00:35:23,855 --> 00:35:26,791 Well, maybe I'll draw one over here, because I need more room, 703 00:35:26,791 --> 00:35:31,662 and I don't want to block what's there. 704 00:35:31,662 --> 00:35:35,032 We go back to our picture and here it is, drawn out for you. 705 00:35:35,032 --> 00:35:37,869 You see that is-- 706 00:35:37,869 --> 00:35:40,037 OK, there is the liquid line, coming in, 707 00:35:40,037 --> 00:35:43,641 volume, OK, enthalpy, visage, and we'll 708 00:35:43,641 --> 00:35:45,276 keep thinking about it as volume. 709 00:35:45,276 --> 00:35:46,544 The liquid line comes in. 710 00:35:46,544 --> 00:35:47,512 You're cooling it down. 711 00:35:47,512 --> 00:35:49,080 There's the thermal expansion. 712 00:35:49,080 --> 00:35:50,515 It's reducing, reducing, and now I 713 00:35:50,515 --> 00:35:52,783 get to the melting temperature, and I become a crystal. 714 00:35:52,783 --> 00:35:55,319 That's if it can become a crystal, 715 00:35:55,319 --> 00:35:59,357 but all of these factors, now, matter. 716 00:36:03,528 --> 00:36:09,433 The melting point of the crystal is always the same number. 717 00:36:09,433 --> 00:36:10,601 It's always the same number. 718 00:36:10,601 --> 00:36:14,372 The melting point, where the crystal melts, 719 00:36:14,372 --> 00:36:17,441 because the crystal is always the same. 720 00:36:17,441 --> 00:36:17,942 Right. 721 00:36:17,942 --> 00:36:22,880 Now, where that melts is always the same temperature. 722 00:36:22,880 --> 00:36:24,916 But notice now, what have I done? 723 00:36:24,916 --> 00:36:27,818 I've super cooled the liquid down, 724 00:36:27,818 --> 00:36:31,489 and on a, I've got a glass that looks like this. 725 00:36:31,489 --> 00:36:32,890 These are glasses. 726 00:36:32,890 --> 00:36:34,992 And on b, I've got a glass that looks like that. 727 00:36:34,992 --> 00:36:37,762 Those are different. 728 00:36:37,762 --> 00:36:42,500 And they have different solidification temperatures. 729 00:36:42,500 --> 00:36:43,467 And what do we call it? 730 00:36:43,467 --> 00:36:45,670 We have a special name for it, too. 731 00:36:45,670 --> 00:36:50,575 We have a special name for it, because it's not crystallizing. 732 00:36:50,575 --> 00:36:53,511 Right, so if this is the volume per mole, 733 00:36:53,511 --> 00:36:58,015 and this is the temperature, it's not crystallizing. 734 00:36:58,015 --> 00:36:59,116 No. 735 00:36:59,116 --> 00:36:59,850 What is it doing? 736 00:36:59,850 --> 00:37:02,753 So that would be the melting point. 737 00:37:02,753 --> 00:37:10,494 It is turning into a glass, and so we call this the glass 738 00:37:10,494 --> 00:37:11,762 transition temperature. 739 00:37:11,762 --> 00:37:13,731 It's a glass transition. 740 00:37:13,731 --> 00:37:17,501 What that means is it is still becoming-- 741 00:37:17,501 --> 00:37:23,007 gesundheit-- a solid, but it's an amorphous solid. 742 00:37:23,007 --> 00:37:25,676 It's not a crystal. 743 00:37:25,676 --> 00:37:27,345 Why did it become an amorphous solid? 744 00:37:27,345 --> 00:37:31,482 Well, maybe I cooled it really fast. 745 00:37:31,482 --> 00:37:35,553 Or maybe it's a really complex structure, right? 746 00:37:35,553 --> 00:37:38,623 Or maybe the viscosity of the material is very high, 747 00:37:38,623 --> 00:37:39,323 and it just-- 748 00:37:39,323 --> 00:37:40,992 as I'm cooling it down, it just couldn't 749 00:37:40,992 --> 00:37:44,428 find the crystal lattice, which is all the way down here. 750 00:37:47,565 --> 00:37:50,801 And you can see from this, that you know, 751 00:37:50,801 --> 00:37:54,038 imagine I take the extreme limit, 752 00:37:54,038 --> 00:37:57,475 and I got my liquid of my silicate groups, 753 00:37:57,475 --> 00:38:02,380 and right as I get below here, I'm like you're all frozen. 754 00:38:02,380 --> 00:38:07,051 I'd literally-- I'd make a glass right here, right up there, 755 00:38:07,051 --> 00:38:09,320 all right. 756 00:38:09,320 --> 00:38:12,423 So I can make glasses that are different from each other. 757 00:38:12,423 --> 00:38:16,894 And you can see that the volume per mole 758 00:38:16,894 --> 00:38:19,363 is increasing as I go up, and you 759 00:38:19,363 --> 00:38:22,500 can understand that, because look, I took a glass. 760 00:38:22,500 --> 00:38:23,234 I didn't let-- 761 00:38:23,234 --> 00:38:24,502 I took a liquid here. 762 00:38:24,502 --> 00:38:25,670 This is the liquid. 763 00:38:25,670 --> 00:38:28,306 I didn't let any of it find crystals sites. 764 00:38:28,306 --> 00:38:29,206 It's a liquid. 765 00:38:29,206 --> 00:38:32,009 But I said, ha, you're frozen. 766 00:38:32,009 --> 00:38:36,580 And it became frozen and stuck at a high volume per mole. 767 00:38:36,580 --> 00:38:40,051 Because it's totally random and amorphous. 768 00:38:40,051 --> 00:38:43,587 It's coming right from all those random liquid degrees 769 00:38:43,587 --> 00:38:47,091 of freedom are just frozen in. 770 00:38:47,091 --> 00:38:50,461 Yeah, but now, I cool it slower. 771 00:38:50,461 --> 00:38:52,563 Maybe that's what happened here, right? 772 00:38:52,563 --> 00:38:54,732 And I give it more time. 773 00:38:54,732 --> 00:38:58,803 And I give it more time to find some of those lattice sites, 774 00:38:58,803 --> 00:39:03,307 and it finds some lattice sites, but then it became a glass 775 00:39:03,307 --> 00:39:05,976 at this temperature, the glass transition temperature, 776 00:39:05,976 --> 00:39:08,079 and everything else is frozen in. 777 00:39:10,881 --> 00:39:13,718 So if I label this, so let's label it the same as there, 778 00:39:13,718 --> 00:39:19,056 if I label a as this one and b as this one, 779 00:39:19,056 --> 00:39:23,728 and this is the crystal, nope, the crystal 780 00:39:23,728 --> 00:39:26,097 would have to go all the way up to here. 781 00:39:26,097 --> 00:39:27,164 There we go. 782 00:39:27,164 --> 00:39:29,834 Right. 783 00:39:29,834 --> 00:39:33,204 So if that's a, that's glass a, and that's glass b, then 784 00:39:33,204 --> 00:39:36,507 which one did I cool faster? 785 00:39:36,507 --> 00:39:38,509 Well, I had to call this one slower-- 786 00:39:38,509 --> 00:39:42,346 if all I changed between them is cooling rates, 787 00:39:42,346 --> 00:39:46,050 then this one is cooled faster. 788 00:39:46,050 --> 00:39:47,651 So let me write it here. 789 00:39:47,651 --> 00:39:53,924 a cooled slower than b. 790 00:39:57,161 --> 00:39:57,661 Right. 791 00:39:57,661 --> 00:40:00,030 Because I get-- and that's this one here. 792 00:40:00,030 --> 00:40:01,565 How fast did you stop the music? 793 00:40:01,565 --> 00:40:02,066 Right. 794 00:40:02,066 --> 00:40:03,734 It's the cooling rate. 795 00:40:03,734 --> 00:40:09,807 OK, so this plot, this volume versus temperature really 796 00:40:09,807 --> 00:40:13,811 allows us to understand how glass forms, or at least we can 797 00:40:13,811 --> 00:40:20,217 plot, you know, what happened, and then try to understand it. 798 00:40:20,217 --> 00:40:23,020 And if it did get all the way to the crystal, 799 00:40:23,020 --> 00:40:26,891 then maybe it means that it's not very viscous as a liquid, 800 00:40:26,891 --> 00:40:30,227 it doesn't have a complex lattice site, 801 00:40:30,227 --> 00:40:35,499 and maybe it didn't even matter how quickly-- oh, metals. 802 00:40:35,499 --> 00:40:40,104 But that's why it's hard to make glasses out of metals. 803 00:40:40,104 --> 00:40:46,544 Because metals have an easy time finding their lattice sites. 804 00:40:46,544 --> 00:40:50,548 Metals as liquids typically aren't very viscous. 805 00:40:50,548 --> 00:40:55,052 And so even if you cool it faster, it's got time. 806 00:40:55,052 --> 00:40:57,354 The musical chairs of metals is easy. 807 00:40:57,354 --> 00:41:00,057 It's an easy game. 808 00:41:00,057 --> 00:41:02,893 That's why the silicates never played musical chairs 809 00:41:02,893 --> 00:41:03,427 with metals. 810 00:41:06,063 --> 00:41:07,665 But I can still do it, and the way 811 00:41:07,665 --> 00:41:09,366 you make a glass out of a metal, the way 812 00:41:09,366 --> 00:41:12,436 you make a metallic glass, which is a really cool material 813 00:41:12,436 --> 00:41:16,006 is you freeze it really quickly. 814 00:41:16,006 --> 00:41:19,176 You will lower the temperature as quickly as you can, 815 00:41:19,176 --> 00:41:21,412 really, really fast, and you freeze in the disorder, 816 00:41:21,412 --> 00:41:23,647 and you make a metallic glass. 817 00:41:23,647 --> 00:41:27,318 OK, so those are the two curves I just talked about there. 818 00:41:27,318 --> 00:41:28,686 That's the glass curve. 819 00:41:28,686 --> 00:41:30,654 This would be the crystal curve. 820 00:41:30,654 --> 00:41:35,493 OK, two different cooling rates on here. 821 00:41:35,493 --> 00:41:40,464 OK, now, here's a picture of float glass. 822 00:41:40,464 --> 00:41:41,966 This is the kind of glass-- 823 00:41:41,966 --> 00:41:47,304 we're going to move from understanding what glass is 824 00:41:47,304 --> 00:41:50,341 and understanding in terms of this temperature versus volume 825 00:41:50,341 --> 00:41:54,712 plot and amorphous solids, and we're 826 00:41:54,712 --> 00:41:56,146 going to move towards understanding 827 00:41:56,146 --> 00:41:58,148 how to modify it, how to control it, 828 00:41:58,148 --> 00:41:59,850 because we do a lot of that. 829 00:41:59,850 --> 00:42:01,385 Here's an example of a factor right-- 830 00:42:01,385 --> 00:42:01,886 I like this. 831 00:42:01,886 --> 00:42:02,753 This is flow glass. 832 00:42:02,753 --> 00:42:05,623 So this is like when you buy, you know, your windows, 833 00:42:05,623 --> 00:42:07,291 or you know, a lot of times, when 834 00:42:07,291 --> 00:42:10,995 you need a very clear, beautiful piece of glass, 835 00:42:10,995 --> 00:42:13,197 you go up to very high temperatures. 836 00:42:13,197 --> 00:42:15,432 All right, so you're taking those silicates. 837 00:42:15,432 --> 00:42:16,600 You make them into a liquid. 838 00:42:16,600 --> 00:42:18,969 Here he is, measuring the temperature. 839 00:42:18,969 --> 00:42:21,572 I don't know what he's doing actually, whatever. 840 00:42:21,572 --> 00:42:24,842 Oh and this isn't showing up very well. 841 00:42:24,842 --> 00:42:26,777 And there's no volume, so double-- 842 00:42:26,777 --> 00:42:27,578 OK, there it is. 843 00:42:27,578 --> 00:42:29,013 So there's the liquid glass. 844 00:42:29,013 --> 00:42:30,214 Why is it called float glass? 845 00:42:30,214 --> 00:42:30,281 [VIDEO PLAYBACK] 846 00:42:30,281 --> 00:42:30,314 [INTERPOSING VOICES] 847 00:42:30,314 --> 00:42:32,950 - The process is monitored continuously by technicians 848 00:42:32,950 --> 00:42:34,351 to ensure quality. 849 00:42:34,351 --> 00:42:39,523 But because it floats on top of another liquid. 850 00:42:39,523 --> 00:42:42,693 That's how you get the glass because so incredibly smooth. 851 00:42:42,693 --> 00:42:44,028 - And ensure uniformity-- 852 00:42:44,028 --> 00:42:45,462 And there it is coming out. 853 00:42:45,462 --> 00:42:48,432 There's a nice wide piece of glass coming out, 854 00:42:48,432 --> 00:42:51,569 and what he says at the end of this, there it is coming out. 855 00:42:51,569 --> 00:42:52,136 [END PLAYBACK] 856 00:42:52,136 --> 00:42:53,771 They can do kilometers and kilometers 857 00:42:53,771 --> 00:42:56,340 per day of this float glass. 858 00:42:56,340 --> 00:42:58,742 You float it over molten tin. 859 00:42:58,742 --> 00:43:02,580 The tin acts like this really nice smooth surface 860 00:43:02,580 --> 00:43:04,949 that you put the glass on top of. 861 00:43:04,949 --> 00:43:07,484 So one liquid on top of another makes a very nice 862 00:43:07,484 --> 00:43:08,953 smooth interface. 863 00:43:08,953 --> 00:43:11,422 And what he talks about, which is what I wanted to capture, 864 00:43:11,422 --> 00:43:13,591 is how important that cooling is. 865 00:43:13,591 --> 00:43:16,961 So the line has to go in a very particular way 866 00:43:16,961 --> 00:43:18,829 after it comes out, as you cool it, 867 00:43:18,829 --> 00:43:21,699 and because it's all about the cooling. 868 00:43:21,699 --> 00:43:26,804 As you come all the way back down to here, room temperature, 869 00:43:26,804 --> 00:43:28,205 right, or as I-- 870 00:43:28,205 --> 00:43:30,841 maybe as I went through this transition, 871 00:43:30,841 --> 00:43:33,744 what's happening inside? 872 00:43:33,744 --> 00:43:36,113 Am I creating a lot of stress? 873 00:43:36,113 --> 00:43:37,615 We just learned about stress. 874 00:43:37,615 --> 00:43:38,882 Am I creating a lot of stress? 875 00:43:38,882 --> 00:43:41,852 Right, or is it going to cool in a nice way? 876 00:43:41,852 --> 00:43:44,555 Are there going to be cracks that form? 877 00:43:44,555 --> 00:43:47,391 So that is one of the most important processing 878 00:43:47,391 --> 00:43:49,493 parameters. 879 00:43:49,493 --> 00:43:53,897 What we'll learn next week is that chemistry is also a really 880 00:43:53,897 --> 00:43:55,132 important pressing parameter. 881 00:43:55,132 --> 00:43:57,301 And that's why you have such good phone screens. 882 00:43:57,301 --> 00:44:00,137 Actually, you don't really, because they always break, 883 00:44:00,137 --> 00:44:03,641 but they would break even more if it weren't for chemistry. 884 00:44:03,641 --> 00:44:07,111 OK, but certainly cooling speed is really important. 885 00:44:07,111 --> 00:44:08,712 So let's go to the-- 886 00:44:08,712 --> 00:44:10,347 OK, now how-- 887 00:44:10,347 --> 00:44:13,550 OK, if you look at glass, remember 888 00:44:13,550 --> 00:44:17,488 I said that it's got order or no order, crystalline, amorphous, 889 00:44:17,488 --> 00:44:19,356 crystalline, amorphous. 890 00:44:19,356 --> 00:44:21,091 How do you tell which one you have? 891 00:44:21,091 --> 00:44:23,761 Who can tell me? 892 00:44:23,761 --> 00:44:27,264 You just learned about it. 893 00:44:27,264 --> 00:44:29,533 What do you do to see if something is a crystal 894 00:44:29,533 --> 00:44:31,935 and which crystal it is? 895 00:44:31,935 --> 00:44:33,370 You shine x-rays on it. 896 00:44:33,370 --> 00:44:35,906 You go to your x-ray source, and you just shine it on, 897 00:44:35,906 --> 00:44:38,208 and you measure where it bounces off. 898 00:44:38,208 --> 00:44:41,545 But see-- so if you did that, so if you look in the circle, 899 00:44:41,545 --> 00:44:43,881 they look the same. 900 00:44:43,881 --> 00:44:45,115 They look the same. 901 00:44:45,115 --> 00:44:46,216 That's crystalline. 902 00:44:46,216 --> 00:44:47,117 That's quartz. 903 00:44:47,117 --> 00:44:48,318 This is glass. 904 00:44:48,318 --> 00:44:50,554 Quartz, glass, crystalline, amorphous. 905 00:44:50,554 --> 00:44:54,124 Right, but if you go to the long range order, there isn't any. 906 00:44:54,124 --> 00:44:57,394 So if I shine x-rays, these are two different types of solids. 907 00:44:57,394 --> 00:44:59,563 Think about it like DCC FCC, but they're not. 908 00:44:59,563 --> 00:45:05,369 They're more complicated of quartz or of silicates. 909 00:45:05,369 --> 00:45:07,771 This is what glass would look like. 910 00:45:07,771 --> 00:45:09,073 Look at that. 911 00:45:09,073 --> 00:45:11,408 There's still like a little bit of a peak there, but not 912 00:45:11,408 --> 00:45:14,344 really, right, because this is from the short range order, 913 00:45:14,344 --> 00:45:18,048 but here's the important part, which is where-- 914 00:45:18,048 --> 00:45:20,284 you can still, even though it's not 915 00:45:20,284 --> 00:45:22,953 that everything is where you think it is, right, 916 00:45:22,953 --> 00:45:26,957 because it in a crystal, you know everything's BCC or FCC. 917 00:45:26,957 --> 00:45:28,158 Every lattice is the same. 918 00:45:28,158 --> 00:45:29,626 You know you can count on it for 10 919 00:45:29,626 --> 00:45:31,929 to the 20 second repetitions. 920 00:45:31,929 --> 00:45:32,863 Here you can't. 921 00:45:32,863 --> 00:45:35,733 You can still control the properties. 922 00:45:35,733 --> 00:45:37,367 You can still control the properties. 923 00:45:37,367 --> 00:45:41,105 So the properties can be highly engineered. 924 00:45:41,105 --> 00:45:42,139 And here's an example. 925 00:45:45,976 --> 00:45:47,878 So these are different types of glass. 926 00:45:47,878 --> 00:45:53,183 This is a glass cup, and this is a glass bottle. 927 00:45:53,183 --> 00:45:55,419 And you might think, it's just glass. 928 00:45:55,419 --> 00:45:57,454 No. 929 00:45:57,454 --> 00:45:58,522 It's not just glass. 930 00:45:58,522 --> 00:46:06,130 It's very complicated mixtures of silica with other things. 931 00:46:06,130 --> 00:46:08,031 Notice, it's got soda. 932 00:46:08,031 --> 00:46:09,867 This is-- like I said, this is not soda, 933 00:46:09,867 --> 00:46:12,002 but it comes from soda, so it's called soda, sodium 934 00:46:12,002 --> 00:46:14,605 oxide in Na2O. 935 00:46:14,605 --> 00:46:20,244 Lime CaO, magnesia, alumina. 936 00:46:20,244 --> 00:46:23,547 All the glass-- you know, unless you pay a whole lot of money 937 00:46:23,547 --> 00:46:28,886 for something made of quartz, almost all the glass you buy 938 00:46:28,886 --> 00:46:31,221 has this kind of stuff in it. 939 00:46:31,221 --> 00:46:34,758 In fact, 90% of all glass is called soda glass, 940 00:46:34,758 --> 00:46:35,592 because it's got-- 941 00:46:35,592 --> 00:46:36,460 that's this one here. 942 00:46:36,460 --> 00:46:40,898 That's this cup, because it's got sodium oxide in it. 943 00:46:40,898 --> 00:46:42,800 And the question is why. 944 00:46:42,800 --> 00:46:45,235 Why do we put these things in glass? 945 00:46:45,235 --> 00:46:47,938 Why did we used to put lead in glass? 946 00:46:47,938 --> 00:46:51,041 In fact, the history is pretty-- 947 00:46:51,041 --> 00:46:52,576 goes back thousands of years. 948 00:46:52,576 --> 00:46:53,477 And I found this. 949 00:46:53,477 --> 00:46:56,513 If you go to ancient Rome, they made glass, 950 00:46:56,513 --> 00:46:58,515 and you can look at what they made glass out of. 951 00:46:58,515 --> 00:47:00,150 They had a little bit less silica. 952 00:47:00,150 --> 00:47:02,953 But they mixed all sorts of things in. 953 00:47:02,953 --> 00:47:07,491 They did not have 3091 back then, 954 00:47:07,491 --> 00:47:10,294 so they didn't really know why this was doing 955 00:47:10,294 --> 00:47:13,864 something useful, but it was. 956 00:47:13,864 --> 00:47:16,834 Now we mix all these oxides, remember I wrote some of them 957 00:47:16,834 --> 00:47:19,436 up here, lime, soda. 958 00:47:19,436 --> 00:47:22,840 We mix those in, and we mix all sorts of other things in, 959 00:47:22,840 --> 00:47:25,475 but now we know why. 960 00:47:25,475 --> 00:47:28,846 And the reason why is all about the chemistry, 961 00:47:28,846 --> 00:47:32,749 and it all goes back to this picture right here. 962 00:47:32,749 --> 00:47:37,054 It all goes back to exactly this Lewis structure that I started 963 00:47:37,054 --> 00:47:39,623 with, which is not on the-- 964 00:47:39,623 --> 00:47:40,724 stop it. 965 00:47:40,724 --> 00:47:42,025 No. 966 00:47:42,025 --> 00:47:44,194 It's stuck here. 967 00:47:44,194 --> 00:47:45,863 Maybe it's here. 968 00:47:45,863 --> 00:47:48,198 Yes. 969 00:47:48,198 --> 00:47:50,300 That made me happy. 970 00:47:50,300 --> 00:47:54,004 This all goes back to the chemistry. 971 00:47:54,004 --> 00:48:00,677 If I deliver, if I deliver into this system something that 972 00:48:00,677 --> 00:48:05,282 gives me charged oxygens, something that provides 973 00:48:05,282 --> 00:48:08,852 a little bit of O minus or O2 minus, 974 00:48:08,852 --> 00:48:11,054 then I could cut this bond back. 975 00:48:11,054 --> 00:48:14,958 I can cut this all the way back to the original silicate, 976 00:48:14,958 --> 00:48:16,593 sort of. 977 00:48:16,593 --> 00:48:18,862 If I had an oxygen with charge on it, 978 00:48:18,862 --> 00:48:24,935 I can go from here back to where I started, right there, 979 00:48:24,935 --> 00:48:27,604 at least for that bond, right? 980 00:48:27,604 --> 00:48:30,908 And so what every single one of these things has in common 981 00:48:30,908 --> 00:48:34,278 is that it can provide into the system 982 00:48:34,278 --> 00:48:37,381 a charged oxygen, a charged oxygen atom. 983 00:48:37,381 --> 00:48:41,218 If this dissociates, it gives we Ca2 plus and O2 minus. 984 00:48:41,218 --> 00:48:44,655 If this dissociates, it gives me two Na pluses and an O2 minus. 985 00:48:44,655 --> 00:48:49,559 Oh, a pattern is forming here, O2 minus, O2 minus, 986 00:48:49,559 --> 00:48:52,162 O2 minus all the way down. 987 00:48:52,162 --> 00:48:55,966 So these modifiers, these things that we use to engineer glass, 988 00:48:55,966 --> 00:49:02,239 they give me the O2 minus, and that is the knife 989 00:49:02,239 --> 00:49:06,610 that I use to cut this glass apart and modify 990 00:49:06,610 --> 00:49:08,111 its properties, and it's where we're 991 00:49:08,111 --> 00:49:09,546 going to pick up on Wednesday. 992 00:49:09,546 --> 00:49:12,516 But because it's a Friday, I want to throw t-shirts out. 993 00:49:13,650 --> 00:49:15,118 We'll do more next week. 994 00:49:15,118 --> 00:49:18,455 Have a really good holiday weekend.