1 00:00:00,030 --> 00:00:02,400 The following content is provided under a Creative 2 00:00:02,400 --> 00:00:03,830 Commons license. 3 00:00:03,830 --> 00:00:06,850 Your support will help MIT OpenCourseWare continue to 4 00:00:06,850 --> 00:00:10,510 offer high-quality educational resources for free. 5 00:00:10,510 --> 00:00:13,390 To make a donation or view additional material from 6 00:00:13,390 --> 00:00:17,490 hundreds of MIT courses, visit MIT OpenCourseWare at 7 00:00:17,490 --> 00:00:18,740 ocw.mit.edu. 8 00:00:21,570 --> 00:00:21,930 PROFESSOR: All right. 9 00:00:21,930 --> 00:00:27,260 So today we're going to start the last section. 10 00:00:27,260 --> 00:00:30,980 We're going to do three lectures on phase diagrams. 11 00:00:30,980 --> 00:00:36,460 And I've given this the label here of Stability, Sustaining 12 00:00:36,460 --> 00:00:37,320 the Solid State. 13 00:00:37,320 --> 00:00:40,500 We've talked a lot about the solid state in 3.091 as the 14 00:00:40,500 --> 00:00:43,870 vehicle for teaching the rudiments of chemistry. 15 00:00:43,870 --> 00:00:47,370 One of the things we have not talked about, is what are the 16 00:00:47,370 --> 00:00:50,600 conditions that sustain the solid state? 17 00:00:50,600 --> 00:00:52,730 How do I know whether something's going to be a 18 00:00:52,730 --> 00:00:54,845 solid, or a liquid, or a gas? 19 00:00:54,845 --> 00:00:56,250 This is very important. 20 00:00:56,250 --> 00:00:59,060 For example, if you're in a foundry, you're running 21 00:00:59,060 --> 00:01:01,350 places, making auto parts, you have to know what the 22 00:01:01,350 --> 00:01:03,790 solidification temperature is of the alloys, so you can get 23 00:01:03,790 --> 00:01:07,150 the parts out quickly and keep productivity high. 24 00:01:07,150 --> 00:01:08,850 It's even important in failure analysis. 25 00:01:08,850 --> 00:01:11,950 You know, when they were looking at things like the 26 00:01:11,950 --> 00:01:16,420 rubble from the World Trade Center by understanding phase 27 00:01:16,420 --> 00:01:20,670 stability, the thermal history was imprinted in the metal. 28 00:01:20,670 --> 00:01:23,600 It's possible to determine what temperatures were 29 00:01:23,600 --> 00:01:27,720 achieved, and therefore, what the chain of events was that 30 00:01:27,720 --> 00:01:29,860 led to the collapse of those buildings. 31 00:01:29,860 --> 00:01:31,680 Now you might say, well, isn't this straightforward? 32 00:01:31,680 --> 00:01:34,350 I mean, for example, you just look up the melting point or 33 00:01:34,350 --> 00:01:35,200 boiling point. 34 00:01:35,200 --> 00:01:39,800 Water, 0 degrees C. Melting point, boiling point, 100 35 00:01:39,800 --> 00:01:41,210 degrees C. 36 00:01:41,210 --> 00:01:44,090 Well, suppose you decide to realize your life's ambition. 37 00:01:44,090 --> 00:01:46,150 You're going to go and scale Mount Everest. 38 00:01:46,150 --> 00:01:48,440 So you pay the $10,000, you get a license from the 39 00:01:48,440 --> 00:01:50,390 Nepalese Government, and you're at base 40 00:01:50,390 --> 00:01:51,710 camp at 20,000 feet. 41 00:01:51,710 --> 00:01:53,870 You're sitting there, you've got your campfire going, 42 00:01:53,870 --> 00:01:56,185 you've got a hankering for a hard-boiled egg. 43 00:01:56,185 --> 00:01:58,570 And you start, you put the eggs into boiling water and 44 00:01:58,570 --> 00:02:01,550 you cook them 10 minutes, you take them out, and they're 45 00:02:01,550 --> 00:02:03,020 still runny. 46 00:02:03,020 --> 00:02:04,550 You say, I must've lost track of time. 47 00:02:04,550 --> 00:02:06,940 So you cook them 20 minutes, and they're still runny. 48 00:02:06,940 --> 00:02:09,250 And you cook them 30 minutes, and they're still runny. 49 00:02:09,250 --> 00:02:12,470 And you eventually come to the realization that at 20,000 50 00:02:12,470 --> 00:02:17,290 feet, the boiling point of water is below the denaturing 51 00:02:17,290 --> 00:02:20,300 temperature of egg yolk. 52 00:02:20,300 --> 00:02:23,930 So now the boiling point is a function of pressure. 53 00:02:28,040 --> 00:02:33,360 So you know, we could have one of these Iron Chef cookoffs, 54 00:02:33,360 --> 00:02:40,360 only the dish is souffle, only we'll have the contest at 55 00:02:40,360 --> 00:02:44,510 Flagstaff, Arizona, where the altitude is so high that the 56 00:02:44,510 --> 00:02:48,940 classical recipes won't work, because the boiling point, the 57 00:02:48,940 --> 00:02:51,820 atmospheric pressure, and everything conspire so that 58 00:02:51,820 --> 00:02:54,235 you're not going to be able to support the souffle. 59 00:02:54,235 --> 00:02:56,360 So you're going to have to understand phase diagrams. 60 00:02:56,360 --> 00:02:59,150 In fact, if you understand phase diagrams, that's your 61 00:02:59,150 --> 00:03:02,650 ticket to being a four-star chef in the kitchen. 62 00:03:02,650 --> 00:03:05,560 Well, here's another place we can look at, where pressure 63 00:03:05,560 --> 00:03:06,760 has an important role. 64 00:03:06,760 --> 00:03:08,650 Let's look under the hood of a car. 65 00:03:08,650 --> 00:03:11,360 You're running an internal combustion engine. 66 00:03:11,360 --> 00:03:16,160 So this is the engine block, and there's 67 00:03:16,160 --> 00:03:17,530 combustion going on inside. 68 00:03:17,530 --> 00:03:19,290 We've got to keep this thing from overeating. 69 00:03:19,290 --> 00:03:20,620 It could damage the metal. 70 00:03:20,620 --> 00:03:22,510 In extreme, you could melt the metal. 71 00:03:22,510 --> 00:03:27,360 So we've got cooling channels in here with water flow. 72 00:03:27,360 --> 00:03:28,880 But then the water's going to heat up, and the 73 00:03:28,880 --> 00:03:29,860 water's going to boil. 74 00:03:29,860 --> 00:03:34,280 So we've got, over here, the radiator. 75 00:03:34,280 --> 00:03:36,500 So it's really a double cooling system. 76 00:03:36,500 --> 00:03:39,290 The water cools the block, and then the 77 00:03:39,290 --> 00:03:40,820 radiator cools the water. 78 00:03:40,820 --> 00:03:41,840 So how's that going to work? 79 00:03:41,840 --> 00:03:45,340 Well, here, the temperature is on the order of about 90 80 00:03:45,340 --> 00:03:50,110 degrees C, and here the temperature inside the engine 81 00:03:50,110 --> 00:03:52,680 block is much greater than 90 degrees C. It's several 82 00:03:52,680 --> 00:03:55,580 hundred degrees C inside that engine block, and we've got 83 00:03:55,580 --> 00:03:57,330 water going like this. 84 00:03:57,330 --> 00:04:02,270 So we've got cooling water flow in this manner. 85 00:04:02,270 --> 00:04:05,630 And now cold water goes in and hot water comes out, and then 86 00:04:05,630 --> 00:04:08,480 we get into the radiator, and we've got channels here, and 87 00:04:08,480 --> 00:04:11,515 we've either got a fan or some kind of air flow. 88 00:04:14,940 --> 00:04:17,200 And so now, what's the gambit here? 89 00:04:17,200 --> 00:04:20,920 I want to see what's going on inside this radiator. 90 00:04:20,920 --> 00:04:28,130 So if this is the wall of the radiator, and in here I've got 91 00:04:28,130 --> 00:04:35,220 water, and over here I've got air, the idea is to have a 92 00:04:35,220 --> 00:04:43,510 high heat flux to get the energy out of the water and 93 00:04:43,510 --> 00:04:44,750 cool it down. 94 00:04:44,750 --> 00:04:47,790 Now, if things get really, really hot in here-- let's say 95 00:04:47,790 --> 00:04:50,690 you're zooming along down the highway at about 90, I mean, 96 00:04:50,690 --> 00:04:54,910 about 65 miles an hour, and all of a sudden you come upon 97 00:04:54,910 --> 00:04:58,400 a collision, and you have to go to a dead stop, all that 98 00:04:58,400 --> 00:05:02,220 energy in the engine is now dumped, and 99 00:05:02,220 --> 00:05:03,580 the water could overheat. 100 00:05:03,580 --> 00:05:06,860 And in the extreme, if it overheats, it can actually go 101 00:05:06,860 --> 00:05:09,080 into a boil. 102 00:05:09,080 --> 00:05:10,070 And this is bad. 103 00:05:10,070 --> 00:05:14,510 Because heat transfer is really good between a liquid 104 00:05:14,510 --> 00:05:16,180 and a solid, and it's really poor 105 00:05:16,180 --> 00:05:18,780 between a gas and a solid. 106 00:05:18,780 --> 00:05:25,380 This is a low heat flux, and this is bad. 107 00:05:25,380 --> 00:05:28,220 High heat flux, that's good. 108 00:05:28,220 --> 00:05:29,710 This is the bubbles. 109 00:05:29,710 --> 00:05:32,480 This is boiling. 110 00:05:32,480 --> 00:05:33,520 And why? 111 00:05:33,520 --> 00:05:36,430 Because what transfers energy? 112 00:05:36,430 --> 00:05:37,370 It's the atoms. 113 00:05:37,370 --> 00:05:39,950 And what's the atom density in a liquid versus the atom 114 00:05:39,950 --> 00:05:41,230 density in a gas? 115 00:05:41,230 --> 00:05:44,870 You just have really crummy heat transfer. 116 00:05:44,870 --> 00:05:48,050 That's why insulation involves dead airspace. 117 00:05:48,050 --> 00:05:52,210 Because you have very poor atom density. 118 00:05:52,210 --> 00:05:57,080 So what can we do in order to try to 119 00:05:57,080 --> 00:05:59,360 repress the bubble formation? 120 00:05:59,360 --> 00:06:03,690 Well, we said if we went up Mount Everest, we went to high 121 00:06:03,690 --> 00:06:08,180 altitude, the boiling point went down. 122 00:06:08,180 --> 00:06:09,470 And why did it go down? 123 00:06:09,470 --> 00:06:11,880 Because the atmospheric pressure is lower. 124 00:06:11,880 --> 00:06:15,180 So why don't we go the inverse here, and we'll put a pressure 125 00:06:15,180 --> 00:06:18,990 cap on the radiator, and make the pressure go up, and when 126 00:06:18,990 --> 00:06:21,930 the pressure goes up, it exerts a back pressure and 127 00:06:21,930 --> 00:06:23,620 represses bubble formation? 128 00:06:23,620 --> 00:06:28,690 So by increasing pressure, we can increase the temperature, 129 00:06:28,690 --> 00:06:30,190 and get the temperature up. 130 00:06:30,190 --> 00:06:32,880 So let's say p equals-- if you look on the top of the 131 00:06:32,880 --> 00:06:36,290 pressure cap, it will say 15 psi. 132 00:06:36,290 --> 00:06:44,100 And 15 psi is almost 14.7 psi, which is exactly 1 atmosphere, 133 00:06:44,100 --> 00:06:48,020 which in SI units is, and I know this to six significant 134 00:06:48,020 --> 00:06:51,340 figures, 101325 Pascals. 135 00:06:51,340 --> 00:06:55,760 Or, you know, from Torricelli, 760 millimeters of mercury, 136 00:06:55,760 --> 00:06:57,510 that's the column that's supported. 137 00:06:57,510 --> 00:07:00,530 So we're at 2 atmospheres pressure in there, and with 138 00:07:00,530 --> 00:07:02,905 two atmospheres of pressure, we can raise the boiling point 139 00:07:02,905 --> 00:07:09,050 to 106 degrees C. And then what we can do, is now change 140 00:07:09,050 --> 00:07:09,970 the composition. 141 00:07:09,970 --> 00:07:12,970 So we change the pressure, and I change the boiling point. 142 00:07:12,970 --> 00:07:14,400 I change the composition. 143 00:07:14,400 --> 00:07:17,260 add 50% ethylene glycol. 144 00:07:20,320 --> 00:07:21,690 So now I've got a one-to-one mix, 145 00:07:21,690 --> 00:07:23,210 ethylene glycol and water. 146 00:07:23,210 --> 00:07:27,170 And that takes the boiling point up to 130 degrees C, or 147 00:07:27,170 --> 00:07:31,640 265 degrees Fahrenheit. 148 00:07:31,640 --> 00:07:37,600 So another example of how we can manage systems. 149 00:07:37,600 --> 00:07:41,030 So when I'm showing you by these several examples, is 150 00:07:41,030 --> 00:07:46,770 that the boiling point is a function of pressure and 151 00:07:46,770 --> 00:07:48,260 composition. 152 00:07:48,260 --> 00:07:50,640 So we can tune the boiling point. 153 00:07:50,640 --> 00:07:54,600 See we were tuning materials properties before. 154 00:07:54,600 --> 00:07:57,900 Now we're tuning physical chemical properties, because 155 00:07:57,900 --> 00:07:59,280 that's what chemistry is all about. 156 00:07:59,280 --> 00:08:00,730 It's about control. 157 00:08:00,730 --> 00:08:02,430 It's about management. 158 00:08:02,430 --> 00:08:05,220 Management to advantage. 159 00:08:05,220 --> 00:08:08,270 So how do we know what to do here? 160 00:08:08,270 --> 00:08:10,240 Can we predict this from first principles? 161 00:08:10,240 --> 00:08:11,080 No. 162 00:08:11,080 --> 00:08:12,860 Systems are still too complicated. 163 00:08:12,860 --> 00:08:14,390 Our models aren't robust enough. 164 00:08:14,390 --> 00:08:18,150 So instead, we turn to an archive. 165 00:08:18,150 --> 00:08:20,165 So we have phase diagrams. 166 00:08:22,800 --> 00:08:27,370 And the phase diagrams guide us in our search for better 167 00:08:27,370 --> 00:08:30,140 management of material systems. 168 00:08:30,140 --> 00:08:32,670 And these are stability maps. 169 00:08:32,670 --> 00:08:35,570 They tell us which phases are stable under which conditions 170 00:08:35,570 --> 00:08:39,100 of pressure, temperature, composition. 171 00:08:39,100 --> 00:08:41,220 You can consider them as archives. 172 00:08:45,070 --> 00:08:47,460 So that's what I want to talk about, because it's really 173 00:08:47,460 --> 00:08:49,540 important to know this stuff. 174 00:08:49,540 --> 00:08:49,950 OK. 175 00:08:49,950 --> 00:08:51,190 So what are we going to do? 176 00:08:51,190 --> 00:08:53,510 So first of all, let's-- 177 00:08:53,510 --> 00:08:54,650 I don't want to write on that one. 178 00:08:54,650 --> 00:08:55,400 This is interesting. 179 00:08:55,400 --> 00:08:56,960 This could be a work of art. 180 00:08:56,960 --> 00:08:58,850 I'd hate to desecrate it. 181 00:08:58,850 --> 00:08:59,860 You like? 182 00:08:59,860 --> 00:09:02,250 This is really good! 183 00:09:02,250 --> 00:09:03,540 So I'm just going to leave that. 184 00:09:03,540 --> 00:09:07,680 That's very good. 185 00:09:07,680 --> 00:09:08,330 That's excellent. 186 00:09:08,330 --> 00:09:08,630 OK. 187 00:09:08,630 --> 00:09:12,200 So I've been talking about phase. 188 00:09:12,200 --> 00:09:13,080 What is a phase? 189 00:09:13,080 --> 00:09:14,490 Let's get the right definition here. 190 00:09:14,490 --> 00:09:15,440 What is a phase? 191 00:09:15,440 --> 00:09:19,920 It's a region uniform chemical composition. 192 00:09:19,920 --> 00:09:21,940 Just to get it down. 193 00:09:21,940 --> 00:09:25,630 it's a region in a material, region of uniform chemical 194 00:09:25,630 --> 00:09:33,060 composition, and it has these other properties. 195 00:09:33,060 --> 00:09:35,130 Uniform chemical composition. 196 00:09:35,130 --> 00:09:38,790 It's physically distinct. 197 00:09:38,790 --> 00:09:41,130 And I'll show you by examples, but let's just get the 198 00:09:41,130 --> 00:09:42,340 definition down. 199 00:09:42,340 --> 00:09:45,980 It's physically distinct, and in the extreme case-- 200 00:09:45,980 --> 00:09:47,500 so that means it's bounded. 201 00:09:47,500 --> 00:09:48,710 It's physically distinct. 202 00:09:48,710 --> 00:09:51,460 That's a fancy way of saying that you can put a 203 00:09:51,460 --> 00:09:53,150 boundary around it. 204 00:09:53,150 --> 00:09:54,480 It's bounded. 205 00:09:54,480 --> 00:09:57,490 And then the other property that it has, it's mechanically 206 00:09:57,490 --> 00:09:58,740 separable in the extreme. 207 00:10:05,930 --> 00:10:09,320 And so that's in the case where you have 208 00:10:09,320 --> 00:10:10,640 a multi-phase system. 209 00:10:10,640 --> 00:10:12,730 You can point to the different p. 210 00:10:12,730 --> 00:10:14,450 So what I'm going to do, is I'm going to 211 00:10:14,450 --> 00:10:15,430 give you some examples. 212 00:10:15,430 --> 00:10:20,400 And so I'm going to let circle p equal number of phases. 213 00:10:23,200 --> 00:10:24,530 I'll give you some examples. 214 00:10:24,530 --> 00:10:25,870 Why am I using circle p? 215 00:10:25,870 --> 00:10:28,720 Because just plain old p is already pressure. 216 00:10:28,720 --> 00:10:31,410 So pressure, so this is kind of a Western motif, you know? 217 00:10:31,410 --> 00:10:33,800 Like a Circle Bar Ranch or something. 218 00:10:33,800 --> 00:10:34,890 So it's a p with a circle. 219 00:10:34,890 --> 00:10:36,640 That's my font. 220 00:10:36,640 --> 00:10:38,110 That's how I say number of phases. 221 00:10:38,110 --> 00:10:40,600 So let's take a look at some examples. 222 00:10:40,600 --> 00:10:43,760 So here's some examples of p equals 1. 223 00:10:43,760 --> 00:10:46,730 So simple one is pure water. 224 00:10:46,730 --> 00:10:47,980 Pure H2O liquid. 225 00:10:47,980 --> 00:10:49,300 It has all of this. 226 00:10:49,300 --> 00:10:52,700 Wherever I have the water, all right, here's some water, it's 227 00:10:52,700 --> 00:10:55,200 all of the same chemical composition. 228 00:10:55,200 --> 00:10:56,940 It is physically distinct. 229 00:10:56,940 --> 00:10:58,510 I can put a boundary around it. 230 00:10:58,510 --> 00:11:00,840 And in this case, there's nothing to separate, because 231 00:11:00,840 --> 00:11:03,010 it's just a one-phase system. 232 00:11:03,010 --> 00:11:05,480 White gold. 233 00:11:05,480 --> 00:11:07,170 White gold is one phase. 234 00:11:07,170 --> 00:11:09,050 Because we have gold. 235 00:11:09,050 --> 00:11:10,160 Obviously we have gold. 236 00:11:10,160 --> 00:11:12,570 If you market something as white gold, it has no gold, 237 00:11:12,570 --> 00:11:13,620 you'll go to prison. 238 00:11:13,620 --> 00:11:17,270 And how do we make white gold go to its white color from the 239 00:11:17,270 --> 00:11:18,190 normal yellow? 240 00:11:18,190 --> 00:11:19,930 We add silver and we add nickel. 241 00:11:19,930 --> 00:11:23,100 And these are all FCC metals, and they substitute for one 242 00:11:23,100 --> 00:11:25,670 another on the lattice, and if you sample anywhere in the 243 00:11:25,670 --> 00:11:27,700 white gold, you get the same chemical 244 00:11:27,700 --> 00:11:29,410 composition, and so on. 245 00:11:29,410 --> 00:11:31,970 Air is an example of a one-phase system. 246 00:11:31,970 --> 00:11:35,230 It's a gas, and in decreasing order, we 247 00:11:35,230 --> 00:11:36,860 have nitrogen, oxygen. 248 00:11:36,860 --> 00:11:37,900 So it's a solution. 249 00:11:37,900 --> 00:11:39,590 We're breathing a solution. 250 00:11:39,590 --> 00:11:43,600 Nitrogen, oxygen, argon are the main constituents. 251 00:11:43,600 --> 00:11:47,730 There's some CO2, some sulfur dioxide if you live near a 252 00:11:47,730 --> 00:11:50,870 power plant, NOx if you're near a tailpipe, and 253 00:11:50,870 --> 00:11:52,490 so on and so forth. 254 00:11:52,490 --> 00:11:59,740 And then the last one I'll give as an example is 255 00:11:59,740 --> 00:12:00,990 calcia-zirconia. 256 00:12:02,760 --> 00:12:03,820 Or cubic zirconia. 257 00:12:03,820 --> 00:12:06,530 Let's just call it cubic zirconia. 258 00:12:06,530 --> 00:12:09,010 The holidays are coming, so we better get 259 00:12:09,010 --> 00:12:10,460 cubic zirconia up here. 260 00:12:10,460 --> 00:12:11,950 That's the poor man's diamond. 261 00:12:11,950 --> 00:12:16,100 Cubic zirconia, which consists of a solid solution of calcium 262 00:12:16,100 --> 00:12:18,700 oxide in zirconium oxide. 263 00:12:18,700 --> 00:12:23,160 This is a solid solution, so it's continuous and chemical 264 00:12:23,160 --> 00:12:25,230 composition identical. 265 00:12:25,230 --> 00:12:29,920 Now, contrast that with two-phase system. 266 00:12:29,920 --> 00:12:31,640 So p equals 2 looks like this. 267 00:12:31,640 --> 00:12:35,830 So let's look at, instead of simple water liquid, if I have 268 00:12:35,830 --> 00:12:37,320 ice cubes in water. 269 00:12:40,560 --> 00:12:43,980 So now I have two different phases, and they're separated 270 00:12:43,980 --> 00:12:46,720 by state of matter. 271 00:12:46,720 --> 00:12:49,290 State of matter is the issue here. 272 00:12:49,290 --> 00:12:51,000 Because I have a solid-- 273 00:12:51,000 --> 00:12:52,400 this is solid-- 274 00:12:52,400 --> 00:12:54,490 and I'm going to put the boundary around them. 275 00:12:54,490 --> 00:12:58,170 The composition of the solid is different from the 276 00:12:58,170 --> 00:12:59,300 composition of liquid. 277 00:12:59,300 --> 00:13:01,820 They're both the same water, but you can tell it's a 278 00:13:01,820 --> 00:13:03,740 different crystal structure and so on. 279 00:13:03,740 --> 00:13:06,820 And I can put boundaries around, and it's 280 00:13:06,820 --> 00:13:07,910 mechanically separable. 281 00:13:07,910 --> 00:13:09,880 You can pull the ice cubes out of the mix. 282 00:13:09,880 --> 00:13:11,710 Milk is two-phase. 283 00:13:11,710 --> 00:13:16,780 Milk has a fatty phase and it has an aqueous phase. 284 00:13:16,780 --> 00:13:18,650 The aqueous phase contains the minerals. 285 00:13:18,650 --> 00:13:20,650 That's why you can drink skim milk and still get your 286 00:13:20,650 --> 00:13:23,560 calcium, because calcium, even the general public knows 287 00:13:23,560 --> 00:13:25,030 calcium is a mineral. 288 00:13:25,030 --> 00:13:28,050 It's not elemental calcium, it's a calcium compound. 289 00:13:28,050 --> 00:13:32,290 But it's ionic, it's soluble in water, and the fat contains 290 00:13:32,290 --> 00:13:33,150 the other parts. 291 00:13:33,150 --> 00:13:36,730 You know from last day, this is one of the lipids. 292 00:13:36,730 --> 00:13:39,910 And so you have fat globules that are mechanically 293 00:13:39,910 --> 00:13:42,150 separable and distinct from aqueous. 294 00:13:42,150 --> 00:13:43,730 So they actually have a different chemical 295 00:13:43,730 --> 00:13:46,370 composition, different type of bonding. 296 00:13:46,370 --> 00:13:46,640 Right? 297 00:13:46,640 --> 00:13:50,500 This is largely nonpolar, and nonpolar doesn't like to 298 00:13:50,500 --> 00:13:54,990 dissolve in something that is polar and hydrogen-bonded. 299 00:13:54,990 --> 00:13:56,860 So they phase separate. 300 00:13:56,860 --> 00:13:58,580 I've been saying phase separate all along. 301 00:13:58,580 --> 00:14:01,290 Now you know what we mean by phase separate. 302 00:14:01,290 --> 00:14:02,890 Here's a third one. 303 00:14:02,890 --> 00:14:05,500 This is really cool, because you won't get this in any 304 00:14:05,500 --> 00:14:08,640 other chemistry class, because only 3.091 305 00:14:08,640 --> 00:14:10,060 talks about such things. 306 00:14:10,060 --> 00:14:12,100 David, can we cut to the document camera? 307 00:14:12,100 --> 00:14:14,580 I want to show you a piece of snowflake obsidian. 308 00:14:18,870 --> 00:14:21,880 Obsidian is a volcanic glass. 309 00:14:27,060 --> 00:14:28,450 So here's the piece of obsidian. 310 00:14:28,450 --> 00:14:33,410 And what you're looking at is, the black area is the glassy 311 00:14:33,410 --> 00:14:38,000 part, and the white is actually some of the obsidian 312 00:14:38,000 --> 00:14:40,510 that has decided to devitrify. 313 00:14:40,510 --> 00:14:42,200 And it is turning crystalline. 314 00:14:42,200 --> 00:14:47,560 And so those are islands of obsidian crystal sitting in a 315 00:14:47,560 --> 00:14:51,305 matrix of obsidian glass. 316 00:14:51,305 --> 00:14:54,460 If we go back to the-- 317 00:14:54,460 --> 00:14:57,020 I picked that up in Yellowstone Park. 318 00:14:57,020 --> 00:14:57,980 It's fantastic. 319 00:14:57,980 --> 00:15:01,690 There's a wall, just a wall of obsidian that comes down. 320 00:15:01,690 --> 00:15:05,150 And I think I've got an image here. 321 00:15:05,150 --> 00:15:05,720 There it is. 322 00:15:05,720 --> 00:15:09,060 This one I pulled off the internet. 323 00:15:09,060 --> 00:15:12,720 So this is crystalline phase, and this is 324 00:15:12,720 --> 00:15:14,200 the amorphous phase. 325 00:15:14,200 --> 00:15:18,030 And the overall composition, it's a glass, it's a silicate. 326 00:15:18,030 --> 00:15:20,050 And why isn't it transparent to visible light? 327 00:15:20,050 --> 00:15:21,440 Because it's got iron in it. 328 00:15:21,440 --> 00:15:24,400 The iron gives it the absorption and capabilities. 329 00:15:24,400 --> 00:15:27,250 The band gap is invisible, so it's black. 330 00:15:27,250 --> 00:15:29,500 But then when this crystallizes, it's got a 331 00:15:29,500 --> 00:15:32,060 different index, and it's mainly SiO2. 332 00:15:32,060 --> 00:15:35,740 It's really the cristobalite phase of the obsidian. 333 00:15:35,740 --> 00:15:37,180 So that's cool. 334 00:15:37,180 --> 00:15:41,690 So this is actually differentiated on the basis of 335 00:15:41,690 --> 00:15:50,700 amorphous and crystalline of something that's virtually the 336 00:15:50,700 --> 00:15:51,960 same chemical composition. 337 00:15:51,960 --> 00:15:57,020 So this could give you an idea of what happens in the area of 338 00:15:57,020 --> 00:15:58,660 phase separation. 339 00:15:58,660 --> 00:15:59,430 OK. 340 00:15:59,430 --> 00:16:02,340 Now the second thing that I have to bring to your 341 00:16:02,340 --> 00:16:05,830 attention, is that these phase diagrams treat systems at 342 00:16:05,830 --> 00:16:07,150 equilibrium. 343 00:16:07,150 --> 00:16:09,990 They're stability maps, and they treat systems at 344 00:16:09,990 --> 00:16:10,680 equilibrium. 345 00:16:10,680 --> 00:16:12,560 So what is equilibrium? 346 00:16:12,560 --> 00:16:16,340 Let's just get one time up here a definition of 347 00:16:16,340 --> 00:16:17,000 equilibrium. 348 00:16:17,000 --> 00:16:22,680 Equilibrium is a condition which there is no net reaction 349 00:16:22,680 --> 00:16:23,270 taking place. 350 00:16:23,270 --> 00:16:24,540 The system could be reacting. 351 00:16:24,540 --> 00:16:27,230 If you're looking at the ice cubes in water, the ice could 352 00:16:27,230 --> 00:16:30,260 be dissolving, and some of the water could be freezing, but 353 00:16:30,260 --> 00:16:33,430 overall, with time, there's no net reaction. 354 00:16:33,430 --> 00:16:36,420 It's a dynamic system with no net reaction. 355 00:16:36,420 --> 00:16:39,430 And it's characterized as the lowest energy state. 356 00:16:42,590 --> 00:16:46,270 Systems strive towards equilibrium. 357 00:16:46,270 --> 00:16:49,040 If it's the lowest energy state, no net reaction then. 358 00:16:49,040 --> 00:16:52,050 If a system is truly at equilibrium, the properties 359 00:16:52,050 --> 00:16:55,190 should be invariant over time, because 360 00:16:55,190 --> 00:16:58,130 there's no net reaction. 361 00:16:58,130 --> 00:16:59,980 You can't prove equilibrium. 362 00:16:59,980 --> 00:17:03,150 You can only demonstrate the absence of equilibrium. 363 00:17:03,150 --> 00:17:04,990 Because at equilibrium, there's nothing, there's no 364 00:17:04,990 --> 00:17:06,240 net reaction. 365 00:17:11,950 --> 00:17:14,070 And it could be attainable by multiple paths. 366 00:17:14,070 --> 00:17:18,910 So in other words, if I have ice as the equilibrium phase, 367 00:17:18,910 --> 00:17:22,940 I can make it by freezing water, and get to the same ice 368 00:17:22,940 --> 00:17:24,700 at the given temperature and pressure. 369 00:17:24,700 --> 00:17:26,960 Or I could sublime. 370 00:17:26,960 --> 00:17:31,150 But if I specify the pressure and the composition, I should 371 00:17:31,150 --> 00:17:33,100 always end up with the same system. 372 00:17:33,100 --> 00:17:35,663 So attainable by multiple paths. 373 00:17:41,030 --> 00:17:42,900 Because it's a stable state, so it doesn't 374 00:17:42,900 --> 00:17:44,490 matter how you got there. 375 00:17:44,490 --> 00:17:45,440 It's a state function. 376 00:17:45,440 --> 00:17:47,840 And you know from your physics, a state function has 377 00:17:47,840 --> 00:17:50,880 the same value, regardless of how you arrived there. 378 00:17:50,880 --> 00:17:53,400 And then the last thing is, I want to differentiate. 379 00:17:53,400 --> 00:17:56,370 See, these are all single phase, but some of them are 380 00:17:56,370 --> 00:18:00,470 just one element, some of them are just one compound, and 381 00:18:00,470 --> 00:18:01,720 some of them have a whole mix. 382 00:18:01,720 --> 00:18:05,780 So we have a way of quantifying the degree of 383 00:18:05,780 --> 00:18:10,270 chemical complexity by using the term called component. 384 00:18:10,270 --> 00:18:12,195 It's a measure of chemical complexity. 385 00:18:21,790 --> 00:18:27,715 It's the number of chemically distinguishable constituents. 386 00:18:32,670 --> 00:18:34,060 And again, these are definitions. 387 00:18:34,060 --> 00:18:38,160 I'll give you some examples so then the 388 00:18:38,160 --> 00:18:40,880 definition comes to life. 389 00:18:40,880 --> 00:18:43,395 I like to think of it as the number of bottles you've got 390 00:18:43,395 --> 00:18:47,460 to pull off the shelf to make the final product. 391 00:18:47,460 --> 00:18:48,210 The building blocks. 392 00:18:48,210 --> 00:18:49,950 So for example, water is just water. 393 00:18:49,950 --> 00:18:51,580 You could say, but it's hydrogen and oxygen. 394 00:18:51,580 --> 00:18:54,830 But if you take 560 or some other thermal class, you'll 395 00:18:54,830 --> 00:18:57,560 learn that they're bound by mole ratio. 396 00:18:57,560 --> 00:19:00,220 You don't have freedom of hydrogen and oxygen. 397 00:19:00,220 --> 00:19:02,980 So it's just one bottle, whereas to make white gold, 398 00:19:02,980 --> 00:19:05,600 you need three bottles. 399 00:19:05,600 --> 00:19:07,810 You need a bottle of gold, a bottle of silver, 400 00:19:07,810 --> 00:19:08,590 and a bottle of nickel. 401 00:19:08,590 --> 00:19:10,240 So that's a three component system. 402 00:19:10,240 --> 00:19:13,440 And I'm going to designate the components by c with a 403 00:19:13,440 --> 00:19:14,280 circle around it. 404 00:19:14,280 --> 00:19:18,670 Because c without a circle is already composition, 405 00:19:18,670 --> 00:19:20,270 concentration. 406 00:19:20,270 --> 00:19:20,560 OK. 407 00:19:20,560 --> 00:19:25,160 So now we can put all of this together, and we'll show the 408 00:19:25,160 --> 00:19:28,480 difference between multicomponent and multiphase. 409 00:19:28,480 --> 00:19:33,070 So we'll make a little table here, and here I'm going to 410 00:19:33,070 --> 00:19:37,260 talk about one-phase systems, and distinguish on the basis 411 00:19:37,260 --> 00:19:38,320 of components. 412 00:19:38,320 --> 00:19:42,540 So if it's single phase single component, that's just water. 413 00:19:42,540 --> 00:19:43,860 One phase, one component. 414 00:19:43,860 --> 00:19:45,160 Simple liquid. 415 00:19:45,160 --> 00:19:50,640 If it's two components one phase, that could be 416 00:19:50,640 --> 00:19:52,930 calcia-zirconia. 417 00:19:52,930 --> 00:19:56,340 I need a bottle of calcia and a bottle of zirconia in order 418 00:19:56,340 --> 00:20:00,350 to make this two component single-phase system. 419 00:20:00,350 --> 00:20:02,320 And then to have three components, 420 00:20:02,320 --> 00:20:05,070 that's the white gold. 421 00:20:05,070 --> 00:20:09,680 It's still single phase, but I need the gold, silver, and the 422 00:20:09,680 --> 00:20:12,860 nickel, whereas if I come over here, I've got two phases. 423 00:20:12,860 --> 00:20:15,480 That could be slush. 424 00:20:15,480 --> 00:20:16,910 Slush, that's ice water. 425 00:20:20,360 --> 00:20:21,420 It's just one component. 426 00:20:21,420 --> 00:20:26,550 I just start with water, and drop it down to 0 Centigrade, 427 00:20:26,550 --> 00:20:29,230 and I'm going to end up with ice crystals in the water. 428 00:20:29,230 --> 00:20:30,600 So that's one component. 429 00:20:30,600 --> 00:20:31,930 I just needed one bottle. 430 00:20:31,930 --> 00:20:33,800 Literally, one bottle. 431 00:20:33,800 --> 00:20:34,230 All right. 432 00:20:34,230 --> 00:20:37,210 Now what about two components, two phases? 433 00:20:37,210 --> 00:20:39,950 Well, we saw earlier when we started thinking about 434 00:20:39,950 --> 00:20:43,720 solubility, we did the bilayer with carbon 435 00:20:43,720 --> 00:20:45,690 tetrachloride and water. 436 00:20:45,690 --> 00:20:49,270 Remember, we dropped potassium permanganate and iodine, and 437 00:20:49,270 --> 00:20:51,380 the potassium permanganate dissolved in the water, and 438 00:20:51,380 --> 00:20:53,540 the iodine dissolved in the carbon tetrachloride? 439 00:20:53,540 --> 00:20:55,200 Two different components. 440 00:20:55,200 --> 00:20:57,550 I need a bottle of carbon tet and a bottle of water. 441 00:20:57,550 --> 00:20:59,010 And they'll phase separate. 442 00:20:59,010 --> 00:21:01,150 They don't dissolve in one another, because this is a 443 00:21:01,150 --> 00:21:04,460 nonpolar liquid, and this is polar hydrogen bonded. 444 00:21:04,460 --> 00:21:06,890 That's the origin of phase separation. 445 00:21:06,890 --> 00:21:08,700 It's all about bonding, and bonding is all about 446 00:21:08,700 --> 00:21:11,690 electronic structure, and that sounds like a good topic for a 447 00:21:11,690 --> 00:21:13,280 class in chemistry. 448 00:21:13,280 --> 00:21:15,260 And then the last one here is obsidian. 449 00:21:19,260 --> 00:21:22,780 The snowflake obsidian, in which the 450 00:21:22,780 --> 00:21:25,220 components are SiO2-- 451 00:21:25,220 --> 00:21:27,020 so I'm going to have three components and 452 00:21:27,020 --> 00:21:28,070 end up with two phases. 453 00:21:28,070 --> 00:21:32,210 SiO2, there's some magnesia, and then the black comes from 454 00:21:32,210 --> 00:21:33,710 the magnetite. 455 00:21:33,710 --> 00:21:34,670 Fe304. 456 00:21:34,670 --> 00:21:37,610 So I've got three bottles off the shelf, and I end up with 457 00:21:37,610 --> 00:21:40,990 something that is crystalline and amorphous. 458 00:21:40,990 --> 00:21:42,830 So that's where I get the two phases. 459 00:21:42,830 --> 00:21:45,040 Three components, two phases. 460 00:21:45,040 --> 00:21:46,540 It's great. 461 00:21:46,540 --> 00:21:48,560 So now I want to look at some stability maps. 462 00:21:48,560 --> 00:21:51,290 And I'm going to start with the simplest of all, which is 463 00:21:51,290 --> 00:21:53,030 the one we know best from human 464 00:21:53,030 --> 00:21:55,030 experience, and that's water. 465 00:21:55,030 --> 00:21:56,910 So we're going to look at the one-- 466 00:21:56,910 --> 00:22:00,150 so it's a one component. 467 00:22:00,150 --> 00:22:09,830 So for water, we start with c equals 1, and the example is 468 00:22:09,830 --> 00:22:11,470 going to be water. 469 00:22:11,470 --> 00:22:13,150 One component phase diagram. 470 00:22:13,150 --> 00:22:17,890 So we don't have a composition axis, because the only thing 471 00:22:17,890 --> 00:22:20,300 we can vary is pressure and temperature. 472 00:22:20,300 --> 00:22:22,760 If we change composition, we've lost water. 473 00:22:22,760 --> 00:22:27,860 So it has to be axiomatically, no variation composition. 474 00:22:27,860 --> 00:22:30,660 All we have is that the coordinates of 475 00:22:30,660 --> 00:22:35,080 temperature and pressure. 476 00:22:35,080 --> 00:22:38,160 So there it is out of the book, and I'm going to draw it 477 00:22:38,160 --> 00:22:42,740 a little bit differently, just to emphasize three of my 478 00:22:42,740 --> 00:22:43,500 favorite words. 479 00:22:43,500 --> 00:22:45,490 Not to scale. 480 00:22:45,490 --> 00:22:47,370 Otherwise you can't see some of the subtle features. 481 00:22:47,370 --> 00:22:51,005 So overall, it's a y-shaped diagram. 482 00:22:53,600 --> 00:22:55,020 And this is pressure. 483 00:22:55,020 --> 00:22:56,970 Let's make it pressure in atmospheres. 484 00:23:00,820 --> 00:23:03,410 Then our human experiences is at 1 atmosphere. 485 00:23:06,650 --> 00:23:09,400 So at the highest temperatures, we expect to 486 00:23:09,400 --> 00:23:16,125 have vapor, and at the lowest temperatures, we expect solid. 487 00:23:19,460 --> 00:23:22,660 And in between, we expect liquid. 488 00:23:22,660 --> 00:23:27,020 And then if we look at the 1 atmosphere isobar, what's 489 00:23:27,020 --> 00:23:28,440 happening on this line? 490 00:23:28,440 --> 00:23:30,500 On the one side of line it's liquid, and the other side of 491 00:23:30,500 --> 00:23:31,460 line, it's vapor. 492 00:23:31,460 --> 00:23:34,550 At this temperature, liquid and vapor coexist. 493 00:23:34,550 --> 00:23:36,030 I call that the boiling point. 494 00:23:36,030 --> 00:23:37,510 So I'm going to put 100 here. 495 00:23:40,420 --> 00:23:45,180 And we already learned from our little example of Mount 496 00:23:45,180 --> 00:23:48,920 Everest that this locust here, this line, is the liquid 497 00:23:48,920 --> 00:23:52,050 equals vapor two phase equilibrium. 498 00:23:52,050 --> 00:23:53,500 And you see how it changes? 499 00:23:53,500 --> 00:23:56,390 If I go to the top of Mount Everest, the pressure is less 500 00:23:56,390 --> 00:23:57,410 than 1 atmosphere. 501 00:23:57,410 --> 00:23:59,940 which means the boiling point of water is below the 502 00:23:59,940 --> 00:24:00,930 denaturing point. 503 00:24:00,930 --> 00:24:02,810 So this actually gives you the map. 504 00:24:02,810 --> 00:24:06,420 Or if I put the pressure cap on, I go up here. 505 00:24:06,420 --> 00:24:08,540 And you can use this in the kitchen again. 506 00:24:08,540 --> 00:24:12,420 If you love wild rice, and you can't wait 45 minutes when you 507 00:24:12,420 --> 00:24:14,760 get home, use a pressure cooker. 508 00:24:14,760 --> 00:24:17,750 What the pressure cooker does, is it allows you to have 509 00:24:17,750 --> 00:24:21,100 liquid up to 130 degrees Celsius. 510 00:24:21,100 --> 00:24:22,050 See, you can't steam it. 511 00:24:22,050 --> 00:24:23,940 You've got to soak it in water. 512 00:24:23,940 --> 00:24:25,175 And you know the Arrhenius Law. 513 00:24:25,175 --> 00:24:28,490 If you can get the temperature up by 30 degrees, you'll cut 514 00:24:28,490 --> 00:24:30,440 the cooking time in half. 515 00:24:30,440 --> 00:24:34,460 So how do you get water, liquid, at 130 degrees? 516 00:24:34,460 --> 00:24:36,920 Then you can cook quicker! 517 00:24:36,920 --> 00:24:38,240 Pressure. 518 00:24:38,240 --> 00:24:38,730 Seal it. 519 00:24:38,730 --> 00:24:42,240 And then you've got liquid water way, way up here. 520 00:24:42,240 --> 00:24:46,630 Now over here, this is solid goes to liquid. 521 00:24:46,630 --> 00:24:48,530 So this is the freezing point line. 522 00:24:48,530 --> 00:24:50,500 At 1 atmosphere, that's 0. 523 00:24:50,500 --> 00:24:51,600 0 Celsius. 524 00:24:51,600 --> 00:24:53,370 And you know, if you go skating-- 525 00:24:53,370 --> 00:24:56,720 so let's say the ice is minus 5 Celsius. 526 00:24:56,720 --> 00:24:59,350 And you're here, but you put your weight on the blades, and 527 00:24:59,350 --> 00:25:01,270 the blades have small area. 528 00:25:01,270 --> 00:25:05,410 So pressure is force per area. 529 00:25:05,410 --> 00:25:07,900 So that puts you up here, and now you cross, and now you 530 00:25:07,900 --> 00:25:11,170 glide on water. 531 00:25:11,170 --> 00:25:12,360 Film of water. 532 00:25:12,360 --> 00:25:13,870 You ever watch a hockey game? 533 00:25:13,870 --> 00:25:14,730 I grew up in Canada. 534 00:25:14,730 --> 00:25:16,580 We used to say, well, the ice is fast. 535 00:25:16,580 --> 00:25:18,520 Why is the ice fast? 536 00:25:18,520 --> 00:25:22,700 Because you get down to temperatures where you just 537 00:25:22,700 --> 00:25:24,335 get the right slickness of water. 538 00:25:24,335 --> 00:25:27,580 If the ice is slow, the temperature is so close that, 539 00:25:27,580 --> 00:25:29,910 you know, you get these big, bruising hockey players, and 540 00:25:29,910 --> 00:25:31,210 they're moving up into here, and it's 541 00:25:31,210 --> 00:25:32,770 like they're dragging. 542 00:25:32,770 --> 00:25:37,050 And if you ever come from Minnesota or North Dakota, if 543 00:25:37,050 --> 00:25:39,560 you've ever skated when the temperature gets down about 544 00:25:39,560 --> 00:25:43,050 minus 20, minus 30? 545 00:25:43,050 --> 00:25:44,630 It's a different experience, because you never 546 00:25:44,630 --> 00:25:45,820 get across this line. 547 00:25:45,820 --> 00:25:49,950 Your blades are just, they can't get a good grip. 548 00:25:49,950 --> 00:25:50,250 See? 549 00:25:50,250 --> 00:25:51,490 Everything you need to know is here. 550 00:25:51,490 --> 00:25:54,800 This is four-star chef, this is 551 00:25:54,800 --> 00:25:56,780 prize-winning hockey player. 552 00:25:56,780 --> 00:25:59,530 We haven't got off the 1 atmosphere line yet. 553 00:25:59,530 --> 00:25:59,870 OK. 554 00:25:59,870 --> 00:26:02,110 So now I'm going to say, this is single phase, right? 555 00:26:02,110 --> 00:26:03,360 It's just vapor. 556 00:26:03,360 --> 00:26:05,870 This is single phase, and this is single phase. 557 00:26:05,870 --> 00:26:08,130 It's all solid. 558 00:26:08,130 --> 00:26:11,510 And along this line, it's two phase, isn't it? 559 00:26:14,970 --> 00:26:16,040 Solid-liquid. 560 00:26:16,040 --> 00:26:17,250 This is ice cubes, isn't it. 561 00:26:17,250 --> 00:26:20,410 Anywhere along this line is ice cubes in water. 562 00:26:20,410 --> 00:26:22,370 Look at this one. 563 00:26:22,370 --> 00:26:23,750 This is liquid vapor. 564 00:26:23,750 --> 00:26:25,890 This is solid, liquid-- 565 00:26:25,890 --> 00:26:30,210 all three of them coexist here. 566 00:26:30,210 --> 00:26:36,910 This is p equals 3, which means, ice cubes floating in 567 00:26:36,910 --> 00:26:38,160 boiling water. 568 00:26:41,370 --> 00:26:42,940 And this happens at only one point. 569 00:26:42,940 --> 00:26:50,270 It's called the triple point, and its coordinates are-- 570 00:26:50,270 --> 00:26:51,480 this is not to scale. 571 00:26:51,480 --> 00:26:55,610 So this is 0.01 degrees C. It's a 572 00:26:55,610 --> 00:26:57,460 1/100 of a degree higher. 573 00:26:57,460 --> 00:27:03,730 And the pressure here is 4.58 millimeters of mercury, which 574 00:27:03,730 --> 00:27:08,080 then you can convert using the 760 as 1 atmosphere. 575 00:27:08,080 --> 00:27:10,070 Oh, and this is solid-vapor. 576 00:27:10,070 --> 00:27:12,000 You can go directly from solid to vapor down here. 577 00:27:12,000 --> 00:27:15,300 If you hang up your clothes on a line and it's minus 20 578 00:27:15,300 --> 00:27:16,800 degrees outside, first thing that 579 00:27:16,800 --> 00:27:17,890 happens, the clothes freeze. 580 00:27:17,890 --> 00:27:19,330 You come back five hours later, and 581 00:27:19,330 --> 00:27:20,080 the clothes are dry. 582 00:27:20,080 --> 00:27:20,660 Well, what happened? 583 00:27:20,660 --> 00:27:22,580 Did somebody take them in? 584 00:27:22,580 --> 00:27:24,820 Run them around the clothes dryer, then 585 00:27:24,820 --> 00:27:25,750 hang them up for you? 586 00:27:25,750 --> 00:27:25,920 No. 587 00:27:25,920 --> 00:27:30,340 You're going directly from solid to vapor, down in here. 588 00:27:30,340 --> 00:27:32,590 So here's the whole story of the phase diagram. 589 00:27:32,590 --> 00:27:34,930 One last thing I want to point out. 590 00:27:34,930 --> 00:27:39,530 Here, you're at a given temperature and it's vapor. 591 00:27:39,530 --> 00:27:42,390 And then you squeeze, squeeze, squeeze, and now things get 592 00:27:42,390 --> 00:27:44,390 closer together, and you go from paper to liquid at 593 00:27:44,390 --> 00:27:45,180 constant temperature. 594 00:27:45,180 --> 00:27:46,290 That makes sense, right? 595 00:27:46,290 --> 00:27:48,430 I start from vapor, constant temperature. 596 00:27:48,430 --> 00:27:50,740 I squeeze it, I get liquid, I keep squeezing, 597 00:27:50,740 --> 00:27:52,150 I should make solid. 598 00:27:52,150 --> 00:27:52,980 Here's vapor. 599 00:27:52,980 --> 00:27:54,510 I squeeze, I get solid, and I squeeze 600 00:27:54,510 --> 00:27:55,550 harder, and I get liquid. 601 00:27:55,550 --> 00:27:59,910 That makes no sense at all, but that's what happens. 602 00:27:59,910 --> 00:28:00,850 What does this tell me? 603 00:28:00,850 --> 00:28:04,680 It tells me that the number of nearest neighbors in the solid 604 00:28:04,680 --> 00:28:05,900 is greater than the vapor. 605 00:28:05,900 --> 00:28:06,700 Yeah, I get that. 606 00:28:06,700 --> 00:28:09,040 But the number of nearest neighbors in the liquid must 607 00:28:09,040 --> 00:28:10,420 be greater than the number of nearest 608 00:28:10,420 --> 00:28:11,770 neighbors in the solid. 609 00:28:11,770 --> 00:28:12,980 This is an exception. 610 00:28:12,980 --> 00:28:16,480 When I see this negative slope, it means that ice cubes 611 00:28:16,480 --> 00:28:18,100 are going to float on water. 612 00:28:18,100 --> 00:28:20,170 That's what I learn from this negative slope. 613 00:28:20,170 --> 00:28:21,520 So let's put that down. 614 00:28:21,520 --> 00:28:26,020 dp by dt when dp by dt is less than zero. 615 00:28:26,020 --> 00:28:27,870 This is for solid equals liquid. 616 00:28:27,870 --> 00:28:31,880 That means that the density of the solid is less than the 617 00:28:31,880 --> 00:28:34,640 density of the liquid. 618 00:28:34,640 --> 00:28:36,350 All from here. 619 00:28:36,350 --> 00:28:36,780 OK. 620 00:28:36,780 --> 00:28:38,640 Good. 621 00:28:38,640 --> 00:28:42,810 So let's look at a few other phase diagrams. 622 00:28:42,810 --> 00:28:46,020 I think I've got a few things up here. 623 00:28:46,020 --> 00:28:47,980 Here's silicon. 624 00:28:47,980 --> 00:28:49,290 Pressure versus temperature. 625 00:28:49,290 --> 00:28:51,940 Its normal melting point is about-- 626 00:28:51,940 --> 00:28:53,650 see, now I said normal melting point. 627 00:28:53,650 --> 00:28:55,920 After today's lecture, if somebody says, what's the 628 00:28:55,920 --> 00:28:57,000 boiling point of water? 629 00:28:57,000 --> 00:28:58,050 You don't go, 100 degrees. 630 00:28:58,050 --> 00:28:59,300 You say, at what pressure? 631 00:29:01,935 --> 00:29:03,780 And they go, oh, I hate you. 632 00:29:03,780 --> 00:29:05,020 I hated you before. 633 00:29:05,020 --> 00:29:05,990 I'm going to use an adverb here. 634 00:29:05,990 --> 00:29:07,020 Now I really hate you. 635 00:29:07,020 --> 00:29:07,630 OK. 636 00:29:07,630 --> 00:29:10,150 So this is the normal melting point of silicon. 637 00:29:10,150 --> 00:29:14,110 It's about 1430 degrees Centigrade, or a 1700 638 00:29:14,110 --> 00:29:15,150 something Kelvin. 639 00:29:15,150 --> 00:29:18,080 And it also has this negative slope. 640 00:29:18,080 --> 00:29:18,980 And what does that tell you? 641 00:29:18,980 --> 00:29:22,510 That liquid silicon is denser than solid silicon, and it's a 642 00:29:22,510 --> 00:29:24,150 good thing it is, because we wouldn't have the 643 00:29:24,150 --> 00:29:26,200 microelectronics age if it weren't for that. 644 00:29:26,200 --> 00:29:28,460 We couldn't have Teukolsky crystal growth and everything 645 00:29:28,460 --> 00:29:30,420 else that makes silicon dirt cheap. 646 00:29:30,420 --> 00:29:31,450 You know why it's dirt cheap? 647 00:29:31,450 --> 00:29:32,440 Because it's made from dirt. 648 00:29:32,440 --> 00:29:35,510 That's why it's dirt cheap. 649 00:29:35,510 --> 00:29:36,240 It's true. 650 00:29:36,240 --> 00:29:37,020 Here's aluminum. 651 00:29:37,020 --> 00:29:38,260 This is normal. 652 00:29:38,260 --> 00:29:41,440 This is the normal solid-liquid equilibrium. 653 00:29:41,440 --> 00:29:44,430 This is FCC metal, which is the closest packed. 654 00:29:44,430 --> 00:29:47,430 Axiomatically, the liquid must be less well-packed. 655 00:29:47,430 --> 00:29:48,030 All right? 656 00:29:48,030 --> 00:29:52,460 So this is dog bites man, this is man bites dog. 657 00:29:52,460 --> 00:29:54,320 This is the unusual one. 658 00:29:54,320 --> 00:29:54,770 OK. 659 00:29:54,770 --> 00:29:56,430 What else do we have? 660 00:29:56,430 --> 00:29:57,140 Nitrogen! 661 00:29:57,140 --> 00:29:58,620 Here's nitrogen. 662 00:29:58,620 --> 00:29:59,200 I drew this. 663 00:29:59,200 --> 00:30:01,120 So there's the 1 atmosphere line. 664 00:30:01,120 --> 00:30:03,750 Nitrogen boils at 77 Kelvin, and it 665 00:30:03,750 --> 00:30:05,680 freezes at about 63 Kelvin. 666 00:30:05,680 --> 00:30:08,320 And it's got the positive slope that you'd expect, and 667 00:30:08,320 --> 00:30:12,570 so solid nitrogen is denser then liquid nitrogen. 668 00:30:12,570 --> 00:30:15,010 And you can remember 77 Kelvin. 669 00:30:15,010 --> 00:30:16,560 You want to remember a few of these things. 670 00:30:16,560 --> 00:30:20,220 I wanted to point out to you that at atmospheric 671 00:30:20,220 --> 00:30:22,520 temperature, ambient temperature, you 672 00:30:22,520 --> 00:30:24,080 can remember 20-20. 673 00:30:24,080 --> 00:30:25,270 20-20 vision. 674 00:30:25,270 --> 00:30:28,850 So at 20 degrees C, it's roughly 20 millimeters of 675 00:30:28,850 --> 00:30:31,120 mercury, is the vapor pressure of water. 676 00:30:31,120 --> 00:30:33,240 It's not exactly true, but it's close enough. 677 00:30:33,240 --> 00:30:34,420 I think it's really 24. 678 00:30:34,420 --> 00:30:36,500 But 20-20 is nice to know. 679 00:30:36,500 --> 00:30:39,240 And what's the street address for MIT? 680 00:30:39,240 --> 00:30:42,490 77 Mass Ave. That's the boiling point of liquid 681 00:30:42,490 --> 00:30:45,390 nitrogen, 77 Kelvin. 682 00:30:45,390 --> 00:30:48,170 So I thought we'd do a few things here. 683 00:30:48,170 --> 00:30:54,320 And I'm going to show you a little bit of fun and games 684 00:30:54,320 --> 00:30:55,250 with liquid nitrogen. 685 00:30:55,250 --> 00:30:58,120 But first, I've been instructed I have to practice 686 00:30:58,120 --> 00:31:01,400 safe laboratory-- 687 00:31:01,400 --> 00:31:05,200 So I'm going to put on my lab coat. 688 00:31:05,200 --> 00:31:06,780 Yes. 689 00:31:06,780 --> 00:31:08,140 It's a nice lab coat. 690 00:31:08,140 --> 00:31:09,100 Mm-hm! 691 00:31:09,100 --> 00:31:10,370 Yeah, look. 692 00:31:10,370 --> 00:31:12,030 You want to know-- 693 00:31:12,030 --> 00:31:13,460 let's go back to this. 694 00:31:13,460 --> 00:31:14,820 They have to know where the-- this is not 695 00:31:14,820 --> 00:31:16,990 just any old lab coat. 696 00:31:16,990 --> 00:31:17,990 This is a nice lab coat. 697 00:31:17,990 --> 00:31:18,880 This is from France. 698 00:31:18,880 --> 00:31:21,060 It's from MAISON DUTECH. 699 00:31:21,060 --> 00:31:21,680 See? 700 00:31:21,680 --> 00:31:22,595 Notice the collar. 701 00:31:22,595 --> 00:31:25,460 It's not that typical, you know. 702 00:31:25,460 --> 00:31:26,560 MAISON DUTECH. 703 00:31:26,560 --> 00:31:27,420 OK. 704 00:31:27,420 --> 00:31:30,880 Let's go back to the phase diagram. 705 00:31:30,880 --> 00:31:37,140 So Dave Broderick is going to help us here. 706 00:31:37,140 --> 00:31:38,990 So we're going to have some fun. 707 00:31:38,990 --> 00:31:41,004 I'm going to put on a face shield so 708 00:31:41,004 --> 00:31:44,776 I don't blind myself. 709 00:31:44,776 --> 00:31:47,340 All right. 710 00:31:47,340 --> 00:31:50,240 Here we go. 711 00:31:50,240 --> 00:31:51,030 All right. 712 00:31:51,030 --> 00:31:52,700 So let's get some liquid nitrogen. 713 00:31:52,700 --> 00:31:53,950 Sounds different, huh? 714 00:31:55,970 --> 00:31:57,912 Sounds terrible for me. 715 00:31:57,912 --> 00:31:58,520 All right. 716 00:31:58,520 --> 00:32:02,080 So we've got some liquid nitrogen here, and I'll pour 717 00:32:02,080 --> 00:32:03,330 it into a Dewar. 718 00:32:20,140 --> 00:32:24,760 So what happens when you wet a sheet of paper with ink with 719 00:32:24,760 --> 00:32:25,650 liquid nitrogen? 720 00:32:25,650 --> 00:32:27,765 What kind of bonding is there in liquid nitrogen? 721 00:32:30,870 --> 00:32:31,370 Look. 722 00:32:31,370 --> 00:32:35,480 No running, no running. 723 00:32:35,480 --> 00:32:36,730 If it's liquid nitrogen. 724 00:32:39,715 --> 00:32:42,600 I tell you, everything you learn here is so valuable 725 00:32:42,600 --> 00:32:45,790 compared all the other stuff you learn here-- 726 00:32:45,790 --> 00:32:46,110 All right. 727 00:32:46,110 --> 00:32:48,450 So there's a couple of things. 728 00:32:48,450 --> 00:32:51,140 So let's look at glass transition temperature. 729 00:32:51,140 --> 00:32:52,320 So this is a latex glove. 730 00:32:52,320 --> 00:32:55,460 You can see it's above its glass transition temperature, 731 00:32:55,460 --> 00:32:58,150 and the cross-links are snapping it back. 732 00:32:58,150 --> 00:33:00,060 What I'm going to do, is take it down below its glass 733 00:33:00,060 --> 00:33:03,960 transition temperature, and turn it glassy and brittle. 734 00:33:15,600 --> 00:33:17,440 So that it's below the TG. 735 00:33:21,210 --> 00:33:23,260 Here's some paraffin. 736 00:33:23,260 --> 00:33:28,806 Paraffin, which is also a polymer here. 737 00:33:28,806 --> 00:33:31,470 Take the paper off. 738 00:33:31,470 --> 00:33:31,760 OK. 739 00:33:31,760 --> 00:33:32,570 So here's paraffin. 740 00:33:32,570 --> 00:33:32,880 Look. 741 00:33:32,880 --> 00:33:34,956 Look at the van der Waals bond. 742 00:33:34,956 --> 00:33:35,815 All right? 743 00:33:35,815 --> 00:33:38,480 This is van der Waals bond. 744 00:33:38,480 --> 00:33:40,730 Now we're going to go below the TG. 745 00:33:52,220 --> 00:33:53,350 It's liquid nitrogen! 746 00:33:53,350 --> 00:33:54,600 It doesn't matter. 747 00:34:00,100 --> 00:34:01,350 OK, you can hear it already. 748 00:34:04,900 --> 00:34:08,340 So it's now below the glass transition temperature. 749 00:34:08,340 --> 00:34:09,290 So what else have we got? 750 00:34:09,290 --> 00:34:10,970 Oh, you've heard of the glass flowers at Harvard? 751 00:34:10,970 --> 00:34:14,460 Well, we've got glass flowers here, so. 752 00:34:14,460 --> 00:34:17,520 Here's a rose. 753 00:34:17,520 --> 00:34:19,818 See, in the proteins, you know, it's above the-- you 754 00:34:19,818 --> 00:34:21,700 know, it's soft. 755 00:34:21,700 --> 00:34:25,250 But now, we're going to put the-- 756 00:34:25,250 --> 00:34:25,730 mm-hm. 757 00:34:25,730 --> 00:34:26,140 Here we go. 758 00:34:26,140 --> 00:34:27,390 You ready? 759 00:34:31,360 --> 00:34:31,780 Oh, come on. 760 00:34:31,780 --> 00:34:32,490 It's not a kitten. 761 00:34:32,490 --> 00:34:33,740 What's the matter? 762 00:34:39,200 --> 00:34:40,490 It's still burbling here. 763 00:34:40,490 --> 00:34:41,854 We have to wait until it's dead. 764 00:34:46,580 --> 00:34:47,830 This is for science. 765 00:34:54,420 --> 00:34:54,630 OK. 766 00:34:54,630 --> 00:34:59,480 Now it's below its glass transition temperature. 767 00:34:59,480 --> 00:35:00,117 Oh, I'm sorry, David. 768 00:35:00,117 --> 00:35:01,367 I should put this over on the other side. 769 00:35:05,130 --> 00:35:07,420 But maybe it's the red, or maybe it's 770 00:35:07,420 --> 00:35:08,250 because it's a rose. 771 00:35:08,250 --> 00:35:11,410 So here's the chrysanthemum. 772 00:35:11,410 --> 00:35:12,670 Today is your day. 773 00:35:15,490 --> 00:35:16,740 Let's go. 774 00:35:19,730 --> 00:35:20,980 Get this thing moving! 775 00:35:24,730 --> 00:35:25,980 Yeah. 776 00:35:31,090 --> 00:35:31,860 So there you have it. 777 00:35:31,860 --> 00:35:32,830 There you have it. 778 00:35:32,830 --> 00:35:33,940 I think that's-- 779 00:35:33,940 --> 00:35:42,742 oh, there's one, may we go back to the slide? 780 00:35:42,742 --> 00:35:44,710 Better put the gloves on for this. 781 00:35:44,710 --> 00:35:45,970 I'll have to write apology letters. 782 00:35:49,750 --> 00:35:49,990 OK. 783 00:35:49,990 --> 00:35:53,660 So we're going to do next, is we're going to look at phase 784 00:35:53,660 --> 00:35:54,470 equilibriums. 785 00:35:54,470 --> 00:35:56,890 There's the melting points and boiling point of oxygen, 786 00:35:56,890 --> 00:35:57,780 argon, and nitrogen. 787 00:35:57,780 --> 00:36:00,970 And what you notice is that nitrogen boils at a lower 788 00:36:00,970 --> 00:36:04,060 temperature then oxygen and argon. 789 00:36:04,060 --> 00:36:08,860 So what I'm going to do, is I'm going to pour some liquid 790 00:36:08,860 --> 00:36:10,930 nitrogen into this beaker. 791 00:36:10,930 --> 00:36:14,550 And then inside the graduated cylinder, I'm going to let it 792 00:36:14,550 --> 00:36:17,070 sit here, and we're going to condense air. 793 00:36:17,070 --> 00:36:18,680 And the result will be that we're going to start 794 00:36:18,680 --> 00:36:22,170 condensing liquid oxygen, and they'll be little bits of 795 00:36:22,170 --> 00:36:24,995 argon ice floating in liquid oxygen. 796 00:36:24,995 --> 00:36:28,850 And liquid oxygen is faintly blue, and it's paramagnetic, 797 00:36:28,850 --> 00:36:31,800 as you know, because it's got the unpaired electrons, which 798 00:36:31,800 --> 00:36:36,700 means that it will levitate in a magnetic field. 799 00:36:36,700 --> 00:36:39,120 I couldn't bring a big magnet in here, but we'll see if we 800 00:36:39,120 --> 00:36:40,000 can make some blue stuff. 801 00:36:40,000 --> 00:36:42,160 And it's foaming, because this would be like pouring water 802 00:36:42,160 --> 00:36:43,990 into something that's-- 803 00:36:43,990 --> 00:36:44,310 I don't know. 804 00:36:44,310 --> 00:36:45,340 300 degrees Centigrade. 805 00:36:45,340 --> 00:36:48,680 But eventually, the heat transfer gets low enough that 806 00:36:48,680 --> 00:36:52,845 you have stability here, and-- 807 00:36:52,845 --> 00:36:54,095 yeah. 808 00:37:04,990 --> 00:37:07,080 OK. 809 00:37:07,080 --> 00:37:08,870 Oh, that's terrific. 810 00:37:08,870 --> 00:37:09,120 OK. 811 00:37:09,120 --> 00:37:10,500 What else have we got? 812 00:37:10,500 --> 00:37:15,995 Let's go back to the slide. 813 00:37:15,995 --> 00:37:17,245 God, I hate this thing. 814 00:37:24,010 --> 00:37:24,310 OK. 815 00:37:24,310 --> 00:37:26,390 So you've been looking at that nitrogen. 816 00:37:26,390 --> 00:37:27,800 Let's look at what's next. 817 00:37:27,800 --> 00:37:28,090 Ah. 818 00:37:28,090 --> 00:37:31,280 Now if you solidify nitrogen here, you get a whole bunch of 819 00:37:31,280 --> 00:37:32,730 different polymorphs. 820 00:37:32,730 --> 00:37:34,030 Different crystal structures. 821 00:37:34,030 --> 00:37:36,630 So there are about five or six different crystallographic 822 00:37:36,630 --> 00:37:39,110 forms of solid nitrogen. 823 00:37:39,110 --> 00:37:41,640 For that, we'd have to bring liquid helium. 824 00:37:41,640 --> 00:37:43,000 4.2 Kelvin. 825 00:37:43,000 --> 00:37:45,210 Very cool stuff. 826 00:37:45,210 --> 00:37:46,510 Here's carbon dioxide. 827 00:37:46,510 --> 00:37:49,660 Now, it also has the positive slope, so solid 828 00:37:49,660 --> 00:37:50,760 will sink in liquid. 829 00:37:50,760 --> 00:37:52,610 But look, the interesting point here. 830 00:37:52,610 --> 00:37:55,400 The triple point is 5 atmospheres. 831 00:37:55,400 --> 00:37:58,750 At atmospheric pressure, you go directly from solid to gas. 832 00:37:58,750 --> 00:37:59,990 It sublimes. 833 00:37:59,990 --> 00:38:01,120 And that's advantageous. 834 00:38:01,120 --> 00:38:04,830 When we use carbon dioxide as a coolant, when it gives up 835 00:38:04,830 --> 00:38:08,520 its enthalpy to cool, it doesn't then turn into liquid. 836 00:38:08,520 --> 00:38:13,560 If you chill something with ice, with water ice, when it 837 00:38:13,560 --> 00:38:16,680 gives up its enthalpy, the object is 838 00:38:16,680 --> 00:38:18,460 now swimming in water. 839 00:38:18,460 --> 00:38:19,210 And that's no good. 840 00:38:19,210 --> 00:38:22,140 So hence we have the term dry ice, because we go directly 841 00:38:22,140 --> 00:38:26,310 from solid to vapor. 842 00:38:26,310 --> 00:38:27,460 And we want to prove this. 843 00:38:27,460 --> 00:38:33,660 So what we've got here is a big block of dry ice. 844 00:38:37,470 --> 00:38:40,850 So this is at minus 78 degrees Celsius, and it's 845 00:38:40,850 --> 00:38:42,040 still stable here. 846 00:38:42,040 --> 00:38:44,670 Well, it's subliming before your eyes. 847 00:38:44,670 --> 00:38:47,570 It's smaller than it was when we started the lecture. 848 00:38:47,570 --> 00:38:50,990 So what I'm going to do now-- 849 00:38:50,990 --> 00:38:55,170 oh, I'm not wearing that stuff. 850 00:38:55,170 --> 00:38:56,720 I guess I'd better. 851 00:38:56,720 --> 00:39:00,540 They're going to write me up on some log, 852 00:39:00,540 --> 00:39:01,960 teaching you bad practice. 853 00:39:01,960 --> 00:39:03,145 But anyways. 854 00:39:03,145 --> 00:39:03,670 All right. 855 00:39:03,670 --> 00:39:05,170 So what we're going to do, is we're going to test the 856 00:39:05,170 --> 00:39:08,130 proposal that this actually goes-- so I've got some water. 857 00:39:08,130 --> 00:39:10,920 Here, David, let's go out to the video. 858 00:39:10,920 --> 00:39:11,865 So let's take some water. 859 00:39:11,865 --> 00:39:13,680 I think we got water from France. 860 00:39:13,680 --> 00:39:14,700 Goes with the lab coat. 861 00:39:14,700 --> 00:39:16,335 This is Evian, OK? 862 00:39:25,260 --> 00:39:30,180 So I pour the Evian into the Florence flask. 863 00:39:30,180 --> 00:39:31,430 This is Florence. 864 00:39:37,310 --> 00:39:42,290 Florence is round, and the Erlenmeyer is the flat one. 865 00:39:42,290 --> 00:39:44,850 So let's move this guy. 866 00:39:44,850 --> 00:39:47,070 You're going in the backstage for a while. 867 00:39:47,070 --> 00:39:47,540 You just keep 868 00:39:47,540 --> 00:39:49,900 condensing All right. 869 00:39:49,900 --> 00:39:51,440 So now, this is here. 870 00:39:51,440 --> 00:39:53,230 Now what we're going to do, is we're going to put some dry 871 00:39:53,230 --> 00:39:54,870 ice in there, and see if we go directly 872 00:39:54,870 --> 00:39:59,150 from solid to a vapor. 873 00:39:59,150 --> 00:40:00,910 Take a chip off the old block, here. 874 00:40:17,450 --> 00:40:17,680 OK. 875 00:40:17,680 --> 00:40:19,590 So now you can see that it's going directly 876 00:40:19,590 --> 00:40:22,030 from solid to vapor. 877 00:40:22,030 --> 00:40:23,820 So that's carbon dioxide bubbles. 878 00:40:23,820 --> 00:40:27,480 And we assume that the phase diagrams is correct. 879 00:40:27,480 --> 00:40:29,980 I mean, another thing we could do, is-- 880 00:40:29,980 --> 00:40:33,342 I mean, I know what club soda tastes like. 881 00:40:33,342 --> 00:40:34,870 I could just test it, right? 882 00:40:40,120 --> 00:40:40,790 Yeah. 883 00:40:40,790 --> 00:40:44,590 It's carbon dioxide. 884 00:40:44,590 --> 00:40:45,840 Now! 885 00:40:47,580 --> 00:40:48,870 Here's the other thing. 886 00:40:48,870 --> 00:40:54,140 You know, Schweppes likes to pride itself on tiny bubbles. 887 00:40:54,140 --> 00:40:57,370 They have a tagline, Tiny Bubbles. 888 00:40:57,370 --> 00:40:57,630 Right? 889 00:40:57,630 --> 00:41:02,550 So here's Schweppes. 890 00:41:02,550 --> 00:41:05,930 And you can see Schweppes, with their 891 00:41:05,930 --> 00:41:07,410 wimpy little tiny bubbles. 892 00:41:07,410 --> 00:41:09,190 Can you get that, David? 893 00:41:09,190 --> 00:41:11,690 But we have, we have big bubbles. 894 00:41:19,100 --> 00:41:19,950 I mean, this is pure. 895 00:41:19,950 --> 00:41:21,080 You can't get any better than that. 896 00:41:21,080 --> 00:41:25,280 I got Evian water, and I got a block of carbon dioxide. 897 00:41:25,280 --> 00:41:27,080 I like making my own carbonated water. 898 00:41:27,080 --> 00:41:28,770 I've taken it to a new level. 899 00:41:28,770 --> 00:41:29,840 OK. 900 00:41:29,840 --> 00:41:31,930 What else do we have? 901 00:41:31,930 --> 00:41:33,890 Well, let's see if we made any liquid oxygen here. 902 00:41:40,840 --> 00:41:42,720 Try this. 903 00:41:42,720 --> 00:41:45,270 I don't know if we got anything here. 904 00:41:45,270 --> 00:41:45,670 Oh yeah! 905 00:41:45,670 --> 00:41:46,140 Oh, wow. 906 00:41:46,140 --> 00:41:47,390 Look. 907 00:41:52,070 --> 00:41:52,280 OK. 908 00:41:52,280 --> 00:41:53,890 So that liquid in there-- oh, I see. 909 00:41:53,890 --> 00:41:55,023 You've got a separate thing. 910 00:41:55,023 --> 00:41:56,382 I don't know if you can see. 911 00:42:00,140 --> 00:42:02,210 It's condensing. 912 00:42:02,210 --> 00:42:05,750 That liquid in there, that's liquid oxygen. 913 00:42:05,750 --> 00:42:09,100 I won't drink this. 914 00:42:09,100 --> 00:42:10,990 But I can inhale it. 915 00:42:10,990 --> 00:42:13,440 Pure oxygen. 916 00:42:13,440 --> 00:42:15,570 I could have a cigarette, and just put the 917 00:42:15,570 --> 00:42:18,310 cigarette in there. 918 00:42:18,310 --> 00:42:23,640 What happens if I put the lit cigarette into the oxygen? 919 00:42:23,640 --> 00:42:26,200 All that happens is that it burns quickly, that's all. 920 00:42:26,200 --> 00:42:27,130 There's no explosion. 921 00:42:27,130 --> 00:42:27,950 It burns quickly. 922 00:42:27,950 --> 00:42:30,990 If you walk into a room full of oxygen, all that happens is 923 00:42:30,990 --> 00:42:32,310 you'll singe your nose, that's all. 924 00:42:32,310 --> 00:42:33,410 There's no explosion. 925 00:42:33,410 --> 00:42:34,780 It's just oxygen. 926 00:42:34,780 --> 00:42:35,740 There's no fuel. 927 00:42:35,740 --> 00:42:38,550 The fuel is just in tobacco, and there's not much. 928 00:42:38,550 --> 00:42:39,220 It's not a problem. 929 00:42:39,220 --> 00:42:40,390 A room full of oxygen? 930 00:42:40,390 --> 00:42:41,390 Pfft! 931 00:42:41,390 --> 00:42:41,660 OK. 932 00:42:41,660 --> 00:42:46,501 Let's go back to the slides. 933 00:42:46,501 --> 00:42:48,780 What have we got here? 934 00:42:48,780 --> 00:42:51,940 We've got some examples of other phase diagrams. 935 00:42:51,940 --> 00:42:53,030 All right. 936 00:42:53,030 --> 00:42:54,820 Yeah. 937 00:42:54,820 --> 00:42:56,070 [MUSIC PLAYBACK: FROM 'PHANTOM OF THE OPERA'] 938 00:43:02,580 --> 00:43:03,840 PROFESSOR: Actually, it's quite tasty. 939 00:43:03,840 --> 00:43:04,340 All right. 940 00:43:04,340 --> 00:43:05,080 So. 941 00:43:05,080 --> 00:43:08,650 Now, here's zirconia. 942 00:43:08,650 --> 00:43:11,440 Now, here's the thing to know about zirconia. 943 00:43:11,440 --> 00:43:13,170 Look at all the different phases. 944 00:43:13,170 --> 00:43:15,565 And cubic zirconia is the one that has a high index of 945 00:43:15,565 --> 00:43:20,460 refraction, but it's stable only at temperatures exceeding 946 00:43:20,460 --> 00:43:24,160 2000 degrees C. So that's no good. 947 00:43:24,160 --> 00:43:27,700 So what I'm going to show you next day is that by changing 948 00:43:27,700 --> 00:43:32,290 the composition, and adding calcium oxide, we open up this 949 00:43:32,290 --> 00:43:35,250 zone here that's labeled cubic, and we get it stable 950 00:43:35,250 --> 00:43:36,940 all the way down to room temperature. 951 00:43:36,940 --> 00:43:39,920 It's an example of changing composition to get the 952 00:43:39,920 --> 00:43:43,160 stability of a phase that we want. 953 00:43:43,160 --> 00:43:44,130 This is carbon. 954 00:43:44,130 --> 00:43:46,700 So down here, the normal form, as we've learned earlier, the 955 00:43:46,700 --> 00:43:48,070 normal form is graphite. 956 00:43:48,070 --> 00:43:50,860 Diamond is formed at elevated temperatures and pressures. 957 00:43:50,860 --> 00:43:52,812 And this is liquid carbon. 958 00:43:52,812 --> 00:43:53,630 All right? 959 00:43:53,630 --> 00:43:57,270 Now, to make artificial diamond, you can try putting 960 00:43:57,270 --> 00:43:59,850 graphite in an anvil, and squeezing, and squeezing, and 961 00:43:59,850 --> 00:44:01,610 squeezing, and coming up into here. 962 00:44:01,610 --> 00:44:04,330 And then it becomes metastable, and then maybe, 963 00:44:04,330 --> 00:44:07,470 because the activation energy to jump from that sp3 964 00:44:07,470 --> 00:44:11,010 hybridized state to sp2 is so high, the diamond is stable. 965 00:44:11,010 --> 00:44:13,820 So you don't have to go running home to see if your 966 00:44:13,820 --> 00:44:16,300 diamond studs are now turning into graphite. 967 00:44:16,300 --> 00:44:16,700 They won't. 968 00:44:16,700 --> 00:44:18,700 Once you get into this zone, they'll stay. 969 00:44:18,700 --> 00:44:20,160 The activation energy is too high. 970 00:44:20,160 --> 00:44:23,850 You need more than 1/40 eV to do it, is necessary. 971 00:44:23,850 --> 00:44:26,820 But in the 1950s, General Electric, its Schenectady 972 00:44:26,820 --> 00:44:30,280 research labs, reasoned that because carbon is so soluble 973 00:44:30,280 --> 00:44:34,130 in iron, they could dissolve carbon in liquid iron, and 974 00:44:34,130 --> 00:44:38,880 then raise the pressure and temperature, and then change 975 00:44:38,880 --> 00:44:42,660 to exsolve and cause carbon to precipitate 976 00:44:42,660 --> 00:44:43,560 out of molten iron. 977 00:44:43,560 --> 00:44:45,340 That's the birth of artificial diamond. 978 00:44:45,340 --> 00:44:46,100 That's how they did it. 979 00:44:46,100 --> 00:44:50,268 Using this concept, but then dissolving it in molten iron. 980 00:44:50,268 --> 00:44:52,760 [MUSIC PLAYBACK: 'DIAMONDS ARE A GIRL'S BEST FRIEND'] 981 00:44:52,760 --> 00:44:53,700 PROFESSOR: I don't know how that got in there. 982 00:44:53,700 --> 00:44:55,450 All right. 983 00:44:55,450 --> 00:44:56,680 Here's one for mercury. 984 00:44:56,680 --> 00:44:59,430 I looked it up, using the tools that you've been taught 985 00:44:59,430 --> 00:45:01,300 here in 3.091. 986 00:45:01,300 --> 00:45:04,620 So this is a paper phase diagram for mercury. 987 00:45:04,620 --> 00:45:07,500 And physicists drive me nuts, because they plot temperature 988 00:45:07,500 --> 00:45:08,330 versus pressure. 989 00:45:08,330 --> 00:45:10,300 I want pressure versus temperature. 990 00:45:10,300 --> 00:45:12,060 So I just turned it around. 991 00:45:12,060 --> 00:45:14,070 And so here's the liquid line. 992 00:45:14,070 --> 00:45:17,950 So you know that liquid mercury is going to float on 993 00:45:17,950 --> 00:45:21,120 solid mercury, and there's a plurality of solid phases. 994 00:45:21,120 --> 00:45:24,230 And these are all different crystal structures. 995 00:45:24,230 --> 00:45:25,370 Now I've got a treat for you. 996 00:45:25,370 --> 00:45:28,590 I was in Barcelona several years ago, and I saw the 997 00:45:28,590 --> 00:45:32,920 mercury fountain that was made by Joan Miro in collaboration 998 00:45:32,920 --> 00:45:33,450 with Calder. 999 00:45:33,450 --> 00:45:36,630 Calder has the big sail outside of East Campus. 1000 00:45:36,630 --> 00:45:39,670 So Calder collaborated with Miro, back in 1001 00:45:39,670 --> 00:45:41,690 the '30s and '40s. 1002 00:45:41,690 --> 00:45:45,480 And this is in honor of the miners of Almaden, where there 1003 00:45:45,480 --> 00:45:46,950 are cinnabar mines. 1004 00:45:46,950 --> 00:45:50,960 And the miners fought bravely against the Fascist forces of 1005 00:45:50,960 --> 00:45:53,600 Franco, and Miro wanted to honor them. 1006 00:45:53,600 --> 00:45:55,872 So here's their museum. 1007 00:45:55,872 --> 00:45:58,150 It's a beautiful place up on top of an 1008 00:45:58,150 --> 00:46:00,200 escarpment over Barcelona. 1009 00:46:00,200 --> 00:46:03,710 And what I'm going to show you is a mercury fountain. 1010 00:46:03,710 --> 00:46:05,160 [MUSIC PLAYBACK] 1011 00:46:05,160 --> 00:46:06,410 This is liquid mercury. 1012 00:46:08,940 --> 00:46:10,636 The speed has not been altered. 1013 00:46:10,636 --> 00:46:14,540 This is a liquid at room temperature, density 13.5, 1014 00:46:14,540 --> 00:46:15,980 metallic bonds. 1015 00:46:15,980 --> 00:46:19,205 Look at it. 1016 00:46:19,205 --> 00:46:20,848 Very high surface tension. 1017 00:46:20,848 --> 00:46:22,098 Look at the way it shimmers. 1018 00:46:24,310 --> 00:46:25,170 Look at this shot. 1019 00:46:25,170 --> 00:46:26,360 This has not been altered. 1020 00:46:26,360 --> 00:46:28,130 That's the way it pours into gravity field. 1021 00:46:30,956 --> 00:46:32,210 It's really fantastic. 1022 00:46:32,210 --> 00:46:34,250 And of course, mercury vapor is toxic, so the 1023 00:46:34,250 --> 00:46:35,220 whole thing is in a-- 1024 00:46:35,220 --> 00:46:36,180 [END MUSIC PLAYBACK] 1025 00:46:36,180 --> 00:46:37,850 PROFESSOR: Oh, that's the-- 1026 00:46:37,850 --> 00:46:40,340 I cut that snippet out of the documentary. 1027 00:46:40,340 --> 00:46:41,460 OK, we don't want to see that. 1028 00:46:41,460 --> 00:46:43,960 So they have the whole thing inside of a 1029 00:46:43,960 --> 00:46:48,930 polymethylmethacrylate cage, to keep the mercury vapor from 1030 00:46:48,930 --> 00:46:51,060 affecting the people that work in the museum. 1031 00:46:51,060 --> 00:46:52,630 Here are some phase diagrams from hell. 1032 00:46:52,630 --> 00:46:53,800 This is bismuth. 1033 00:46:53,800 --> 00:46:55,110 And look at bismuth. 1034 00:46:55,110 --> 00:46:57,830 Bismuth is like water, and like silicon. 1035 00:46:57,830 --> 00:47:00,590 So the solid is less dense than the liquid. 1036 00:47:00,590 --> 00:47:04,170 But look at all of these different phases. 1037 00:47:04,170 --> 00:47:04,800 Here's sulfur. 1038 00:47:04,800 --> 00:47:05,570 Sulfur is crazy. 1039 00:47:05,570 --> 00:47:08,680 Look, phases in the solid phase, there's even phases in 1040 00:47:08,680 --> 00:47:10,330 the liquid! 1041 00:47:10,330 --> 00:47:12,130 Different phases. 1042 00:47:12,130 --> 00:47:12,990 They're allotropes. 1043 00:47:12,990 --> 00:47:13,810 Here's sulfur. 1044 00:47:13,810 --> 00:47:16,865 Elemental sulfur, the disulfide, hexasulfide. 1045 00:47:16,865 --> 00:47:19,890 It makes rings, it makes long chains. 1046 00:47:19,890 --> 00:47:21,320 And these are called allotropes. 1047 00:47:21,320 --> 00:47:23,950 They're different forms of the same element. 1048 00:47:23,950 --> 00:47:29,520 So oxygen is O. There's the diatomic molecule. 1049 00:47:29,520 --> 00:47:32,290 And the triatomic molecule, which is ozone, these are all 1050 00:47:32,290 --> 00:47:33,540 allotropes of oxygen. 1051 00:47:35,790 --> 00:47:36,720 What else do we have? 1052 00:47:36,720 --> 00:47:37,030 OK. 1053 00:47:37,030 --> 00:47:37,880 This is polymorphs. 1054 00:47:37,880 --> 00:47:40,090 So this is alpha goes to beta. 1055 00:47:40,090 --> 00:47:41,310 See, different crystal structures. 1056 00:47:41,310 --> 00:47:43,720 You could see with your naked eye what's going on here. 1057 00:47:43,720 --> 00:47:45,720 Different crystal structures. 1058 00:47:45,720 --> 00:47:47,820 And then this goes to lambda, and then finally, they're 1059 00:47:47,820 --> 00:47:48,850 pouring here. 1060 00:47:48,850 --> 00:47:50,710 And if you get a very high cooling rate, and you've got 1061 00:47:50,710 --> 00:47:52,670 those long chains, what happens? 1062 00:47:52,670 --> 00:47:53,880 You don't form the crystal. 1063 00:47:53,880 --> 00:47:55,280 You form the amorphous form. 1064 00:47:55,280 --> 00:47:58,110 So they'll call this forming plastic sulfur. 1065 00:47:58,110 --> 00:47:58,810 We know better. 1066 00:47:58,810 --> 00:48:00,300 It's amorphous sulfur. 1067 00:48:00,300 --> 00:48:01,550 It's not plastic sulfur. 1068 00:48:03,580 --> 00:48:05,350 Here's water, a complete diagram. 1069 00:48:05,350 --> 00:48:07,400 Now, this is in kilobars. 1070 00:48:07,400 --> 00:48:09,260 So there's all the different phases of water. 1071 00:48:09,260 --> 00:48:10,450 There's the negative line. 1072 00:48:10,450 --> 00:48:12,450 That's the thing here. 1073 00:48:12,450 --> 00:48:13,850 But at very, very high. 1074 00:48:13,850 --> 00:48:15,350 Look at all the different phases of water. 1075 00:48:15,350 --> 00:48:16,370 And they have numbers on them. 1076 00:48:16,370 --> 00:48:17,940 If you read Kurt Vonnegut's Cat's 1077 00:48:17,940 --> 00:48:19,650 Cradle, there's ice nine. 1078 00:48:19,650 --> 00:48:23,720 You get that going, it freezes the whole world, right? 1079 00:48:23,720 --> 00:48:25,560 But here's, I draw your attention on this one. 1080 00:48:25,560 --> 00:48:26,850 You see this point here? 1081 00:48:26,850 --> 00:48:29,110 This is ice seven. 1082 00:48:29,110 --> 00:48:31,840 At 100 degrees C, it's solid. 1083 00:48:31,840 --> 00:48:32,945 You need 25 kilobars. 1084 00:48:32,945 --> 00:48:37,000 So we could go over to the lab, take some water, put 25 1085 00:48:37,000 --> 00:48:41,600 kilobars on it, make solid ice at 100 degrees C. 1086 00:48:41,600 --> 00:48:43,020 And it'll be stable. 1087 00:48:43,020 --> 00:48:43,220 Look! 1088 00:48:43,220 --> 00:48:44,500 This is minus 78. 1089 00:48:44,500 --> 00:48:45,730 It's been here for a long time. 1090 00:48:45,730 --> 00:48:49,060 So now I come into a cocktail party with this, I drop this 1091 00:48:49,060 --> 00:48:54,150 ice cube into a glass of aqueous beverage, it sinks to 1092 00:48:54,150 --> 00:48:59,460 the bottom, and the beverage heats up to the boiling point. 1093 00:48:59,460 --> 00:49:02,350 That's what this is telling you! 1094 00:49:02,350 --> 00:49:06,200 That'll get you popularity instantly. 1095 00:49:06,200 --> 00:49:07,660 How did you do that? 1096 00:49:07,660 --> 00:49:09,850 How did you do that? 1097 00:49:09,850 --> 00:49:12,070 And up here is the supercritical fluid, the last 1098 00:49:12,070 --> 00:49:13,600 thing we haven't said anything about. 1099 00:49:13,600 --> 00:49:14,040 Look. 1100 00:49:14,040 --> 00:49:16,410 If you take a gas, and you keep squeezing it and 1101 00:49:16,410 --> 00:49:20,080 squeezing it, eventually the gas molecules are close enough 1102 00:49:20,080 --> 00:49:22,470 together that they're indistinguishable from the 1103 00:49:22,470 --> 00:49:23,590 liquid phase. 1104 00:49:23,590 --> 00:49:26,700 Or if you start here, with the liquid, and you keep raising 1105 00:49:26,700 --> 00:49:31,540 the temperature, the density goes lower and lower until the 1106 00:49:31,540 --> 00:49:36,090 molecules are far enough apart that you can't tell this zone, 1107 00:49:36,090 --> 00:49:41,270 whether it's a rarefied liquid or a highly compressed gas. 1108 00:49:41,270 --> 00:49:42,860 The properties criss-cross. 1109 00:49:42,860 --> 00:49:43,940 This is supercritical. 1110 00:49:43,940 --> 00:49:49,840 It has liquid-like transport properties, and vapor-like 1111 00:49:49,840 --> 00:49:50,780 chemical properties. 1112 00:49:50,780 --> 00:49:54,150 So you can end up doing things that are very, very different. 1113 00:49:54,150 --> 00:49:56,300 Now, I'm going to give you an example of decaffeinating 1114 00:49:56,300 --> 00:49:59,020 coffee by taking the coffee, going up into the 1115 00:49:59,020 --> 00:50:01,900 supercritical regime, which allows you to extract the 1116 00:50:01,900 --> 00:50:04,340 caffeine, and not brew the coffee. 1117 00:50:04,340 --> 00:50:07,070 So you want to just get the-- well, if you just heat it up, 1118 00:50:07,070 --> 00:50:09,920 you'll make the coffee. 1119 00:50:09,920 --> 00:50:10,930 So here's an example. 1120 00:50:10,930 --> 00:50:12,360 It's called solvent extraction. 1121 00:50:12,360 --> 00:50:14,910 Historically, this solvent was methylene chloride, which is 1122 00:50:14,910 --> 00:50:16,900 also used as paint stripper. 1123 00:50:16,900 --> 00:50:19,810 We don't do that anymore to coffee. 1124 00:50:19,810 --> 00:50:21,580 They did in the '60s! 1125 00:50:21,580 --> 00:50:22,020 They did. 1126 00:50:22,020 --> 00:50:24,290 They also used trichloroethylene. 1127 00:50:24,290 --> 00:50:26,750 It works really well to leech out the caffeine. 1128 00:50:26,750 --> 00:50:29,780 How much is left in there for you to taste in your coffee? 1129 00:50:29,780 --> 00:50:30,210 I don't know. 1130 00:50:30,210 --> 00:50:34,320 Maybe that's why people were so excited in the '60s to 1131 00:50:34,320 --> 00:50:36,160 drink their decaffeinated Sanka. 1132 00:50:36,160 --> 00:50:36,610 I don't know. 1133 00:50:36,610 --> 00:50:41,240 But anyway, so you take the green beans in carbon dioxide 1134 00:50:41,240 --> 00:50:45,250 as supercritical, and drop the caffeine level, and then you 1135 00:50:45,250 --> 00:50:49,110 play with temperature and pressure to go over the KSP. 1136 00:50:49,110 --> 00:50:54,810 The caffeine salts out, and then you recycle the CO2. 1137 00:50:54,810 --> 00:50:55,130 OK. 1138 00:50:55,130 --> 00:50:56,190 I hope I've given you some 1139 00:50:56,190 --> 00:50:58,700 introduction to phase diagrams. 1140 00:50:58,700 --> 00:51:00,320 And we'll see you on Monday.