As we quickly learn with water, matter can be in distinct phases: solid, liquid, gas and plasma; it all depends on temperature. But why do different materials require different temperatures? And what’s actually happening to the atoms themselves as the material switches phases?
Fraser: Astronomy Cast episode 288 for January 27th, 2013, Phases of Matter. Welcome to Astronomy Cast our weekly fact based journey through the cosmos. We hope you understand not only what we know, but how we know what we know. My name is Fraser Cane, I’m the publisher of Universe Today, and with me is Dr. Pamela Gay a professor at Southern Illinois University Edwardsville. Hey Pamela how are you doing?
Pamela: I’m doing well, how are you doing Fraser?
Fraser: Doing great. I know you’re very cold…
Pamela: I am.
Fraser: …so hopefully during the show you don’t slip into some kind of hypodermic state and pass out in the middle of it. Now have you got any interesting things going on in Cosmo Quest that you might want to mention?
Pamela: We are beta testing mercury mappers, we are going live with a whole series of cool hang-outs that are related to Astronomy Cast and I think pretty much all of us, and this includes you, are going to be at science Io this year so be sure to come by, say hi, and we might even have shwag in our pocket to hand to you.
Fraser: I’m going to be doing a talk on the virtual star parties at Science Io for 15 minutes and I’m going to try and get some astronomy happening live while we’re doing it. Should be great. Now one quick thing, if you’re listening to the show and you really love it, if you could go to iTunes and write a review for us that would be super fantastic. The more reviews will help pop us up to the top of the rankings and the listings. Then when people are looking for a show to listen to, they will see ours and give it a shot and that really helps us out. So if have a few seconds and you have never reviewed Astronomy Cast that would help us a TON. That’s over on iTunes so just look for Astronomy Cast on iTunes and there is a way to review. If you’re not a member if iTunes, you don’t like Apple, don’t worry about it, we’re not going to hold your feet to the fire.
Fraser: So as we learn early on with water, matter can be in distinct phases: solid, liquid, gas, and plasma. It all depends on temperature and pressure. Why do different materials require different temperatures and what is actually happening to the atoms themselves when as the material switches fazes. I think I can remember chemistry class, physics class back in high school when we would delve into the phases of matter. The teacher said “…and then there is plasma” I remember solid, liquid, and gas but plasma? Can we kinda take it back then and talk about early scientist beginning to delve into the phases of matter.
Pamela: Well I think it’s one of those things that is pretty much as far back as people were willing to conduct science we have had a basic idea of elemental forces, elementals in general, earth, fire, water, and air. Part of trying to break down this universe we live in is trying to understand how things transition between solid, liquid and gas. The only things we had a firm understanding of for a long time were things like metals, which you have to make fairly liquid to make all the cool things you need to wage war like swords. And clearly things like water where you went from ice, to drinkable, to steam, but trying to understand this there is this basic motion that: Heat something up, make fire, fire changes the state and then when things cool off the state changes in the other direction.
Fraser: I guess they knew pretty early on that water in the solid form and water in the liquid form and water in the gas form were all the same thing, that they were all water. They got pretty comfortable with that idea that you could move these elements back and forth. They did have some pretty goofy ideas about the different elements: earth, air, fire, water, alchemical. How did all that play into it?
Pamela: In general in trying to figure out the basics really took until we started getting to the modern scientific revelation; up until we started realizing that atoms exist. It was hard to comprehend what gas is when we couldn’t separate out the different constituencies of the gas. The phases of matter, well the big picture idea: solid, liquid, gas, is an old concept. The scientific idea of it is only a few hundred years old.
Fraser: Ok, so, what is actually going on here. We’ve got our water, it’s turning into gas or its turning into ice, or plasma, what’s actually going on?
Pamela: (Laughs) So what we’re doing is we’re changing how that actually atoms or molecules of a different compound are connected to one another. When you are dealing with a gas the atoms are completely not connected to one another so they are flying free and they’re going on collisions where they bounce off of one another. They have no bonds keeping them as part of a whole. When you start to deal with liquids you’ve cooled things down enough so that their velocities, when they come together, they kind of stick and then it’s as if you have multiples together and these two might go to become connected and these two become connected so you have more like a square dance of atoms and molecules where they slowly change off how they’re generally ionically bound to one another. As you cool things down even further then you start to build solid bonds where these two, and these two, and these two and all of the different combinations lock together in various ways. Depending exactly on the atomic structure, what you’re dealing with, in some cases, you can get beautiful crystal formations, in other cases you just end up with a haphazard way of mixing the different atoms and molecules into a solid. So these are the three basic phases of matter but then you can end up with some specialties so as you transform into a plasma, plasma is still a special form of gas. In the case of plasma, the electrons are excited and as they bounce between different energy levels and they actually leave their host atoms and molecules they give off light. When you’re looking at a fluorescent light bulb, that’s a plasma. When you are looking at a star, that’s a plasma too. When you go the other direction to Bose-Einstein condensate, which is where you cool special types of gas down to a millionth of a degree or so, at that point they take on very special atomic properties again and in this case you end up with a really funky clump of material where all of the atoms achieve the lowest energy states they can while not having overlapping energy states.
Fraser: So is the Bose-Einstein condensate a special form of matter? Does it work as one of the phases of matter?
Pamela: It’s depending on who you talk to. They’re either going to call it a special state of matter or a special phase of matter. It’s definitely not a solid. This is something where they typically make Bose-Einstein condensates out of rubidium atoms and when they super cool these Rubidium atoms they end up clumping up into a very strangely moving blob. It’s this weird “other” and it’s not determined by the bonding like you do between solid, liquid, and gas. Rather it’s defined by the energy levels of the specific atoms and how they all strive to get to the lowest possible energy level that they can.
Fraser: I think it’s absolutely fascinating how they do this. Don’t they shoot a laser at the Rubidium atoms to extract energy from them until they move into this stage?
Pamela: It’s a two step process to create a Bose-Einstein condensate. First step is you have a set of magnetically bound together rubidium atoms but they are all moving in a swarm. That movement has its own energy so as long as those suckers are moving you can’t achieve a millionth of a degree. So they tune lasers to slowly but surely confine the velocities of these atoms to a smaller and smaller and smaller velocity and they actually have to do things like take into account what is the specific doplar shifted energy level of the electrons inside of the rubidium. Because they have color matched the color of the laser to the color of the transition of the electrons in the rubidium, at a specific, the rubidium is moving velocity. They are able to change the velocity much in the same way you would imagine someone is roller skating towards you and you throw a basketball at them and when they catch the basketball is slows down their velocity. It’s kind of a crazy process but it works. As they slowly tune the color of the laser, they’re able to get the rubidium atoms moving at lower and lower velocities. That’s step one. Step two they actually use evaporative cooling, so just like you cool off by evaporating water off of your surface; sweating is a more normal way of saying that, they are able to cool down the Rubidium by stripping away the faster moving rubidium off of the surface.
Fraser: Now does anything change with the property of the matter apart from the way the molecules are bouncing around; whether they are locked like soldiers in the Bose-Einstein condensate, or if they are in a solid or a liquid or a gas. Does anything change about the matter’s nature?
Pamela: Well the first thing that was noticed when they were creating the first Bose Einstein Condensates, almost; they didn’t quite get it cold enough, but when they were first trying to create Bose-Einstein condensates out of helium 4, they noticed it created what is called a super fluid. This is a fluid that experiences no frictional forces as it flows and so this weird, absolute lack of friction, is one of the cooler properties as you approach getting to a Bose-Einstein condensate. Then you also end up with basically everything, when you look at the distribution of it, it will spread itself out in funky ways, you’ll end up with material trying to climb the sides of containers. It just behaves in odd ways. One of the problems that we have is that it takes a whole lot of effort and energy to create one of these Bose-Einstein condensates. That sounds kind of strange that it takes a ton of energy to cool it off so it has no energy but that’s the reality of what we’re doing. We can only create basically a miniscule amounts of this so we don’t fully understand all the properties yet because we’re just not creating it in large amounts yet.
Fraser: As you move from, say from solid to liquid or liquid to gas or even gas to plasma does the matter itself take on different properties chemically or is it just the same stuff but a different phase?
Pamela: (Laughs) Well the atoms are certainly staying the same but what’s changing is the kinematic motions and the kinematic motions of a certain degree decide how well atoms are or are not bond to one another. Depending on the situation when you have a solid, you have all of these atoms that are very close to one another, and in some cases, are what is called ionically bound to one another. Ionic bonds are when two atoms are sharing electrons back and forth but it’s not that hardcore bond that you get from things like H2O which is a covalent bond. If you have atoms that, when you put them together their electrons essentially complete one complete shell of electrons. It’s like two puzzle pieces where one has the sticky-outty bits that matches the other one’s inny bits. Atoms do that as well and it’s through those types of ionic sharing electron bonds that you’re able to get metallic solid for instance.
Fraser: Now is that one of those one of those situations like with water. I know with water when it freezes is actually becomes less dense right? and floats on top of the water?
Pamela: Water is a bizarre substance. It’s one of the very few things that does become less dense as it becomes a solid. What’s happening here is a liquid, as atoms flow past one another, very temporarily, sharing one another’s electrons but in a very loose way where the kinetic energies that are causing the molecules to flow, those kinetic energies are greater than the binding energies that are trying to hold the atoms together. As they cool, as the motion slows down, the atoms form crystalline structures and it’s the nature of the crystalline structure that causes the atoms to get pushed apart into very specific configurations that cause the solid to end up having a much lower density than liquid does.
Fraser: Now obviously we’ve all experienced this. You leave an ice cube out on your table and it’s going to melt. This is a phase change. What is going on with these phase changes? What needs to be there for you to be able to get these changes?
Pamela: Well in order to go from one phase to another you have to add energy to the system that gets the atoms moving, gets the molecules moving, depending on what it is. When you take, for instance, lead. Say you have lead… I hope it’s not a food implement, lead is poisonious. Lets go with iron. Iron won’t kill you as readily. Lets say you have a nice iron old fashioned dagger of some sort. I don’t know why but you do. It’s a nice friendly solid.
Frasier: Dagger? Really? …anyway I won’t question your analogies, please continue
Pamela: (Laughs) So if you take something that will release energy when burned like wood, it releases that energy in the form, quite often, of infrared and other forms of light. So you stick the dagger on top of the fire and it’s probably more than just wood, and as the temperature increases, as more and more radiation, radiated light, is concentrated on that dagger the atoms will start trying to move, trying to move, trying to move, and eventually the heat energy that has been injected into those vibrating atoms are going to exceed the binding energies and it’s going to begin to melt. Now eventually were you to use something a whole lot hotter than wood; a whole lot more releasing of energy, you could actually convert that into a gas in which case you are completely breaking down all the abilities of the atoms to bond onto one another and their kinetic energy is so great they simply bounce off one another when they come near instead of bonding to one another.
Fraser: And if you go the other way? Right? If you’re extracting energy from the system, heat from the system?
Pamela: Well extracting energy is a difficult process involving laser beams.
Fraser: …well if things are cooling down?
Pamela: If something is able to radiate its heat off into the surrounding using its own infrared radiation. So you take your red hot dagger and you set it aside and that red hot is IR radiation and optical radiation escaping. As it cools down it’s losing energy to its environment so losing energy to the molecules with gas around it, losing energy in all sorts of ways thermal transferred to the surface beneath it and as it cools down the kinetic energy of the molecules are slowing down and eventually have all of the atoms pretty much locked together into this solid form.
Fraser: Now you can get situations where matter can jump forms right? You can get things that can go from solid exactly to gas like frozen carbon dioxide.
Pamela: It’s sublimate, yes. There is (SOMETHING) called phase diagrams and at different points there is, for instance, a triple point of water where at just the right temperature, pressure, density combination you can have water going from solid to liquid to gas with just the slightest changes and so this is that magic triple point where water can exist in all three phases depending on which direction you approach it from. Depending on the density pressure you get lots of different things that can go from this solid to gas phase. On the moon you can have water-ice that can sublimate into water-gas. On the surface of Mars you can have carbon dioxide or water and both will go straight from liquid to gas and this is simply a matter of, at these pressures, there is nothing holding the atoms together so as they go from being bound together in a solid they simply bypass that stage where they are slightly bound together as a liquid and goes straight into a gaseous form.
Fraser: And so pressure is kind of the magic ingredient with this. I know when you buy a hiking stove and you go up to a high altitude and boil water it takes you less time?
Pamela: A lot longer.
Fraser: It takes you longer, that’s right, since the pressure is lower
Fraser: So you can have situations as well where you have conditions of very high pressure that change everything as well. You can think about passing down through Jupiter where they have tons of different types of water-ice.
Pamela: Well what’s interesting is you can actually boil things simply by changing the pressure under which it is. So you can end up boiling water by lowering the pressure that it’s under. You can turn nitrogen into a gas, and nitrogen into liquid just by changing the pressure that it’s under. When you’re trying to figure out what phase of matter you’re looking at, you have to consider the pressure, the density of the atoms, the temperature and it’s from all three of these things that we are able to figure out what phase we should mathematically have at the end of the day.
Fraser: So what are some extreme environments that we can find unusual situations. You’ve mentioned one already which is that if you have ice on the moon it going to be sublimating straight from ice into gas. Another is in Jupiter you can encounter different kinds of ice which are produced at different pressures right?
Pamela: There to be specific you’re dealing with different types of gaseous ice and while water does have different crystalline structures depending on how quickly or how slowly you cool it down, I think the best way to consider this is look at Titan. It’s a methane environment that’s very similar to earth. Here on Earth our environment allows water to be liquid, solid or gas depending on very minor differences in your kitchen. If you go to Titan you have the exact same boundary conditions for methane. You have methane rain coming from the sky, methane ice on the surface, methane gas in the atmosphere and so I’ve dealt with thinking about this for so long that it’s not weird or extreme, it’s just the way Titan is.
Fraser: It’s plenty weird just so you know.
Pamela: (Laughs) I think the most interesting application of this, in some regards, is if you very, very slowly cooled down water-ice you can end up with perfectly clear ice that looks more like glass than your normal “has all types of white flaws in it” ice cube. One interesting application of this is if you make a perfectly spherical ice cube, it will melt slower and you can use it in whiskey to have whiskey that is at the correct temperature and isn’t too watered down. It’s always good to know how to use chemistry to make the perfect glass of whiskey.
Fraser: (Laughs) Right of course. I’ll use that in scotch. What about really extreme places like say the surface of neutron stars and inside white dwarves and things like that? Is it still just solid or have you reached some other phase of matter? We call it degenerate matter right?
Pamela: Electron degenerate gas and this is again one of those things where it’s hard to think of it as another phase of matter but it’s definitely a different behavior at the atomic level. This doesn’t have as much to do with the kinetic properties of matter the way solid, liquid, gas, has to do with the kinetic properties but rather this has to do with how the electrons and the Pauli-exclusion principle come into play. With Bose-Einstein condensates you have to worry about what are the energy levels of the atoms. The atoms each actually only have specific allowed energies but with the electron degenerate gas and white dwarf what you’re worrying about is, what are the energy levels of all of the electrons because the atoms are so tightly packed together that the electrons basically form a crystalline structure where they are trying to avoid having two atoms with the exact same, spin up, spin down characteristics and the same energy level; Pauli-exclusion principle will not allow that. You end up with the latest work of electrons that the atomic nuclei are suspended within.
Fraser: So it’s still a phase of matter then? It’s a gas?
Pamela: It’s a crystal. So it’s a solid. Electron degenerate stars are for the most part solids and we think that there carbon atoms form diamonds actually but it’s the electrons that have this quantum mechanical defined nature that says “the electrons can only get this close and no closer” and so thinking of the different phases of matter isn’t entirely how a chemist would want you to think of it I don’t think. It is a different behavior of the atom at a quantum level.
Fraser: So the last thing that I would like to talk about is plaaaasma. The sun is, what is it, a miasma of incandescent plasma? No? It’s a “They Might be Giants” song?
Fraser: What’s going on here. How do you turn a gas into a plasma and what is the nature of plasma?
Pamela: So, plasma is a special type of gas. If you’re trying to do the mathmatics of how do the atoms move, how do they collide off of one another, that’s still all related to standard gas laws. What makes a plasma different are the electrons inside a plasma are excited to higher levels and excited things, excited electrons, don’t stay excited permanently and as they cascade back down to the lower energy levels they give off light. Day to day the gas around us is not emitting light. This is good because if the air in this room were emitting light I couldn’t see my screen in front of me so plasmas tend to be okay at a certain level because they are so busy giving off light that light can get through them. This light that is bouncing around inside the plasma actually helps feed the system because a photon emitted in the transition of one atom can go out, hit another atom, cause it to get excited, and you end up with this feeding system but due to the random nature of the directions that the light is coming off, you do end up with light eventually being emitted. Lasers are actually a special case of this where you end up with coherent stimulated emission. We’ve done an entire show on this that you can go back to listen to. With the plasma you simply have over excited electrons that are getting excited through the various collisions and through energy being driven into this system in your fluorescent bulb, it’s the electricity from the wall. In the sun it’s the nuclear reactions going on in the center. Whatever the source of energy that is exciting all of the atoms, their electons are the ones that are expressing that excitement by getting excited and then collapsing and giving out light in the process of the collapse.
Fraser: But you get some interesting properties with plasma. One, it glows with the neon sign, which is nice that it’s not filling the air, but also, we get situations where plasma coming from the sun interacts with the earths magnetic field, and
Pamela: They’re charged particles at that stage
Fraser: Yeah, yeah, and now you have this situation where you can move it around with a magnet.
Pamela: I think moving it around with a magnet is a very strange way to think of it because now I have this idea that “yes you can move a magnet around on various types of plasma and actually see the things moving” but magnetic fields is actually what that magnet is creating. Moving charged particles generate a magnetic field and magnetic fields move charged particles. It’s this neat dynamic interplay. Plasma when it’s in motion generates magnetic fields and standing magnetic fields can move the plasma and that’s just kind of cool.
Fraser: That is really cool. So do you think there will be any more phases of matter every discovered or has it sort of been fully explained?
Pamela: I think in terms of the kinetic states of energy I think we’re good. In terms of weird quantum mechanical states, we still don’t know what the heck to make of the inside of a black hole. I think just like Bose-Einstein condensates are weird quantum mechanically defined structures just like electron degenerate gasses are weird, quantum mechanic defined way of mass being. I think inside of black holes we have yet to figure out what the heck that is and there’s the potential to either be raw bits, particle physics at play, or maybe even some new structure we can’t even imagine.
Fraser: Let’s just assume its another form of matter which can’t….
Pamela: Yeah, yeah I don’t do that (Laughs)
Fraser: Okay, well thank you very much Pamela that was great.
Pamela: My pleasure