So What is Materials Science (and Engineering)?

So this is my 100th post, and I felt like it should be kind of special. So I want to cover a question I get a lot, and one that’s important to me; what exactly is materials science? My early answer was that “it’s like if physics and chemistry had a really practical baby.” One of my favorite versions is a quote from this article on John Goodenough, one of the key figures in making rechargeable lithium ion batteries: “In hosting such researchers, Goodenough was part of the peculiar world of materials scientists, who at their best combine the intuition of physics with the meticulousness of chemistry and pragmatism of engineering”. Which is a much more elegant (and somewhat ego-boositng) way of wording my description. In one of my first classes in graduate school, my professor described materials science as “the study of defects and how to control them to obtain desirable properties”.

A more complete definition is some version of the one that shows up in most introductory lessons: materials science studies the relationship between the structure of a material, its properties, its performance, and the way it was treated. This is often represented as the “materials science tetrahedron”, shown below. Which turns out to be something people really love to use. (You also sometimes see characterization float in the middle, because it applies to all these aspects.)

A tetrahedron with blue points at the vertices. The top is labelled structe, the bottom three are properties, processing, and performance.

The materials science tetrahedron (with characterization floating in the middle).

Those terms may sound meaningless to you, so let’s break them down. In materials science, structure goes beyond that of chemistry: it’s not just what makeup of an atom or molecule that affects a material, but how the atoms/molecules are arranged together in a material has a huge effect on how it behaves. You’re probably familiar with one common example: carbon and its various allotropes. The hardness of diamond is partially attributed to its special crystal structure. Graphite is soft because it is easy to slide the different layers across each other. Another factor is the crystallinity of a material. Not all materials you see are monolithic pieces. Many are made of smaller crystals we call “grains”. The size and arrangement of these grains can be very important. For instance, the silicon in electronics is made in such a way to guarantee it will always be one single crystal because boundaries between grains would ruin its electronic properties. Turbine blades in jet engines and for wind turbines are single crystals, while steels used in structures are polycrystalline.

On the top is a diamond and a piece of graphite. On the bottom are their crystal structures.

Diamond and its crystal structure is on the left; graphite on the right.

Processing is what we do to a material before it ends up being used. This is more than just isolating the compounds you’ll use to make it. In fact, for some materials, processing actually involves adding impurities. Pure silicon wouldn’t be very effective in computers. Instead, silicon is “doped” with phosphorus or boron atoms and the different doping makes it possible to build various electronic components on the same piece. Processing can also determine the structure – temperature and composition can be manipulated to help control the size of grains in a material.

A ring is split into 10 different sections. Going counterclockwise from the top, each segment shows smaller crystals.

The same steel, with different size grains.

Properties and performance are closely related, and the distinction can be subtle (and honestly, it isn’t something we distinguish that much). One idea is that properties describe the essential behavior of a material, while performance reflects how that translates into its use, or the “properties under constraints“. This splits “materials science and engineering” into materials science for focusing on properties and materials engineering for focusing on performance. But that distinction can get blurred pretty quickly, especially if you look at different subfields. Someone who studies mechanical properties might say that corrosion is a performance issue since it limits how long a material could be used at its desired strength. Talk to my colleagues next door in the Center for Electrochemical Science and Engineering and they would almost all certainly consider corrosion to be a property of materials. Regardless, both of these depend on structure and processing. Blades in wind turbines and jet engines are single crystals because this reduces fatigue over time. Structural steels are polycrystals because this makes them stronger.

Now that I’ve thought about it more, I realize the different parts of the tetrahedron explain the different ways we define materials science and engineering. My “materials science as applied physics and chemistry” view reflects the scale of structures we talk about, from atoms that are typically chemistry’s domain to the crystal arrangement to the larger crystal as a whole, where I can talk about mechanics of atoms and grains. The description of Goodenough separates materials science from physics and chemistry through the performance-driven lens of pragmatism. My professor’s focus on defects comes from the processing part of the tetrahedron.

The tetrahedron also helps define the relationship of materials science and engineering to other fields. First, it helps limit what we call a “material”. Our notions of structure and processing are very different from the chemical engineers, and work best on solids. It also helps define limits to the field. Our structures aren’t primarily governed by quantum effects and we generally want defects, so we’re not redundant to solid-state physics. And when we talk about mechanics, we care a lot about the microstructure of the material, and rarely venture into the large continuum of mechanical and civil engineers.

At the same time, the tetrahedron also explains how interdisciplinary materials science is and can be. That makes sense because the tetrahedron developed to help unify materials science. A hundred years ago, “materials science” wouldn’t have meant anything to anyone. People studying metallurgy and ceramics were in their own mostly separate disciplines. The term semiconductor was only coined in a PhD dissertation in 1910, and polymers were still believed to be aggregates of molecules attracted to each other instead of the long chains we know them to be today. The development of crystallography and thermodynamics helped us tie all these together by helping us define structures, where they come from, and how we change them. (Polymers are still a bit weird in many materials science departments, but that’s a post for another day)

Each vertex is also a key branching off point to work with other disciplines. Our idea of structure isn’t redundant to chemistry and physics, but they build off each other. Atomic orbitals help explain why atoms end up in certain crystal structures. Defects end up being important in catalysts. Or we can look at structures that already exist in nature as an inspiration for own designs. One of my professors explained how he once did a project studying turtle shells from an atomic to macroscopic level, justifying it as a way to design stronger materials. Material properties put us in touch with anyone who wants to use our materials to go into their end products, from people designing jet engines to surgeons who want prosthetic implants, and have us talk to physicists and chemists to see how different properties emerge from structures.

This is what attracted me to materials science for graduate school. We can frame our thinking on each vertex , but it’s also expected that we shift. We can think about structures on a multitude of scales. Now I joke that being a bad physics major translates into being great at most of the physics I need to use now. The paradigm helps us approach all materials, not just the ones we personally study. Thinking with different applications in mind forces me to learn new things all the time. (When biomedical engineers sometimes try to claim they’re the “first” interdisciplinary field of engineering to come on the scene, I laugh thinking that they forget materials science has been around for decades. Heck, now I have 20 articles I want to read about the structure of pearl to help with my new research project.) It’s an incredibly exciting field to be in.

The Coolest Part of that Potentially New State of Matter

So we’ve discussed states of matter. And the reason they’re in the news. But the idea that this is a new state of matter isn’t particularly ground-breaking. If we’re counting electron states alone as new states of matter, then those are practically a dime a dozen. Solid-state physicists spend a lot of time creating materials with weird electron behaviors: under this defintion, lots of the newer superconductors are their own states of matter, as are topological insulators.

What is a big deal is the way this behaves as a superconductor. “Typical” superconductors include basically any metal. When you cool them to a few degrees above absolute zero, they lose all electrical resistance and become superconductive. These are described by BCS theory, a key part of which says that at low temperatures, the few remaining atomic vibrations of a metal will actually cause electrons to pair up and all drop to a low energy. In the 1970s, though, people discovered that some metal oxides could also become superconductive, and they did at temperatures above 30 K. Some go as high as 130 K, which, while still cold to us (room temperature is about 300 K), is warm enough to use liquid nitrogen instead of incredibly expensivve liquid helium for cooling. However, BCS theory doesn’t describe superconductivity in these materials, which also means we don’t really have a guide to develop ones with properties we want. The dream of a lot of superconductor researchers is that we could one day make a material that is superconducting at room temperature, and use that to make things like power transmission lines that don’t lose any energy.

This paper focused on an interesting material: a crystal of buckyballs (molcules of 60 carbon atoms arranged like a soccer ball) modified to have some rubidium and cesium atoms. Depending on the concentration of rubidium versus cesium in the crystal, it can behave like a regular metal or the new state of matter they call a “Jahn-Teller metal” because it is conductive but also has a distortion of the soccer ball shape from something called the Jahn-Teller effect. What’s particularly interesting is that these also correspond to different superconductive behaviors. At a concentration where the crystal is a regular metal at room temperatures, it becomes a typical superconductor at low temperatures. If the crystal is a Jahn-Teller metal, it behaves a lot like a high-temperature superconductor, albeit at low temperatures.

This is the first time scientists have ever seen a single material that can behave like both kinds of superconductor. This is exciting becasue this offers a unique testing ground to figure out what drives unconventional superconductors. By changing the composition, researchers change the behavior of electrons in the material, and can study their behavior, and see what makes them go through the phase transition to a superconductor.

Making Fuel Out of Seawater Is Only One Part of An Energy Solution

So I recently saw this post about a recent breakthrough the Navy made in producing fuel from water make a small round on Facebook from questionable “alternative news” site Addicting Info and it kind of set off my BS detector. First, because this story is a few months old. It actually turned out the article was from April, so part of my skepticism was unfounded. But the opening claim that this wasn’t being reported much in mainstream outlets is wrong, as several sites beat them to the punch (even FOX NEWS! Which would probably make Addicting Info’s head explode.). The other thing that struck me as odd was how the Addicting Info piece seemed to think this technology is practically ready to use right now.  That surprised me, because for nearly the last two years, my graduate research at UVA has been focused on developing materials that could help produce fuel from CO2.

This Vice article does a pretty good job of debunking the overzealous claims made by the Addicting Info piece and others like it. As Vice points out, you need electricity to make hydrogen from water. Water is pretty chemically stable in most of our everyday lives. The only way the average person ends up splitting water is if they have metal rusting, which would be a really slow way to generate hydrogen, or by putting a larger battery in water for one of those home electrolysis experiments.

The Naval Research Lab seems kind of unique among the groups looking at making fuel from CO2 in that they’re extracting hydrogen and CO2 from water as separate processes from the step where they are combined into hydrocarbons. Most of the other research in this area looks at having metal electrodes help this reaction in water (nearly any metal from the middle of the periodic table can split CO2 with enough of a negative charge) . Because of water’s previously mentioned stability, they often add a chemical that can more easily give up hydrogen. A lot of groups use potassium bicarbonate, a close relative of baking soda that has potassium instead of sodium, to help improve the conductivity of the water and because the bicarbonate ion really easily gives up hydrogen. In these set-ups, the goal is for the electricity to help the metal break off an oxygen from a CO2 to make CO, and when you get enough CO, start adding hydrogen to the molecules and linking them together.

A chemical diagram shows a CO2 molecule losing a carbon atom on a copper surface to make CO. When another CO is nearby, the two carbon atoms link together.

Carbon atoms are initially removed from CO2 molecules on a copper surface, forming CO. When CO get close to each other, they can bond together. From Gattrell, Gupta, and Co.

But basically, no matter what reaction you do, if you want to make a hydrocarbon from CO2, you need to use electricity, either to isolate hydrogen or cause the CO2 to become chemically active. As the Vice article points out, this is still perfectly useful for the Navy, because ships with nuclear reactors continually generate large amounts of electricity, but fuel for aircraft must be replenished. If you’re on land, unless you’re part of the 30% of the US that gets electricity from renewable sources or nuclear plants, you’re kind of defeating the point. Chemical reactions and industrial processes always waste some energy, so burning a fossil fuel, which emits CO2, to make electricity that would then be used to turn CO2 back into fuel would always end up with you emitting more CO2 than you started with.

However, this process (or one like it) could actually be useful in a solar or wind-based electricity grid. Wind and solar power can be sporadic; obviously, any solar grid must somehow deal with the fact that night exists, and both wind and solar power can be interrupted by the weather. (Nuclear power doesn’t have this issue, so this set-up would be irrelevant.) However, it’s also possible for solar and wind to temporarily generate more electricity than customers are using at the time. The extra electricity can be used to power this CO2-to-fuel reaction, and the fuel can be burned to provide extra power when the solar or wind plants can’t generate enough electricity on their own. This is also where the Vice article misses something important. Jet fuel can’t have methane, but methane is basically the main component of natural gas, which is burned to provide about another 30% of electricity generated in the US today. And because methane is a small molecule (one carbon atom, four hydrogen atoms) it can be easier to make than the long hydrocarbons needed for jet fuel.

Also, one thing I’m surprised I never see come up when talking about this is using this for long-term human space exploration as a way to prevent to maintain a breathable atmosphere for astronauts and to build materials. If you can build-up the carbon chains for jet fuel, you could also make the precursors to lots of plastics. The International Space Station is entirely powered by solar panels, and solar panels are typically envisioned as being part of space colonies. Generally, electricity generation shouldn’t be a major problem in any of the manned missions we’re looking at for the near future and this could be a major way to help future astronauts or space colonists generate the raw materials they need and maintain their environment.

If you want to read more about the Naval Research Lab’s processes, here are some of the journal articles they have published lately:

http://pubs.acs.org/doi/abs/10.1021/ie301006y?prevSearch=%255BContrib%253A%2BWillauer%252C%2BH%2BD%255D&searchHistoryKey= http://pubs.acs.org/doi/abs/10.1021/ie2008136?prevSearch=%255BContrib%253A%2BWillauer%252C%2BH%2BD%255D&searchHistoryKey= http://pubs.acs.org/doi/abs/10.1021/ef4011115 http://www.nrl.navy.mil/media/news-releases/2014/scale-model-wwii-craft-takes-flight-with-fuel-from-the-sea-concept

Catching up with SHIELD: Asgardian Science and a Conflict of Interest

So Agents of SHIELD is semi-regularly back after a break for the Olympics. And evidently another break until April. But the episodes that aired this month were good, and other people are enjoying Agents of SHIELD more now that it seems to have hit its stride. I don’t plan on obsessively following the show on here, but there were some interesting science developments I wanted to talk about.

Simmons, wearing glasses, is seated on the left. Coulson is seated on on the right.  They are on a train and a window shows fields behind them.

On a non-science note, Simmons yelling “And all your prostitutes!” to Coulson role-playing her father in T.R.A.C.K.S. may be my favorite line of the show so far.

The more interesting things happened in this last week’s episode “Yes Men” that featured Lady Sif from the Thor movies, and this should all be fairly free of spoilers.

  • When Lady Sif arrives on Earth, Fitz mentions the energy pattern in the atmosphere matches what Dr. Jane Foster (Natalie Portman’s character) saw in New Mexico. Do Fitz or Simmons know that SHIELD basically stole her data and in Thor 2 she was trying to dodge SHIELD while studying other anomalies?
  • Sif is surprised to see Coulson alive. After seeing the Thor: The Dark World, it seems clear that Asgard doesn’t have pure resurrection technology, but her complete surprise here seems to rule out my previous theory that Asgard may have given some tech to SHIELD to help.
  • When Lady Sif gets on the Bus, Coulson tries to show her how to operate the crazy touchable hologram table they have to show the reports on Lorelei’s potential activity. Lady Sif cuts him off immediately and says “it’s primitive technology other realms had ages ago”, definitely reminding viewers that in the MCU, Asgard has incredibly advanced technology compared to what we have on Earth. I actually enjoyed Sif kind of putting us in our place, but it still seems a bit weird she would operate it so easily. Look at how hard some people find it to just switch from Windows to Mac or vice versa, even though that’s the same basic idea. And going backwards to a technology you’re not familiar with can be incredibly frustrating. (In my sophomore physics lab, my partner and I had to use a computer from the 80s because it had the software we needed to operate the particle detector. We spent 15 minutes waiting for the computer to boot up and finally our professor pointed out that the operating system was DOS and we had to type in commands because graphical desktops had not been developed for operating systems yet.)
  • In Sif’s introduction, we hear of a different aspect of Asgardian life. She openly says Lorelei’s power is sorcery and doesn’t give any explanation to how it works, and when asked about why it only affects men, she says they have an “inherent weakness” women do not. So is magic very advanced science/technology or a separate thing? (Thor says science and magic are one and the same in Asgard in the first movie.) Lorelei doesn’t use any tool over the course of the show to control her men. Interestingly, some sort of electronic collar can neutralize her power, so it does seem like aspects of both.
  • The collar that can stop Lorelei’s power is broken. Fitz is asked to fix it. Lady Sif comments that it may be hard because Asgardian metals are different than Earth metals; in particular, they tend to be denser. It fits into the theme of things from Asgard being hardier than things from Earth, but it doesn’t really make sense from a materials science point of view. Yes, this is nitpicky, but how often do materials scientists actually get to critique pop culture errors in their field?

I’ve mentioned in the past that the reason I love SHIELD is because of Fitz and Simmons’ sense of morality as scientists. And there was an interesting conflict this episode between Coulson and Simmons’, but it’s a bit spoilery if you haven’t seen “T.A.H.I.T.I.” yet, so it will be below the cut. Also, this show really needs to quit making things acronyms just for the sake of it.  Continue reading

Why I Love Agents of SHIELD

So I finally caught up on TV with a post-finals DVR binge and watched the last three episodes of Agents of SHIELD for the fall. And I still love it. I’ve always loved it. Evidently this puts me in a minority on the Internet.

Penny Arcade, why?

Talking to a friend, I realized I love it so much because of one thing: FitzSimmons. Or more accurately, two things: Jemma Simmons and Leo Fitz. (Although others think they are basically one character.)

Why do I love the two characters that other people view ambivalently? Because they’re scientists. Okay, technically Fitz is an engineer, but their roles are very similar in the show. And both scientists and engineers end up using the scientific method, and in their work, Fitz and Simmons use a lot of technology. With Fitz and Simmons, Agents of SHIELD shows science and technology as forces for good, and that’s something we haven’t seen much on TV shows lately. I’m particularly excited by the fact that they’re actually full characters in the show, not recurring lab rats who just dump tech on the protagonists as needed like Q does in James Bond (or Marshall from ALIAS). Also, the things they talk about typically make some kind of sense (I’ve only heard the term “pure energy” once, but “gravitonium” makes no sense whatsoever).

What strikes me as particularly important is that they’re ethical scientists. I realize this sounds like an incredibly low bar, but seriously, this isn’t something we’ve seen on major TV shows lately. People (especially children) tend to be scared of the people they see working in science-related fields on TV. And honestly, I can’t blame them. The entire backstory of LOST and Heroes seemed to be related to mysterious mad science. It is incredibly important to me that Fitz and Simmons comment on how unethical Project Centipede is, and that in the pilot, they angsted over the uncertainty of whether or not they could help Michael Peterson without hurting him.  In the third episode, their favorite professor calls out the villain of the week for hypocrisy in his technological development.

Pretty big spoilers below the jump, if you haven’t been watching the episodes after the winter break.

Continue reading

A Day Without Satellites

The BBC has a short fictional piece about what would happen if all the world’s satellites stopped working. While that is unlikely, it’s an interesting look at how much satellites are integrated into everyday technology. For instance, while the Internet is mostly an Earth-based affair with undersea cables connecting continents, I didn’t know that that the atomic clocks on GPS satellites were used by data centers and Internet exchange points to timestamp Internet data packets. One thing I’m a bit confused by is how much the article claims international telephone calls would be disrupted. I could see things like aid workers and military units who are in areas with little landline or mobile infrastructure being affected, but I thought most international calls on landlines and regular cell phones were done through the undersea cable network.

While this article may be drastic, it is important to note that our satellites are increasingly at risk of damage and it’s an issue that increasingly concerns industry and governments.