Spiffy Material of the Indeterminate Time Period: Glass

The odds are pretty good that you are within 5 feet of a piece of glass right now (unless you have someone read you my blog posts out loud, in which case it might be farther). In fact, glass, in the form of fiber optics, was almost certainly involved in you getting to this blog.

The term glass, as commonly used, actually refers to class of materials with similar properties (like metal), rather than a specific material (like copper). The defining feature of glass is the lack of crystal structure. Unlike typical metals or ceramics, glasses have no defined order once you move more then a few atoms away from your initial position. This results in some unique behaviors, such as a viscosity transition that depends on temperature (excitingly called the glass transition temperature). Certain glasses are almost infinitely recyclable.

Most glasses you encounter on a daily basis are silica-based (SiO2), from the Pyrex labware and cookware (borosilicate) to cheap glass bottles (soda lime silicate) to smartphone screens (alkali-stuffed aluminosilicate) to LCD screens (aluminosilicate). If you're old-fashioned (yet still on the internet), your CRT monitor contains multiple types of glass, including a very lead-rich glass for the funnel, which is now posing a problem for waste management as people toss their old CRT displays for shiny new flat-screens. Glasses, at least the kind for vision, are typically *not* made out of glass anymore.

In terms of materials science, there are two type of compounds found in glasses: network formers and network modifiers. Network formers are what gives glass its structure and rigidity. Common network formers include silica, borate and alumina. Network modifiers typically are ionizing oxides, and are very helpful in lowering the working temperature glass. Modifying compounds are things such a soda, lime (CaO), potassium oxide, and other alkali oxides. These don't include compounds like cobalt, or gold, which are used to color the glass, but in rather smaller quantities.

Glass can be processed in a fantastic number of ways as well. They can be die-formed, like for drinking glasses, blown, float cast, or drawn into fibers. Some experiments even study glasses formed while levitated. Torchwork typically involves welding manipulator rods on, heating the glass with a propane-oxygen torch (glass has a very high melting point), and pulling the glass with those rods, or various tools.

Glass has also been used by humans for thousands of years, and has been traced as far back as Mesopotamia. To put this in context, this is during the early Bronze age. It's been a part of human history for a very, very long time. And that's pretty darn spiffy.

Spiffy Material of the Indeterminate Time Period: Aluminum

Sadly, BNL never made a music video for this song, so here's their lead singer in a bathroom: http://youtu.be/9pVgj6bawus

Aluminum. It's everywhere, from around your burrito to the bodies of airplanes, but at one time, it was the most precious metal on earth. It's one of the lightest metallic elements, and one of the most abundant elements in the earth crust. So how was it so precious that Napoleon III, who used silver as his regular utensils,  gold for high ranking guests, saved his aluminum flatware for only the most honored guests? Processing.

While abundant, aluminum is almost never found in its elemental form. Aluminum almost instantly forms a thin protective oxide layer, which is what gives it such fantastic corrosion resistance. Unlike silver flatware, you don't have to regularly polish your aluminum, because the oxide layer is transparent, unlike black AgO. However, this makes extracting aluminum from its mineral forms difficult. In the early years of  aluminum processing, the Wöhler process, in which anhydrous aluminum chloride is reacted with potassium, was used. However, aluminum chloride is not the most abundant form of aluminum. 


Bauxite, made of several different forms of aluminum oxide, is the most common source of aluminum in the modern era. The Hall–Héroult process is used to extract pure aluminum, first dissolving the bauxite in molten sodium hexafluoroaluminate (also known as cryolite), and then electrolytically separating the pure aluminum from the molten salt bath. While natural cryolite was once used, reserves are largely depleted, and it is now instead synthesized from fluorite.  Fortunately, aluminum is entirely recyclable.


Take a minute to look around, and figure out everything around you that's made of aluminum, and think about how less than 200 years ago, it would have been worth more than it's weight in gold. Spiffy, huh?

Spiffy Material of the Indeterminate Time Period: Dry Ice

Unlike my previous post on graphene, a material with theoretical promise and some practical applications, I'd like to talk to you about something more fun: dry ice.

Recently, the experimentalist portion of my group was looking to form supercritical liquid CO2 in an autoclave, and before purchasing expensive pre-pressurizing equipment, wanted to try dry ice. Logistically, the easiest thing was for me to stop by a grocery store and pick some up. Unfortunately, the experiment failed, and I took the extra home, where I discovered Mr. ME had never played with it.Thus, I am reminded of it's basic spiffiness.

Dry ice is spiffy for a number of reason, but mostly, because it sublimates at standard temperature and pressure conditions. Sublimation means it skips directly from the solid phase to the gaseous phase, hence the name "dry" ice. If you live in a dry climate with decent sunlight, you can also observe the sublimation of snow (sunlight is necessary to reflect off the vapor and make it visible). It only happens in dry conditions, though, when the vapor pressure of water in the atmosphere is sufficiently low.

Phase diagrams for materials like dry ice describe the state of the materials as a function of temperature and pressure, as shown below. These diagrams are created by simultaneously solving the Gibb's energy equations for different structures and looking for boundary conditions where two or more phases are stable.



Sadly, personal experimentation has demonstrated that while it will not dilute your martini or whiskey, dry ice won't make it terribly chilled either. I suspect this is due to the Leidenfrost effect. I will just have to cave and order these.

Spiffy Material of the Indeterminate Time Period: Graphene & Graphene Oxide

As you may be aware, in 2010, the Nobel Prize for Physics was awarded to Geim and Novoselov for their work with graphene. Wired already did a nice little piece on why it won the Nobel Prize, but they focused more on the possible applications of the material, rather than it's already awesome properties and history.

Graphene may be the first Nobel Prize awarded made possible by Scotch tape. Single layers of graphene were first separated by peeling tape off of a block of high-purity graphite. Graphene sheets are effectively two-dimensional, and within the plane of the sheet, are the strongest material ever tested.  They also have remarkably high electron and hole mobility, making them ideal for many electronics applications.

So what is graphene being used in so far? Researchers at the University of Technology Sydney have figured out how to make a paper out of it. It's been used as a transparent anode in organic LEDs and organic photovoltaics. It's little sister, graphene oxide (GO), on the other hand, is a little more practical. It kills E. coli with surprising efficiency. It has also been used as reinforcement for epoxy composites. With as little as 0.125 weight % GO, the fracture toughness of the composite (i.e., how hard it is to start and propagate a crack) increased by 65%. To get equivalent improvements with carbon nanotubes, it took roughly 3%, and graphene oxide is much cheaper to produce.

Basically, it's pretty darn spiffy.