Tuesday, August 30, 2011

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.

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