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Q & A: Glass vapor?

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Most recent answer: 10/22/2007
Q:
Our class is studying the states of matter. My question is if glass can be a solid and a liquid can it be a gas?
- Alex (age 9)
North Ward Elementary, Tuscola, IL
A:
If something is a gas, then itís not a glass. But the ingredients of ordinary glass can be heated up enough not only to liquify but also to evaporate into a gas.

Most familiar glasses consist mostly of silicon dioxide, SiO2, the main ingredient in sand. Crystallized silicon dioxide is known as quartz, while in glass the molecules do not line up in a nice, orderly crystal.

Because glass is disordered, Iíve heard it described as a "liquid that flows really really slowly." But in many ways it acts more like a solid than a liquid. The other reason glass isnít really a solid is that there is no sharp phase transition between the freely-flowing hot liquid and the rigid, cold stuff we put in our windows, like there is for water freezing (which all happens at one temperature and gives off heat). Liquid glass just gets gooey and then hard when cooled. Most people who deal with it and stuff like it donít insist that all materials are "solids", "liquids", or "gases". We refer to materials like glass as "glasses", which are not quite solid nor really liquid either. (Another name might be "disordered solids".)

But on to your question about glass gas -- the boiling point of silicon dioxide is 2230 Celsius. Addition of impurities will probably raise this boiling point.

Tom (w mike)

(published on 10/22/2007)

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