What Is Glass?
You may have heard a couple of things about glass, the most surprising of which, and one that I first heard when I was fourteen, is that glass is a liquid, and related to this was a statement that if you pushed against glass for long enough, you would come out on the other side of it. But are these things true of glass,? And what the heck is it anyway? It’s time for some investigative chemistry!
States of matter aren’t simply divided into three distinct sets. For one, most people know that plasma’s a thing, and one in a thousand people will have probably heard the term Bose-Einstein condensate at some point, but you’d be pushing logic to argue that a table is just as solid as honey, or that a glass of water is just as liquid as honey. The arrangement of particles in a substance can form more than just three distinct sets of things, there’s a continuum, as with a lot of the things we assume are distinct, and that continuum is relatively easy to see between liquid and solid. We’ve all watched something melt at some point, and the object isn’t a block one second and a pool in another.
So where does glass fit into this? It’s made by a melting process, but it’s also cooled down, so where does it fall? Well, glass is an amorphous solid, the most common of which in human cultures is SiO2 (silicon dioxide), which, in it’s crystalline form, we call quartz. You might have guessed this already from the previous sentence, but glass isn’t crystalline, which is largely what defines it as amorphous. Glass can be formed by melting materials and then cooling them below what we call a ‘glass transition temperature’ where the amorphous solid will soften near its melting point, if this is done quickly enough, then there will not be time for the molecules to form lattices and therefore crystallize. Glass in chemistry is defined by the ‘glass transition’ we mentioned earlier in which a brittle solid into a softer, more malleable state
Let me back up, lattices are how we find metals in nature, an arrangement of compounds that form a regularly shaped network often drawn as a cube. Their regular structure is repeated and this is what we see as crystals, regularly-shaped macroscopic results of the interaction between charged particles. Check it out in the picture below.
Glass, despite common misconceptions, does not flow once it has cooled and solidified into what we would recognize as glass. This idea is one of the driving forces behind the idea that glass is a liquid, but, from its chemical composition, it appears to be more solid than liquid, just an amorphous solid. The idea behind this may originate from the way glass used to be made, but the idea that ancient windows have more glass on their bases because glass flows like the liquids we know and love has been debunked by Wikipedia of all things, which should tell you something. It is an odd and interesting solid though, and it’s not surprising that its form inspires questions.
[image credits: wikimedia commons, kaffee.50webs.com]