| From: Alan™ ® | 26/10/00
0:20:19 |
| Subject: re: Is glass liquid? | post id:
157145 |
| I'm not really happy with the
answers in this thread or most of the ones in earlier threads I found.
So..... Firstly glass is definitely a solid. It is termed an amorphic solid. The term amorphic means that it has no crystal structure. Now this is not all that uncommon, some plastics are non crystalline, rapidly cooled iron-silicon alloys used for metal cassette tapes, anodized layers on aluminium. So the lack of a crystal structure does not indicate that the substance is a liquid. The way this misconception about glass being a liquid started was during the dark ages, the technique to produce even thickness glass was lost. I understand that in older cultures they actually have found glass that was still even in thickness. So what happened in the middle ages? Well because the glass was not of even thickness, the glass fitters, did the really sensible thing and put the thicker edge on the bottom. Thus putting less stress on the glass and reduce the likelyhood of it accidently fracturering. Having said that glass is a solid, I'm going to appear to contridict myself. Because it does flow, so does steel (and I'd assume all other solids). There is a process called creep. With creep material when it's under load (even of it's self), will have atoms migrate under the infuence of the load (gravity in this case) and voids (holes) will migrate the opposite way. Generally this process is extremely slow, particularly when at room temperature for most objects that have a reasonably high melting point. But for steel, if you raised the temperature to 100°C below the melting point, and load it, the process can be very visible. The presence of a crystal struture, or the lack there of does not effect whether the material creeps. The primary factor affecting this property, is the mobility of the atoms in the solid. So as temperature increase, mobility increases and the process speeds up. By definition the process of creep occurs, within the elastic region, so the loads are relatively small, that is below the load required to permanently deform the material and it occurs below the melting point. | |