Re: IONS

[Doug Craigen <dcc@cyberspc.mb.ca>]

David Dockstader wrote:
> The difference between "glass" and "quartz" is a matter of crystal structure
> not purity or chemical composition.  Having a crystal does not ensure purity.

We wade into a semantic minefield ...  When the word "glass" is used I
have to listen very carefully to determine what is actually being talked
about.  A glass is a subset of amorphous materials and silicate glasses
are a subset of those.  My theses were in the study of amorphous
silicon, silicon hydrides and silicon nitrides.  All of these have too
high an average coordination number to be likely candidates for glasses,
but all can be readily made amorphous.  In very general terms the
disinction is that a glass is a material which can be taken from a
definitive liquid state and cooled steadily, at a slow rate (i.e. not
"splat quenching"), and steadily increase in viscosity until it is
considered to be solid without any first order phase transitions or
crystalline order.  Glasses tend to have average coordination numbers of
6^0.5  Silica would have an average coordination number of 8/3 which is
a bit high to be a likely candidate.  The role of the boron, sodium etc
oxides is to lower the average coordination number a bit, making a more
suitable material.  So amorphous silica can certainly be made, but I
don't think it qualifies as a glass.  "Quartz" is a reference to
particular crystalline structures of SiO2, and may not be particularly
pure.  I have heard the term "amorphous quartz" used frequently, however
I don't know if this is considered correct useage by whatever high
authority there is that ultimately decides these things, hence I avoid
using the term myself.

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Doug Craigen          "Technology with purpose"
                       http://www.dctech.com