🚀 go-pugleaf

>From: gadfly@ihlpa.UUCP (Gadfly)
>> While glass is amorphous and has some fluid and colloid properties,
>> it is not a liquid.

>I promise never to try to be helpful about old net ramblings again.
>I tried to summarize this thing so it could meet a merciful end, and
>what happens?  (1) I get mail about not phrasing the question correctly,
>(2) I get mail about forgetting the *real* answer--Freon.  I suspect
>that the question expected the answer "glass" since these folk quizzes
>tend to be very superficial, and it's common folk knowledge (the truth
is another matter) that glass is a liquid.

>ken perlow   

Sorry to disappoint you Ken, but glasses really are super-cooled liquids.
The reason lies in the lack of the activation energy found in crystalline
materials.  I really do not wish to bore the net with statistical thermo-
dynamics and the like, so I will instead quote from "Nature and Properties
of Engineering Materials" by Zbigniew D. Jastrzebski (Finally a name more
difficult than mine  :-]  ), John Wiley & Sons, NY, 1959.

   X-Ray analyses show that the relative positions of atoms in glasses
   are similar to those of liquids.  This means that there exists among
   the atoms a short-range order, but also a long-range disorder.  Hence
   glasses are generally regarded as supercooled liquids which are unstable
   with respect to their crystalline phases.
   
   ... glasses do not possess definite melting points but soften gradually
   over a wide range of temperatures.

   Glass on cooling from its molten state shows an increase in viscocity,
   thus becoming more and more viscous as the temperature decreases.  On
   further cooling, however, a temperature range is reached at which the 
   glass undergoes a rather sharp change from a viscous to a hard and brittle
   material. [Note, he did not say solid.]  The range of temperature at which
   this change occurs is called the glass transistion temperature, T sub g,
   which is often referred to as a second order transition.  Below the glass
   transition temperature the structure of glass is effectively "frozen,"
   but for the most part, it retains the characteristic structure of a liquid.

This book also presents several graphs showing the viscocity of glass.  These
graphs were taken from several references such as: Corning Glass Works,
"Properties of Selected Commercial Glasses"; Morey, "The Properties of Glass";
and Jones, "Glass." At room temperature, ordinary glass shows a viscocity of
about 10 to the 20th poises.  Water for comparison shows a viscocity of about
0.01 poise at the same temperature.  This shows that while glass is not a
solid at room temperature, it is a lot thicker than molasses on a cold winter
morning.  :-)

To answer several other questions about glass, hydrogen should be present in
only negligible amounts in glass since any hydrogen present in molten glass
would be oxidized by the oxides present to form steam which would vaporize off.
Glass is made in an oxidizing atmosphere as opposed to most metals and alloys
which can contain considerable dissolved hydrogen.  Also, the mirrors in most
large reflecting telescopes use fuzed silica rather than soda-lime glass.  This
material shows a more crystalline structure than ordinary glass; it is similar
to that of quartz (a three dimensional network of silicon atoms bonded through
oxygen links) with the exception that the bond angles are not constant, causing
an irregular arrangement of atoms.  Colloids can be arbitrarily defined as
matter is a fine state of subdivision, larger than atomic and simple molecular
dimensions, but smaller than particles visible to the naked eye.  Glass by 
itself would not qualify, but ruby glass with colloidal particles of gold
dispersed in the glass might.

I hope this treatise will end the discussion on hydrogen-less liquids about
the house.  Glass, freon (at least the varieties most commonly used in household
refrigeration units) and carbon tetrachloride are equally correct answers.
Let's find some new controversy to argue over, this one has been around for
over six months!  Only this time, we should find a subject where computer
science types have a fair chance of understanding the physics.  :-)  Oops!
Sorry about that, folks.  I can hear the mob beating on the door!

                                           Barry L. Ornitz
                                           Eastman Chemicals Division Research
                                           Kingsport, TN