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The Glassy State
1. THE GLASSY STATE
Glass is a state of matter.
Glasses combine some properties of crystals and some of liquids but are
distinctly different from both.
Glasses have the mechanical rigidity of crystals, but the random
disordered arrangement of molecules that characterizes liquids.
Glasses are usually formed by melting crystalline materials at very
high temperatures. When the melt cools, the atoms are locked into a random
(disordered) state before they can form into a perfect crystal
arrangement.
2. COMPOSITION
Glass can do most anything. From bottles to spacecraft windows, glass
products include three types of materials:
FORMERS
are the basic ingredients. Any chemical compound that can be melted and
cooled into a glass is a FORMER. (With enough heat, 100% of the earth's
crust could be made into glass.)
FLUXES
help FORMERS to melt at lower, more practical to achieve temperatures.
STABILIZERS
combine with FORMERS and FLUXES to keep the finished glass from
dissolving, crumbling, or falling apart.
Chemical composition determines what a glass can do. There are already
tens of thousands of workable glass compositions and new ones are being
developed every day.
FORMERS
Most commercial glass is made with sand that contains the most common
FORMER, Silica. Other FORMERS include:
Anhydrous Boric Acid
Anhydrous Phosphoric Acid But melting sand by itself is too expensive
because of the high temperatures required (about 1850°C, or 3360°F).
THEREFORE...
FLUXES
are added which let the FORMER melt more readily and at lower
temperatures (1300°C, or 2370°). These include:
Soda Ash
Potash
Lithium Carbonate
But FLUXES also make the glass chemically unstable, liable to dissolve
in water or form unwanted crystals. THEREFORE...
STABILIZERS
are added to make the glass uniform and keep its special structure
intact. These include:
Limestone
Litharge
Alumina
Magnesia
Barium Carbonate
Strontium Carbonate
Zinc Oxide
Zirconia
3. PROPERTIES
MECHANICALY STRONG
Has great inherent strength. Weakened only by surface imperfections,
which give everyday glass its fragile reputation. Special tempering can
minimize surface flaws.
HARD
Surface resists scratches and abrasions.
ELASTIC
Gives under stress - up to a breaking point - but rebounds exactly to
its original shape.
CHEMICAL CORROSION- RESISTANT
Affected by few chemicals. Resists most industrial and food acids.
THERMAL SHOCK- RESISTANT
Withstands intense heat or cold as well as sudden temperature changes.
HEAT - ABSORBENT
Retains heat, rather than conducts it. Absorbs heat better than metal.
OPTICAL
REFLECTS
BENDS
RANSMITS
ABSORBS light with great accuracy.
ELECTRICAL INSULATING
Strongly resists electric current. Stores electricity very efficiently.
Silica: Silicon dioxide, a mineral that is one of the essential
ingredients of glass. The most common form of silica used in glassmaking has
always been sand.
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