Page 17 - Curriculum Visions Dynamic Book

Glass is not entirely corrosion proof. Some extremely harsh acids and alkalis will attack it. They include hydrofluoric acid and concentrated phosphoric acid, hot concentrated alkalis, and superheated water.
The corrosive effect of hydrofluoric acid can be turned to advantage. It is actually used to etch the surface of glass, making decorative effects or a “ground glass” finish used in camera eyepieces and elsewhere.
Hydrofluoric acid is by far the most powerful of the corrosive acids; it attacks any type of silicate glass.
Acids and alkalis have different effects on glass because they react with different components. The acids react with the alkalis (soda and lime), while the alkalis react with the silica.
Alkalis dissolve the silica. Because silica is such a large part of glass, taking it away leaves almost nothing behind. Provided
there is sufficient alkali, it will dissolve
glass at a constant rate. Acids, on the other hand, dissolve the soda and lime in the
glass. Because there is less of them than silica, dissolving leaves the glass surface pitted
and covered with tiny holes. Thus,
while acid attack is very fast to begin
with, it slows down over time because
fresh acid has to penetrate deeper and
deeper into the glass to find substances
to attack. Water also can corrode glass,
but the rate is extremely slow unless
(Left and below)
Glass etched using hydrofluoric acid.
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