SCHOTT Technical Glasses

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2.3 The significance of chemical stability
2.3.1 Corrosion resistance in chemical plant applications
For such applications, the glasses must be resistant to the
various chemical solutions to such a degree that manifold
reactions can take place without running the risk of damaging
the laboratory glass or the equipment by strong ablation.
Moreover, no interfering amounts of glass components
must be released into the reaction mixture. Attack by acids
is of particular importance, both in laboratories and in chemical
technology. Here, borosilicate glasses with their high
acid resistance are superior to other materials. Up to the
boiling point, their reactivity is very low; it then increases
with increasing acid concentration, but decreases again at
higher concentrations (Figure 3). The alkali attack, in contrast,
increases exponentially with increasing alkali concentration
(Figure 2).
A comparison of the effect of the alkaline mixture (concentration
of alkaline components about 1 mol/l) with the effect
of 6 mol/l hydrochloric acid (the most aggressive acid used
in acid resistance tests) under standard conditions shows
that the alkali attack increases by a factor of 1000 after extended
exposure.
2.3.2 Release of glass constituents
In various processes of chemical technology, pharmaceuticals,
and laboratory work, the material glass is expected to
release no constituents (or a very minimum) into the reacting
solutions or stored specimens.
Production of floated borosilicate glass