Question

Explain the following observations and offer suggestions how to eliminate the problem: (a) A ceramic component, formed from a very fine powder, is rapidly attacked in an aggressive liquid environment. The component experiences minimal stresses, but it is possible neither to change the composition of the ceramic nor to alter the service environment. (b) A small industrial laboratory is having problems with hydrofluoric acid and alkali solution leakage from their soda-lime-silicate glass containers.

Answer 1

HF reacts with glass (SiO2).

SiO2+4HF?SiF4+2H2O

HF2?HFX2X? ions are adsorbed on surface silanol groups, the HFHF molecules on vicinal silanol groups and H+HX+ on surface bridging oxygens in siloxane units. [...] These are transformed into surface groups such as ?Si?F?Si?F and ?Si?O?SiF3?Si?O?SiFX3. The adsorption of HFHF and HF2?HFX2X? increases the electronic density on the bridging oxygen in the siloxane unit. This, in turn, makes these oxygens more basic, so more H+HX+ ions are adsorbed, which leads to more siloxane bonds being broken per time unit, i.e. a kind of catalytic effect. [...] The catalytic action of H+HX+ ions on breaking siloxane bonds also occurs in the dissolution of glasses in acidic and weakly alkaline solutions.