Though silica glass is highly resistant to chemical attack, care must be
taken in the handling of it to avoid contamination. At elevated temperatures, fused
quartz
will undergo a slow process of devitrification, changing from its amorphous state to a
stable crystalline state called cristoballite. The process of devitrification is
accelerated in the presence of impurities on the surface. To minimize the amount of
devitrification, a cleaning method similar to the one below should be
used: |
|
| Step 1: Organic and metallic removal: clean the
sample with a strong degreaser, such as nitric acid or hydrogen peroxide. |
|
| Step 2: Removal of the outer layer of quartz: etch
the part in hydrofluoric acid (ex. 5% hydrofluoric acid for 3 minutes) to expose a pristine silica surface. |
|
| Step 3: Rinse off acid: rinse in
DI water to remove traces of hydrofluoric acid without re-contaminating the glass. |
|
| Step 4:
Rinse off acid: rinse in DI water spray
to remove traces of hydrofluoric acid without re-contaminating the glass. |
|
| Step 5: LetDry: dry the part in a clean, dust free
environment. |
|
| Additional Precautions |
1) Always wear clean, lint free glove or powder free latex
gloves. Avoid direct contact of the glass with bare hands. The skin's natural salts contain
alkali metal elements such as sodium and potassium that speed devitrification. |
|
2) After cleaning with detergents, always clean in diluted
hydrofluoric acid, followed by a DI water rinse. |
|
3) Take into consideration the
concentration and temperature of the hydrofluoric acid. Both of these strongly influence the
etching rate of the quartz. |
