Process materials (gases and chemicals)

What degradation tends to occur when quartz parts in heat-treatment furnaces are used at high temperature for a long time?

  1. ADevitrification (the glass crystallizes and turns cloudy white)
  2. BIt becomes conductive
  3. CIt becomes magnetic
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Answer: A. Devitrification (the glass crystallizes and turns cloudy white)

Prolonged use at high temperature makes quartz glass devitrify, turning into crystal (cristobalite) from the surface. Devitrified areas crack more easily because of thermal expansion mismatch and shed particles, so parts are replaced periodically. Contamination such as alkali metals accelerates devitrification.

  • A. Correct. It devitrifies, crystallizing and turning cloudy.
  • B. Quartz remains an insulator at high temperature.
  • C. Quartz is not magnetic.
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