Quartz glass is widely used in high-temperature furnaces due to its exceptional heat resistance, low thermal expansion, and excellent chemical purity. However, during forming, cutting, and machining, internal stresses inevitably develop within the material. Proper annealing is therefore essential to ensure long-term stability and reliable performance in extreme thermal environments.

1. Purpose of Annealing

The primary goal of annealing quartz glass is stress relief. Residual stress can cause deformation, micro-cracking, or sudden failure when the glass is exposed to rapid temperature changes. By carefully reheating and cooling the glass under controlled conditions, internal stresses are redistributed and reduced, improving thermal shock resistance.

2. Annealing Temperature Control

Quartz glass requires much higher annealing temperatures than borosilicate glass. Typically, annealing is performed at 1,050–1,200°C, depending on the glass purity and component thickness. Precise temperature uniformity is critical; uneven heating can introduce new stress rather than eliminate existing ones.

3. Controlled Heating Rate

Heating must occur gradually to avoid thermal gradients. Thick quartz components require slower ramp-up rates to ensure the entire cross-section reaches a uniform temperature. Rapid heating can lead to surface expansion while the core remains cooler, creating stress concentration.

4. Slow and Uniform Cooling

The cooling phase is the most critical part of the annealing process. Quartz glass must be cooled slowly through the strain point to prevent stress reformation. Controlled furnace cooling is preferred over natural air cooling, especially for large or thick parts used in furnace chambers.

5. Clean Environment Requirements

Annealing should be performed in a clean or inert atmosphere to prevent surface contamination, devitrification, or chemical reaction at high temperatures. Even minor impurities can affect optical clarity and mechanical strength.

Conclusion

Proper annealing of quartz glass ensures dimensional stability, enhances thermal shock resistance, and extends service life in high-temperature furnace applications. Strict temperature control and slow cooling are the foundation of reliable quartz components.