The properties of quartz glass are intimately associated with its purity. Various impurities are unavoidably introduced during the preparation process of quartz glass, which gives rise to the occurrence of defects in quartz glass and the alteration of its properties. Common defects in quartz glass can be classified into two categories: structural defects and macroscopic defects.

Structural defects

Structural defects pertain to the flaws arising from the introduction of impurities, primarily encompassing hydroxyl and metal impurities, within the atomic mesh structure of quartz glass. The introduction of these impurities disrupts the original lattice structure of the quartz glass, thereby inducing alterations in its various properties, among which the optical properties undergo the most significant changes. The metal impurities present in quartz glass impact absorption within the ultraviolet spectrum, while the hydroxyl group affects absorption within the infrared spectrum. Additionally, the existence of hydroxyl will also diminish the chemical stability, structural strength, heat resistance, and optical uniformity of quartz glass.

In the semiconductor industry, excessive metal impurities in quartz glass will directly influence the electrical characteristics of the product. Optical inhomogeneity is also a structural defect of quartz glass, which is frequently caused by the preparation process of quartz glass and exerts a significant impact on its optical application. The existence of alkali metal impurities and hydroxyl groups will further promote the crystallization of quartz glass at high temperatures.

Macroscopic defects

Macroscopic defects in quartz glass are typically caused by the impurities of raw materials or an improper preparation process. Common macroscopic defects include bubbles, inclusions, streaks, and cracking resulting from thermal stress. The viscosity of fused quartz is extremely high, which renders the removal of bubbles within it a challenging process. The generation of bubbles is primarily associated with the melting process of quartz glass. An improper melting method will result in the inner unmelted quartz raw material being encapsulated by the molten quartz on the outer surface, thereby hindering the escape of bubbles. The thermal stress of quartz glass manifests during the cooling process and is induced by the temperature differential between the various regions of the glass. An uneven distribution of thermal stress can result in an increased optical inhomogeneity of quartz glass, which may ultimately lead to the formation of cracks in the glass when the thermal stress exceeds a certain threshold.

Different from structural defects, the occurrence of macroscopic defects on a quartz glass product frequently implies its scrapping, so the preparation process of quartz glass needs to be stringently controlled to prevent any macroscopic defects in actual production.