The preparation of quartz glass can be divided into two main categories. The first type refers that the quartz glass is obtained by melting natural quartz crystal or silica as raw materials, which is called natural quartz glass. According to the different heat sources and processes, the methods of the first type can be subdivided into electric melting, gas refining, plasma melting, etc.. The second type refers that the quartz glass is synthesized through chemical reaction with silicon-containing compounds (including silicon halide, hydrogenated silicon and silicone, etc.) as raw materials, which is called synthetic quartz glass. According to the different reaction principles, the methods of the second type can be divided into: plasma chemical vapor deposition method (PCVD), flame hydrolysis deposition method (FHD), sol-gel method.

Regarding the preparation of high-purity quartz glass, two typical preparation methods are briefly described below.

1. Electric meltingmethod

In the electric melting method, the powdered quartz as raw material in the crucible is firstly melted by electric heating (resistance heating or electromagnetic induction heating), and then the quartz glass is formed through the glass transition process under rapid cooling.

For quartz glass obtained by electric melting method, its quality mainly depends on the purity of raw materials. Metal impurities in quartz raw materials are usually difficult to be removed, so the metal impurities in quartz glass made by electric melting method are generally high and unmanageable. However, the moisture in quartz powder can be effectively removed by drying, so through electric melting method, the quartz glass with lower hydroxyl content can be produced.

2. Chemical vapor deposition method with two steps

Chemical vapor deposition method with two steps (two-step CVD) can be divided into two steps. In the first step, a hydrolysis reaction is carried out at a lower temperature to produce SiO2 particles in the shape of soot, and then those SiO2 particles are deposited on the substrate to obtain loose SiO2 form, which is a kind of amorphous SiO2 with a porous structure. The second step is to transfer the loose form of SiO2 to a high temperature heating furnace for dehydroxylation, and the quartz glass is finally made through the sintering and cooling process.

The two-step chemical vapor deposition (CVD) method is a new technology that has been developed in China in recent years. It can produce quartz glass with low hydroxyl or controllable hydroxyl content, which essentially avoids the entering of metal impurities, so it has broad prospects for development. However, the two-step CVD method is still facing a series of technical challenges, mainly in the immature technique and the lack of understanding of the key scientific issues in the preparation process, which limits it to become the mainstream technology for the preparation of quartz glass in the industry. Furthermore, the quartz glass preparation industry is confronted with a number of challenges, including the occurrence of glass bubbles and the difficulty in controlling the thermal modification process, which in turn affects the quality of the quartz glass.