1 Overview of the development of the fused silica industry
Fused quartz, also known as quartz glass, is a supercooled liquid made from natural quartz, including silica and crystal as raw materials, through high-temperature fusion. China's quartz glass industry is developing rapidly with the development of China's national defense technology and military industry. , The output and quality of quartz glass have been greatly improved. China's quartz glass industry has introduced foreign advanced technology and technological innovation at the same time, and the product variety and output have increased rapidly. However, compared with the foreign advanced technology level, there is still a big gap in the high purity of quartz glass, melting equipment and energy-saving control.
The manufacturing process of fused silica is special and different from general glass products. There are two major difficulties in the production of fused silica: one is that the melting temperature is high, the viscosity is large, and the bubbles are difficult to eliminate; the second is that the purity of fused silica must be improved to obtain excellent performance, and the total amount of impurities is less than one ten thousandth.
Donghai County, Jiangsu Province has large reserves of quartz raw materials and high purity. It is China's silicon material industrial base. As China's fused silica raw material production base, Donghai County has an annual output of more than 200,000 tons of high-quality fused silica raw materials, with a domestic market share of more than 80%. At present, the production process commonly used by Donghai County fused silica raw material production enterprises is: crushing selected high-quality silica raw materials (SiO2 content> 99%), such as vein quartz, into small particles, and then in a graphite rod heating furnace (using high-quality steel plate). It is rolled into a cylindrical furnace body with a certain volume) and melted in the furnace, directly cooled and then crushed and classified into blocks. In terms of fused silica melting equipment, most enterprises in China still use medium-carbon rod resistance heating primary production equipment, and the control is still constant power heating, and the energy consumption in the melting process is relatively high.
The fused silica industry is a high energy consumption industry with a large demand for electrical energy, and energy consumption accounts for more than 50% of the production cost of fused silica. In 2009, Donghai County's industrial electricity consumption was 69789 million kilowatt-hours, and from January to April 2010, the county's industrial electricity consumption was 268.33 million kilowatt-hours. Taking the fused silica industry as an example, there are more than 350 quartz smelting furnaces in more than 50 fused silica enterprises in the county, with an installed capacity of 97040kVA. The contradiction between the supply and demand of electric energy is increasing, and the production cost of fused silica production enterprises is increasing, resulting in a reduction in profit margins and hindering the development of the industry. Improving product quality and reducing energy consumption have become an important way to improve the economic efficiency of enterprises.
SiO2 has a high melting temperature and is easy to react with other substances to form silicate. Therefore, it is a major technical problem to select refractory materials that have good insulation effects and do not react with fused silica, and select refractory materials that do not affect the quality of fused silica in design research. At present, the heat preservation method adopted in the production of fused silica in China is mainly self-heat preservation, that is, heat preservation and heat insulation with part of unfused quartz to avoid refractory materials.
Contaminate fused silica. The self-heat preservation process has poor heat preservation effect in actual production, and redness of the furnace shell often occurs. The self-insulation process not only wastes much energy, but also has a low production rate of fused silica, and the quality is not easy to guarantee. There are almost zero reports on refractories used in the production of fused silica in China, and a very small number of reports are mainly researches on refractory materials for quartz glass tubes and furnaces.
2 Classification of Fused Silica
Fused silica generally includes two types: transparent quartz glass and opaque quartz glass. The SiO2 content in the transparent quartz glass is greater than 99.995%, which is made by high-purity quartz powder or silicon tetrachloride as raw materials by high temperature melting; the SiO2 content in the opaque quartz glass is greater than 99.85%, which is made of ordinary quartz powder and Quartz sand is made by high-temperature melting of raw materials.
In recent decades, the application fields of fused silica have become wider and wider, which has promoted the rapid development of the fused silica industry, and many new varieties have been continuously developed. For example, powder optical grade fused silica glass, opaque fused silica glass, low hydroxyl fused silica glass and synthetic optical grade fused silica glass developed by HERAE-US in Germany. The cerium-doped tube, iron-doped tube and fused silica glass with ultra-high purity and wide ultraviolet transmission capability developed by GEQUARTZ in the United States.
Fused silica glass tubes for electric light sources have been produced on a large scale in China, and some products have reached the advanced level of foreign countries, because of their price advantages are extremely competitive.
3 Application of Fused Silica
Because of its excellent physical and chemical properties, fused silica is widely used in electronics, electrical appliances, military, aerospace, optical communications, electric light sources, chemical engineering, metallurgy, instrumentation, optical lenses, anti-corrosion materials, refractory materials and other fields .
Fused silica is widely used in high-tech fields: high-purity high-temperature resistant quartz glass tubes, high-purity coated crucibles, quartz glass for optical communications and quartz glass for lasers have all developed rapidly.
3.1 Application in the electric light source industry
Electric light sources convert electrical energy into light energy and are widely used in daily lighting, industrial and agricultural production, national defense, and scientific research. Common low-intensity energy-saving lamps, germicidal lamps, and high-intensity Ley lamps, sodium lamps, metal halide lamps, infrared lamps, and ultraviolet germicidal lamps are all fused silica electric light source products. Germicidal lamps are widely used in the catering industry and the medical and health industries.
3.2 Application in the optical fiber industry
Fused silica material is not only an important basic material for optical fiber preforms, but the entire process of optical fiber production is also inseparable from fused silica products. Good raw materials are the guarantee for the production of stable quality optical fiber products. As an important raw material in MCVD, PCVD and their derivative process technologies, high-purity fused silica substrate tubes have strict requirements on size and purity. For example, the deposition of new layers of substrate tubes requires light guide grade. At present, although some of the quartz glass products for optical fibers in China have reached a certain level, there is still a lack of cutting-edge products such as high-purity, high-precision quartz glass base tubes and outer tubes.
3.3 Applications in the aerospace industry
Fused silica has a low thermal expansion coefficient and excellent radiation resistance, so it is widely used in the aerospace industry. The code-named 7971 fused silica developed by Corning Corporation has an average linear thermal expansion coefficient of zero in the range of 0 to 200°C. It has good thermal stability, low density, good rigidity, and good polishing performance. This fused silica can be used to make a mirror blank with a diameter
of 3.96m. , Used for large astronomical telescopes. Ultraviolet radiation resistant fused silica can filter ultraviolet rays to protect internal sensors. Fused silica is widely used as a structural part in spacecraft and space shuttles.
3.4 Applications in electronic information and semiconductor industries
With the rapid development of China's electronic information, semiconductor, and integrated circuit industries, the fused silica manufacturing industry has risen rapidly. For example, the fused silica diffusion tube used in the key processes of doping, diffusion, oxidation, and annealing of single crystal silicon wafers; the quartz bell jar used in the silicon wafer epitaxy process; the support used in the silicon wafer pickling and ultrasonic cleaning process; the control unit Quartz crucible used in the crystalline silicon process, etc.
3.5 Applications in other industrie
The propagation speed of ultrasonic signals in fused silica is lower than that of metals, and the delay temperature coefficient is lower. It can be used as ultrasonic delay glass for radar applications. Ultrasonic waves can be delayed by more than 1 microsecond through the multiple reflections of large polygonal fused silica. The reflected radar signal is used to determine the position of a moving target, which has practical application value.
Fused quartz has the characteristics of acid resistance, high temperature resistance, and high chemical purity. It is an ideal material for the production of chemical equipment. The quartz glass rectification tower is used to prepare laboratory distilled water.
Fused silica is an indispensable material in the smelting industry. Fused silica can withstand a temperature difference of 300°C and is used to produce high-temperature observation windows for industrial furnaces.
Fused silica has good chemical stability and low thermal expansion coefficient, and can be used to manufacture precision instruments, such as interferometers, wavelength meters, gyroscopes, gravimeters and other high-precision instruments.
Fused silica is widely used in various industries due to its superior performance. With the development of science and technology, the application of fused silica will be more extensive.
Energy consumption and quality issues in the production of quartz glass, especially energy consumption, have become a bottleneck restricting the silicon material industry. Optimizing the operation and structure of the fused silica production process, designing and researching refractory materials, and developing and reforming key equipment to reduce the production process high energy consumption and improving the quality of fused silica are not only inevitable requirements for realizing a low-carbon economy, but also an urgent problem to be solved in China's quartz glass industry.