Fused quartz, also known as quartz glass, is a supercooled liquid made from natural quartz, including silica and crystal, through high-temperature melting. China`s quartz glass industry is developing rapidly with the development of China’s semiconductor and national defense technology. The output and quality of quartz glass have been greatly improved. However, compared with the advanced foreign technology level, the high purity of quartz glass, melting equipment and energy saving There is still a gap in control.
Current status of the fused silica industry
Fused silica is divided into two categories: transparent and opaque. Transparent fused silica can be divided into ordinary quartz glass, high-purity quartz glass and doped quartz glass. According to the shape of the product, it can be divided into: pipe, bar, plate, crucible, bell jar and quartz glass fiber quartz wool. In terms of special functions, there are low-temperature expansion fused silica, radiation-resistant fused silica, ultraviolet or infrared fused silica glass, etc.
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.
The fused silica industry has developed rapidly in recent decades, and fused silica companies at home and abroad have developed many new varieties to meet the needs of different fields. Such as the low hydroxyl fused silica glass, powder optical grade fused silica glass, synthetic optical grade fused silica glass and opaque fused silica glass developed by HERAEUS in Germany. U.S. GE QUARTZ company developed titanium-doped tubes for ultraviolet germicidal lamps, cerium-doped tubes for special electric light sources, and fused silica glass with ultra-high purity and wide ultraviolet transmission capabilities.
China has adopted a continuous melting process to manufacture fused silica glass tubes for electric light sources. Some products have caught up with the advanced level of foreign countries and have strong competitiveness due to lower prices. However, the current energy consumption problems in the production of fused silica have led to the continuous increase of production costs of enterprises, the reduction of profit margins, and the hindrance of the development of the industry. Energy consumption accounts for more than 50% of the production cost of fused silica, and energy consumption has become a bottleneck restricting the development of the silicon material industry.
Application prospects of fused silica
The outstanding superiority of fused silica is its unique comprehensive performance that other materials do not have, that is, very low thermal conductivity, excellent thermal vibration resistance, high deformation temperature and softening temperature, and very low thermal conductivity. Very low dielectric loss and optical transmittance in a very wide spectral range from ultraviolet to infrared.
Application in electric light source industry
Electric light sources are devices that convert electrical energy into light energy, and are widely used in daily lighting, industrial and agricultural production, national defense, and scientific research. The main products of fused silica electric light sources include low-intensity energy-saving lamps, germicidal lamps and high-intensity mercury lamps, sodium lamps, metal halide lamps, etc., in addition to infrared lamps and ultraviolet germicidal lamps. Germicidal lamps are mainly used in medical and health, catering industry, and disinfection treatment. Mercury lamps and sodium lamps are mainly used for large squares and road lighting.
Application in the optical fiber industry
Fused silica material is the main auxiliary material in the production of optical fiber preforms and optical fiber production. Without excellent quality raw materials, it is impossible to produce stable quality optical fiber products, and thus cannot be mass-produced. High-purity fused silica substrate tube is one of the important raw materials in MCVD, PCVD and their derivative process technology. It has strict size and purity requirements. As a new layer of deposition substrate tube in the fiber manufacturing process, it requires light guide level. It can be seen that the purity and intrinsic quality of the material are very high.
Fused silica material is an important basic material for optical fiber preforms, and fused silica products also run through the entire process of optical fiber production such as rod making and drawing. At present, some of the quartz glass products for optical fibers in China have reached the international average level, but they lack cutting-edge products , Such as high-precision, high-purity quartz glass base tube and outer tube.
Application in electronic information and semiconductor industry
The rapid development of electronic information and semiconductor manufacturing in China has also put forward clear requirements for key materials, which has promoted the rapid development of related industries. Fused silica manufacturing has become a beneficiary of the development of electronic information, semiconductor, and integrated circuit industries. Quartz glass is widely used because of its high purity, high temperature resistance, and low thermal expansion. Such as: fused silica diffuser used in key processes such as doping, diffusion, oxidation, and annealing of monocrystalline silicon wafers; quartz bell jars used in the epitaxy process of silicon wafers; brackets used in the pickling and ultrasonic cleaning of silicon wafers; control Quartz crucible used in the single crystal silicon process.
Application in the optical industry
Due to the excellent properties of fused silica, it is widely used as lenses, prisms, camera lenses, astronomical telescopes, etc. in various optical systems, high and low temperature spectrum test systems. Because of its high permeability and high temperature resistance, fused silica is widely used in high temperature observation windows in industrial kilns, boilers and other high temperature occasions. In terms of laser technology, various types of quartz optical fibers and UV-filtered quartz glass are widely used in laser medical treatment, industrial laser processing, laser ranging, sensing, instrumentation and other fields.
Application in the aerospace industry
Fused silica has a very low thermal expansion coefficient and excellent radiation resistance, so it has a wide range of applications in the aviation industry. The code-named 7971 fused silica developed by Corning Corporation of the United States has an ultra-low coefficient of expansion, with an average linear thermal expansion coefficient of zero in the range of 0 to 200°C. It has particularly good thermal stability, low density, good stiffness, and good polishing performance. This type of fused silica is used to make blanks for large-scale astronomical telescopes, which can produce mirror blanks with a diameter of 3.96m.
Ultraviolet radiation resistant fused silica has good resistance to high-energy rays, and can filter ultraviolet rays to protect the internal sensor. Fused silica can also be used as structural parts in spacecraft and space shuttles.
Applications in other industries
As the ultrasonic delay glass on the radar, the propagation speed of the ultrasonic signal in fused silica is ten times smaller than that of metal, and it has the characteristics of low delay temperature coefficient. If the large-scale fused silica is processed into a polygon, the ultrasonic wave can be delayed by more than 1 microsecond after multiple reflections in the polygonal glass, so that the radar signal of the moving target can be identified from a series of reflections, and the direction of the moving target can be determined, which has practical significance.
In the chemical industry, fused silica is an ideal material for some chemical production equipment because of its acid resistance, high temperature resistance, and high chemical purity. Quartz glass rectification tower is generally used in the preparation of laboratory rectified water.
In the smelting industry, fused silica is also an essential material. To measure the temperature of the steel liquid surface, the outer cover is transparent fused silica. In industrial kilns, fused silica is usually used as a high temperature observation window to observe the melting situation in the furnace. Can withstand a temperature difference of 300°C.
In addition, fused silica has the characteristics of extremely low thermal expansion coefficient and excellent chemical stability, so it can be used to manufacture precision instruments, such as: wavelength meters, interferometers, gravimeters, gyroscopes and other high-precision instruments.
In short, fused silica is widely used in various industries due to its superior performance. With the development of science and technology, its application prospects will be broader.