Chang’e-4 achieved the first soft landing of a human probe on the back of the moon and the first relay communication between the back of the moon and the earth, opening a new chapter in human lunar exploration. Chang’e-4 successfully landed after 26 days of flight, and it is inseparable from the solar sensor (used for spacecraft orbit control and attitude control). It’s a must.
Quartz glass is known as the “crown” in glass materials. It is a kind of glass with SiO2 as a single component, which has super mechanical properties, thermal properties, optical properties and electrical properties. It plays an irreplaceable role in semiconductors, optical devices, optical communications, solar energy and other industries. High-purity quartz sand is currently the main raw material for smelting quartz glass instead of crystal ore.
1. Classification of quartz glass
According to different melting processes, commercial quartz glass is mainly divided into the following four categories:
(1) Electrofusion process under vacuum atmosphere, the raw material is high-purity quartz sand (40 mesh ~ 80 mesh). The hydroxyl content is small (1ppmw~10ppmw), but relatively speaking, the content of bubbles and metal impurities is high, Al (30ppmw~100ppmw), Na (4ppmw). Commercial names are Infrasil, G.E. 105, 201, 204.
(2) Gas refining process, using hydrogen or other hydrogen-containing fuel and oxygen as energy sources to fuse quartz glass, and the raw material is high-purity quartz sand (100 mesh ~ 200 mesh). During the smelting process, there is less metal pollution and less bubbles, but due to the hydrogen-oxygen atmosphere, the hydroxyl group contains 150ppmw~400ppmw. Commercial names are Herasil, Homosil, Optosil, G.E.104.
(3) Flame hydrolysis to synthesize quartz glass (CVD), and SiCl4 is sprayed into a hydrogen-oxygen flame for hydrolysis. Basically no metal impurities, but with high hydroxyl (1000ppmw) and Cl (100ppmw). Trade names Suprasil S, Spectrosil, Corning 7940.
(4) Synthetic quartz glass (PCVD), hydrolyze SiCl4 in anhydrous plasma flame. Similar to the third one but with only 0.4 ppmw for hydroxyl and 200 ppmw for Cl. Commercial names SuprasilW, SpectrosilWF, Corning7943.
2. Characteristics of quartz glass
(1) In terms of thermal properties, quartz glass has good resistance to high temperature deformation and thermal vibration. Its softening point (1665°C) is close to the melting point of platinum; the average linear expansion coefficient is very low (α=5.4×10-7/°C), which is only 1/10~1/20 of ordinary glass, that is, it is quickly put into high temperature. In cold water, it won’t shatter.
(2) In terms of chemical properties, quartz glass is extremely inactive and is a good acid-resistant material (except for hydrofluoric acid), and does not react with acids even at high temperatures. It is especially suitable for high-temperature acid-resistant combustion, cooling devices, preparation and storage devices for acid chemicals, and various chemical experimental glassware.
(3) In terms of optical performance, it has good light transmittance for the entire spectrum. The high optical transmittance in the ultraviolet and infrared range is not available in general optical glass, and can be used as prisms and lenses for various optical equipment; high temperature Operations, reactor windows; optical fibers and optoelectronic devices in the field of optical communication; using its high light transmittance, coupled with high temperature stability and thermal shock resistance, it is widely used in the field of high temperature lamps, such as ultraviolet lamps , infrared lamps, mercury lamps, xenon lamps and halogen lamps and other high temperature lamps.
(4) In terms of electrical applications, quartz glass is an excellent insulating material. The resistance value (1016Ωm) at room temperature is 100 times that of ordinary glass (1014Ωm), which is suitable for manufacturing high-frequency and high-voltage insulators with high temperature resistance.
3. Application fields of quartz glass
(1) Semiconductor: Quartz products are important semiconductor consumables and are used in the whole process of semiconductor processing. The silica in the quartz glass has high purity and stable chemical properties, and does not react with any acid except hydrofluoric acid and phosphoric acid. The requirements of cleaning and other containers are widely used in the semiconductor production process. In addition, due to the low refractive index and strong temperature resistance of quartz glass, it can meet the requirements of the mask for high optical transmittance and low thermal expansion rate of the base material, and is an important material for high-precision glass masks.
(2) Optical fiber: Silica glass material is the main consumable material in the production of optical fiber preform and optical fiber drawing. The refractive index of quartz glass is extremely low, the absorption coefficient is small and the light transmission band range is wide, and optical fiber, as a light transmission tool transmitted by the principle of total internal reflection, has extremely high requirements on the refractive index, so quartz glass is widely used in optical fiber manufacturing , the main products are preform, furnace tube, quartz tube and so on.
(3) Optics: Components composed of quartz glass are key components in optical instruments. Transparent quartz glass has good optical properties and low refractive index, and can meet any light transmission band in the range of 185-3500mμ, so it can be used as both an ultraviolet-transmitting material for optical instruments and an infrared-transmitting material. The main products are spectrographs, Infrared cameras, prisms and lenses. At the same time, quartz glass has strong thermal stability, and the value is between 800 and 1000 ° C. Optical quartz glass is also widely used in high-altitude high-temperature photography, such as high-temperature operation peep windows, high-precision rangefinders and large astronomical telescopes.
4. Quartz Glass Market Competitive Landscape
The quartz glass market is a typical monopoly market. The quality of quartz glass is mainly affected by the preparation method and process, and the leading companies in the industry maintain high technical barriers. At present, only 6 quartz glass manufacturing companies in the world have obtained TEL certification, of which four are overseas companies including Momentive, Heraeus, Quincy, and Tosoh, and Chinese-funded companies include Philippine and Quartz.