High-purity quartz has excellent physical and chemical properties such as high temperature resistance, corrosion resistance, high strength, high light transmittance, low thermal expansion coefficient, etc., and is widely used in semiconductors, optical fiber communications, photovoltaics, optics, electric light sources and other fields, and is an important support and irreplaceable material for strategic emerging industries.
The preparation of high-purity quartz mainly includes two technologies, such as physical and chemical processing purification and chemical synthesis, due to the depletion of natural crystals that can be used as high-purity quartz raw materials in China, the existing vein quartz raw material ores are mainly small and medium-sized, and it is difficult to process and purify, so China's high-purity quartz raw material ores are highly dependent on imports.
In recent years, many companies have begun to focus on the preparation of high-purity quartz by chemical synthesis, and have begun to lay out the field of high-purity synthetic quartz sand.
Preparation technology of high-purity synthetic quartz.
Gas phase synthesis.
The gas phase synthesis method is the flame hydrolysis method, which is similar to the gas phase silica process, and its principle is to use silicon or silicone chloride (such as SiCl4 or CH3SiCl3, etc.) raw materials, which are gasified and mixed with hydrogen and oxygen, and hydrolyzed at high temperature to form mist SiO2, and finally obtained through cooling, separation, deacidification and other gas-solid separation. The product obtained by this method is fumed SiO2, with a particle size of less than 100nm, a fluffy and porous appearance, a large specific surface area, high chemical purity and good dispersion.
The production process of gas phase synthesis is simple, the synthesis conditions are easy to control, the reaction speed is fast, and it is suitable for large-scale productionDue to the high temperature environment required in the process, the HCL generated by the reaction will seriously corrode the equipment, so the requirements for the material and heating form of the production equipment are relatively strict. Due to the high energy consumption and high processing cost of the gas phase method, further research is needed in the aspects of reaction conditions and equipment selection.
Chemical precipitation.
Chemical precipitation is one of the most widely used methods for synthesizing quartz powder. The principle of producing SiO2 by precipitation method: sodium silicate and carbon dioxide or acid solution (adding hydrochloric acid, sulfuric acid or nitric acid) are used as raw materials, mixed and reacted under a certain synthesis temperature and the action of surfactants to obtain metasilicic acid precipitation, and then SiO2 is prepared by filtration, washing, drying and calcination processes.
The preparation of synthetic quartz by precipitation method has the advantages of convenient operation, simple production process, easy availability of raw materials and low energy consumptionHowever, the presence of impurities such as Fe3+, Al3+, and Ca2+ will promote the formation of clots, which will seriously affect the quality of the product, resulting in poor product performance, low purity, large particle size, and easy agglomerationThere are also shortcomings such as low concentration of reaction system, fast precipitation speed, and difficult to control the precipitation processIn addition, the treatment of waste acid and wastewater brings certain damage to the environment.
Dissolve-gel method.
The sol-gel method uses inorganic salts or metal alkoxides (generally ethyl silicate) as raw materials, alcohol as co-solvents, and acid or alkali solutions as catalysts to hydrolyze, polycondensation reaction to form SiO2 gel, filtration and washing of the organic solvent in the gel, drying and calcination to obtain SiO2 powder.
SiO2 is prepared by sol-gel method, the production process is simple, the synthesis conditions are easy to control, the requirements for equipment materials are not strict, and there are no other additives in the process, so the SiO2 prepared has high purity, good uniformity and large specific surface area. However, the cost is high, the production cycle is long, and the industrialization value is not large;In addition, because there are many variables in the experimental process, accurate control cannot be achieved (such as hydrolysis system, drying method and sintering pathway, etc.), so it is only in the laboratory test stage.
Liquid phase hydrolysis of silicon tetrachloride.
The principle of silicon tetrachloride liquid phase hydrolysis method is that SiCl4 is in contact with pure water for hydrolysis or polycondensation reaction, and then the reaction products are washed, filtered, dried, calcined, screened and other processes to prepare SiO2 powder. The SiCl4 liquid phase hydrolysis method was used to prepare high-purity quartz powder, and the SiO2 powder was of high purity and low hydroxyl content due to the lack of carbon in the raw material. However, in the process of large-scale production, the hydrolysis and polycondensation reaction of silicon tetrachloride and water is violent, the intermediate process is difficult to control, the powder is easy to agglomerate, and the density of the quartz powder formed is low. Therefore, in order to meet the needs of industrial production, this method still needs to be more deeply controlled by its process (such as hydrolysis control, drying and sintering process, etc.) to effectively reduce the occurrence of particle agglomeration.
High-purity synthetic quartz sand layout enterprise.
Jianghan New Materials. On February 7, 2023, Jianghan New Materials said that it has found a new way in the field of ultra-high-purity 6N-grade synthetic quartz sand technology research and development, relying on existing silane products as raw materials to synthesize ultra-high-purity 6N-grade quartz sand, with a total amount of metal ions of 01ppm, hydroxyl content of 60ppm, the technical indicators can meet the needs of high-end quartz application fields, and can effectively guarantee raw materials and control costs through industrial collaboration. The company's 6N grade ultra-high purity quartz sand is a high-purity quartz sand prepared by a synthesis process, which can be used to produce various quartz products including quartz crucibles.
In May, Jianghan New Materials said that in terms of research and development of synthetic quartz sand, the pilot test work is being carried out smoothly, and the company has successfully trial-produced 6N-grade quartz sand on the pilot line, and according to the test results, the production process is continuously adjusted and optimized to improve the quality and process performance of the trial product and reduce costs.
Kaisheng Technology. On March 31, 2023, Kaisheng Technology said that the company's main process route for synthesizing quartz sand is to prepare organosilanes from industrial silicon, and then use the sol-gel method to prepare nano-scale quartz powder and micron-level quartz sand, with high product purity and doping of related elements to meet different functional requirements. In the pre-project section, industrial silicon is used as the main raw material to prepare organosilanes, which can not only ensure product consistency, but also make the product have better cost advantages. The purity of synthetic quartz sand products developed by the company can reach 6N-7N, and a 5,000-ton production line is currently under construction, and the main target markets are chip polishing materials, photovoltaic crucible materials, semiconductor packaging materials and manufacturing materials.
On September 28, Kaisheng Technology said that the synthetic quartz project is being constructed as planned, and the equipment installation is expected to be completed around the end of this year. After the completion of the company's synthetic quartz sand project, the products used for semiconductor grade are mainly benchmarked against foreign countries, and the current market is more than 300,000 tons according to different application fields.
Shijing Technology. On May 4, 2023, Anhui Shijing Solar Energy Technology Co., Ltd. and Wuxi Weixinyuan Electric Power Co., Ltd. signed a "Strategic Cooperation Agreement" to cooperate and focus on the technology development and product research and development of high-purity quartz sand. According to the agreement, the two parties will establish a cooperation mechanism to establish a project company to focus on the research, development and production of 6N grade high-purity quartz sand. Its product applications include but are not limited to chip polishing materials, photovoltaic crucible materials, semiconductor packaging materials and pharmaceutical manufacturing materials.
In October, Shijing Technology said on the interactive platform that the 6N quartz sand project in cooperation with Wuxi Weixinyuan Power is currently progressing smoothly as planned.
The 2nd Anhui International Quartz Industry Conference and Exhibition 2024.