Where does high purity quartz come from?

(Quartz) is a very common mineral in our daily life. The composition is SiO2. The single crystal of SiO2 is crystal, while the polycrystal forms chalcedony and agate. The ordinary glass we usually see is SiO2 without a crystal structure. The sand on the beach is basically composed of quartz and feldspar. I believe that everyone is not unfamiliar with quartz. However, in recent years, with the promulgation of the US ban on “cores” and the rise of quartz stock prices, quartz has been transformed, setting off a “high-purity quartz sand fever”. What is high purity quartz? What is the difference between it and our common quartz? What kind of sand can be used to make chips?

High-purity quartz refers to quartz and its products with extremely high purity of SiO2 and extremely low content of impurity elements, which are widely used in semiconductor, photovoltaic, optical fiber, precision optics, advanced lighting equipment, new glass and other industries. However, because different industries require different qualities of quartz, there is no universal quality evaluation index for high-purity quartz. Different people have different definitions. Early research believed that the impurity content of high-purity quartz should be less than 50×10-6, that is, quartz with a purity of SiO2 greater than 99.995% is high-purity quartz. The Norwegian Geological Survey proposed more detailed indicators, requiring not only the total mass of impurities to be less than 5/100,000, but also the content of Al should be less than 3/100,000, the content of Ti should be less than 1/100,000, Na and K should be less than 8 parts per million, the content of Li and Ca should be less than 5 parts per million, the content of Fe should be less than 3 parts per million, the content of P should be less than 2 parts per million, and the content of B should be less than millionth. In 2014, Flook proposed a new quality index according to the needs of the market and industry. It believes that the quartz with a purity of 99.95% SiO2 and a total impurity content of less than 5/10,000 is high-purity quartz, and quartz with a purity of 99.5%~99.8% can meet the requirements of semiconductors. Quartz with a purity of less than 99.5% can be used in the transparent glass industry according to the requirements of the production industry of fillers, optical fibers, and LCD screens.

Chinese scholar Wang Ling believes that quartz with a purity of more than 99.9% SiO2 is high-purity quartz. In recent years, the emerging new glass industries such as photovoltaic glass and ultra-white float glass have lowered the purity requirements for SiO2. Therefore, considering different index systems, considering the quality of raw ore, testing methods, existing purification processes and industry quality requirements, the standard for high-purity quartz adopted in my country is: quartz with a purity of SiO2 greater than 99.9%.

In the process of natural crystallization, quartz is often doped with trace impurities, mainly gangue minerals, inclusions, and lattice impurities in the crystal gap. Like our usual river sand and natural sand, which contain too many impurities, the silicon content of river sand is generally 65%~85%, and the silicon content is too low to be used for the production of chips. The type and content of impurity elements will affect the performance of quartz. For example, the presence of Al will affect the light transmission rate in quartz. Metal elements such as Fe and Mn reduce the light transmittance of quartz. Quartz with excessive P and B content It cannot be used in the photovoltaic industry, so when producing high-purity quartz, it is necessary to purify the raw material ore to minimize Al, K, Na, Li, Ca, Mg, Fe, Mn, Cu, Cr, Ni, B, P, etc. impurity content.

Compared with ordinary glass, ultra-white glass is crystal clear, has high light transmittance, and has extremely low iron content (the mass fraction of Fe2O3 does not exceed 150×10-6), which is only 1/1 of that of ordinary glass. 10, or even lower, when the iron content exceeds the standard, the resulting glass will not only decrease in transparency, but also show a yellow-green color. And ultra-white glass is safer, its self-explosion rate is only about 1/10,000, which is much lower than that of ordinary glass (the self-explosion rate is about 3/1,000), especially suitable for the construction of important buildings and high-rise buildings, such as The “Bird’s Nest” and “Water Cube” stadiums of the Beijing Olympic Games, the “China Pavilion” of the Shanghai World Expo, the Beijing National Grand Theater, and the Nanjing China Art Center all have ultra-clear glass. Therefore, in terms of impurity element content and silicon content requirements, the new glass industry and semiconductor industry will have more stringent requirements.