Photovoltaic Industry, Irreplaceable Quartz Sand

Quartz is the main mineral component of many rocks such as granite and gneiss, and it is a very important industrial mineral. Quartz resources are widely used in photovoltaic field, and it is one of the key basic raw materials for photovoltaic industry.

Raw Material for Industrial Silicon: Silica Ore

Silica ore is the most important raw material for industrial silicon smelting, and it is also the general name of quartz-based minerals such as vein quartz, quartzite and quartz sandstone. Industrial silicon, also known as silicon metal, is made of silica ore (the main component is silicon dioxide), charcoal, coal and petroleum coke and other carbonaceous reductants, generated by high-temperature reduction reaction, industrial silicon can be prepared as polysilicon after further purification.

Photovoltaic silicon, solar grade polysilicon, is the core raw material of photovoltaic power generation system, is the upstream raw material of photovoltaic industry chain, is a gray-black solid with a metallic luster, has a high melting point, hardness, brittleness, chemical inactivity at room temperature and other characteristics, and semiconducting properties, it is an extremely important semiconductor materials, known as photovoltaic industry chain of the "black gold! ". The current mainstream polysilicon production technology is mainly improved Siemens method and silane fluidized bed method, the product form for the rod silicon and granular silicon.

Polysilicon can be used as raw material for pulling monocrystalline silicon. Monocrystalline silicon production process includes no crucible suspension zone melting method and crucible straight pulling method. Crucible-free suspended zone melting method refers to the use of high-frequency coils in the vacuum furnace room, the single crystal seed crystal and polysilicon rods in contact with the melting zone, and ultimately produce high-purity, small-diameter monocrystalline silicon.

Crucible straight pulling method is also known as Cheklausky method, the method needs to clean the raw material polycrystalline silicon first to remove its surface impurities, and then the seed crystal is stuck in the pulling rod fixture, after the introduction of the crystal, put the shoulder, isodiametric growth, closing and other processes, and ultimately produce monocrystalline silicon.

Raw Material of Quartz Crucible: High Purity Quartz Sand

Quartz crucible is actually a kind of container, which is made of high purity quartz sand through mold shaping and high temperature production using electric arc method. It is characterized by high temperature resistance, long service time, high purity, etc. It is mainly used as auxiliary consumables for semiconductor and solar energy pulling monocrystalline silicon rods.
In monocrystalline silicon production, quartz crucible is a one-time use of molten silicon and crystal growth of key materials, the production cost of monocrystalline silicon and the quality of product yield have a direct impact.

The quartz crucible used for monocrystalline silicon production in China usually adopts double-layer or triple-layer structure, and the purity of quartz sand directly affects the quality of silicon rods for crystal pulling. The lower the purity of quartz sand, the more likely to produce black spots and bubbles in the high temperature melting process. When used as inner layer sand, long time in high temperature environment will make the quartz crucible inner wall contained air bubbles released by heat, thus affecting the stability and success rate of monocrystalline silicon wafer production. Therefore, the inner sand requires higher purity of quartz sand and higher price. China quartz crucible with inner sand and other high-purity quartz high-end products still need to be imported from the United States, Norway, etc., while the quality requirements of the quartz crucible slightly lower in the outer sand, the raw material of its ore also need to be imported from India and other countries to solve the problem. Generally speaking, the raw material of inner sand for quartz crucible is granite pegmatite quartz from Spruce Pine area of North Carolina, USA, which is characterized by w(SiO2)≥99.998% (4N8) and stable quality. The raw material for the middle sand is vein quartz A grade ore imported from India and other countries, characterized by w(SiO2) ≥99.998% (4N8). The main raw material of the outer sand is the quality and stability of India and other countries imported a little inferior vein quartz A-grade or close to A-grade B-grade ore, characterized by w(SiO2)≥99.995% (4N5). Quartz crucible product quality directly affects the quality and cost of direct-pulled monocrystalline silicon, while the upgrading of crystal pulling process puts forward higher requirements for quartz crucible purity, life and size, further stimulating the demand for high-end quartz crucible. Quartz sand as the core raw material for making quartz crucible, its quality level and cost level largely determines the performance and cost of quartz crucible, therefore, it is necessary to improve the quality of high purity quartz sand from quartz mineral source screening, processing and other aspects, so as to improve the quality of quartz crucible to meet the demand in the manufacture of photovoltaic direct-drawing monocrystalline silicon.

Photovoltaic Glass Raw Material: Low Iron Quartz Sand

PV glass is an important accessory in the PV industry chain and an irreplaceable part of PV power generation modules, while quartz sand is one of the main raw materials for the production of PV glass, and the quality of quartz sand has an important impact on the quality of PV glass. PV glass is different from ordinary glass, which is made by deep-processing of ultra-white glass. Ultra-white glass is a kind of ultra-transparent low iron glass, also known as low iron glass, high transparent glass, with a low self-explosive rate, color consistency, high visible light transmittance, good permeability, low ultraviolet transmittance, etc. Transmittance is one of the most important indicators affecting the performance of photovoltaic ultra-white glass, due to the easy staining of iron ions to ensure that photovoltaic ultra-white glass of the high transmittance of photovoltaic ultra-white glass, photovoltaic ultra-white glass requires a lower amount of iron content. Photovoltaic glass production requires low iron content of super white quartz sand ore, accounting for about 13% of the cost of glass; China's high-quality low-iron super white quartz sand ore is relatively scarce, concentrated in Anhui Fengyang, Guangdong Heyuan, Hunan, Guangxi and Hainan, etc., the industry exists in a certain degree of natural monopoly; to the current photovoltaic glass leader, for example, Xinyi photovoltaic and Follett's production base is concentrated in Beihai, Guangxi, Anhui Wuhu and Fengyang, etc., supporting high-quality silica sand ore, the production base is concentrated in Beihai, Anhui Wuhu and Fengyang. The production bases of Xinyi photovoltaic and Follett are concentrated in Beihai of Guangxi, Wuhu of Anhui Province and Fengyang, etc., which are equipped with high-quality silica sand mines, and the quality of raw materials is stable and the cost is low, which is conducive to improving the stability of the finished products and reducing the production cost.

Quartz raw materials exist in a variety of impurities, such as Fe, Al, K, Na, Ca, etc., and in the production of ultra-white glass is the most harmful impurities of iron impurities, which can exist in the form of free form, but also can be thin films, lattice substitution or inclusions in the form of minerals, which require a series of processes to be effectively removed.

For the removal of iron impurities, need to go through a series of physical and chemical deep-processing process, according to the removal method is mainly divided into physical method (washing and grading desliming, scrubbing, magnetic separation, re-election), chemical method (flotation, acid leaching) and microbial methods, etc., in the quartz raw material deep-processing process can be based on the form of iron impurities and the state of the existence of a combination of these methods, in order to find a suitable for the source of the ore deep processing process.

Conclusion

Quartz sand plays an irreplaceable role in the photovoltaic industry in industrial silicon, quartz crucibles and photovoltaic glass. With the growing global demand for renewable energy, the rapid development of the photovoltaic industry and the high increase in the installed capacity of photovoltaics, its demand for quartz sand has also seen rapid growth.