Quartz is a framework-like structure oxide mineral with the advantages of high hardness, stable chemical properties, and good thermal insulation. Quartz is widely used in optical fiber transmission and photovoltaic fields because of its high refractive index. At the same time, quartz has light transmittance. , can be made into quartz glass, known as “the crown of glass materials”.
High-purity quartz is used in high-tech fields such as the production of semiconductor crystalline silicon, which is made into silica crucibles to hold high-temperature silicon melts. The excellent performance and wide application of quartz make it stand out in the era of high-tech development. Quartz resource is not only one of the key basic raw materials of photovoltaic power generation industry, but also an important strategic non-metallic mineral resource.
Solar photovoltaic power generation is a technology that directly converts light energy into electrical energy by using the photovoltaic effect of the semiconductor interface. It has developed rapidly in recent years.
At present, the main structural components of photovoltaic power generation panels are: laminates (from top to bottom tempered glass, EVA, cells, backplane), aluminum alloy frame, junction box, silica gel (bonding each component). Among them, the components that use quartz resources as the basic raw materials in the manufacturing process include tempered glass, battery, silica gel and aluminum alloy. Different components have different requirements for quartz sand and different dosages.
The tempered glass layer mainly plays a protective role and protects the internal structures such as cells located under it. It is required to have good light transmittance and transparency, high energy conversion rate, low self-explosion rate, high strength and thinness. At present, the most widely used solar tempered glass is low-iron ultra-white glass. Low-iron ultra-white glass usually requires the main elements in quartz sand: SiO2≥99.30%, Fe2O3≤60ppm, etc. Quartz resources used to make solar photovoltaic glass mostly use quartzite and quartz sandstone , coastal quartz sand and other resources are obtained through beneficiation and purification.
The main structure of solar photovoltaic panels
Cells are the core components of photovoltaic power generation, mainly including monocrystalline silicon cells, polycrystalline silicon cells, amorphous silicon cells and multi-compound cells. The most widely used are monocrystalline silicon cells and polycrystalline silicon cells. Compared with polycrystalline silicon cells, monocrystalline silicon cells have the advantages of high light conversion rate (15%~21%, mostly around 18%) and long service life, but the production cost is high and limited by the physical properties of the material, it must reach more than 30%. The possibility of conversion rate is small; compared with monocrystalline silicon cells, the light conversion efficiency of polycrystalline silicon cells is low (12%~18.5%, mostly around 16%). Compared with monocrystalline silicon cells, the light conversion efficiency of polycrystalline silicon cells is low. It has a short service life and is gradually being replaced by monocrystalline silicon cells; amorphous silicon cells have the advantages of thinness, light weight, good flexibility, etc., and have a wide range of applications, especially suitable for photovoltaic building integration, but their light conversion efficiency Low; multi-compound batteries (such as gallium arsenide, cadmium sulfide batteries, etc.) have high photoelectric conversion efficiency, but are expensive, and are mostly used in important fields such as aerospace, and have no practical value for large-scale industrialization.
The production of photovoltaic monocrystalline silicon and polycrystalline silicon is usually made of metal silicon. Affected by the cost, the metal silicon used to make polycrystalline silicon has higher requirements on quartz raw materials. It is usually made of quartz sand with SiO2>99.9% after smelting and purification. The quartz resources used in the production of polycrystalline silicon It can be obtained from high-quality quartzite, quartz sandstone, vein quartz and other resources.
The crucibles, diffusion tubes and other materials used in the production of polycrystalline silicon and monocrystalline silicon are photovoltaic grade high-purity quartz sand. Generally, it is required that the total content of impurity elements in quartz sand SiO2≥99.99% should be less than 25ppm, of which K, Li, and Na are less than 2.5 ppm. The ultra-high-purity quartz content is greater than 99.999% (Al<8 ppm, Fe<0.05 ppm, Ti<1.3 ppm, etc.). Take Union Ming Company of the United States as an example, its IOTA standard is recognized internationally, and its product purity reaches 99.9994%. There are two methods for preparing high-purity quartz: synthesis method and purification method, in which the synthesis method relies on synthesizing crystals, using carbon tetrachloride vapor deposition and sol-gel method for liquid deposition. Due to the high cost of synthesis and the gradual depletion of crystal resources, the optimization of purification methods has been put on the agenda, which is the practical reason for the development of quartz purification.
The main methods of quartz purification are physical treatment, chemical treatment and biological treatment. Further subdivisions include high temperature calcination, microwave heating, water quenching, grinding, screening, color separation, magnetic separation, flotation, acid leaching, ultrasonic treatment, chlorination roasting, etc. At present, the quartz resources that can produce this type of high-purity quartz sand in the world are mainly obtained from granite quartz (a small part is extracted from vein quartz), and such resources are mainly concentrated in the United States. The quartz raw materials used in the production of quartz crucibles by my country Quartz Co., Ltd., Fudong and other companies are basically imported from the United States.
Silicone is mainly used for sealing, sealing each component with the aluminum alloy frame, the junction of the component and the junction box, etc. At present, silica gel is mostly made from metal silicon. The metal silicon used for silica gel has lower requirements on quartz resources than that of polycrystalline silicon and single crystal silicon. Usually, the quartz sand quality SiO2>99.0% can be obtained from quartz resources.
Aluminum alloys mainly add a small amount of metallic silicon during the smelting process to enhance performance. Silicon metal silicon for smelting is similar to silica gel, and has lower quality requirements for quartz sand.
The 21st century belongs to the future of silicon-based materials. With the rapid development of emerging industries such as semiconductors and photovoltaic cells, the demand for the quantity and quality of materials is increasing. Therefore, how to effectively purify quartz (especially high-purity and ultra-high-purity quartz) has become a current and future research hotspot. The main component of quartz is silica.