The difference between silicon metal 553 grade and 441 grade metal silicon is basically the difference in purity. The first is the problem of different raw materials. Among industrial silicon, 553 silicon content is only about 98.5%, about 15 yuan per kilogram, 441 silicon content is about 99%, about 18 yuan per kilogram, the best 211 silicon content is about 99.6%, about 28 yuan per kilogram money.
Specifically, industrial silicon is obtained by a high-temperature reaction of quartz and carbon in an electric arc furnace: SiO2+C=Si+CO2. Quartz is divided into low quality (such as sea sand, and sandstone) and high quality (such as vein quartzite). Carbon as a reducing agent is also available in poor quality (such as charcoal) and good quality (such as anthracite). The difference in these raw materials determines that the purity of industrial silicon is guaranteed. From a cost point of view, it is clear that the higher the quality of the raw material, the more expensive it will be.
For applications that do not require high purity, such as adding aluminum/iron alloys, or as raw materials for organic silicon products such as fully synthetic engine oil, heat dissipation silicone grease, and silicone rubber, the introduction of a small number of impurities has little effect. It is cheaper and more economical to use 98.5% silicon.
Let’s talk about applications with high-purity requirements. For example, solar panels are made from monocrystalline or polycrystalline silicon wafers as substrates. Even with a 99.6% product, the purity is far from enough. But we still have to start with 99.6% industrial silicon raw materials.
After further smelting, some solvents are used to remove impurities, and after cooling, they grow into independent crystals (monocrystalline silicon is generally a round rod, and polycrystalline silicon is generally a square ingot), and the purity must reach 99.9999%. This product is relatively expensive, about 50 yuan per kilogram for polycrystalline silicon, and 90 yuan per kilogram for monocrystalline silicon.