As an important part of chemical instruments, the crucible is the container for melting and refining metal liquids and heating and the reaction of solid and liquid, which is the basis for the smooth chemical reaction. Crucibles were originally made of clay, and one of the earliest uses of platinum was for crucibles. With the development of preparation technology, crucible can now be composed of any material capable of melting or changing its contents.
There are many kinds, models and specifications of the crucible, which can be chosen arbitrarily, with strong applicability, and can guarantee the purity of the melted material. The ceramic crucible is an important part of the crucible. According to raw materials, ceramic crucible can be divided into quartz crucible, corundum crucible, boron nitride crucible, zirconia crucible, etc., which are used in different occasions according to their properties.
Quartz ceramic crucible
Quartz ceramic crucible is a ceramic crucible made of high purity fused quartz with fine structure, low thermal conductivity, small thermal expansion coefficient, good thermal shock stability, good electrical performance and good chemical resistance, is widely used in glass deep processing industry, metallurgy industry, electronic industry, chemical industry, aerospace and other fields. In general, the shape of quartz ceramic crucible is mainly square and cylindrical.
With the attention and development of environmental protection energy, solar energy, as a green energy, has been widely valued in the world. The amount of polycrystalline silicon used for solar energy conversion has increased dramatically, thus promoting the rapid development of polycrystalline silicon production. Therefore, the corresponding large-size thin-walled square fused quartz ceramic crucible is also increasing rapidly, and the international market is very optimistic.
Corundum crucible, formally known as alumina crucible, is commonly referred to as corundum crucible when the content of alumina exceeds 95%. Corundum crucible is strong and resistant to melting, high temperature, acid and alkali, cold and extreme heat, as well as chemical corrosion, which is suitable for melting samples of weak alkaline substances such as Na2CO3 without water, but not suitable for melting samples with strong alkaline and acidic materials as fluxes.
99.70% of corundum crucible at oxidation and reduction atmosphere of 1650 ℃ to 1700 ℃ has good insulation and mechanical strength. According to the application conditions, alumina crucible has a variety of sizes and shapes to choose from.
Boron nitride crucible
The commonly used types of boron nitride include cubic boron nitride (C-BN) and pyrolytic boron nitride (P-BN). The boron nitride crucible is usually composed of P-BN. P-BN ceramics have good heat resistance, thermal stability, thermal conductivity, high-temperature dielectric strength, and are ideal heat dissipation materials and high-temperature insulation materials.
Due to the excellent chemical stability of P-BN, which can resist the erosion of most of the molten metal, and because of the high-temperature insulation, high thermal conductivity and low thermal expansion properties mentioned above, it is the most suitable material to be used in strict environmental conditions such as semiconductor manufacturing process. P-BN crucible is often used for smelting metal and semiconductor, and the temperature of use in the vacuum can be as high as 1800 degrees.
Zirconia has a higher melting point than zirconium and is one of the most refractory materials in nature. Even if heated to 1900 ℃, zirconium oxide also won't react with the molten aluminum, iron, nickel and platinum metals, silicate and acid slag, etc., so the zirconia crucible can successfully smelt platinum, palladium, ruthenium, and cesium precious metals and their alloys.
Compared with alumina, zirconia is more expensive, but it is a special oxide refractory material that can be used in the high-temperature furnace above 2000 ℃, which is something that no other oxide can replace.
Yttrium oxide crucible
Yttrium oxide (Y2O3) ceramics is a high-performance ceramics with excellent heat resistance, corrosion resistance, and high-temperature stability. The melting point of yttrium oxide is greater than 2400 ℃, and it is difficult to react with some active metals (such as Ti, Al, Hf, Nb, etc.) at high temperature. The crucible, mainly composed of high purity Y2O3, has a potential for melting Ti and Ti alloys, or any oxygen-sensitive melting process.
However, Y2O3 is difficult to process because of its high melting point. Since Y2O3 itself is very brittle, the crucible may rupture if the heating or cooling rate is too fast.