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Synthesis and application of metal borides


With the progress of modern science and technology, metal boride plays a more and more important role, which has been on the stage of material industry from the original role of raw materials. Due to its incomparable characteristics of flame retardancy, heat resistance, high hardness, high strength, wear-resisting catalysis, energy saving and light weight, as well as its wide use in national economy and people's life, boride product development has been concerned by scientists all over the world. For example, borohydride (sodium borohydride, lithium borohydride), due to its inherent characteristics, can be used as high-energy fuel for rockets and high shovel reductants for organic synthesis; Boron metal compounds such as aluminum boride, titanium boride, boron nitride, boron carbide are used in the atomic energy industry, aerospace industry, high-speed cutting, telecommunications, electronics industry; Boron is used in special alloys and car airbags, and because of the large neutron absorption cross section of the B-10 isotope, it is used as a counter tube and as a control rod in atomic reactors. Magnesium borate, aluminum borate whisker, magnesium diboride as superconducting materials. In recent years, it has been applied in some important fields.


Zirconium boride

Vulgar zirconium diboride, molecular formula ZrB2, molecular weight 11284.

The manufacturing method of zirconium boride is: boron trifluoride and zirconium reaction, zirconium dioxide, boric acid and carbon in a high temperature furnace heating to 1900 ℃, the element boron and zirconium oxide in a vacuum heating to 1000 ~ 1750 ℃.

(1) high purity zirconium diboride production method

Gas phase halides are deposited in nitrogen onto a heated tungsten substrate.

(2) Metal borides prepared by melt electrolysis

Electrolytic cell composition CaO+CaF2 +2B2 O3 +1/6 ZrO2, temperature 1 000 ℃, product ZrB2 purity 99.6%, melt electrolytic method to get the purest boride ZrB2, impurities is graphite. The composition of the cell and a small amount of metal or boron and the ratio of gold to boron in borides can be controlled by the ratio of metal oxide to boron oxide in the cell.

(3) The industrial synthesis method of zirconium boride is mainly using zirconia to reduce boride, reducing agent can be carbon or boron carbide (B4C). Using boron carbide is better than using carbon because zirconium boride synthesized by carbon reduction is derived from boron anhydride. Whether using arc melting or solid state reaction synthesis process, due to the low boiling point of boron anhydride above 1 000 ℃, a large amount of volatilization makes the chemical composition of synthesized zirconium boride change a lot and the temperature of melting method is high and the electromelting speed is fast It will cause serious contamination of the products by Shimmer crucible and may produce a large number of by-products zirconium carbide. The single phase product of zirconium diboride can be prepared by using boron carbide as reducing agent.

Calcium boride

Molecular formula: CaB6, molecular weight 104.94.

Titanium boride

Titanium diboride ceramic metal composite has high corrosion resistance and high temperature stability. Titanium diboride based materials (35% ~ 73% Ti2, The addition of 8%-10% Al, the rest is BN) can improve the sintering performance and obtain the nectar material, so as to improve the corrosion resistance. The specific resistance of (1.2 ~ 4)×10-5 ψ • M has high stability to steam and liquid metals due to the formation of aluminum nitride in the interaction between aluminum and boron nitride. It fills holes and reduces the porosity of the product (up to 4% ~ 5%). In addition, the addition of aluminum can promote sintering due to the formation of liquid phase. It is suggested that the ceramic-metal composites should be prepared by hot pressing at a temperature below 1800 ℃.