Hafnium is often +4 in the compound, the main compound is hafnium dioxide (HfO2), other common hafnium compounds are hafnium tetrachloride, hafnium hydroxide, hafnium carbide and hafnium boride, among which hafnium dioxide and hafnium tetrachloride are the raw material for preparing metal hafnium, and hafnium hydroxide is used to prepare other hafnium compounds.
Properties: White powder with three crystal structures: monoclinic, tetragonal and cubic. The densities are 10.3 g/cm3, 10.1 g/cm3 and 10.43g/cm3 respectively. The melting point is 2780~2920K, the boiling point is 5400K. The coefficient of thermal expansion is 5.8x10-6/℃. It is insoluble in water, hydrochloric acid and nitric acid, but soluble in concentrated sulfuric acid and fluoroxic acid.
Preparation: It is prepared by thermal decomposition or water decomposition of compounds such as hafnium sulfate and hafnium oxychloride.
Application: Raw material for producing metal hafnium and hafnium alloy. Used as refractory materials, anti-radioactive coatings and catalysts.
Hafnium tetrachloride(HfCl4)
Properties: white crystal block. Strong hygroscopicity. Soluble in acetone and methanol. When it meets with water, it will be hydrolyzed to produce HfOCl2. It will volatilize when heated to 250℃. It is irritating to eyes, respiratory system and skin.
Preparation: It is prepared by the action of chlorine on the mixture of hafnium oxide and carbon.
Application: Raw material for preparing hafnium metal
Hafnium Hydroxide(H4HfO4)
Properties: It usually exists as the hydrated oxide HfO2-nH2O, hardly soluble in water, easily soluble in inorganic acid, insoluble in ammonia, and rarely soluble in sodium hydroxide. When heated to 100°C, hafnium oxyhydroxide HfO (OH) 2.
Preparation: A white hafnium hydroxide precipitate is obtained from the reaction of hafnium (IV) salt with ammonia water.
Application: used to prepare other hafnium compounds
Properties: Density 12.7g/cm3, melting point 3890℃, it is the highest flame point among known single compounds. It has high melting point, high elastic coefficient, good electrical and thermal conductivity, small thermal expansion, and good impact performance.
Preparation: Usually hafnium dioxide and carbon are used to synthesize powder in an inert or reducing atmosphere.
Application: Used in the nose cone of the rocket nozzle to return to the atmosphere, and ceramics.
Properties: gray with metallic luster crystals, flame point 3250℃, high conductivity, stable chemical properties. It hardly reacts with all chemical reagents (except HF) at room temperature.
Preparation: It is prepared by mixing and heating hafnium dioxide, boron carbide or boron oxide, and carbon powder.
Application: Used as a high temperature resistant alloy.
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