Technical parameters of zirconium materials
Zirconium and titanium have many similar physical and chemical properties. For example, their melting points are both very high, pure titanium: 1668 ℃, pure zirconium: 1852 ℃. Both zirconium and titanium are highly chemically active, and zirconium is higher than titanium, but both can form a dense passivation film on the surface, which has high corrosion resistance. In most highly corrosive media, zirconium has better corrosion resistance than titanium, which is why zirconium is more expensive than titanium, but is still used in many chemical equipment. Since zirconium and hafnium often coexist in zirconium ore, the content of hafnium in zirconium ore is about 2%-3% of the content of zirconium. The physical and chemical properties of zirconium and hafnium are similar in all aspects. It is costly to produce zirconium with a hafnium content of less than 0.01% from zirconium and hafnium coexisting zirconium ore. Since the physical and chemical properties of zirconium and hafnium are very similar, it is not necessary to reduce the hafnium content in the production of chemical grade zirconium. Generally, the hafnium content in zirconium does not exceed 4.5%. Although my country has nuclear grade zirconium material standards, there are no national standards or industry standards for chemical grade zirconium materials (under preparation). Zirconium is also a passivating metal, which is easy to combine with oxygen to form a dense passivation film on the surface, which makes zirconium resistant to corrosion by most organic acids, inorganic acids, strong alkalis, molten salts, high temperature water and liquid metals. It has excellent corrosion resistance in hydrochloric acid of all concentrations below the boiling point at normal pressure, but there is a possibility of hydrogenation in hydrochloric acid above 149 ℃. Zirconium can be used in nitric acid below 250 ℃ with a mass fraction not exceeding 70%, but it is easy to ignite in concentrated nitric acid with very little water content. Zirconium is corrosion-resistant in organic acids, but not in hydrofluoric acid, concentrated sulfuric acid, concentrated phosphoric acid, aqua regia, bromine water, hydrobromic acid, fluosilicic acid, calcium hypochlorite, and fluoboric acid. It is not corrosion-resistant in oxidizing chloride solutions such as copper chloride and ferric chloride, but it is corrosion-resistant in reducing chloride solutions.
When zirconium is in the air, it will peel severely at 425 ℃, generate white zirconium oxide at 540 ℃, and absorb oxygen and become brittle above 700 ℃. Zirconium reacts with nitrogen above 400 ℃, and reacts strongly around 800 ℃. Vacuum annealing cannot remove oxygen and nitrogen in zirconium. Zirconium begins to absorb hydrogen above 300 °C, which will cause hydrogen embrittlement. Hydrogen can be eliminated by vacuum annealing at 1000 °C.
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