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It is a ductile, shiny and silvery metal. It resists corrosion and is chemically similar to zirconium. The properties of hafnium are affected by the presence of zirconium impurities and these two elements are among the most difficult to separate. The only notable difference between them is the density (zirconium is half as dense as hafnium). As with zirconium, hafnium is extracted from the ore as a pure metal by reducing the tetrahalide by magnesium, the reaction is carried out under an argon atmosphere because the two metals could combine with other gases (nitrogen, for example).

Hafnium resists corrosion in air and water due to the formation of an oxide film (passivation), although powdered hafnium burns in air. It is unaffected by alkalis or acids, except for hydrofluoric acid.

Like titanium and zirconium, the two other stable elements of group IVB of the periodic table, it has two allotropic crystalline forms: hexagonal compact at room temperature (phase ), and cubic centered at high temperature (phase ); their transition temperature is around 1,750 C.

Like most rare metals, hafnium is a non-renewable resource, almost all of the resource comes from the purification of zirconium.

Physical characteristics (complementary to those given opposite)

Atomic radius = 0.167 nm
Ionic radius = 0.081 nm
Coefficient of thermal expansion between 0 and 100 C = 6.0C6 / K
Mechanical characteristics

At 20 C
Brinell hardness = 1,400 to 1,600 MPa
Tensile strength = 350 to 500 MPa
0.2% elastic limit = 150 to 250 MPa
Elongation = 30% to 40%
Modulus of elasticity = 140,000 MPa
Resilience = 6 to 7 kgm / cm2
At 320 C
Tensile strength = 280 MPa
0.2% elastic limit = 150 MPa
Elongation = 45%
Modulus of elasticity = 100,000 MPa
Resilience = 11 kgm / cm2

  

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