Appearance and Characteristics
Harmful effects:
Hafnium is considered to be non-toxic. In powdered form it is pyrophoric (can ignite spontaneously).
Characteristics:
Hafnium is a lustrous, silvery, ductile metal. Chemically it is similar to zirconium. When present in compounds, hafnium exists mostly in the oxidation state IV. Hafnium resists corrosion due to the formation of an oxide film on exposed surfaces. It is unaffected by all acids (apart from hydrogen fluoride) and all alkalis. Hafnium reacts with the halogens to form tetrahalides, and at high temperatures it reacts with carbon, boron, nitrogen, oxygen, silicon and sulfur.
Uses of Hafnium
Hafnium is used for nuclear reactor control rods because of its ability to absorb neutrons and its good mechanical and corrosion resistance qualities. This is in complete contrast to zirconium, which although is chemically is very similar to hafnium, is very poor at absorbing neutrons. Zirconium is therefore used in the cladding (outer layer) of fuel rods through which it is important that neutrons can travel easily.
Hafnium is also used in photographic flash bulbs, light bulb filaments, and in electronic equipment as cathodes and capacitors. Hafnium alloys with several other metals, such as iron, niobium, tantalum and titanium. Hafnium-niobium alloys, for example, are heat resistant and are used in aerospace applications, such as space rocket engines. Hafnium carbide is used to line high temperature furnaces / kilns due to its refractory properties (it does not melt at high temperatures). Hafnium-based compounds are used in gate insulators in the 45 nm generation of integrated circuits for computers. Hafnium oxide-based compounds are being introduced into silicon-based chips to produce smaller, more energy efficient and performance packed processors.