Titanium alloys are strong and light (about half the weight of steel), and so are valuable as engineering materials. They are used principally in the manufacture of aircraft, where such properties are especially important. Their resistance to seawater makes them of use in shipbuilding. Titanium dioxide is widely employed as a white pigment in the manufacture of paint; it has an advantage over lead-based pigments in that it is chemically unreactive and does not combine with impurities in the air to produce toxic compounds.
Although zirconium and hafnium are similar in many ways, they differ markedly in their capacity for absorbing neutrons. Zirconium, which is a very poor absorber of neutrons, is used to clad fuel rods in nuclear reactors. Because hafnium, which is often present in zirconium in small quantities, is a very good absorber of neutrons, it is must be removed from the zirconium before such a use is possible. This ability to absorb neutrons, however, makes hafnium of use in the control rods found in nuclear submarines.
