The dioxide is also widely used as a paint pigment, especially for exterior paints. Titanates are formed from the dioxide, which is weakly acidic. An interesting example is barium titanate, which is piezoelectric and can be used as a transducer for the interconversion of sound and electricity. It is also an important catalyst in the polymerization of olefins. Titanium esters, formed by the reaction of the tetrachloride with alcohols, are used as waterproofing agents on fabrics.
Titanic sulfate is used as a textile mordant.
Titanium metal and its alloys are light in weight and have very high tensile strength, even at high temperatures. These metals are utilized in aircraft and spacecraft construction and in naval ships, guided missiles, and lightweight armor plate for tanks. Titanium compounds are widely distributed in nature. Rutile, the native dioxide, and ilmenite, which contains, besides titanium, iron and oxygen, are its chief sources. The metal cannot be produced by reduction of the dioxide, because titanium reacts with both oxygen and nitrogen at high temperatures.