Titanium dioxide

Pigments of titanium dioxide exists in two forms - anatase and rutile and produced by two technological schemes: chlorine and sulfate processes. Both, anatase and rutile forms of titanium dioxide can be produced by any method. 
Sulfate process was introduced to industry in 1931, for  production of the anatase form of titanium dioxide, and later, in 1941 - rutile. In this method, ore that contains titanium (ilmenite et al.), is dissolved in sulfuric acid, forming a solution of titanium sulfate, iron and other metals. 
Then, in a number of chemical reactions, including chemical reduction, purification, precipitation, washing and calcination, forming titanium dioxide base with required particle size. The structure of crystals (anatase or rutile) is controlled in the process of nucleation and calcination.
Chlorine method was invented in 1950 by DuPont company for production of rutile titanium dioxide. This method involves high temperature phase of reaction. Titaniferous ore is reacted with chlorine gas under reduced pressure, thereby forming titanium tetrachloride TiCl4 and other metal chloride impurities, which are removed afterwards. TiCl4 of high purity is then oxidized at high temperature resulting in the formation of titanium dioxide.
World production capacity for titanium dioxide, by chlorine process exceed capacity of sulfate process, and continue to grow.
As mentioned above, titanium dioxide exists in two crystal structures: anatase and rutile. The two forms differ in the density of molecular structure and arrangement of atoms within molecule. Thus rutile form has a much shorter distance between titanium and oxygen atoms. Rutile titanium dioxide has a high hiding power compared to anatase, whereby more frequently used.

Titanium dioxide is widely used in industry, production of PVC (polyvinylchloride) products (such as the PVC window profiles), paint, welding electrodes, chemical fiber, paper, ceramics, concrete tinting, in food and pharmaceutical manufacturing.