Patent ID: 7029648

Claim:
A process for making durable rutile titanium dioxide pigment by vapor phase deposition of surface treatments on the titanium dioxide pigment particle surface, the process comprising the steps of: (a) reacting titanium tetrachloride vapor and aluminum chloride and at least a stoichiometric amount of oxygen in a plug flow reactor to form a product stream containing more than 99% rutile titanium dioxide particles; (b) introducing silicon tetrachloride into the reactor at one or more points downstream of the point where the titanium tetrachloride, aluminum chloride, and oxygen were contacted and where at least 97% of the titanium tetrachloride has been converted to titanium dioxide to form the durable rutile titanium dioxide pigment wherein at least 85% of the titanium dioxide pigment particles are completely covered by a uniform layer formed from a mixture of amorphous aluminum oxide and amorphous silicon dioxide; and (c) withdrawing from the reactor the durable rutile titanium dioxide pigment, whereby the silicon tetrachloride introduced in (b) does not influence crystal phase or pigment carbon black undertone.