Titanium dioxide having increased sintering activity

Abstract

A crystalline titanium dioxide powder, containing aggregated primary particles, wherein a BET surface area of the aggregated primary particles is from 30 to 65 m 2 /g, and a rutile content of a sum of crystalline modifications in the crystalline titanium dioxide is from of 50-70%.

1 . A crystalline titanium dioxide powder, comprising:
 aggregated primary particles,   
     wherein
 a BET surface area of the aggregated primary particles is from 30 to 65 m 2 /g, and 
 a rutile content of a sum of crystalline modifications in the crystalline titanium dioxide is from of 50-70%. 
 
   
   
       2 . The crystalline titanium dioxide powder according to  claim 1 , wherein
 a proportion of aggregates and/or agglomerates having a diameter of more than 45 μm is in a range of from 0.0001 to 0.05% by weight.   
   
   
       3 . The crystalline titanium dioxide powder according to  claim 1 , wherein a chloride content is in a range of from 0.0001 to 0.1% by weight. 
   
   
       4 . The crystalline titanium dioxide powder according to  claim 1 , wherein a tamped density of the titanium dioxide powder is in a range from 20 to 200 g/l. 
   
   
       5 . The crystalline titanium dioxide powder according to  claim 1 , wherein a sintering activity as measured by a % decrease in BET upon treatment at 800° C. for 3 hours is greater than 60%. 
   
   
       6 . A method for the preparation of the titanium dioxide powder according to  claim 1 , comprising:
 introducing at a controlled rate for each stream, separate streams of titanium tetrachloride vapour; hydrogen, and air or oxygen-enriched air into a mixing chamber,   igniting the mixture of titanium tetrachloride vapour, hydrogen and primary air in a burner;   burning the flame into a reaction chamber; and   separating from the gaseous substances, the solid TiO 2  formed in the burning;   
     wherein the controlled rates are selected according to the equation:
     A= 10 5 {[(TiCl 4 ×H 2 )/(amount of air×total gas)]/ BET]}   
 wherein 
 A is a value of from 6-12×10 5  g/m 2 , 
 TiCl 4  is the controlled rates for introducing the titanium tetrachloride vapour in units of kmol/h, 
 H 2  is the controlled rate for introducing the hydrogen in units of kmol/h, 
 amount of air is the controlled rate for introducing the primary air in units of kmol/h, 
 total gas is the total controlled rate of all the gases in kmol/h, and 
 BET is expressed in units of m 2 /g. 
 
   
   
       7 . The method according to  claim 6 , further comprising:
 vaporizing the titanium tetrachloride, wherein a temperature for the vaporizing is less than 200° C.   
   
   
       8 . The method according to  claim 6 , further comprising:
 introducing a secondary air stream at a controlled rate into the reaction chamber.   
   
   
       9 . The method according to  claim 8 , wherein a ratio of the primary air controlled rate to secondary air controlled rate is in a range of from 10:1 to 1:10. 
   
   
       10 . The method according to  claim 8 , wherein at least one of the primary air stream and secondary air stream is preheated to a temperature of from 50° C. to 500° C. 
   
   
       11 . The method according to  claim 8 , wherein at least one of the primary air stream and secondary air stream is enriched with oxygen. 
   
   
       12 . The method according to  claim 6 , wherein a value of gamma is in a range from 1 to 9, and gamma is a ratio of moles hydrogen introduced into the mixing chamber to a stoichiometric molar amount of hydrogen based on a molar amount of titanium tetrachloride introduced into the mixing chamber. 
   
   
       13 . The method according to  claim 6 , wherein a value of lambda is in a range of from 1 to 9, and lambda is a ratio of the molar amount of oxygen introduced to the mixing chamber to a stoichiometric molar amount of oxygen based on the molar amount of titanium tetrachloride introduced into the mixing chamber. 
   
   
       14 . The method according to  claim 8 , wherein a value of lambda is in a range of from 1 to 9, and lambda is a ratio of the molar amount of oxygen introduced to the mixing chamber and the reaction chamber to a stoichiometric molar amount of oxygen based on the molar amount of titanium tetrachloride introduced into the mixing chamber. 
   
   
       15 . The method according to  claim 6 , further comprising:
 treating the separated TiO 2  with steam and optionally air,   
     wherein a temperature of the steam treatment is in the range of from 250 to 750° C. 
   
   
       16 . The method according to  claim 8 , further comprising:
 treating the separated TiO 2  with steam and optionally air,   
     wherein a temperature of the steam treatment is in the range of from 250 to 750° C. 
   
   
       17 . A method for preparing a ceramic material comprising:
 sintering the crystalline titanium dioxide powder according to  claim 1 .   
   
   
       18 . A ceramic material prepared according to the method of  claim 17 . 
   
   
       19 . An article, comprising: the ceramic material according to  claim 18 .