Degussa Aktiengesellschaft

Evonik Degussa Gmbh

Oswin Klotz

Kai Schumacher

Uwe Diener

Rainer Golchert

Martin Moerters

Christian Schulze-Isfort

Nina Schuhardt

Michael Hagemann

Christian Schulze Isfort

Provided is a crystalline TiOpowder in the form of aggregated primary particles having a variable sintering stability at a BET surface area of 70-100 m/g and a rutile content of greater than 10% but less than or equal to 40%, and a process for preparing the crystalline TiOpowder, which involves: introducing a TiClvapor and, separately therefrom, Hand a primary air into a mixing chamber to produce a gaseous mixture; igniting the gaseous mixture in a burner to produce a flame, which is burned into a reaction chamber to produce the crystalline TiOpowder and gaseous substances; and separating the crystalline TiOpowder from the gaseous substances, wherein the relative amounts of TiClvapor, Hand primary air are selected to provide crystalline TiOpowder having the aforementioned BET surface area and rutile content, with the proviso that factor A has a value of 0.1-0.4 g/min accordance within the following formula: factor A=10{[(TiClvapor&#xd7;H)/(amount of air&#xd7;gaseous mixture)]/BET]}.

Titanium dioxide having a variable sintering stability

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/g, and a rutile content of a sum of crystalline modifications in the crystalline titanium dioxide is from of 50-70%.

Titanium dioxide having increased sintering activity

Silicon-titanium mixed oxide powder produced by flame hydrolysis, which consists of aggregates of primary particles, with a BET surface area of 90&#xb1;15 m/g, a titanium dioxide proportion of 50&#xb1;8 wt. % and an anatase/rutile ratio of 60:40 to 70:30. It is produced in that a mixture of silicon halide, titanium halide, hydrogen and primary air is ignited in a burner and the flame is burned into a reaction chamber closed off from the surrounding air, and secondary air and a gas, which increases the temperature in the reaction chamber by combustion and/or which slows down the cooling in the reaction chamber because of low heat transfer, are additionally introduced into the reaction chamber. It can be used in toner compositions.

Silicon-titanium mixed oxide powder produced by flame hydrolysis

A silicon-titanium mixed oxide powder contains aggregates of primary particles selected from amorphous silicon dioxide particles, crystalline titanium dioxide particles, and silicon-titanium mixed oxide particles each having an amorphous silicon dioxide fraction and a crystalline titanium dioxide fraction. The silicon-titanium mixed oxide particles predominate in the powder. The powder exhibits a BET surface area of from 20 to 200 m/g, and a titanium dioxide content in a range of from greater than 10 wt. % to less than 70 wt. %. An X-ray diffractogram of the powder exhibits the diffraction patterns of rutile and anatase, with a rutile/anatase ratio of from 2:98 to 98:2. The powder can be produced by vaporizing a silicon halide and a titanium halide at temperatures of less than 180&#xb0; C., performing combustion with hydrogen and air in a reaction chamber that is closed off from the earth's atmosphere, separating the solids from gaseous substances, and subsequently removing halide-containing substances from the solids to the greatest possible extent by treatment with steam at temperatures of from 250 to 700&#xb0; C. The powder can be used in toners.

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Westerngrund, Germany

Oswin Klotz