Flame-hydrolytically produced titanium dioxide mixed oxide, method of its production and its use

Abstract

Flame-hydrolytically produced titanium dioxide mixed oxide having a BET surface of 10 to 150 m.sup.2 /g and 1 to 30% by weight aluminum oxide or 1 to 30% by weight silicon dioxide is produced by evaporating aluminum chloride or silicon tetrachloride, transferring the evaporated aluminum chloride or silicon tetrachloride, together with an inert gas, into the mixing chamber of a burner, mixing them with hydrogen, air and gaseous titanium tetrachloride, burning the resulting 4-component mixture in the reaction chamber of the burner, and separating the titanium dioxide mixed oxide from the gaseous reaction products.

Description

The present invention relates to a flame-hydrolytically produced titanium dioxide mixed oxide, a method of its production and its use.

BACKGROUND OF THE INVENTION

It is known that titanium dioxide mixed oxide can be produced hydrolytically in the gaseous phase. Thus, published German Patent Application DE-A 9 52 891 describes a method of producing mixed oxides of aluminum and titanium or of titanium and silicon in which the temperature is maintained in the range between 250.degree. and 650.degree. C.

Published German Patent Application DE-A 29 31 810 (U.S. Pat. No. 4,297,143) describes a flame-hydrolytically produced silicon dioxide--titanium dioxide mixed oxide containing 99.9 to 91.1% by weight silicon dioxide and 0.1 to 9.9% by weight titanium dioxide.

Published German Patent Application DE-A 36 11 449 describes a flame-hydrolytically produced aluminum oxide--titanium oxide mixed oxide containing 56% by weight aluminum oxide and 44% by weight titanium dioxide.

SUMMARY OF THE INVENTION

The present invention provides a flame-hydrolytically produced titanium dioxide mixed oxide with a BET surface of 10 to 150 m.sup.2 /g which contains 1 to 30% by weight aluminum oxide or 1 to 30% by weight silicon dioxide as a component of the mixed oxide.

In a preferred embodiment of the invention, the titanium dioxide mixed oxide can have the following physico-chemical properties:

______________________________________Al.sub.2 O.sub.3 content (% by weight)1-30SiO.sub.2 content (% by weight)1-30Specific surface (m.sup.2 /g)10-150Primary (unagglomerated) particle sie(nm) 5-100Stamping density (g/l)50-400Annealing loss (2 hours at 1,000.degree. C.) (% by weight)0.5-5Chloride content (% by weight)<1Rutile content (%)20-90______________________________________

The invention also provides a method of producing a flame-hydrolytically produced titanium dioxide mixed oxide in which anhydrous aluminum chloride or silicon tetrachloride is evaporated, transferred together with an inert gas, e.g. nitrogen, into the mixing chamber of a conventional burner, mixed in the burner with hydrogen, air and gaseous titanium tetrachloride in such proportions that the correspondingly composed desired Al.sub.2 O.sub.3 /TiO.sub.2 mixed oxide or SiO.sub.2 /TiO.sub.2 mixed oxide results, the 4-component mixture is burned in a reaction chamber, then the solid titanium oxide mixed oxide is separated from the gaseous reaction products and freed, if necessary, in moist air from adhering hydrogen chloride.

The flame-hydrolytic conversion of the invention can be carried out at temperatures of 1,000.degree. to 3,000.degree. C.

The titanium dioxide mixed oxide of the invention can be used for the production of catalysts, catalytic carriers, photocatalysts, ceramics, automobile paints and cosmetic articles (especially as UV absorbers in sunscreen agents) and as heat stabilizers in silicone rubbers.

The titanium dioxide mixed oxide of the invention advantageously has a rather high temperature resistance of the surface. It is fine, very homogenous, very pure and highly dispersible.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention is illustrated by the following examples:

EXAMPLES

AlCl.sub.3 and TiCl.sub.4 or SiCl.sub.4 and TiCl.sub.4 are volatilized in two separate evaporators (evaporator temperatures: AlCl.sub.3 250 .degree. C., SiCl.sub.4 100.degree. C., TiCl.sub.4 200 C.) and the chloride vapors conducted by means of nitrogen into the mixing chamber of a burner. There, they are mixed with hydrogen and dried air and/or oxygen and burned in a reaction chamber. The reaction products are cooled in the coagulation zone to approximately 110.degree. C. The mixed oxides are subsequently separated with a filter. Adhering chloride is removed by treating the powder with moist air at a temperature between 500.degree. and 700.degree. C.

Tables 1 and 2 list the reaction conditions and the product properties for various mixed oxides.

Temperature resistance of the specific surface

The specific surface of mixed oxides 4 and 9 was determined, by way of example, after calcination at temperatures between 500.degree. and 800.degree. C. The residence time was 4 hours in each instance. Undoped pyrogenic titanium oxide P 25 (BET 50 m.sup.2 /g) was used as reference material. The results are shown in FIG. 1.

The specific surface of P 25 breaks in sharply after 600.degree. C.

The doping with aluminum oxide yields a material with a distinctly more stable surface (800.degree. C.: 30 m.sup.2 /g instead of 12 m.sup.2 /g in the case of P 25).

The addition of silicon dioxide yields a powder whose surface is stable over the tested temperature range.

The novel materials can be used at high temperatures and are therefore especially suitable for the production of catalysts and catalytic carriers.

TABLE 1__________________________________________________________________________Al.sub.2 O.sub.3 /TiO.sub.2 mixed oxides Stamping Annealing Chloride TiCl.sub.4 AlCl.sub.3 H.sub.2 Air Al.sub.2 O.sub.3 BET Density loss contentNo. (g/h) (g/h) (l/h) (l/h) (%) (m.sup.2 /g) (g/l) (%) (%)__________________________________________________________________________1 264 19 236 1643 6.1 98 159 1.6 0.062 236 50 236 1643 16.2 103 145 1.7 0.153 1466 114 448 1276 6.6 56 308 1.1 0.104 1363 188 448 1276 11.2 47 329 0.7 0.165 1292 285 448 1276 16.7 58 272 1.0 0.15__________________________________________________________________________ TABLE 2__________________________________________________________________________SiO.sub.2 /TiO.sub.2 mixed oxides Stamping Annealing Chloride TiCl.sub.4 SiCl.sub.4 H.sub.2 Air SiO.sub.2 BET Density loss contentNo. (g/h) (g/h) (l/h) (l/h) (%) (m.sup.2 /g) (g/l) (%) (%)__________________________________________________________________________6 268 17 236 1643 5.0 105 162 1.1 0.027 231 54 236 1643 16.5 112 151 0.9 0.028 1423 118 448 1276 6.5 47 287 1.3 0.139 1346 208 448 1276 9.5 49 274 1.0 0.0910 1258 296 448 1276 16.5 48 258 1.2 0.06__________________________________________________________________________

BRIEF DESCRIPTION OF FIGURES OF DRAWING

In the drawings

FIG. 1 is a graph showing the Temperature Stability of the specific surface; and

FIG. 2 is a schematic view of a burner which can be used to carry out the process of the present invention.

In carrying out the invention in the apparatus shown in FIG. 2, the gas-forming metal chlorides, i.e., titanium tetrachloride and aluminum chloride or silicon tetrachloride, are introduced with an inert gas through the inlets 4 and 5 into the mixing chamber 8. Hydrogen and dried air are preheated and introduced through the inlets 6 and 7 into the mixing chamber 8. The four component mixture is advanced into the combustion chamber 1 of the burner and burned in a flame. In order to sustain the flame, an additional quantity of hydrogen can be supplied through the annular chamber 2 which surrounds the combustion chamber 1.

Claims

1. A sunscreen agent comprising as a UV absorber a flame-hydrolytically produced titanium dioxide mixed oxide having a BET surface of 10 to 150 m.sup.2 /z which contains 1 to 30% by weight of a member of the group consisting of aluminum oxide and silicon dioxide as a component of the mixed oxide, and a balance of the titanium dioxide and unavoidable impurities.