Surface-modified, pyrogenically produced mixed oxides, method of their production and use

Abstract

Surface-modified, pyrogenically produced mixed oxides which contain two or more components of the series SiO.sub.2, Al.sub.2 O.sub.3, TiO.sub.2, ZrO.sub.2, Fe.sub.2 O.sub.3, Nb.sub.2 O.sub.5, V.sub.2 O.sub.5, WO.sub.3, SnO.sub.2, GeO.sub.2 and have been surface-modified with one to several compounds of the following groups:(a) organosilanes of the type (RO).sub.3 Si(C.sub.n H.sub.2n+1),(b) R'.sub.x (RO).sub.y Si(C.sub.n H.sub.2n+1),(c) X.sub.3 Si(C.sub.n H.sub.2n+1),(d) X.sub.2 (R')Si(C.sub.n H.sub.2n+1),(e) X(R').sub.2 Si(C.sub.n H.sub.2n+1),(f) (RO).sub.3 Si(CH.sub.2).sub.m --R',(g) (R").sub.x (RO).sub.y Si(CH.sub.2).sub.m --R',(h) X.sub.3 Si(CH.sub.2).sub.m --R',(i) (R)X.sub.2 Si(CH.sub.2).sub.m --R',(j) (R).sub.2 X Si(CH.sub.2).sub.m --R',(k) Silazanes of the type ##STR1## (l) Cyclic polysiloxanes, (m) Polysiloxanes or silicone oils.

Description

FIELD OF THE INVENTION

The invention relates to surface-modified, pyrogenically produced mixed oxides and methods of their production and use.

BACKGROUND INFORMATION

SUMMARY OF THE INVENTION

Subject matter of the invention constitutes surface-modified, pyrogenically produced mixed oxides which contain two or more components of the series SiO.sub.2, Al.sub.2 O.sub.3, TiO.sub.2, ZrO.sub.2, Fe.sub.2 O.sub.3, Nb.sub.2 O.sub.5, V.sub.2 O.sub.5, WO.sub.3, SnO.sub.2, GeO.sub.2 and were surface-modified with one or several compounds of the following groups:

(a) Organosilanes of the type (RO).sub.3 Si(C.sub.n H.sub.2n+1) R=alkyl, such as e.g. methyl-, ethyl-, n-propyl-, i-propyl-, butyl-- n=1-20 (b) Organosilanes of the type R'.sub.x (RO).sub.y Si(C.sub.n H.sub.2n+1) R=alkyl, such as e.g. methyl-, ethyl-, n-propyl-, i-propyl-, butyl-- R=alkyl such as e.g. methyl-, ethyl-, n-propyl-, i-propyl-, butyl-- n=1-20 x=y=3 x=1, 2 y=1, 2 (c) Halogenorganosilanes of the type X.sub.3 Si(C.sub.n H.sub.2n+1) X=Cl, Br n=1-20 (d) Halogenorganosilanes of the type X.sub.2 (R')Si(C.sub.n H.sub.2n+1) X=Cl, Br R'=alkyl, such as e.g. methyl-, ethyl-, n-propyl-, i-propyl-, butyl-- n=1-20 (e) Halogenorganosilanes of the type X(R').sub.2 Si(C.sub.n H.sub.2n+1) X=Cl, Br R'=alkyl, such as e.g. methyl-, ethyl-, n-propyl-, i-propyl-, butyl-- n=1-20 (f) Organosilanes of the type (RO).sub.3 Si(CH.sub.2).sub.m --R' R=alkyl, such as methyl-, ethyl-, propyl-- m=0, 1-20 R'=methyl-, aryl (e.g. --C.sub.6 H.sub.5, substituted phenyl groups) --C.sub.4 F.sub.9, OCF.sub.2 --CHF--CF.sub.3, --C.sub.6 F.sub.13, --O--CF.sub.2 --CHF.sub.2 --NH.sub.2, --N.sub.3, --SCN, --CH.dbd.CH.sub.2, --OOC(CH.sub.3)C.dbd.CH.sub.2 --OCH.sub.2 --CH(O)CH.sub.2 ##STR2## --NH--COO--CH.sub.3, --NH--COO--CH.sub.2 --CH.sub.3, --NH--(CH.sub.2).sub.3 Si(OR).sub.3 --S.sub.x --(CH.sub.2).sub.3 Si(OR).sub.3 (g) Organosilanes of the type (R").sub.x (RO).sub.y Si(CH.sub.2).sub.m --R' ##EQU1## R'=methyl-, aryl (e.g. --C.sub.6 H.sub.5, substituted phenyl groups) --C.sub.4 F.sub.9, OCF.sub.2 --CHF--CF.sub.3, --C.sub.6 F.sub.13, --O--CF.sub.2 --CHF.sub.2 --NH.sub.2, --N.sub.3, --SCN, --CH.dbd.CH.sub.2, --OOC(CH.sub.3)C.dbd.CH.sub.2 --OCH.sub.2 --CH(O)CH.sub.2 ##STR3## --NH--COO--CH.sub.3, --NH--COO--CH.sub.2 --CH.sub.3, --NH--(CH.sub.2).sub.3 Si(OR).sub.3 --S.sub.x --(CH.sub.2).sub.3 Si(OR).sub.3 (h) Halogenorganosilanes of the type X.sub.3 Si(CH.sub.2).sub.m --R' X=Cl, Br m=0, 1-20 R'=methyl-, aryl (e.g. --C.sub.6 H.sub.5, substituted phenyl groups) --C.sub.4 F.sub.9 OCF.sub.2 --CHF--CF.sub.3, --C.sub.6 F.sub.13, --O--CF.sub.2 --CHF.sub.2 --NH.sub.2, --N.sub.3, --SCN, --CH.dbd.CH.sub.2, --OOC(CH.sub.3)C.dbd.CH.sub.2 --OCH.sub.2 --CH(O)CH.sub.2 ##STR4## --NH--COO--CH.sub.3, --NH--COO--CH.sub.2 --CH.sub.3, --NH--(CH.sub.2).sub.3 Si(OR).sub.3 --S.sub.x --(CH.sub.2).sub.3 Si(OR).sub.3 (i) Halogenorganosilanes of the type (R)X.sub.2 Si(CH.sub.2).sub.m --R' X=Cl, Br R=alkyl, such as methyl-, ethyl-, propyl-- m=0, 1-20 R'=methyl-, aryl (e.g. --C.sub.6 H.sub.5, substituted phenyl groups) --C.sub.4 F.sub.9, OCF.sub.2 --CHF--CF.sub.3, --C.sub.6 F.sub.13, --O--CF.sub.2 --CHF.sub.2 --NH.sub.2, --N.sub.3, --SCN, --CH.dbd.CH.sub.2, --OOC(CH.sub.3)C.dbd.CH.sub.2 --OCH.sub.2 --CH(O)CH.sub.2 ##STR5## --NH--COO--CH.sub.3, --NH--COO--CH.sub.2 --CH.sub.3, --NH--(CH.sub.2).sub.3 Si(OR).sub.3, --S.sub.x --(CH.sub.2).sub.3 Si(OR).sub.3 (j) Halogenorganosilanes of the type (R).sub.2 X Si(CH.sub.2).sub.m --R' X=Cl, Br R=alkyl m=0, 1-20 R'=methyl-, aryl (e.g. --C.sub.6 H.sub.5, substituted phenyl groups) --C.sub.4 F.sub.9, OCF.sub.2 --CHF--CF.sub.3, --C.sub.6 F.sub.13, --O--CF.sub.2 --CHF.sub.2 --NH.sub.2, --N.sub.3, --SCN, --CH.dbd.CH.sub.2, --OOC(CH.sub.3)C.dbd.CH.sub.2 --OCH.sub.2 --CH(O)CH.sub.2 ##STR6## --NH--COO--CH.sub.3, --NH--COO--CH.sub.2 --CH.sub.3, --NH--(CH.sub.2).sub.3 Si(OR).sub.3 --S.sub.x --(CH.sub.2).sub.3 Si(OR).sub.3 (k) Silazanes of the type ##STR7## R=alkyl R'=alkyl, vinyl (1) Cyclic polysiloxanes of the type D 3, D 4, D 5 in which D 3, D 4 and D 5 signify cyclic polysiloxanes with 3, 4 or 5 units of the type --O--Si(CH.sub.3).sub.2 --, e.g. octamethylcyclotetrasiloxane=D 4 ##STR8## (m) polysiloxanes or silicone oils of the type ##STR9## R=alkyl such as C.sub.n H.sub.2n+1 in which n=1 to 20, aryl such as phenyl- and substituted phenyl groups, (CH.sub.2).sub.n --NH.sub.2, H R'=alkyl such as C.sub.n H.sub.2n+1 in which n=1 to 20, aryl such as phenyl- and substituted phenyl groups, (CH.sub.2).sub.n --NH.sub.2, H R"=alkyl such as C.sub.n H.sub.2n+1 in which n=1 to 20, aryl such as phenyl- and substituted phenyl groups, (CH.sub.2).sub.n --NH.sub.2, H R'"=alkyl such as C.sub.n H.sub.2n+1 in which n=1 to 20, aryl such as phenyl- and substituted phenyl groups, (CH.sub.2).sub.n --NH.sub.2, H

Further subject matter of the invention is constituted by a method of producing the surface-modified, pyrogenically produced mixed oxides in accordance with the invention which is characterized in that two or more metal chlorides of the series SiCl.sub.4, AlCl.sub.3, TiCl.sub.4, ZrCl.sub.4, FeCl.sub.3, NbCl.sub.5, VOCl.sub.3, WOCl.sub.4, WCl.sub.6, SnCl.sub.4 and GeCl.sub.4 are evaporated [vaporized] together or separately, transferred together with an inert gas, e.g. nitrogen, into the mixing chamber of a known burner, mixed there with hydrogen, air and/or oxygen, the multi-component mixture burned in a reaction chamber, the solid mixed oxides separated thereafter from the gaseous reaction products and optionally freed in moist air from adhering hydrogen chloride and the pyrogenically produced mixed oxides placed in a suitable mixing container, the mixed oxides sprayed under intensive mixing optionally with water at first and then with the surface-modifying reagent or the mixture of several surface-modifying reagents, mixed again 15 to 30 minutes and subsequently tempered at a temperature of 100 to 400.degree. C. for a period of 1 to 6 hours.

The water used can be acidified with an acid, e.g. hydrochloric acid, from pH 7 to 1. The surface-modifying reagent used can be dissolved in a suitable solvent such as e.g. ethanol. The mixing and/or tempering can be carried out in an atmosphere of protective gas such as, for example, nitrogen.

Further subject matter of the invention constitutes a method of producing the surface-modified, pyrogenically produced mixed oxides which is characterized in that two or more metal chlorides from the series SiCl.sub.4, AlCl.sub.3, TiCl.sub.4, ZrCl.sub.4, FeCl.sub.3, NbCl.sub.5, VOCl.sub.3, WOCl.sub.4, WCl.sub.6, SnCl.sub.4 and GeCl.sub.4 are evaporated [vaporized] together or separately, transferred together with an inert gas, e.g. nitrogen, into the mixing chamber of a known burner, mixed there with hydrogen, air and/or oxygen. The multi-component mixture is burned in a reaction chamber, the solid mixed oxides separated thereafter from the gaseous reaction products and optionally freed in moist air from adhering hydrogen chloride and mixed as homogeneously as possible with organohalogen silanes with the exclusion of oxygen, the mixture heated together with slight amounts of water vapor and optionally together with an inert gas in a continuous process [continuous-current process which takes place in a continuous manner] in an upright treatment space designed as a tubular oven to temperatures of 200 to 800.degree. C., preferably 400 to 600.degree. C., the solid and gaseous reaction products separated from each other and the solid products optionally deacidified and dried.

Further subject matter of the invention constitutes the use of the surface-modified, pyrogenically produced mixed oxides in accordance with the invention as

Reinforcement filler in silicone rubber and gum, Charge stabilizer and flow aid in toner powder, Free-flow agent, Anti-blocking aid, e.g. in foils, UV blocker, e.g. in cosmetics, Thickening agent, e.g. in paints.

DETAILED DESCRIPTION OF THE INVENTION

Examples

Examples for the Production of Mixed Oxides

Metal chlorides 1 and 2 are volatilized in separate evaporators 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 down to approximately 110.degree. C. in the coagulation zone and the mixed oxides produced are subsequently separated off with a filter. Adhering chloride is removed by treating the powders with moist air at temperatures between 500 and 700.degree. C.

The reaction conditions and the product qualities for the various mixed oxides are collated in table 1.

Examples for the Production of Surface-Modified Mixed Oxides

The reaction conditions and stoichiometric ratios for the surface modification are shown in table 2. The physico-chemical data are collated in table 3.

TABLE 1__________________________________________________________________________Reaction conditions and product qualities of a few mixed oxidesMixed Metal Metal Tapped Loss on Chlorideoxide Oxide 1 Oxide 2 chloride chloride H.sub.2 Air BET density ignition contentexample (wt. %) (wt. %) 1 (g/h) 2 (g/h) (l/h) (l/h) (m.sup.2 /g) (g/l) (%) (%)__________________________________________________________________________1 SiO.sub.2 TiO.sub.2 SiCl.sub.4 TiCl.sub.4 470 3280 95 85 0.6 0.1 7.5 92.5 50 5162 Al.sub.2 O.sub.3 SiO.sub.2 AlCl.sub.3 SiCl.sub.4 300 1300 179 104 2.9 0.12 15 85 126 7783 Fe.sub.2 O.sub.3 TiO.sub.2 FeCl.sub.3 TiCl.sub.4 525 3079 53 175 1.2 0.3 2 98 29 16974 Fe.sub.2 O.sub.3 TiO.sub.2 FeCl.sub.3 TiCl.sub.4 525 3079 46 185 1.7 0.4 7 93 107 16135 SiO.sub.2 ZrO.sub.2 SiCl.sub.4 ZrCl.sub.4 800 2420 121 48 0.9 0.24 87 13 1303 1356 Al.sub.2 O.sub.3 TiO.sub.2 AlCl.sub.3 TiCl.sub.4 448 1276 47 329 0.7 0.16 11 89 188 7937 Al.sub.2 O.sub.3 TiO.sub.2 AlCl.sub.3 TiCl.sub.4 525 3579 72 120 1.1 0.6 25 75 464 12698 TiO.sub.2 ZrO.sub.2 TiCl.sub.4 ZrCl.sub.4 525 3080 59 218 0.9 0.15 95 5 1661 78__________________________________________________________________________ TABLE 2__________________________________________________________________________ Modifying Amount of Amount of reagent water solvent Tempering Tempering Mixed Modifying (g/100 g (g/100 g (g/100 g time temperatureExample Designation oxide reagent* mixed oxide) mixed oxide) mixed oxide) (h) (.degree. C.)__________________________________________________________________________ 9 VT 772 4 1 10 0 0 4 14010 VT 773 4 2 10 0 0 2 12011 VT 774 4 3 10 0 0 2.5 25012 VT 816 3 1 10 0 0 3 18013 VT 817 3 2 10 0 0 2 12014 VT 818 3 3 10 0 0 2.5 25015 VT 775 2 1 20 0 0 4 14016 VT 776 2 2 16 0 0 2 12017 VT 777 2 3 15 0 0 2 25018 VT 819 8 1 10 0 0 4 18019 VT 820 8 2 10 0 0 2 12020 VT 821 8 3 10 0 0 2.5 25021 VT 900 4 2 12 5 0 2.5 14022 VT 901 3 2 10 0 10** 2.5 14023 VT 747 6 2 5 0 0 2 12924 VT 748 6 2 10 0 0 2 12025 VT 749 6 4 10 0 0 2 12026 VT 750 7 2 10 0 0 2 12027 VT 751 7 4 10 0 0 2 12028 VT 719 5 1 10 5 0 3 13029 VT 734 1 3 10 0 0 2 250__________________________________________________________________________ Footnotes to Table 2: *1 = hexamethyldisilazane = (CH.sub.3).sub.3 Si--NH--Si(CH.sub.3).sub.3 2 = trimethoxyoctylsilane = (CH.sub.3 O).sub.3 Si--(CH.sub.2).sub.7 --CH.sub.3 ##STR10## 4 = trimethoxypropylsilane = (CH.sub.3 O).sub.3 Si--CH.sub.2 --CH.sub.2 --CH.sub.3 - ** = ethanol TABLE 3__________________________________________________________________________ Specific surface Tapped Loss of Carbon according to density Drying loss ignition contentExample Designation BET (m.sup.2 /g) (g/l) (%) (%) pH (%)__________________________________________________________________________ 9 VT 772 40 269 0.0 1.3 6.4 0.510 VT 773 36 280 0.1 4.7 3.4 3.611 VT 774 27 301 0.2 3.9 3.4 2.712 VT 816 45 258 0.4 1.1 7.5 0.513 VT 817 39 288 0.7 3.9 3.4 3.514 VT 818 32 292 0.0 3.6 3.6 2.915 VT 775 124 127 0.5 3.4 6.6 1.716 VT 776 111 136 1.0 9.5 4.2 5.817 VT 777 101 136 0.9 4.7 4.2 2.918 VT 819 51 245 0.5 0.7 9.0 0.419 VT 820 45 275 0.0 4.4 4.0 3.620 VT 821 35 275 0.0 2.3 4.1 2.521 VT 900 34 275 0.1 4.9 3.5 3.922 VT 901 38 282 0.6 4.0 3.6 3.623 VT 747 31 396 0.2 1.7 3.7 2.024 VT 748 23 409 0.3 4.8 4.0 3.925 VT 749 26 402 0.3 2.3 4.1 1.826 VT 750 56 161 0.3 16.8 3.8 3.927 VT 751 55 162 0.2 2.7 4.1 2.028 VT 719 60 60 0.1 1.1 6.4 1.329 VT 734 74 114 0.5 2.5 4.2 2.5__________________________________________________________________________

Claims

1. Surface-modified, pyrogenically produced mixed oxides which contain two or more components from the series consisting of SiO.sub.2, Al.sub.2 O.sub.3, TiO.sub.2, ZrO.sub.2, Fe.sub.2 O.sub.3, Nb.sub.2 O.sub.5, V.sub.2 O.sub.5, WO.sub.3, SnO.sub.2, and GeO.sub.2 which have been freed from adhering hydrogen chloride in moist air and do not undergo a drying step prior to hydrophobing and were surface-modified with one or more compounds of the following groups:

(a) Organosilanes of the formula (RO).sub.3 Si(C.sub.n H.sub.2n+1)

R=alkyl

n=1-20

(b) Organosilanes of the formula R'.sub.x (RO).sub.y Si(C.sub.n H.sub.2n+1)

R=alkyl

R'=alkyl

n=1-20

x+y=3

x=1, 2

y=1, 2

(c) Halogenorganosilanes of the formula X.sub.3 Si(C.sub.n H.sub.2n+1)

X=Cl, Br

n=1-20

(d) Halogenorganosilanes of the formula X.sub.2 (R')Si(C.sub.n H.sub.2n+1)

X=Cl, Br

R'=alkyl

n=1-20

(e) Halogenorganosilanes of the formula X(R').sub.2 Si(C.sub.n H.sub.2n+1)

X=Cl, Br

R'=alkyl

n=1-20

(f) Organosilanes of the formula (RO).sub.3 Si(CH.sub.2).sub.m --R'

R=alkyl

m=0, 1-20

R'=methyl-, aryl

--C.sub.4 F.sub.9, OCF.sub.2 --CHF--CF.sub.3, --C.sub.6 F.sub.13, --O--CF.sub.2 --CHF.sub.2

--NH.sub.2, --N.sub.3, --SCN, --CH.dbd.CH.sub.2,

--OOC(CH.sub.3)C.dbd.CH.sub.2,

--OCH.sub.2 --CH(O)CH.sub.2, ##STR11## --NH--COO--CH.sub.3, --NH--COO--CH.sub.2 --CH.sub.3, --NH--(CH.sub.2).sub.3 Si(OR).sub.3

(g) Organosilanes of the formula (R").sub.x (RO).sub.y Si(CH.sub.2).sub.m --R' ##EQU2## R'=methyl-, aryl --C.sub.4 F.sub.9, OCF.sub.2 --CHF--CF.sub.3, --C.sub.6 F.sub.13, --O--CF.sub.2 --CHF.sub.2

--NH.sub.2, --N.sub.3, --SCN, --CH.dbd.CH.sub.2,

--OOC(CH.sub.3)C.dbd.CH.sub.2

--OCH.sub.2 --CH(O)CH.sub.2 ##STR12## --NH--COO--CH.sub.3, --NH--COO--CH.sub.2 --CH.sub.3, --NH--(CH.sub.2).sub.3 Si(OR).sub.3

(h) Halogenorganosilanes of the formula X.sub.3 Si(CH.sub.2).sub.m --R'

X=Cl, Br

m=0, 1-20

R'=methyl-, aryl

--C.sub.4 F.sub.9, OCF.sub.2 --CHF--CF.sub.3, --C.sub.6 F.sub.13, --O--CF.sub.2 --CHF.sub.2

--NH.sub.2, --N.sub.3, --SCN, --CH.dbd.CH.sub.2,

--OOC(CH.sub.3)C.dbd.CH.sub.2

--OCH.sub.2 --CH(O)CH.sub.2 ##STR13## --NH--COO--CH.sub.3, --NH--COO--CH.sub.2 --CH.sub.3, --NH--(CH.sub.2).sub.3 Si(OR).sub.3

(i) Halogenorganosilanes of the formula (R)X.sub.2 Si(CH.sub.2).sub.m --R'

X=Cl, Br

R=alkyl

m=0, 1-20

R'=methyl-, aryl

--C.sub.4 F.sub.9, OCF.sub.2 --CHF--CF.sub.3, --C.sub.6 F.sub.13, --O--CF.sub.2 --CHF.sub.2

--NH.sub.2, --N.sub.3, --SCN, --CH.dbd.CH.sub.2,

--OOC(CH.sub.3)C.dbd.CH.sub.2

--OCH.sub.2 --CH(O)CH.sub.2 ##STR14## --NH--COO--CH.sub.3, --NH--COO--CH.sub.2 --CH.sub.3, --NH--(CH.sub.2).sub.3 Si(OR).sub.3

(j) Halogenorganosilanes of the formula (R).sub.2 X Si(CH.sub.2).sub.m --R'

X=Cl, Br

R=alkyl

m=0, 1-20

R'=methyl-, aryl

--C.sub.4 F.sub.9, OCF.sub.2 --CHF--CF.sub.3, --C.sub.6 F.sub.13, --O--CF.sub.2 --CHF.sub.2

--NH.sub.2, --N.sub.3, --SCN, --CH.dbd.CH.sub.2,

--OOC(CH.sub.3)C.dbd.CH.sub.2

--OCH.sub.2 --CH(O)CH.sub.2 ##STR15## --NH--COO--CH.sub.3, --NH--COO--CH.sub.2 --CH.sub.3, --NH--(CH.sub.2).sub.3 Si(OR).sub.3

(k) Silazanes of the formula ##STR16## R=alkyl R'=alkyl, vinyl

(l) Cyclic polysiloxanes of the formula D 3, D 4, D 5, ##STR17## (m) polysiloxanes or silicone oils of the formula ##STR18## R=alkyl, aryl, (CH.sub.2).sub.n --NH.sub.2, H R'=alkyl, aryl, (CH.sub.2).sub.n --NH.sub.2, H

R"=alkyl, aryl, (CH.sub.2).sub.n --NH.sub.2, H

R'"=alkyl, aryl, (CH.sub.2).sub.n --NH.sub.2, H , wherein n=1-20.

2. Surface-modified, pyrogenically produced mixed oxides according to claim 1 which have been sprayed with additional water prior to hydrophobing.

3. A process for the preparation of surface-modified, pyrogenically produced mixed oxides according to claim 1, wherein two or more metal chlorides selected from the group consisting of SiCl.sub.4, AlCl.sub.3, TiCl.sub.4, ZrCl.sub.4, FeCl.sub.31, NbCl.sub.5, VOCl, WoCl.sub.4, WCl.sub.6, SnCl.sub.4, and GeCl.sub.4 are evaporated together or separately, transferred together with an inert gas into the mixing chamber of a known burner, mixed there with hydrogen, air and/or oxygen, the multi-component mixture is burned in a reaction chamber, the solid mixed oxides are then separated from the gaseous reaction products and freed from adhering hydrogen chloride in moist air, and the progenically produced mixed oxides are charged to a suitable mixing vessel, the mixed oxides are aprayed, with intensive mixing, and subsequently with the surface-modifying reagen or the mixture of several surface-modifying reagents, mixed agin for 15 to 30 minutes and subsequently heat-treated at a temperature of 100 to 400.degree. C. for a period of 1-6 hours.

4. A process for the preparation of surface-modified, pyrogenically produced mixed oxides according to claim 1, wherein two or more metal chlorides selected from the group consisting of SiCl.sub.4, AlCl.sub.3, TiCl.sub.4, ZrCl.sub.4, FeCl.sub.3, NbCl.sub.5, VOCl, WoCl.sub.4, WCl.sub.6, SnCl.sub.4, and GeCl.sub.4 are evaporated together or separately, transferred together with an inert gas into the mixing chamber of a known burner, mixed there with hydrogen, air and/or oxygen, the multi-component mixture is burned in a reaction chamber, the solid mixed oxides are then separated from the gaseous reaction products and freed from adhering hydrogen chloride in moist air, and mixed as homogeneously as possible with organohalogen silanes with the exclusion of oxygen, and the mixture together with small quantities of water vapor and optionally together with an inert gas is heated to temperatures from 200 to 800.degree. C., in the continuous co-current process in a treatment chamber having the form of an upright tubular furnace, the solid and gaseous reaction products are separated from each other, and the solid products are deacidified and dried.

5. The process of claim 4 wherein the temperature is 400 to 600.degree. C.

6. The process according to claim 3 which further comprises the step of spraying with additional water prior to hydrophobing.

7. The process according to claim 4 which further comprises the step of spraying with additional water prior to hydrophobing.

8. The process according to claim 5 which further comprises the step of spraying with additional water prior to hydrophobing.

9. A surface-modified, pyrogenically produced mixed oxide according to claim 1 in the form of a reinforcing filler in silicone rubber or rubber, a charge stabilizer or free-flow agent in a toner powder, a free-flow agent, an anti-blocking agent, a UV blocker, or a thickener.