Metal oxide-containing dispersion with high salt stability

Abstract

Aqueous dispersion containing a hydrophilic metal oxide powder comprising a metal oxide and a surface modification of the metal oxide, wherein a) the metal oxide is selected from the group consisting of TiO.sub.2, ZrO.sub.2, SiO.sub.2, Al.sub.2O.sub.3, Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, Sb.sub.2O.sub.3, WO.sub.3, CeO.sub.2 and mixed oxides thereof and b) the surface modification b1) comprises silicon atoms and aluminum atoms and b2) the silicon atoms are at least partly bonded to a hydrocarbon radical via a C atom and b3) the Al/Si molar ratio of the surface modification is 1:2-1:20.

Claims

1. An aqueous dispersion containing a hydrophilic metal oxide powder comprising a metal oxide and a surface modification of the metal oxide, wherein: a) the metal oxide is a mixed aluminum-silicon oxide; and b) the surface modification comprises: b1) silicon and Al atoms; b2) wherein the silicon atoms are at least partly bound to a hydrocarbon radical by a C atom; and b3) wherein the Al/Si molar ratio of the surface modification is 1:2-1:20; wherein the surface modification has the formula Si(CH.sub.2).sub.nY.sub.mR, wherein Si is the Si atom bonded to a hydrocarbon radical via a C atom, n=1, 2 or 3 and m=0 or 1; wherein the Al.sub.2O.sub.3/SiO.sub.2 weight ratio in the surface-modified metal oxide powder is 0.1:99.9-5:95; and wherein: when m=1: R=H, CH.sub.3, C.sub.2H.sub.5, OH, OCH.sub.3, OC.sub.2H.sub.5, C(O)OCH.sub.3, C(O)OC.sub.2H.sub.5, OC(O)CH.sub.3, OC(O)CHCH.sub.2, OC(O)CHCH(CH.sub.3), C(O)CH.sub.3, C(O)H, NH.sub.2; or ##STR00004## when m=0: R=OH, OCH.sub.3, OC.sub.2H.sub.5, C(O)OCH.sub.3, C(O)OC.sub.2H.sub.5, OC(O)CH.sub.3, OC(O)CHCH.sub.2, OC(O)CHCH(CH.sub.3), C(O)CH.sub.3, C(O)H, or NH.sub.2; and Y=(OCR.sup.1R.sup.2CR.sup.3R.sup.4).sub.o, where o=1-30, and R.sup.1, R.sup.2, R.sup.3, R.sup.4=independently of one another H or CH.sub.3, or (OCR.sup.1R.sup.2CR.sup.3R.sup.4CR.sup.5R.sup.6).sub.p, where p=1-30, R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6=independently of one another H or CH.sub.3, NHCH.sub.2CH.sub.2O, NH(CH.sub.2).sub.2NH(CH.sub.2).sub.2, or NH(CH.sub.2).sub.2NH(CH.sub.2).sub.2.

2. The aqueous dispersion of claim 1, wherein the proportion of water is 50-90 wt % and the proportion of surface-modified metal oxide powder is 10-50 wt %.

3. The aqueous dispersion of claim 1, wherein Y=(OCR.sup.1R.sup.2CR.sup.3R.sup.4)O, o=5-15 and R.sup.1, R.sup.2, R.sup.3, R.sup.4=H.

4. The aqueous dispersion of claim 3, wherein the proportion of water is 50-90 wt % and the proportion of surface-modified metal oxide powder is 10-50 wt %.

5. The aqueous dispersion of claim 1, wherein no more than 100 ppm of dispersants are present.

6. The aqueous dispersion of claim 1, wherein the Al.sub.2O.sub.3/SiO.sub.2 weight ratio in the surface-modified metal oxide powder is in the range 0.2:99.8-3:97.

7. The aqueous dispersion of claim 1, wherein the dispersion has a median particle diameter d.sub.50 of 40-200 nm.

8. A surface-modified mixed aluminum-silicon oxide powder, wherein: a) the Al.sub.2O.sub.3/SiO.sub.2 weight ratio is 0.1:99.9-5:95; b) the surface modification: b1) comprises silicon atoms and aluminum atoms; b2) comprises the formula Si(CH.sub.2).sub.nY.sub.mR, wherein Si is the Si atom bonded to a hydrocarbon radical via a C atom, n=1, 2 or 3 and m=0 or 1; and b3) comprises an Al/Si molar ratio of 1:2-1:20; and wherein: when m=1: R=H, CH.sub.3, C.sub.2H.sub.5, OH, OCH.sub.3, OC.sub.2H.sub.5, C(O)OCH.sub.3, C(O)OC.sub.2H.sub.5, OC(O)CH.sub.3, OC(O)CHCH.sub.2, OC(O)CHCH(CH.sub.3), C(O)CH.sub.3, C(O)H, NH.sub.2, or ##STR00005## when m=0: R=OH, OCH.sub.3, OC.sub.2H.sub.5, C(O)OCH.sub.3, C(O)OC.sub.2H.sub.5, OC(O)CH.sub.3, OC(O)CHCH.sub.2, OC(O)CHCH(CH.sub.3), C(O)CH.sub.3, C(O)H, or NH.sub.2; and Y=(OCR.sup.1R.sup.2CR.sup.3R.sup.4)O, where o=1-30, and R.sup.1, R.sup.2, R.sup.3, R.sup.4=independently of one another H or CH.sub.3, or (OCR.sup.1R.sup.2CR.sup.3R.sup.4CR.sup.5R.sup.6).sub.p, where p=1-30, R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6=independently of one another H or CH.sub.3, NHCH.sub.2CH.sub.2O, NH(CH.sub.2).sub.2NH(CH.sub.2).sub.2, or NH(CH.sub.2).sub.2NH(CH.sub.2).sub.2.

9. The surface-modified mixed aluminum-silicon oxide powder of claim 8, wherein Y=(OCR.sup.1R.sup.2CR.sup.3R.sup.4).sub.o, o=5-15 and R.sup.1, R.sup.2, R.sup.3, R.sup.4=H.

10. The surface-modified mixed aluminum-silicon oxide powder of claim 8, wherein the Al.sub.2O.sub.3/SiO.sub.2 weight ratio in the surface-modified metal oxide powder is 0.2:99.8-3:97.

11. A process for producing the aqueous dispersion of claim 1, comprising: dispersing in an aqueous solvent a powder comprising mixed aluminum-silicon oxides and having hydroxyl groups at the surface of particles in the powder; subsequently adding a surface modifying agent; reacting the mixture; and optionally removing the hydrolysis product, wherein the surface modifying agent is obtained by mixing: a) a compound with the structure of X.sub.4-a[Si(CH.sub.2).sub.nY.sub.mR].sub.a with b) at least one metal compound selected from the group consisting of aluminum alkoxides, aluminum acetylacetonates, and sodium aluminate; wherein a=1, 2 or 3; n=1, 2 or 3; m=0 or 1, wherein: when m=1: R=H, CH, C.sub.2H.sub.5, OH, OCH, OC.sub.2H.sub.5, C(O)OCH.sub.3, C(O)OC.sub.2H.sub.5, OC(O)CH.sub.3, OC(O)CHCH.sub.2, OC(O)CHCH(CH.sub.3), C(O)CH.sub.3, C(O)H, NH.sub.2; or ##STR00006## and when m=0: R=OH, OCH, OC.sub.2H.sub.5, C(O)OCH.sub.3, C(O)OC.sub.2H.sub.5, OC(O)CH.sub.3, OC(O)CHCH.sub.2, OC(O)CHCH(CH.sub.3), C(O)CH.sub.3, C(O)H, or NH.sub.2; and Y=(OCR.sup.1R.sup.2CR.sup.3R.sup.4).sub.o, where o=1-30, and R.sup.1, R.sup.2, R.sup.3, R.sup.4=independently of one another H or CH, or (OCR.sup.1R.sup.2CR.sup.3R.sup.4CR.sup.5R.sup.6).sub.p, where p=1-30, R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6=independently of one another H or CH.sub.3, NHCH.sub.2CH.sub.2O, NH(CH.sub.2).sub.2NH(CH.sub.2).sub.2, or NH(CH.sub.2).sub.2NH(CH.sub.2).sub.2.

12. The process of claim 11, wherein Y=(OCR.sup.1R.sup.2CR.sup.3R.sup.4).sub.o, o=5-15 and R.sup.1, R.sup.2, R.sup.3, R.sup.4=H.

13. The process of claim 11, wherein the metal oxide powder is introduced in the form of an aqueous dispersion.

14. The process of claim 11, wherein the process comprises reacting the mixture by adjusting the pH to 11 or higher, subjecting the mixture to thermal treatment at a temperature of 50-95 C. over a period of 1-30 minutes and then optionally adjusting the pH to 8-10.

15. The process of claim 11, wherein a metal oxide powder produced by pyrogenic means is employed.

16. The process of claim 11, wherein X is selected from the group consisting of H, OH, OCH.sub.3, OC.sub.2H.sub.5, OCH.sub.2CH.sub.2H.sub.3, OCH(CH.sub.3).sub.2, and Cl.

Description

EXAMPLES

(1) Salt Stability at 60 C.

(2) 28.500 g of NaCl, 0.220 g of NaHCO.sub.3, 4.066 g of Na.sub.2SO.sub.4, 1.625 g of CaCl.sub.22H.sub.2O, 3.162 g of MgCl.sub.26H.sub.2O, 0.024 g of SrCl.sub.26H.sub.2O and 0.721 g of KCl are dissolved in 900 g of deionized water (DI water) and the solution made up to 1 litre with DI water.

(3) 99.5 g of this solution are initially charged into a 125 ml wide-necked bottle made of NALGENE FEP (tetrafluoroethylene-hexafluoropropylene copolymer; Thermo Scientific), 0.5 g of the dispersion under test is added and the mixture is homogenized by shaking. The mixture is stored in a drying cabinet at 60 C. and the occurrence of a precipitate is visually monitored.

(4) Salt Stability at 90 C.

(5) 99.5 g of a NaCl solution (3 wt %) are initially charged into a 125 ml wide-necked bottle made of NALGENE FEP (tetrafluoroethylene-hexafluoropropylene copolymer; Thermo Scientific), 0.5 g of the dispersion under test is added and the mixture is homogenized by shaking. The mixture is stored in a drying cabinet at 90 C. and the occurrence of a precipitate is visually monitored.

(6) Input Materials

(7) Dispersion of mixed silicon-aluminum oxide AEROSIL MOX 170

(8) The powder has the following properties:

(9) 99 wt % silicon dioxide, 1 wt % aluminum oxide. The BET surface area is 173 m.sup.2/g. (Al.sub.2O.sub.3/SiO.sub.2).sub.ttl/(Al.sub.2O.sub.3/SiO.sub.2).sub.surface=0.9.

(10) A 100 l stainless steel mixing vessel was initially charged with 37 kg of water. Subsequently, under shear conditions (Ystral Conti-TDS 3 (stator slots: 4 mm ring and 1 mm ring, rotor-stator gap about 1 mm), an initial 10 kg of AEROSIL MOX 170 are aspirated. The remaining 5 kg were aspirated stepwise in amounts of about 1 kg each time. After addition was complete the mixture was sheared at 3000 rpm for a further 30 min. To grind any residual proportions of coarse particles this predispersion was passed in two runs through a Sugino Ultimaizer HJP-25050 high-energy mill at a pressure of 2500 bar with diamond nozzles of 0.25 mm in diameter, thus subjecting it to further intensive grinding. The concentration of AEROSIL MOX 170 is 20 wt %. The median particle diameter d.sub.50 is determined by static light scattering (LA-950, Horiba Ltd., Japan) as 112 nm.

(11) LUDOX SM 30, Grace, is an aqueous, NaOH-stabilized, colloidal silica dispersion having a particle size of 8 nm and an SiO.sub.2 content of 30 wt %.

(12) LUDOX HS 40, Grace, is an aqueous, NaOH-stabilized, colloidal silica dispersion having a particle size of 12 nm and an SiO.sub.2 content of 40 wt %.

(13) LUDOX CL, Grace, is an aqueous dispersion of Al-coated, colloidal silica having a particle size of 22 nm. The pH is 3.5-4.5, the solids content 39-43 wt %.

(14) Surface Modifying Agents

(15) OM1: 2-[methoxy(polyethyleneoxy).sub.6-9 propyl]trimethoxysilane

(16) OM2: aluminum isopropoxide

(17) Water: this is fully deionized water.

(18) Aqueous sodium hydroxide solution: 25 wt % NaOH

(19) hydrochloric acid: 20 wt % HCl

(20) Production of Mixtures of OM1 and OM2

(21) Mixture 1: Al/Si ratio=1:6.5

(22) 20 g of OM2 are added to 150 g of OM1 and the mixture is heated to 70 C. while stirring. After cooling, insoluble components are removed by centrifuging. RFA analysis of the ash shows 11.5 wt % Al.sub.2O.sub.3 and 88.5 wt % SiO.sub.2.

(23) This corresponds to an Al/Si molar ratio of 1:6.5.

(24) Mixture 2: Al/Si ratio=1:13: further proportions of OM1 are added to mixture 1.

(25) Mixture 3: Al/Si ratio=1:26: further proportions of OM1 are added to mixture 1.

Example 1 (Inventive)

(26) 10.25 g of mixture 1 are slowly added to 40 g of the dispersion of mixed silicon-aluminum oxide with stirring. There is an initial viscosity increase though this falls again upon further addition. The mixture is then adjusted to pH 11 with aqueous sodium hydroxide solution with stirring and the mixture is heated to 90 C. After 10 minutes at 90 C. the mixture is left to cool to room temperature and the mixture is adjusted to pH 9 with hydrochloric acid.

(27) d.sub.50=123 nm; salt stability at 90 C. is 3 weeks (precipitate visually perceptible).

Example 2 (Inventive)

(28) 10.25 g of mixture 2 are slowly added to 40 g of the dispersion of mixed silicon-aluminum oxide with stirring. There is an initial viscosity increase though this falls again upon further addition. The mixture is then adjusted to pH 11 with aqueous sodium hydroxide solution with stirring and the mixture is heated to 90 C. After 10 minutes at 90 C. the mixture is left to cool to room temperature and the mixture is adjusted to pH 9 with hydrochloric acid.

(29) d.sub.50=122 nm; salt stability at 90 C. is 2 weeks.

Example 3 (Comparative)

(30) 10.25 g of mixture 3 are slowly added to 40 g of the dispersion of mixed silicon-aluminum oxide with stirring. There is an initial viscosity increase though this falls again upon further addition. The mixture is then adjusted to pH 11 with aqueous sodium hydroxide solution with stirring and the mixture is heated to 90 C. After 10 minutes at 90 C. the mixture is left to cool to room temperature and the mixture is adjusted to pH 9 with hydrochloric acid. Salt stability at 90 C. is just a few hours.

Example 4 (Comparative)

(31) 10.25 g of OM1 are added slowly with stirring to 40 g of the dispersion of mixed silicon-aluminum oxide. There is an initial viscosity increase though this falls again upon further addition. The mixture is then adjusted to pH 11 with aqueous sodium hydroxide solution with stirring and the mixture is heated to 90 C. After 10 minutes at 90 C. the mixture is left to cool to room temperature and the mixture is adjusted to pH 9 with hydrochloric acid. Salt stability at 90 C. is just a few hours.

Example 5 (Comparative)

(32) 4.3 g of OM1 are added dropwise over 3 hours at 80 C. with stirring to 100 g of a LUDOX 30 SM dispersion diluted with deionized water to 10 wt %. The mixture is stirred at 80 C. for a further 6 hours. The salt stability at 60 C. is 1 day.

Example 6 (Comparative)

(33) 30 g of OM1 are added to 249 g of LUDOX HS 40. The dispersion is heated to 80 C. and stirred at this temperature for 16 hours. The salt stability at 60 C. is 1 day.

Example 7 (Comparative)

(34) 26.7 g of LUDOX CL are diluted to 20 wt % with 13.3 g of DI water. 13.0 g of OM1 are added to this sol slowly and with stirring. The mixture is then adjusted to pH 11 with aqueous sodium hydroxide solution with stirring and the mixture is heated to 90 C. After 10 minutes at 90 C. the mixture is cooled and adjusted to pH 9 with hydrochloric acid. The salt stability at 60 C. is 2 days.

(35) The inventive dispersion of examples 1 and 2 exhibit good salt stability at a temperature of 90 C.

(36) In example 3 (comparative) the proportion of SiO.sub.2 in the surface modification is increased compared to inventive examples 1 and 2.

(37) In examples 4-6 (comparative) the surface modification contains no Al. These dispersions exhibit markedly lower stability.

(38) In example 7 (comparative) the surface modification contains only Al. This dispersion too exhibits a markedly lower stability.

Example 9 (Inventive): Redispersible Powder

(39) A dispersion produced according to example 1 is used to generate an easily redispersible powder with the aid of a Mini Spray Dryer B-290 from BCHI Labortechnik GmbH using nitrogen as the hot gas medium. Stirring-in using a magnetic stirrer affords a d.sub.50 of 155 nm, with a dissolver after 5 minutes at 2000 rpm a d.sub.50 of 136 nm and with an ULTRA-TURRAX T 25, IKA-Werke GmbH & CO. KG after a minute at 9000 rpm a d.sub.50 of 130 nm.