# US 5,352,481 A · Process for forming particles having a uniform size distribution

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- Number: US 5,352,481 A
- Document ID: US5352481A
- Status: Granted
- Kind: A
- Application number: 08/055,424
- Filed: 1993-04-29
- Granted: 1994-10-04
- Earliest claimed: 1992-05-29
- Assignees: Hughes Aircraft Company
- Inventors: Chan S. Bak; Hiroshi Kimura; Ricardo C. Pastor
- Web page: https://patentgrep.com/patent/US5352481A

## CPC

- C04B 35/624: Sol-gel processing
- B01J 2/006: {Coating of the granules without description of the process or the device by which the granules are obtained (to prevent the granules sticking together B01J2/30)}
- B01J 2/08: Gelation of a colloidal solution
- B22F 1/065: Spherical particles
- C04B 35/6264: {Mixing media, e.g. organic solvents}
- C04B 35/62805: {Oxide ceramics}
- C04B 35/62807: {Silica or silicates}
- C04B 35/62894: {with more than one coating layer}
- C04B 41/009: {characterised by the material treated}
- C04B 41/4584: {Coating or impregnating of particulate or fibrous ceramic material (C04B20/10, C04B35/628 take precedence)}
- C04B 41/52: Multiple coating or impregnating {multiple coating or impregnating with the same composition or with compositions only differing in the concentration of the constituents, is classified as single coating or impregnation}
- C04B 41/81: Coating or impregnation
- C04B 41/89: for obtaining at least two superposed coatings having different compositions
- H01B 3/10: metallic oxides (ceramics H01B3/12)
- C04B 2235/3232: Titanium oxides or titanates, e.g. rutile or anatase
- C04B 2235/3298: Bismuth oxides, bismuthates or oxide forming salts thereof, e.g. zinc bismuthate
- C04B 2235/3418: Silicon oxide, silicic acids or oxide forming salts thereof, e.g. silica sol, fused silica, silica fume, cristobalite, quartz or flint
- C04B 2235/441: Alkoxides, e.g. methoxide, tert-butoxide
- C04B 2235/528: Spheres
- C04B 2235/5445: submicron sized, i.e. from 0,1 to 1 micron
- C04B 2235/5481: Monomodal
- C04B: LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE {(roofing granules E04D7/005)}; CERAMICS (devitrified glass-ceramics C03C10/00); REFRACTORIES; TREATMENT OF NATURAL STONE
- B01J: CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B22F: WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER (making alloys by powder metallurgy C22C); APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- H01B: CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES (selection for magnetic properties H01F1/00; waveguides H01P {; printed circuits H05K})

## Abstract

A process is provided for fabricating coated particles of a substantially uniform particle size. The process comprises coating small particles of well-defined crystalline phases with a polymerized gel. The process results in a ball-type sol-gel coating of the particles to provide particles which have a narrow size distribution. In many instances, crystalline particles of irregular shape have a substantially spherical shape upon coating with the sol-gel. In instances where the core is a high melting point material, such as an oxide, nitride, or carbide, the coat formulation can effect a low sintering temperature, which permits forming films of the particles at a much lower temperature than would otherwise be possible.

## Claims

### Claim 1

A process for forming particles having a substantially uniform size distribution and provided with an outer coating having a melting point of less than 900.degree. C. to enable sintering of said particles at a temperature less than 900.degree. C., comprising:
(a) providing titania powder comprising core particles of irregular shape and broad particle size distribution;
(b) coating said titania powder with a first coating consisting essentially of a silica gel by
(1) suspending said powder in a suspending medium consisting essentially of an alcohol, said suspending medium acting as a solvent for a silicon alkoxide and containing a quantity of water,
(2) adding said silicon alkoxide to said suspending medium, and
(3) allowing said silicon alkoxide to hydrolyze and condense on the surface of said core particles to form said silica sol-gel; and
(c) coating said first coating of silica gel with a second coating consisting essentially of a bismuth oxide gel by
(1) suspending said silica-gel coated particles in an alcohol, said alcohol acting as a solvent for a bismuth alkoxide and containing a quantity of water,
(2) adding said bismuth alkoxide to said suspending medium, and
(3) allowing said bismuth alkoxide to hydrolyze and condense on the surface of said first coating of silica gel to form said second coating of said bismuth oxide gel.

### Claim 2 (depends on 1)

The process of claim 1 wherein said core particles have a particle size ranging from about 0.1 to 2 .mu.m.

### Claim 3 (depends on 1)

The process of claim 1 wherein said alcohol is selected from the group consisting of methanol, ethanol, n-propanol, and iso-propanol.

### Claim 4 (depends on 1)

The process of claim 1 wherein said bismuth alkoxide comprises an alkoxy group comprising from 1 to 5 carbon atoms.

### Claim 5

A process for forming particles having a substantially uniform size distribution and provided with an outer coating having a melting point of less than 900.degree. C. to enable sintering of said particles at a temperature less than 900.degree. C., comprising:
(a) providing titania powder comprising core particles of irregular shape and broad particle size distribution;
(b) coating said titania powder with a first coating consisting essentially of a silica gel by
(1) suspending said powder in ethanol containing a quantity of water and a pH-adjusting agent,
(2) adding silicon tetra-ethoxide to said ethanol, and
(3) allowing said silicon tetra-ethoxide to hydrolyze and condense on the surface of said titania powder to form said silica gel; and
(c) coating said first coating of silica gel with a second coating consisting essentially of a bismuth oxide gel by
(1) suspending said silica-gel coated particles in an alcohol, said alcohol acting as a solvent for a bismuth alkoxide and containing a quantity of water,
(2) adding said bismuth alkoxide to said suspending medium, and
(3) allowing said bismuth alkoxide to hydrolyze and condense on the surface of said first coating of silica gel to form said second coating of said bismuth oxide gel.

### Claim 6 (depends on 5)

The process of claim 5 wherein said core particles have a particle size ranging from about 0.1 to 2 .mu.m.

### Claim 7 (depends on 5)

The process of claim 5 wherein said alcohol is selected from the group consisting of methanol, ethanol, n-propanol, and iso-propanol.

### Claim 8 (depends on 5)

The process of claim 5 wherein said bismuth alkoxide comprises an alkoxy group comprising from 1 to 5 carbon atoms.