# US 11,998,986 B2 · Alumina sintered body and method for manufacturing the same

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- Number: US 11,998,986 B2
- Document ID: US11998986B2
- Status: Granted
- Kind: B2
- Application number: 18/145,994
- Filed: 2022-12-23
- Published: 2023-06-29
- Granted: 2024-06-04
- Earliest claimed: 2021-12-28
- Assignees: Coorstek Gk
- Applicants: CoorsTek KK
- Inventors: Takuya Nakagawa; Yuji Fukasawa
- Web page: https://patentgrep.com/patent/US11998986B2

## CPC

- B22F 3/16: in successive or repeated steps
- C04B 35/111: Fine ceramics
- B22F 1/10: Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
- C04B 35/62695: {Granulation or pelletising (devices for shaping artificial aggregates from ceramic mixtures B28B1/004)}
- C04B 35/63416: {Polyvinylalcohols [PVA]; Polyvinylacetates}
- C04B 35/638: Removal thereof
- C04B 35/64: Burning or sintering processes (C04B33/32 takes precedence {; powder metallurgy B22F})
- B22F 2201/00: Treatment under specific atmosphere
- B22F 2207/01: Composition gradients
- B22F 2301/052: Aluminium
- C04B 2235/3201: Alkali metal oxides or oxide-forming salts thereof
- 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 2235/5436: micrometer sized, i.e. from 1 to 100 micron
- C04B 2235/604: Pressing at temperatures other than sintering temperatures
- C04B 2235/6565: Cooling rate
- C04B 2235/6581: Total pressure below 1 atmosphere, e.g. vacuum
- C04B 2235/6582: Hydrogen containing atmosphere
- C04B 2235/72: Products characterised by the absence or the low content of specific components, e.g. alkali metal free alumina ceramics
- C04B 2235/725: Metal content
- C04B 2235/75: Products with a concentration gradient
- 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
- 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

## Abstract

An alumina sintered body having a low dielectric loss tangent and a method for manufacturing the alumina sintered body are provided. An alumina sintered body contains Al2O3 99.50 mass % or more, and 99.95 mass % or less and sodium and silicon, wherein at a surface layer A in any given cross-section and a central portion B of the cross-section in a depth direction from the surface layer A, a concentration ratio of sodium to silicon in the surface layer A is smaller than the concentration ratio of sodium to silicon at the central portion B.

## Claims

### Claim 1

An alumina sintered body containing Al2O3 in an amount of 99.50 mass % or more, and 99.95 mass % or less, the alumina sintered body further containing sodium and silicon,
wherein a dielectric loss tangent (a value of tan δ) at 4 GHz is 1×10−4 or less,
wherein at a surface layer A in any given cross-section and at a central portion B of the cross-section in a depth direction from the surface layer A, a concentration ratio of sodium to silicon in the surface layer part A is smaller than the concentration ratio of sodium to silicon at the central portion B,
wherein the concentration ratio of sodium to silicon of the alumina sintered body is 0.3 or less, and
wherein the surface layer part A is within a range of 10 mm from a surface in the depth direction, and the central portion B is a region within a range of 10 mm in the depth direction centering at a center of the cross-section.

### Claim 2 (depends on 1)

The alumina sintered body recited in claim 1, wherein an aspect ratio of an Al2O3crystal grain in the surface layer part A is smaller than the aspect ratio of the Al2O3 crystal grain at the central portion B.

### Claim 3 (depends on 1)

A method for manufacturing the alumina sintered body recited in claim 1, comprising:
a step of granulating granules from a mixture of alumina powder as raw material to which silicon dioxide powder used as a silicon content is added, and mixed with a binder and solvent, using a spray granulator,
a step of forming compacts by molding the obtained granules,
a step of degreasing the compacts, and
a step of sintering the degreased compacts at a temperature between 1300° C. and 1800° C. in a reducing atmosphere or vacuum,
wherein the concentration ratio of sodium to silicon at the surface layer part A in any given cross-section is smaller than the concentration ratio of sodium to silicon at the central portion B of the cross-section in the depth direction from the surface layer part A, by allowing the sodium content to volatile from the degreased compacts.

### Claim 4 (depends on 1)

The alumina sintered body recited in claim 1, wherein the concentration ratio of sodium to silicon in the surface layer part A is 0.072 to 0.119 and the concentration ratio of sodium to silicon at the central portion B is 0.117 to 0.214.