# US 7,612,006 B2 · Conductive silicon nitride materials and method for producing the same

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- Number: US 7,612,006 B2
- Document ID: US7612006B2
- Status: Granted
- Kind: B2
- Application number: 11/664,072
- Filed: 2005-09-27
- Published: 2008-03-27
- Granted: 2009-11-03
- Earliest claimed: 2004-10-01
- Assignees: Yokohama TLO Company, Ltd.
- Inventors: Katsutoshi Komeya; Junichi Tatami; Takeshi Meguro; Tomofumi Katashima; Toru Wakihara
- Web page: https://patentgrep.com/patent/US7612006B2

## CPC

- C04B 35/593: obtained by pressure sintering
- B82Y 30/00: Nanotechnology for materials or surface science, e.g. nanocomposites
- C04B 35/5935: {obtained by gas pressure sintering}
- C04B 35/638: Removal thereof
- F16C 33/32: Balls
- C04B 2235/3206: Magnesium oxides or oxide-forming salts thereof
- C04B 2235/3217: Aluminum oxide or oxide forming salts thereof, e.g. bauxite, alpha-alumina
- C04B 2235/3225: Yttrium oxide or oxide-forming salts thereof
- C04B 2235/3232: Titanium oxides or titanates, e.g. rutile or anatase
- C04B 2235/3244: Zirconium oxides, zirconates, hafnium oxides, hafnates, or oxide-forming salts thereof
- C04B 2235/3258: Tungsten oxides, tungstates, or oxide-forming salts thereof
- C04B 2235/3826: Silicon carbides
- C04B 2235/3865: Aluminium nitrides
- C04B 2235/3869: Aluminium oxynitrides, e.g. AlON, sialon
- C04B 2235/3878: Alpha silicon nitrides
- C04B 2235/3886: Refractory metal nitrides, e.g. vanadium nitride, tungsten nitride
- C04B 2235/3895: Non-oxides with a defined oxygen content, e.g. SiOC, TiON
- C04B 2235/526: characterised by the length of the fibers
- C04B 2235/5264: characterised by the diameter of the fibers
- C04B 2235/5288: Carbon nanotubes
- C04B 2235/5445: submicron sized, i.e. from 0,1 to 1 micron
- C04B 2235/604: Pressing at temperatures other than sintering temperatures
- C04B 2235/658: Atmosphere during thermal treatment
- C04B 2235/661: Multi-step sintering
- C04B 2235/766: Trigonal symmetry, e.g. alpha-Si3N4 or alpha-Sialon
- C04B 2235/77: Density
- C04B 2235/80: Phases present in the sintered or melt-cast ceramic products other than the main phase
- C04B 2235/85: Intergranular or grain boundary phases
- C04B 2235/96: Properties of ceramic products, e.g. mechanical properties such as strength, toughness, wear resistance
- C04B 2235/963: Surface properties, e.g. surface roughness
- C04B 2235/9669: Resistance against chemicals, e.g. against molten glass or molten salts
- 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
- B82Y: SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- F16C: SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS

## Abstract

To provide a sintered silicon nitride with conductivity and densification, an oxide of titanium group elements, such as titanium oxide, hafnium oxide, zirconium oxide and the like, aluminum oxide and/or aluminum nitride is added as needed to silicon nitride-oxidant of rare-earth elements-aluminum oxide system or silicon nitride-oxide of rare-earth elements-magnesia system, and then specified quantity of carbon nonotube (CNT) is added to the above mixture. CNT generates silicon carbide after the reaction with contiguous or proximal silicon nitride and the like depending on the sintering duration at high temperature. Since silicon carbide is generated along with nanotubes, the silicon carbide functions as conductor with excellent heat resistance, corrosion resistance and the like.

## Claims

### Claim 1

A sintered silicon nitride with a conductivity of higher than 10−1Ω−1 m−1 produced by (a) preparing a mixture, comprising 0.5 to 10 weight percent of rare-earth compounds in terms of oxide, 0.1 to 5 weight percent of aluminum oxide or its precursor, 0 to 5 weight percent of aluminum nitride, 0.1 to 5 weight percent of oxides of titanium group or other titanium group compounds in terms of equimolar titanium nitride wherein the titanium group compounds can be converted to nitrides of titanium group elements by sintering, and silicon nitride powder as a balance, and further comprising 0.3 to 12 weight percent of carbon nanotubes (CNT) relative to 100 weight percent of the foregoing mixture, wherein the silicon nitride powder has an average grain diameter of less than 1.0 μm and contains less than 1.7 weight percent of oxygen content and more than 90 weight percent of alpha phase type silicon nitride, and (b) sintering the mixture by a normal pressure sintering method or an ambient pressure sintering method.

### Claim 2 (depends on 1)

The sintered silicon nitride of claim 1, comprising a matrix phase of crystal grains composed of silicon nitride and a grain boundary phase composed mainly of Si—R—Al—O—N compounds, wherein R represents rare-earth elements.

### Claim 3 (depends on 1)

The sintered silicon nitride of claim 1, wherein the mixture further comprises from 0.1 to 5 weight percent of at least one compound selected from magnesium and tungsten converted to oxide base.

### Claim 4 (depends on 1)

The sintered silicon nitride of claim 1, comprising a matrix phase of crystal grains composed of silicon nitride and a grain boundary phase composed mainly of Si—R—Mg—O—N compounds or Si—R—Mg—O—N compounds, wherein R represents rare-earth elements.

### Claim 5 (depends on 1)

The sintered silicon nitride of claim 1, wherein said CNT has a diameter of 0.4 to 200 nm and a longitudinal diameter of 1 to 1000 μm.

### Claim 6

A method for producing a sintered silicon nitride with a conductivity of higher than 10—1Ω−1m−1, comprising (a) forming a mixture into a desired shape and degreasing thereof, wherein the mixture comprises 0.5 to 10 weight percent of rare-earth compounds in terms of oxide, 0.1 to 5 weight percent of aluminum oxide or its precursor, 0 to 5 weight percent of aluminum nitride, 0.1 to 5 weight percent of oxides of titanium group with average grain diameter of less than 1.0 μm or other titanium group compounds in terms of equimolar titanium nitride wherein the titanium group compounds can be converted to nitrides of titanium group elements by sintering, and silicon nitride powder as a balance, and further comprising 0.3 to 12 weight percent of carbon nanotubes (CNT) relative to 100 weight percent of the previous mixture, wherein the silicon nitride powder has an average grain diameter of less than 1.0 μm and contains less than 1.7 weight percent of oxygen content and more than 90 weight percent of alpha phase type silicon nitride, and (b) sintering the shaped mixture at 1600 to 1900° C. by a normal pressure sintering method or an ambient pressure sintering method.

### Claim 7 (depends on 6)

The method for producing sintered silicon nitride of claim 6, further comprising applying a hot isostatic pressing (HIP) to the sintered silicon nitride obtained by the previous sintering process at a pressure of more than 30MPa and a temperature of from 1600 to 1850° C. under a non-oxidizing atmosphere.

### Claim 8 (depends on 2)

The sintered silicon nitride of claim 2, wherein the mixture further comprises from 0.1 to 5 weight percent of at least one compound selected from magnesium and tungsten converted to oxide base.

### Claim 9 (depends on 2)

The sintered silicon nitride of claim 2, wherein said CNT has a diameter of 0.4 to 200 nm and a longitudinal diameter of 1 to 1000 μm.

### Claim 10 (depends on 3)

The sintered silicon nitride of claim 3, wherein said CNT has a diameter of 0.4 to 200 nm and a longitudinal diameter of 1 to 1000 μm.

### Claim 11 (depends on 4)

The sintered silicon nitride of claim 4, wherein said CNT has a diameter of 0.4 to 200 nm and a longitudinal diameter of 1 to 1000 μm.

### Claim 12 (depends on 8)

The sintered silicon nitride of claim 8, wherein said CNT has a diameter of 0.4 to 200 nm and a longitudinal diameter of 1 to 1000 μm.

### Claim 13 (depends on 1)

The sintered silicon nitride of claim 1 wherein said CNT has a diameter of 0.4 to 200 nm and a longitudinal diameter of 1 to 1000 μm.