# US 6,723,672 B1 · High-strength magnesia partially stabilized zirconia

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- Number: US 6,723,672 B1
- Document ID: US6723672B1
- Status: Granted
- Kind: B1
- Application number: 09/889,548
- Filed: 2001-07-17
- Granted: 2004-04-20
- Earliest claimed: 1999-01-26
- Assignees: Carpenter Advanced Ceramics, Inc.
- Inventors: Martin D. Stuart; Wilson H. Ta
- Web page: https://patentgrep.com/patent/US6723672B1

## CPC

- C04B 35/486: Fine ceramics
- C04B 35/6303: {Inorganic additives}
- C04B 2235/3205: Alkaline earth oxides or oxide forming salts thereof, e.g. beryllium oxide
- 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 2235/3222: Aluminates other than alumino-silicates, e.g. spinel (MgAl2O4)
- C04B 2235/3826: Silicon carbides
- C04B 2235/3843: Titanium carbides
- C04B 2235/604: Pressing at temperatures other than sintering temperatures
- C04B 2235/6565: Cooling rate
- C04B 2235/72: Products characterised by the absence or the low content of specific components, e.g. alkali metal free alumina ceramics
- C04B 2235/765: Tetragonal symmetry
- C04B 2235/78: Grain sizes and shapes, product microstructures, e.g. acicular grains, equiaxed grains, platelet-structures
- C04B 2235/786: Micrometer sized grains, i.e. from 1 to 100 micron
- 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: 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

A high strength ceramic body and a method of making same are disclosed. The ceramic body is formed of ceramic composition containing 2.8-5.0% by weight MgO, an effective amount of grain growth inhibiting material, and the balance being essentially zirconia. The crystalline microstructure of the ceramic body comprises grains of cubic zirconia having an average grain size of less than about 30 microns in major dimension, 0.1-8.7% by volume of discrete particles of the grain growth inhibiting material, and precipitates of tetragonal zirconia having a substantially ellipsoidal shape with a long dimension of about 0.1-0.4 microns.

## Claims

### Claim 1

A Mg-PSZ ceramic body formed from a ceramic powder composition consisting essentially of about 2.8-5.0% by weight MgO, an effective amount of a grain growth inhibiting additive, not more than about 0.3 mole % of yttria, ceria, other rare earth oxide, or strontia, and the balance being essentially zirconia, wherein said ceramic body has a crystalline microstructure comprising grains of cubic zirconia having an average grain size of less than about 30 microns in major dimension, discrete precipitates of tetragonal zirconia within the grains of cubic zirconia, and about 0.1-8.7% by volume of discrete particles of a grain growth inhibiting material which is or is formed from the grain growth inhibiting additive.

### Claim 2 (depends on 1)

The ceramic body of claim 1 wherein the grain growth inhibiting material is an inorganic compound that is insoluble and stable in the Mg-PSZ at a temperature in the range of about 1600° C. to about 1850° C.

### Claim 3 (depends on 2)

The ceramic body of claim 2 wherein the grain growth inhibiting material is selected from the group consisting of magnesium aluminate spinel, silicon carbide, titanium carbide, and mixtures thereof.

### Claim 4 (depends on 1)

The ceramic body of claim 1 wherein the ceramic powder composition contains about 0.05-4.0% by weight alumina and wherein the discrete particles of the grain growth inhibiting material comprise discrete particles of magnesium aluminate spinel.

### Claim 5 (depends on 4)

The ceramic body of claim 4 wherein at least a portion of the discrete particles of magnesium aluminate spinel reside at the grain boundaries of the cubic zirconia.

### Claim 6 (depends on 5)

The ceramic body of claim 5 wherein a further portion of the discrete particles of magnesium aluminate spinel reside within the grains of cubic zirconia.

### Claim 7 (depends on 4)

The ceramic body of claim 4 wherein the discrete particles of magnesium aluminate spinel have an average size of less than about 5 microns in major dimension.

### Claim 8 (depends on 1)

The ceramic body of claim 1 wherein the discrete precipitates of tetragonal zirconia have a substantially ellipsoidal shape with a major dimension of about 0.1-0.4 microns.

### Claim 9 (depends on 1, 2, 3, 4, 5, 6, 7)

The ceramic body set forth in any of claims 1 to 7, or 8 wherein the ceramic powder composition of contains about 3.0-4.5% by weight MgO and about 0.2-2.5% alumina.

### Claim 10 (depends on 9)

The ceramic body set forth in claims 9 wherein the crystalline microstructure of the ceramic body comprises about 0.5-5.0% by volume of particles of magnesium aluminate spinel.

### Claim 11

A ceramic body formed from a powder mixture consisting essentially of about 2.8-5.0% by weight magnesia, about 0.05-4.0% by weight alumina, not more than about 0.3 mole % yttria, ceria, other rare earth oxide, or strontia, and the balance essentially zirconia, wherein the ceramic body has a crystalline microstructure comprising:
grains of cubic zirconia having an average grain size of less than about 30 microns in major dimension;
1-8.7% by volume of particles of magnesium aluminate spinel residing at the boundaries of the cubic zirconia grains and having an average size of less than about 5 microns in major dimension; and
precipitates of tetragonal zirconia formed within the grains of cubic zirconia, said tetragonal zirconia precipitates having a substantially ellipsoidal shape with a long dimension of about 0.1-0.4 microns.

### Claim 12 (depends on 11)

A ceramic body as set forth in claim 11 wherein the ceramic powder mixture consists essentially of about 3.0-4.5% by weight MgO, about 0.2-2.5% alumina, and the balance is essentially zirconia.

### Claim 13 (depends on 12)

The ceramic body set forth in claim 12 wherein the crystalline microstructure of the ceramic body comprises about 0.5-5.0% by volume of particles of magnesium aluminate spinel.

### Claim 14 (depends on 1)

A method of making a ceramic body as set forth in claim 1 comprising the steps of:
a. mixing a zirconia powder, a magnesia powder, and a grain growth inhibiting additive to form a homogeneous powder mixture;
b. consolidating the homogeneous powder mixture to form a green body;
c. firing the green body at a maximum temperature in the range of about 1600° C. to about 1850° C. and for a time sufficient to form a polycrystalline cubic zirconia phase having particles of a grain growth inhibiting material residing at the grain boundaries of the cubic zirconia phase, the grain growth inhibiting material being or being formed from the grain growth inhibiting additive; and
d. cooling the fired body at a controlled cooling rate to form the ceramic body, wherein said controlled cooling rate comprises:
i) cooling the fired body from the maximum firing temperature to about 1400° C. at a rate in the range of about 100° C./hr to about 500° C./hr;
ii) cooling the fired body from about 1400° C. to about 1200° C. at a rate in the range of about 40° C./hr to about 200° C./hr; and then
iii) cooling the fired body from about 1200° C. to below about 600° C. at a rate in the range of about 100° C./hr to about 300° C./hr.

### Claim 15 (depends on 14)

The method of claim 14 wherein the mixing step comprises the step of using as the grain growth inhibiting additive an inorganic compound that is insoluble and stable in the zirconia phase at a temperature in the range of about 1600° C. to about 1850° C.

### Claim 16 (depends on 14)

The method of claim 14 wherein the mixing step comprises the step of using as the grain growth inhibiting additive a material selected from the group consisting of magnesium aluminate spinel, silicon carbide, titanium carbide, and mixtures thereof.

### Claim 17 (depends on 14)

The method of claim 14 further comprising the step of heat treating the ceramic body at a temperature in the range of about 1000° C. to about 1500° C.