US4954462A — Microcrystalline alumina-based ceramic articles

Claim 1

Independent Claim 109 words

A solid, fired refractory article comprising in the range of 0.1 to 7.0 percent by weight iron equivalence and at least 60% alumina by weight in which at least 99 percent of the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites wherein the average crystallite diameter is less than 0.5 micrometer, at least 95 percent of the alpha alumina crystallites are less than 0.5 micrometer in diameter and no grains are larger than 0.5 micrometer in diameter, the density of the article is greater than 90% of theoretical density, and the surface roughness height of the article is less than 100 nm.

Claim 2

Dependent Claim 109 words

A solid, fired refractory article comprising in the range of 0.1 to 7.0 percent by weight iron equivalence and at least 60% alumina by weight in which at least 99 percent of the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites wherein the average crystallite diameter is less than 0.5 micrometer, at least 95 percent of the alpha alumina crystallites are less than 0.5 micrometer in diameter and no grains are larger than 0.5 micrometer in diameter, the density of the article is greater than 90% of theoretical density, and the surface roughness height of the article is less than 100 nm.

Claim 3

Dependent Claim 18 words

The article according to claim 1 wherein the average alpha alumina crystallite diameter is less than 0.3 micrometer.

Claim 4

Dependent Claim 17 words

The article according to claim 1 further comprising an effective amount of at least one modifying additive.

Claim 5

Dependent Claim 16 words

The article according to claim 3 wherein said modifying additive is silica or a precursor thereof.

Claim 6

Dependent Claim 14 words

The article according to claim 1 comprising at least 90 percent alumina by weight.

Claim 7

Dependent Claim 18 words

The article according to claim 1 which is a fiber, bead, flake, bubble, irregularly shaped particle or coating.

Claim 8

Dependent Claim 9 words

The article according to claim 1 which is transparent.

Claim 9

Dependent Claim 33 words

The article according to claim 3 wherein said modifying additive is selected from the group consisting of a colloidal or particulate metal oxide, or a colloidal or particulate precursor to a metal oxide.

Claim 10

Dependent Claim 32 words

The article according to claim 1 or 3 which is selected from the class consisting of beads, flakes, bubbles, and randomly shaped particles, wherein the alpha alumina crystallites are substantially randomly oriented.

Claim 11

Dependent Claim 22 words

The article according to claim 3 wherein said additive is selected from the group consisting of zirconia, silica, magnesia, and precursors thereof.

Claim 12

Dependent Claim 10 words

The article according to claim 6 which is a fiber.

Claim 13

Dependent Claim 10 words

The article according to claim 4 which is a fiber.

Claim 14

Dependent Claim 23 words

The fiber according to claim 11 wherein at least 95 percent of the alpha alumina crystallites are less than 0.25 micrometers in diameter.

Claim 15

Dependent Claim 26 words

The fiber according to claim 11 wherein at least 95 percent of the alpha alumina crystallites are uniformly oriented as determined by optical and X-ray analysis.

Claim 16

Dependent Claim 16 words

The fiber according to claim 11 wherein said fiber is a flexible, high modulus ceramic fiber.

Claim 17

Dependent Claim 12 words

The article of claim 6 wherein said article is a ceramic bead.

Claim 18

Dependent Claim 100 words

A solid, shaped and fired refractory article comprising in the range of 0.1 to 7.0 percent by weight iron equivalence and at least 60 percent alumina by weight in which at least 99 percent of the alumina is in the alpha phase comprising alpha alumina crystallites wherein at least 99 percent of the alpha alumina crystallites are less than 0.2 micrometer in diameter and all are less than 0.7 micrometer in diameter, and the specific surface area of the article is greater than 15 m 2 /g and the surface roughness height of the article is less than 100 nm.

Claim 19

Dependent Claim 100 words

A solid, shaped and fired refractory article comprising in the range of 0.1 to 7.0 percent by weight iron equivalence and at least 60 percent alumina by weight in which at least 99 percent of the alumina is in the alpha phase comprising alpha alumina crystallites wherein at least 99 percent of the alpha alumina crystallites are less than 0.2 micrometer in diameter and all are less than 0.7 micrometer in diameter, and the specific surface area of the article is greater than 15 m 2 /g and the surface roughness height of the article is less than 100 nm.

Claim 20

Dependent Claim 26 words

The article according to claim 17 having a microporous interior and having an alpha alumina sheath, said sheath having greater than 90 percent of theoretical density.

Claim 21

Dependent Claim 110 words

A ceramic microsphere comprising in the range of 0.1 to 7.0 weight percent iron equivalence and at least 60% alumina by weight in which at least 99 percent of the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites wherein the average crystallite diameter is less than 0.5 micrometer and at least 95 percent of the alpha alumina crystallites are less than 0.5 micrometer in diameter and all are less than 0.7 micrometer in diameter, and the density of the article is greater than 90% of theoretical density, and said microsphere has a size greater than 0 and up to 500 micrometers in diameter.

Claim 22

Dependent Claim 110 words

A ceramic microsphere comprising in the range of 0.1 to 7.0 weight percent iron equivalence and at least 60% alumina by weight in which at least 99 percent of the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites wherein the average crystallite diameter is less than 0.5 micrometer and at least 95 percent of the alpha alumina crystallites are less than 0.5 micrometer in diameter and all are less than 0.7 micrometer in diameter, and the density of the article is greater than 90% of theoretical density, and said microsphere has a size greater than 0 and up to 500 micrometers in diameter.

Claim 23

Dependent Claim 12 words

The microsphere according to claim 19 wherein said microsphere is a bead.

Claim 24

Dependent Claim 9 words

The microsphere according to claim 20 which is retroreflective.

Claim 25

Dependent Claim 9 words

The microsphere according to claim 19 which is transparent.

Claim 26

Dependent Claim 10 words

The microsphere according to claim 19 which is a bubble.

Claim 27

Dependent Claim 107 words

A ceramic fiber comprising in the range of 0.1 to 7.0 weight percent iron equivalence and at least 60% alumina by weight in which at least 99 percent of the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites wherein the average crystallite diameter is less than 0.5 micrometer and at least 95 percent of the alpha alumina crystallites are less than 0.5 micrometer in diameter and at least 99 percent are less than 0.7 micrometer in diameter, said fiber having an average microscopic roughness height of less than 100 nm and a density of at least 90% of theoretical density.

Claim 28

Dependent Claim 107 words

A ceramic fiber comprising in the range of 0.1 to 7.0 weight percent iron equivalence and at least 60% alumina by weight in which at least 99 percent of the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites wherein the average crystallite diameter is less than 0.5 micrometer and at least 95 percent of the alpha alumina crystallites are less than 0.5 micrometer in diameter and at least 99 percent are less than 0.7 micrometer in diameter, said fiber having an average microscopic roughness height of less than 100 nm and a density of at least 90% of theoretical density.

Claim 29

Dependent Claim 93 words

A solid, fired refractory article comprising in the range of 0.1 to 7.0 percent by weight iron equivalence and at least 60% alumina by weight in which at least 99 percent of the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites wherein the average crystallite diameter is in the range of 0.3-0.4 micrometer, and no grains are larger than 0.4 micrometer, the density of the article is greater than 90% of theoretical density, and the surface roughness height of the article is less than 100 nm.

Claim 30

Dependent Claim 93 words

A solid, fired refractory article comprising in the range of 0.1 to 7.0 percent by weight iron equivalence and at least 60% alumina by weight in which at least 99 percent of the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites wherein the average crystallite diameter is in the range of 0.3-0.4 micrometer, and no grains are larger than 0.4 micrometer, the density of the article is greater than 90% of theoretical density, and the surface roughness height of the article is less than 100 nm.

Claim 31

Dependent Claim 173 words

A process for forming an alumina-based ceramic article, the process comprising the steps: a. preparing a solution of a basic aluminum salt or other hydrolyzable alumina precursor and iron-containing nucleating agents, said nucleating agents being hydrous iron polymers which are formed by hydrolysis of an iron salt solution; b. forming the solution into a desired form or coating, and at least one of gelling and drying the solution to obtain a solid form; and c. calcining the solid; the ceramic article comprising in the range of 0.1 to 7.0 percent by weight iron equivalence and at least 60% alumina by weight in which at least 99 percent of the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites wherein the average crystallite diameter is less than 0.5 micrometer and at least 95 percent of the alpha alumina crystallites are less than 0.5 micrometer in diameter and all are less than 0.7 micrometer in diameter, and the density of the article is greater than 90% of theoretical density.

Claim 32

Dependent Claim 173 words

A process for forming an alumina-based ceramic article, the process comprising the steps: a. preparing a solution of a basic aluminum salt or other hydrolyzable alumina precursor and iron-containing nucleating agents, said nucleating agents being hydrous iron polymers which are formed by hydrolysis of an iron salt solution; b. forming the solution into a desired form or coating, and at least one of gelling and drying the solution to obtain a solid form; and c. calcining the solid; the ceramic article comprising in the range of 0.1 to 7.0 percent by weight iron equivalence and at least 60% alumina by weight in which at least 99 percent of the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites wherein the average crystallite diameter is less than 0.5 micrometer and at least 95 percent of the alpha alumina crystallites are less than 0.5 micrometer in diameter and all are less than 0.7 micrometer in diameter, and the density of the article is greater than 90% of theoretical density.

Claim 33

Dependent Claim 28 words

The method according to claim 26 wherein said iron-containing nucleating agent has been introduced into the article precursor in the form of a discrete particulate or colloidal form.

Claim 34

Dependent Claim 37 words

The method according to claim 27 where the iron-containing nucleating agent has been introduced into the article precursor in the form of a particulate or colloidal form with average particle size less than 20 nm in diameter.

Claim 35

Dependent Claim 25 words

The method according to claim 26 further comprising the addition of an effective amount of at least one modifying additive prior to the forming step.

Claim 36

Dependent Claim 23 words

The method according to claim 29 wherein said additive is selected from the group consisting of silica, magnesia, zirconia, and a precursor thereof.

Claim 37

Dependent Claim 15 words

The method according to claim 26 further comprising the step of sintering the calcined solid.

Claim 38

Dependent Claim 17 words

The method according to claim 26 further comprising the steps of compacting and sintering the calcined solids.

Claim 39

Dependent Claim 17 words

The method according to claim 26 wherein said solution of step b. is coated upon a substrate.

Claim 40

Dependent Claim 164 words

A process for forming an alumina-based ceramic article, the process comprising the steps: a. preparing a solution comprising a basic aluminum salt or other hydrolyzable alumina precursor and iron-containing nucleating agents, said nucleating agents being hydrous iron polymers which are formed by hydrolysis of an iron salt solution; b. forming the solution into a desired form or coating, and at least one of gelling and drying the solution to obtain a solid form; and c. calcining the solid; the ceramic article comprising in the range of 0.1 to 7.0 percent by weight iron equivalence and at least 60% alumina by weight in which at least 99 percent of the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites wherein the average crystallite diameter is less than 0.5 micrometer and at least 95 percent of the alpha alumina crystallites are less than 0.7 micrometer in diameter and the density of the article is greater than 90% of theoretical density.

Claim 41

Dependent Claim 164 words

A process for forming an alumina-based ceramic article, the process comprising the steps: a. preparing a solution comprising a basic aluminum salt or other hydrolyzable alumina precursor and iron-containing nucleating agents, said nucleating agents being hydrous iron polymers which are formed by hydrolysis of an iron salt solution; b. forming the solution into a desired form or coating, and at least one of gelling and drying the solution to obtain a solid form; and c. calcining the solid; the ceramic article comprising in the range of 0.1 to 7.0 percent by weight iron equivalence and at least 60% alumina by weight in which at least 99 percent of the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites wherein the average crystallite diameter is less than 0.5 micrometer and at least 95 percent of the alpha alumina crystallites are less than 0.7 micrometer in diameter and the density of the article is greater than 90% of theoretical density.

Claim 42

Dependent Claim 163 words

A process for forming an alumina-based ceramic fiber, the process comprising the steps: a. preparing a solution comprising a basic aluminum salt or other hydrolyzable alumina precursor and iron-containing nucleating agents, said nucleating agents being hydrous iron polymers which are formed by hydrolysis of an iron salt solution; b. forming the solution into a fiber shape, and at least one of gelling and drying the solution to obtain a solid fiber; and c. calcining the solid fiber; the ceramic fiber comprising in the range of 0.1 to 7.0 percent by weight iron equivalence and at least 60% alumina by weight in which at least 99 percent of the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites wherein the average cyrstallite diameter is less than 0.5 micrometer and at least 95 percent of the alpha alumina crystallites are less than 0.7 micrometer in diameter and the density of the fiber is greater than 90% of theoretical density.

Claim 43

Dependent Claim 163 words

A process for forming an alumina-based ceramic fiber, the process comprising the steps: a. preparing a solution comprising a basic aluminum salt or other hydrolyzable alumina precursor and iron-containing nucleating agents, said nucleating agents being hydrous iron polymers which are formed by hydrolysis of an iron salt solution; b. forming the solution into a fiber shape, and at least one of gelling and drying the solution to obtain a solid fiber; and c. calcining the solid fiber; the ceramic fiber comprising in the range of 0.1 to 7.0 percent by weight iron equivalence and at least 60% alumina by weight in which at least 99 percent of the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites wherein the average cyrstallite diameter is less than 0.5 micrometer and at least 95 percent of the alpha alumina crystallites are less than 0.7 micrometer in diameter and the density of the fiber is greater than 90% of theoretical density.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1993-09-03	1994-03-05	1994-09-04	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1997-09-03	1998-03-05	1998-09-04	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2001-09-03	2002-03-05	2002-09-04	$7700.00	Window Closed / Lapsed

Microcrystalline alumina-based ceramic articles

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