EP0294208A2
Expired / Lapsed
EP
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Microcrystalline alumina-based ceramic articles
Assignee: 3M Co
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Filing: 1988-06-03
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Granted: —
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Expires: 2008-06-03
Abstract
Abstract Microcrystalline alpha-alumina based ceramic articles comprising at least 60% alumina by weight in which substantially all the alumina is in the alpha phase having a uniform grain structure comprising alpha alumina crystallites with an average crystallite size less than 0.5 micrometer and a density greater than 90% theoretical are disclosed. Ceramic articles particularly useful as high modulus refractory fibers, among other shaped bodies such as beads, flakes, coatings, and shaped or randomly-shaped abrasive particles, are produced from a unique sol-gel process wherein hydroxy iron polymers are utilized to nucleate the alpha alumina transformation. An inherent advantage of the unique process disclosed is the resulting fine grained microstructure which is essential if a ceramic article such as an alpha alumina fiber is to have reasonable strength.
Inventors
- 👤 Thomas E. C/O Minnesota Mining And Wood
- 👤 David M. C/O Minnesota Mining And Wilson
- 👤 Harold G. C/O Minnesota Mining And Sowman
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-06 19:59
CPC Classifications
C; C04; C04B; C04B35/00; C04B35/622; C04B35/62227; C04B35/71; C01; C01F; C01F7/00; C01F7/02; C01F7/30; C04B35/01; C04B35/10; C04B35/111; C04B35/1115; C04B35/62231; C04B35/62236; C04B35/624; C09; C09K; C09K3/00; C09K3/14; C09K3/1409; C09K3/1418; C01P; C01P2002/00; C01P2002/60; C01P2004/00; C01P2004/01; C01P2004/03; C01P2004/10; C01P2004/51; C01P2004/60; C01P2004/62; C01P2006/00; C01P2006/10; C01P2006/12
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
71 words
A solid, shaped and fired refractory article comprising at least 60% alumina by weight in which substantially all 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 substantially all 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 2
Dependent Claim
71 words
A solid, shaped and fired refractory article comprising at least 60% alumina by weight in which substantially all 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 substantially all 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 3
Dependent Claim
30 words
The article according to claim 1 further comprising in the range of more than zero and up to 7.0 weight percent, compared to the total fired product, of equivalent iron.
Claim 4
Dependent Claim
19 words
The article according to claims 1 and 2 further comprising an effective amount of at least one modifying additive.
Claim 5
Dependent Claim
33 words
The article according to claim 3 wherein said modifying additive is selected from the group consisting of a metal oxide or a precursor to a metal oxide, or silica or a precursor thereof.
Claim 6
Dependent Claim
28 words
The article according to claims 1 to 4 which is a fiber, bead, flake, bubble, powder, randomly-shaped particle, an abrasive particle, or a ceramic coating on a support.
Claim 7
Dependent Claim
19 words
The article according to claims 1 to 5 having a microporous interior and a substantially dense alpha alumina sheath.
Claim 8
Dependent Claim
89 words
In the sol-gel method for forming an alumina-based ceramic article, the process comprising: a. preparing a solution of a basic aluminum salt or other hydrolyzable alumina precursor; 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; and d. optionally, at least one of compacting and sintering the calcined solid; the improvement comprising introducing a chemically effective amount of iron-containing nucleating agents into the mixture before the drying step.
Claim 9
Dependent Claim
89 words
In the sol-gel method for forming an alumina-based ceramic article, the process comprising: a. preparing a solution of a basic aluminum salt or other hydrolyzable alumina precursor; 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; and d. optionally, at least one of compacting and sintering the calcined solid; the improvement comprising introducing a chemically effective amount of iron-containing nucleating agents into the mixture before the drying step.
Claim 10
Dependent Claim
28 words
The method according to claim 7 wherein said iron-containing nucleating agent has been introduced into the article precursor in the form of a discrete particulate or colloidal form.
Claim 11
Independent Claim
41 words
The method according to claims 7 and 8 wherein the iron-containing nucleating agent has been introduced into the article precursor in the form a particulate hydrous iron polymer or hydrous iron-containing particle formed by the hydrolysis of an iron salt solution.
Claim 12
Independent Claim
27 words
The method according to claims 7 to 9 further comprising the addition of an effective amount of at least one modifying additive prior to the forming step.
References Cited (Backward Citations)
No citation records indexed.
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