Microcrystalline alumina-based ceramic articles

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.

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.

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.