Stemcor Corporation

The Standard Oil Company

Kennecott Corporation

Tadeusz M Korzekwa

Wolfgang D Boecker

Sai-Kwing Lau

Stephen Chwastiak

Carl H McMurtry

Crystalline silicon carbide wherein at least 90 weight percent of the silicon carbide is formed from a plurality of hexagonal crystal lattices wherein at least 80 weight percent of the crystals formed from the lattices contain at least a portion of opposing parallel base faces separated by a distance of from 0.5 to 20 microns. The crystals may be in the form of separate particles, e.g. separate platelets, or may comprise an intergrown structure. The crystalline silicon carbide of the invention is produced by heating a porous alpha silicon carbide precursor composition comprising silicon and carbon in intimate contact to a temperature of from 2100.degree. C. to 2500.degree. C. in a non-reactive atmosphere. The materials are high performance materials finding use in reinforcing, high temperature thermal insulating, improvement of thermal shock resistance, and modification of electrical properties.

Method for making hexagonal silicon carbide platelets with the addition

Hexagonal silicon carbide platelets and preforms and methods for making

A method for grinding silicon carbide to a submicron powder which comprises grinding a silicon carbide feed material having an average particle size of between 1 and 200 microns in a liquid slurry in a contamination free high energy autogenous attrition mill in the presence of silicon carbide media for a sufficient time to obtain a specific surface area of at least 5 m.sup.2 /g and preferably at least 9 m.sup.2 /g. The media is of high purity and has an average particle size of less than 4 mm and preferably less than 2.5 mm. The ground material is then further treated so that the average particle size is less than one micron and so that greater than 97 numerical percent of the particles of the finished powder is smaller than 5 microns. The invention includes the finished powder.

Autogenous attrition grinding

A method for reducing the particle size of an initial silicon carbide powder to a milled powder having an average particle size of below 1 micron but greater than an average of about 0.2 micron, without grinding media contamination. The method comprises milling the larger particles in a vibratory mill in the presence of sintered silicon carbide media comprising silicon carbide pellets having both curved and flat surfaces and a maximum dimension of from about 0.5 to 5 centimeters. The grinding occurs in the presence of a fluid, preferably a liquid, for a sufficient time and at a sufficient vibrational energy to obtain said milled powder having such smaller average particle size. At least 90% of the pellets in the silicon carbide media have a specific gravity (density) greater than 3.05 g/cm.sup.3. The invention includes the unique media, which may be used for various grinding operations, and includes unique milled powders. One of the unique powders has particles which have an average length to width ratio of greater than 2.5. Another of the unique powders is black silicon carbide containing from 200 to 2,000 parts per million of aluminum in solid solution.

Vibratory grinding of silicon carbide

The present invention provides a method of pressureless sintering silicon carbide in which the silicon carbide starting material is in the form of a multimodal composition, or mixture, of coarse and submicron particles. The present sinterable silicon carbide mixtures consist of separate fractions of sized particles. Each fraction is present in amounts of from about 5 to about 75% by weight of the mixture, and more preferably from about 10 to about 65% by weight of the mixture. One fraction has a particle size ranging between about 0.21 mm (210 microns) to about 3.4 mm (3400 microns) and preferably the larger particles have a size less than about 2.4 mm. A second fraction has a particle size ranging between about 0.003 mm (3 microns) up to about 0.21 mm. A third fraction has a size less than 0.003 mm, but has an average size less than 1 micron. The present products are produced by sintering particulate silicon carbide in the presence of a sintering aid and a slight excess carbon. Generally, sintering temperatures range from about 1900.degree. C. to about 2300.degree. C. depending upon the sintering atmosphere.

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Lewiston, NY, United States of America

Tadeusz M Korzekwa