Preparation of SiC whiskers

Claim 2

A process for the manufacture of SiC whiskers comprising the steps of: (1) Selecting an organic fiber from the group consisting of polymers, copolymers, and terpolymers of acrylonitrile oxidized in air at a temperature from 200° to 400° C.; (2) Grinding or chopping the fiber obtained in step 1 to form a short fiber of approximately 10 to 100μ length; (3) Mixing the ground fiber obtained above with amorphous SiO 2 ; (4) Placing the mixture obtained above in a furnace and increasing the temperature to a carbide-forming temperature within the range of of 1400° to 1800° C. in a non-oxidizing atmosphere; (5) When the temperature reaches said carbide-forming temperature, maintaining the mixture at that temperature in an atmosphere of inert gas for a period of 1 to 4 hours; and (6) Removing the product from the furnace.

Claim 3

The process of claim 1 wherein the non-oxidizing atmosphere in step 4 is CO.

Claim 4

The process of claim 1 wherein the inert gas and the non-oxidizing atmosphere is argon.

Claim 5

The process of claim 1 in which the SiO 2 is formed by ashing rice hulls at a temperature of 400° to 700° C. to obtain SiO 2 .

Claim 6

The process of claim 1 wherein from 30 to 60% SiO 2 and from 70 to 40% oxidized organic fiber by weight are used as the ingredients of the carbide-forming mixture.

Claim 7

The process of claim 1 wherein the mixture is held at the carbide-forming temperature for approximately 1 hour.

Claim 8

The process of claim 1 wherein the mixture is held at a carbide-forming temperature of 1500° C.

Claim 9

The process of claim 1 wherein the organic fiber after oxidation at 200° to 400° C. in Step 1 is further carbonized at 800° to 1000° C. in nitrogen.

Claim 10

The process of claim 8 wherein the amorphous SiO 2 is diatomaceous earth.

Claim 11

The process of claim 1 in which the oxidized fiber is carbonized at 800° to 1000° C. then is further treated at a temperature of 1200° to 2200° C. in nitrogen to form a graphitized fiber.

Claim 12

A process for the manufacture of SiC whiskers comprising the steps of: (1) Carbonizing alpha-cellulose in nitrogen, for about one hour at 400° to 700° C.; (2) Mixing about 55 parts by wt. carbonized alphacellulose with about 45 parts by wt. amorphous SiO 2 obtained by ashing rice hulls at a temperature from 400° to 700° C.; (3) Placing the mixture in an inert atmosphere of argon; and (4) Rapidly heating the mixture at about 100° C. rise per minute to a carbide-forming temperature within the range of 1400° to 1800° C., and maintaining the mixture at that temperature under said inert atmosphere of argon for approximately one hour.

Claim 13

A process for the manufacture of SiC whiskers comprising the steps of: (1) Carbonizing alpha-cellulose in nitrogen, for about one hour at 400° to 700° C.; (2) Mixing about 55 parts by wt. carbonized alphacellulose with about 45 parts by wt. amorphous SiO 2 obtained by ashing rice hulls at a temperature from 400° to 700° C.; (3) Placing the mixture in an inert atmosphere of argon; and (4) Rapidly heating the mixture at about 100° C. rise per minute to a carbide-forming temperature within the range of 1400° to 1800° C., and maintaining the mixture at that temperature under said inert atmosphere of argon for approximately one hour.

Claim 14

A process for the manufacture of SiC whiskers comprised of: (1) Ashing rice hulls at a temperature from about 400° to 700° C. to form amorphous SiO 2 ; (2) Mixing the ash with ground fibers from 10 to 100μ in length selected from the group consisting of polyacrylonitrile fibers oxidized in air at 200° to 400° C., carbonized polyacrylonitrile fibers, graphitized polyacrylonitrile fibers, graphitized viscose rayon, carbonized mesophase petroleum pitch fibers, and fibrous alpha-cellulose carbonized in a nonoxidizing atmosphere; (3) Placing the mixture obtained in an inert atmosphere of argon; (4) Increasing the temperature at a rate of from 100° C. to 200° C. per minute from ambient to a carbide-forming temperature between 1400° C. and 1800° C., holding the mixture at that temperature in argon for a period of approximately one hour to form SiC whiskers; and (5) Removing the product from the heating chamber.

Claim 15

A process for the manufacture of SiC whiskers comprised of: (1) Ashing rice hulls at a temperature from about 400° to 700° C. to form amorphous SiO 2 ; (2) Mixing the ash with ground fibers from 10 to 100μ in length selected from the group consisting of polyacrylonitrile fibers oxidized in air at 200° to 400° C., carbonized polyacrylonitrile fibers, graphitized polyacrylonitrile fibers, graphitized viscose rayon, carbonized mesophase petroleum pitch fibers, and fibrous alpha-cellulose carbonized in a nonoxidizing atmosphere; (3) Placing the mixture obtained in an inert atmosphere of argon; (4) Increasing the temperature at a rate of from 100° C. to 200° C. per minute from ambient to a carbide-forming temperature between 1400° C. and 1800° C., holding the mixture at that temperature in argon for a period of approximately one hour to form SiC whiskers; and (5) Removing the product from the heating chamber.

Claim 16

The process of claim 1 wherein the temperature of the mixture is raised to the carbide-forming temperature at a rate of approximately 100° C. to 200° C. per minute.

Claim 17

The process of claims 1, 11, or 12 wherein the product obtained is ashed in air at 500° to 700° C.

Claim 18

The process of claims 1, 11, or 12 wherein the product is screened into a fraction retained on a 65 mesh per inch screen, a fraction passing a 65 mesh per inch screen and retained on a 100 mesh per inch screen containing the SiC whiskers, and a fraction passing a 100 mesh per inch screen.

Claim 19

The process of claim 13 wherein the fraction passing a 100 mesh per inch screen is further reacted with amorphous SiO 2 formed by ashing rice hulls at 400° to 700° C. to form SiC whiskers.