Production of SiC from rice hulls and silica

Claim 2

A process for the manufacture of SiC whiskers comprising the steps of: 1--Carbonizing rice hulls in a non-oxidizing atmosphere at a temperature between about 450° to 700° C.; 2--Comminuting the carbonized rice hulls to a fine powder; 3--Ashing a second portion of rice hulls in air at a temperature between about 450° to 700° C.; 4--Mixing the C and SiO 2 products thus obtained; and 5--Heating the mixture thus obtained in an inert atmosphere at a carbide-forming temperature between 1400° to 1600° C. for a time sufficient to form SiC whiskers.

Claim 3

The process of claim 1 wherein from 10 to 30 parts of rice hull ash obtained in step 3 are added to 100 parts of the carbonized rice hulls obtained in step 1.

Claim 4

The process of claim 1 wherein the rice hulls are carbonized for approximately one hour at approximately 550° C. in nitrogen.

Claim 5

The process of claim 1 wherein the rice hulls are ashed in air for approximately one hour at approximately 620° C.

Claim 6

The process of claim 1 wherein the mixture from step 4 is held at approximately 1500° C. for approximately four hours.

Claim 7

The process of claim 1 wherein the inert atmosphere of step 5 is argon.

Claim 8

The process of claim 1 wherein from 14 to 28 parts of Fe 2 O 3 or Fe is added to 100 parts of the SiO 2 from step 3.

Claim 9

A process for the manufacture of SiC whiskers comprising the steps of: (1) Oxidizing a first portion of rice hulls in air at a temperature from about 450° to 700° C. to form an ash; (2) Mixing said ash with a particulate source of carbon selected from the group consisting of graphite flour, activated carbon powder, and calcined petroleum coke, at a ratio of about 55 parts by wt. of said ash with 45 parts by wt. of said particulate carbon source; (3) Placing the mixture thus formed in a chamber with an atmosphere of argon flowing continuously through said chamber in sufficient volume to displace essentially all the air in said chamber; (4) Raising the temperature of said mixture from ambient to a preselected temperature within the range of 1400° to 1600° C. at an incremental rate of at least 100° C. per minute; and (5) Maintaining said mixture at the said preselected temperature in said argon atmosphere for about one hour.

Claim 10

A process for the manufacture of SiC whiskers comprising the steps of: (1) Oxidizing a first portion of rice hulls in air at a temperature from about 450° to 700° C. to form an ash; (2) Mixing said ash with a particulate source of carbon selected from the group consisting of graphite flour, activated carbon powder, and calcined petroleum coke, at a ratio of about 55 parts by wt. of said ash with 45 parts by wt. of said particulate carbon source; (3) Placing the mixture thus formed in a chamber with an atmosphere of argon flowing continuously through said chamber in sufficient volume to displace essentially all the air in said chamber; (4) Raising the temperature of said mixture from ambient to a preselected temperature within the range of 1400° to 1600° C. at an incremental rate of at least 100° C. per minute; and (5) Maintaining said mixture at the said preselected temperature in said argon atmosphere for about one hour.

Claim 11

The process of claim 1 or 8 wherein the product from step 5 is ashed in air at 500° to 650° C. to remove any remaining excess unreated C.

Claim 12

The process of claim 1 or 8 wherein the product from step 5 is treated with hydrofluoric acid to remove any remaining excess unreated SiO 2 .

Claim 13

The process of claim 1 or 8 wherein the mixture of SiO 2 and carbon is heated rapidly from ambient temperature to a preselected carbide forming temperature within the range of 1400° to 1600° C., preferably 1500° C., at a rate of temperature increase of approximately 100° C. to 200° C. per minute.