Abstract: A process for producing silicon carbide fibers is provided, comprising the steps of mixing a silicon supply source powder including a mixture of silicon powder and silicon dioxide powder having a molar mixing ratio of 1:0.1 to 1:2 with activated carbon staple fibers having a length of 0.1 to 50 mm and a fiber thickness of 1 to 20 .mu.m and a specific surface area of 300 to 2000 m.sup.2 /g determined by the BET nitrogen absorption method; and heating the resultant mixture at a temperature of 1200 to 1500.degree. C. to directly convert the activated carbon staple fibers, in an atmosphere substantially free from substances reactive with carbon, silicon, silicon oxides and silicon carbide at the above mentioned temperature, to silicon carbide fibers.

Abstract: Silicon carbide fibers having a high mechanical strength at a high temperature, an excellent heat resistance and a uniform structure are produced by activating carbon fibers which have been produced by heat-treating organic carbon fibers such as cellulose, polyacrylonitrile or petroleum pitch, polyimide or phenol resin fibers in an oxidative gas atmosphere and carbonizing the heat-treating organic fibers in an inert gas, with an activating gas, for example, water vapor, to convert them to the activated porous carbon fibers having a specific surface area of 100 to 3,000 m.sup.2 /g, a length of 5 mm or more and a thickness of 5 to 100 .mu.m; reacting the activated porous carbon fibers with a silicon monoxide gas at a temperature of 800.degree. C. to 2,000.degree. C. under a reduced pressure of 10.sup.2 Pa or less to convert them to silicon carbide fibers having a length of 5 mm or more, without generating whiskers; and optionally the resultant silicon carbide fibers are heat-treated at a temperature of 800.

Abstract: A silicon carbide material in the form of fibers, sheets or three-dimensionally structured articles useful as a reinforcing material and heat-insulating material, is produced by reacting an activated porous carbon material in the form of, for example, fibers, sheets or three-dimensionally structured articles, and having a specific surface area of 100 to 2500 m.sup.2 /g, with silicon monoxide gas at a temperature of 800.degree. C. to 2000.degree. C. and then heat-treating the resultant silicon carbide material in a non-oxidative gas atmosphere containing nitrogen and substantially no oxygen at a temperature of 800.degree. C. to 2000.degree. C.

Abstract: A hydrophilic fibers modified with a substantially water-insoluble inorganic compound is produced by immersing hydrophilic fibers, for example, pulp fibers, in an aqueous solution of a water-soluble inorganic compound (a) selected from aluminates, silicates and zincates of alkali metals with a precipitant (b) containing an aqueous solution of hydrochloric acid or sulfuric acid, adjusting the amount of the aqueous solution impregnated in the hydrophilic fibers to 60 to 400% based on the weight of the hydrophilic fibers, and bringing the hydrophilic fibers with the aqueous solution of the inorganic compound (a) into contact with the precipitant (b), to thereby cause the resultant substantially water-insoluble compound to be precipitated in and fixed to the hydrophilic fibers.

Abstract: A hydrophilic fibers modified with a substantially water-insoluble inorganic compound is produced by immersing hydrophilic fibers, for example, pulp fibers, in an aqueous solution of a water-soluble inorganic compound (a) which is precipitated when brought into contact with a precipitant (b), adjusting the amount of the aqueous solution impregnated in the hydrophilic fibers to 60 to 400% based on the weight of the hydrophilic fibers, and bringing the hydrophilic fibers with the aqueous solution of the inorganic compound (a) into contact with the precipitant in the state of a gas or aqueous solution to thereby cause the resultant substantially water-insoluble compound to be precipitated in and fixed to the hydrophilic fibers.