Abstract: Silicon carbide fibers having an excellent mechanical strength and a superior heat resistance can be produced by the process in which activated carbon fibers having a thickness of 1 to 30 &mgr;m and a BET specific surface area of 700 to 1500 m2/g are reacted with a silicon and/or silicon oxide gas at 1200 to 1500° C. under a reduced pressure or in an inert gas atmosphere; and the resultant SiC fibers are heat treated in the presence of a boron-containing substance and optionally a carbon-containing substance at 1700 to 2300° C. in an inert gas atmosphere, wherein the fibers may be in the form of a shaped article, for example, a sheet or honeycomb structure.

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 first guide roll, a second guide roll and a backing roll are mounted on a movable frame. A feed roll is disposed substantially perpendicularly below the second guide roll upstream of the second guide roll relative to a direction of movement of a base sheet. The distance between the feed roll and the second guide roll is ninety (90) to two hundred and ten (210) times as long as a distance of travel of the backing roll when the backing roll is moved away from a coating roll.

Abstract: A neutral sizing agent of emulsion type to be added to paper pulp for facilitating the disaggregation and recovery of waste paper in making paper including paper board, said sizing agent being produced, for example, by dispersing in an aqueous emulsifying dispersion medium a polymerizable hydrophobic monomer such as styrene or 2-ethylhexyl methacrylate by using as an emulsifying dispersing agent a copolymer having units of one or more monomers given by the formula ##STR1## or ##STR2## wherein R is H or CH.sub.3,X is a halogen atom,A is a (C.sub.2 -C.sub.6) alkylene group, andY is an anion,and a monomer given by the formula ##STR3## wherein R.sup.1, R.sup.2 are H or CH.sub.3, and then subjecting the resultant dispersion to a radical emulsion polymerization.