Abstract: An optical fiber preform includes a core made from a fluoride glass which is doped with a rare earth, and a cladding surrounding the core. The cladding is made from one of an oxide glass and a fluoroxide glass. The core has a characteristic of amplification at 1.3 .mu.m-band. The cladding does not have absorption at 1.3 .mu.m-band. The preform is useful as a material for a fiber optical amplifier in optical communication systems.

Abstract: A method of forming a fiber glass preform includes the steps of: (a) pouring a cladding glass into a mold; (b) pouring a core glass on a flat horizontal upper surface of the cladding glass so as to form a united glass body having the core glass and the cladding glass under a condition that viscosity of the cladding glass and viscosity of the core glass are adjusted to certain predetermined values respectively so that the core glass is separated from and placed on the cladding glass; (c) cooling the united glass body to solidify the same so that the cladding glass is deformed by contraction thereof so as to produce a depression at a top middle portion thereof and that the core glass is deformed so as to form a projected portion thereof to fill the depression therewith; (d) separating the united glass body into an upper portion and a lower portion comprising the projected portion of the core glass; and (e) extruding the lower portion of the united glass body so as to form the fiber glass preform.

Abstract: Crystallization of a fluoride glass article is suppressed by treating the surface(s) of the fluoride glass article with a solution of a fluorine-containing alkali metal compound or a fluorine-containing ammonium compound such as, e.g., LiPF.sub.6, NaBF.sub.4 or NH.sub.4 BF.sub.4, in a nonaqueous solvent such as, e.g., ethanol, N,N-dimethylformamide or acetonitrile. The treatment can be made at room temperature.

Abstract: A graphite fluoride can be produced safely and in high yield on a commercial production scale by a process comprising reacting a carbon material having an average size of 100.mu. to 10 mm with fluorine. Further, when the fluorination reaction is stopped before completion thereof and the graphite fluoride product is subjected to sifting with a sieve to separate a desired graphite fluoride from the raw carbon material remaining unreacted.

Abstract: A method of preparing graphite fluoride such as (CF).sub.n or (C.sub.2 F).sub.n by heterogeneous contact reaction between a carbon material such as graphite or petroleum coke and fluorine gas at about 200.degree.-550.degree. C. In the gas phase of the reaction system, the total concentration of higher fluorocarbons having more than four carbon atoms formed by side reactions is controlled so as not to become above 3% by volume by, for example, condensation or catalytic decomposition of at least a portion of the higher fluorocarbons in the gas flowed out of the reaction chamber for recirculation. Such control is highly effective for prevention of rapid and violent decomposition of the graphite fluoride existing in the solid phase of the reaction system induced by sudden decomposition of the higher fluorocarbons in the reaction system to lower fluorocarbons.

Abstract: Graphite fluoride, such as (CF).sub.n or (C.sub.2 F).sub.n, in powder form coated with a vinylic polymer, e.g. polymethyl methacrylate, which is bonding to the surfaces of the graphite fluoride particles by graft polymerization. The polymer-coated graphite fluoride retains unique properties of graphite fluoride such as high lubricating ability, can readily be dispersed in water and organic liquids, and can readily be press-shaped with or without the addition of a synthetic resin powder. The polymer-coated graphite fluoride is prepared by dispersing graphite fluoride in powder form and at least one vinylic monomer which undergoes radical polymerization in a mixture of water and either a water-soluble organic solvent or a surface-active agent, and then adding a polymerization initiator to the aqueous dispersion. The polymerization reaction takes place even at room temperature and can be promoted by heating up to 70.degree. C.

Abstract: A polymer-coated particulate inorganic material, e.g. graphite, graphite fluoride or molybdenum disulfide, is obtained by preparing a reaction system containing a liquid medium, fine particles of the inorganic material, at least one vinylic monomer which undergoes radical polymerization or copolymerization and a polymerization initiator and allowing the vinylic monomer(s) in the reaction system to undergo polymerization and to bond to the surfaces of the inorganic material particles by graft polymerization. To enhance the efficiency of graft polymerization to thereby realize uniform coating even when the inorganic material is very low in surface energy as typified by graphite fluoride, the pH of the reaction system is adjusted to a value ranging from 5 to 9 by adding alkali to the reaction system soon after the addition of the polymerization initiator or alternatively by treating the inorganic material with alkali in advance of preparation of the reaction system.

Abstract: A lubricant comprising a partially defluorinated graphite fluoride obtained by exposing a dispersion of raw material graphite fluoride to electromagnetic radiation, followed by the separation of the resulting partially degraded graphite fluoride. The partially defluorinated graphite fluoride is not only excellent in lubricating properties but also has excellent compatibilities with resins, greases and oils. The excellent compatibilities of the partially defluorinated graphite fluoride are effective in preventing the unfavorable deposition of the graphite fluoride in a liquid lubricant composition and advantageously lead to improvement in the moldability of any graphite fluoride-resin composition, thereby enabling the ultimate composition to exhibit excellent lubricating properties.