Nkk Corporation

Nippon Kokan Kabushiki Kaisha

Government Industrial Research Institute

Hiroaki Nishio

Michitaka Sato

Keiji Watanabe

Tsuneo Miyashita

Takeshi Kawashima

Jun Harada

Akira Kato

Hiroyuki Yoshida

Yasushi Ueno

Kazuya Yabuta

Yoshio Takagi

Osamu Takeuchi

Kazuo Kunioka

Hideyuki Yoshikoshi

Hideharu Yamamoto

Shoji Kubodera

Yasuo Okuyama

Teruo Shimotsuma

Sazo Nakamura

Michitaka Satoh

Kazushi Kishi

Seiki Umebayashi

Shiro Torizuka

Method for repair and/or reinforcement of partition-type heat exchanger

A boron-nitride-containing material of multi-component system is obtained at a low cost by heating a mixed powder containing a boride and an oxide in a nitrifying atmosphere, whereby a part or the whole of the oxide is reduced with the element bonded to boron of the boride to convert the raw materials to one or more kinds of an oxide having less bonded oxygen, an acid nitride, a nitride, a carbide, and a boride and also boron nitride is formed. A sintered product of a boron-nitride-containing material is obtained by packing a mixed powder containing borides in a heat-resistant mold and heating the packed powders in a nitrifying atmosphere while restraining the packed powders by the mold. The sintered product is obtained in which neither expansion nor deformation occurred and no cracks formed.

Boron nitride containing material

Boron nitride-containing material and method thereof

Method of producing ceramic sintered body having dense ceramic membrane

A dewaxing method of a metal and/or ceramic molded body which comprises immersing the metal and/or ceramic molded body formed through a plastic molding in a boiling solvent to extract the dispersion medium contained in the molded body with said solvent. According to the method of the invention, the dewaxing time can be shortened from about 150 hours to the sum of about 54 hours for the solvent extraction and about 11 hous for dewaxing under heating. The dewaxed molded body is a sound body containing no crack nor expansion.

Dewaxing method of metal or ceramic molded body

A method for manufacturing carbon material having good resistance to oxidation, comprising coating carbon material, which is a sintered body or a porous body, with an inorganic polysilazane; heating the carbon material coated with the inorganic polysilazane in an inert atmosphere to form amorphous silicon nitride on the surface of the carbon material; and reheating the heated carbon material in a non-nitriding and non-oxidizing atmosphere, the amorphous silicon nitride being decomposed and silicon carbide being formed on the surface of the carbon material; the reheating being conducted at a temperature of 1300.degree. C. to 1900.degree. C. and the non-nitriding and non-oxidizing atmosphere having a partial pressure of nitrogen determined with reference to a graph wherein the abscissa is a temperature in .degree.C. and the ordinate is partial pressure of nitrogen in atmospheres, the partial pressure being defined within an area under a line connecting a first point corresponding to 1300.degree. C. and 0.1 atmospheres and a second point corresponding to 1900.degree. C. and 20 atmospheres.

Method for manufacturing carbon material having good resistance to

An apparatus for removing the dispersion medium in a metal or ceramic molded body which comprises a dispersion medium-removing vessel includes a condensing zone located in a upper part and a boiling zone located in a lower part, a separator to separater a solvent in the dispersion medium solution discharged from the vessel by heating the solution at a temperature higher than the boiling point of the solvent to evaporate it, the boiling zone being connected with the separator through a pipe to transport the dispersion medium solution and a pipe to transport the vaporized solvent to form a circuit, and a pump provided in the circuit. In the apparatus since the dispersion medium is removed in the boiling solvent, keeping a constant temperature is easy. The dispersion medium is promptly removed by contacting it with a solution of which the concentration of the dispersion medium is always low due to continuous removal of the dispersion medium in the separator. Since the boiling point of the solvent is about 20.degree. to 150.degree. C., the molded body is gently heated. Therefore, the occurrence of defects such as cracks is rare in the molded body.

Apparatus for removing dispersion medium in metal or ceramic molded body

A method for forming a ceramic film comprises the steps of boiling a solution containing ceramics, dipping a base material into the solution, taking the base material out of the solution and drying the base material taken out of the solution in the presence of vapor of said boiling solution. The solution is a solution, in which ceramics is dispersed or dissolved. The solution is a solution, in which a precursor of ceramics is dispersed or dissolved.

Method for forming a ceramic film

In a hot isostatic pressing (HIP) method, only the probe of a dilatometer is set in the pressurized heating space of the HIP apparatus, and the probe is attached to a test piece having a greater specific surface area made of the same material as the body to be treated. The test piece is treated by HIP together with the body to be treated, and the beginning of the contraction of the test piece is detected by the dilatometer. Then, the body is densified by keeping the pressure and the temperature not lower than those at the beginning of contraction of the test piece. According to the method of the invention, since suitable HIP treating conditions are determined immediately, each body to be treated can be treated by only one HIP suitably without repeating the troublesome HIP process. Also, since the body can be treated by HIP without elevating the temperature beyond the necessary temperature, the crystal grain growth of the body to be treated can be inhibited.

Hot isostatic pressing method

A method of molding polysilazane which includes heating a liquid sheet composed of liquid polysilazane alone or containing not more than 30 wt. % of a ceramic powder or a ceramic precursor to form a highly viscous sheet having a viscosity coefficient of 10.sup.4 to 10.sup.6 poise, fitting the highly viscous sheet to a forming mold, and heating to set the sheet. According to the method of the invention, molded bodies are easily obtained which have relatively uniform thickness, and are excellent in transferability, homogeneous and show less defects.

Method of molding polysilazane

A method of producing a silicon nitride sintered body which comprises using an amorphous Si.sub.3 N.sub.4 powder having a mean particle size of 5 to 50 nm, a nitrogen content of 30 to 39 wt. %, an oxygen content of 1 to 10 wt. %, the sum of the nitrogen content and the oxygen content being 38 to 42 wt. % and an unavoidable impurities content of less than 500 ppm as the raw material to form a molded body, sealing the molded body in a capsule and treating it with HIP in the range of 1000.degree. to 1800.degree. C. and 1000 to 2000 atm until the density becomes 3.1 to 3.4 g/cm.sup.3. In the method of the invention, active surface energy of silicon nitride powder is utilized as the driving force for sintering due to using a super fine powder. The super fine powder improves sintering ability by uniform mixing. The sintering ability is further improved by substituting a suitable amount of the nitrogen in the silicon nitride with oxygen. By the above means, the sintering strength can be secured under not severe sintering conditions. As a result, a sintering aid can be omitted.

Method of producing silicon nitride sintered body

A mold for slip casting comprising a compact formed out of a mixture having an organic matter and powders, the organic matter being capable of being extracted by supercritical fluid and the powders being incapable of being extracted by the supercritical fluid, and furthermore, a method for slip casting comprising a compact formed out of an organic matter capable of being extracted by supercritical fluid and having a melting point of 0.degree. to 150.degree. C. The organic matter is any one selected from the group of methyl carbonate, t-butyle alcohol, stearic acid stearyl alcohol and paraffin.

Mold for slip casting

A method for molding powders to form a shaped compact comprising the steps of

Method for molding powders

A method of casting a powdered material. A slurry is formed by dispersing metal powder or ceramic powder into a dispersing medium mainly consisting of a substance extractable by a liquid or supercritical carbon dioxide and having a melting point between 0.degree. C. and 100.degree. C., and the slurry is poured into a liquid non-absorbing mold where the slurry is cooled to freeze and solidify into a molding. The main constituent of the dispersing medium in the molding is extracted and removed by the liquid or supercritical carbon dioxide.

Method of casting powder materials

In the method of invention, the formability is imparted to the slurry of a metal or ceramic powder by employing a porous mold and removing the dispersion medium through the evaporation or thermal decomposition thereof, or by using a silazane oil as the dispersion medium and curing it by heating. Since the phase change usually accompanying volume change does not occur in the dispersion medium, strain and deformation rarely occur in the molded body. As result, the sintered body obtained has high dimensional accuracy.

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Tokyo, Japan

Hiroaki Nishio