Abstract: A process is disclosed for producing a corrosion-resistant ceramic member, which process includes the steps of preparing a sintered body made of a ceramic material containing at least aluminum, immersing the ceramic sintered body in hydrofluoric acid, and forming a film of aluminum fluoride at a surface layer portion of the ceramic sintered body by heating the ceramic sintered body.

Abstract: A corrosion-resistant member includes a substrate made of a ceramic material and having a diameter of at least 200 mm, and a film of chemically vapor deposited silicon carbide having a thickness of not less than 0.5 mm and covering at least such a portion of the surface of the substrate that is to contact a corrosive material. A process is disclosed for producing such a corrosion-resistant member, which process includes thermally treating the film at a temperature higher, by not less than 50.degree. C. centigrade, than a film-forming temperature at which the film of silicon carbide is formed, after the formation of the silicon carbide film.

Abstract: A gas-tight article includes a sintered body composed mainly of a silicon carbide, and a film of silicon carbide formed on a surface of the sintered body by chemical vapor deposition and covering said surface of the sintered body, wherein cracks are formed in the film of the silicon carbide, and the cracks are filled with metallic silicon.

Abstract: A method for manufacturing a ceramic shell-and-tube type heat exchanger having a plurality of heat transfer tubes and tubular plates joined to both the end portions of these heat transfer tubes which has the steps of inserting the heat transfer tubes of sintered tubular ceramics into through-holes of the tubular plates of unsintered plate-like ceramics having a plurality of the through-holes, standing the heat transfer tubes vertically to a floor surface, and then firing them in a condition where the tubular plates are positioned at both the upper and lower end portions of the heat transfer tubes, thereby integrally joining the tubular plates to both the end portions of the plurality of heat transfer tubes by the utilization of a difference between firing shrinkage ratios of both the members, the method having the steps of interposing at least one tubular plate between the tubular plate positioned at the upper end portions and the tubular plate positioned at the lower end portions of the heat transfer tubes,

Abstract: In a process for producing a silicon nitride sintered material, a silicon nitride raw material powder selected from raw material powder lots such that the silicon nitride raw material powder has a dispersion .delta.N.beta..sub.1 of weight fraction of .beta.-silicon nitride, of 65% or less, is used. A process for producing a silicon nitride sintered material controls the firing conditions so that the raw material being fired gives, at any stage of firing, a dispersion .delta.N.beta..sub.2 of weight fraction of .beta.-silicon nitride, of 65% or less between the surface portion and the central portion. The first process allows for production of a silicon nitride sintered material having excellent properties in high-temperature strength, etc., at a high reproducibility and stability. The second process allows for production, of in any production batch, a silicon nitride sintered material very low in scattering of properties (e.g., density and strength) between the central portion and the surface portion.

Abstract: A silicon nitride ceramic of the present invention possesses excellent strength of the surface, including a silicon nitride and a rare earth oxide compound and being characterized in that the ratio of the transverse rupture strength, at a room temperature, of the fired surface used as a tensile surface to the transverse rupture strength, at a room temperature, of the worked surface used as a tensile surface subjected to the working so as to have the surface roughness of R.sub.MAX 0.8 .mu.m or less is 0.7 or more, and the strength ratio is satisfied even when any portion besides the fired surface is utilized as the tensile surface to be worked to have the surface roughness of R.sub.MAX 0.8 .mu.m or less. The present invention also provides a process for producing a silicon nitride ceramic including the steps of: (1) mixing .alpha.-Si.sub.3 N.sub.4 powder and .beta.-Si.sub.3 N.sub.4 powder to obtain a raw material powder so as to satisfy the formula indicated by 0.05.ltoreq..beta./.alpha.+.beta..ltoreq.0.

Abstract: A ceramic blade for a hybrid type gas turbine blade has a dovetail portion, a platform portion formed on the dovetail portion and blade portions formed on the platform portion. The number of the blade portions formed on one platform portion is two or more. The upper surface of the platform portion is shaped into an arc-like form, and the dovetail portion is linearly formed in a tangential direction to a turbine rotation direction. By the utilization of this blade, the hybrid type gas turbine blade can inhibit the leakage of a gas and can be easily manufactured and is excellent in durability.

Abstract: A ceramic material is a calcined article obtained by calcining a molded ceramic article and in which the pores of the calcined article are impregnated with a substance which can be removed at a temperature lower than a sintering temperature for the molded ceramic article. A method for manufacturing a ceramic product includes the steps of calcining a molded ceramic article, impregnating the open pores of the calcined ceramic article with a substance which can be removed at a temperature lower than a sintering temperature for the calcined ceramic article, mechanically machining the ceramic article to impart a desired shape thereto, removing the substance from the ceramic article, and then sintering the ceramic article. Large-sized ceramic products having a high strength and an excellent shape accuracy and having complex shapes can be manufactured at low costs.

Abstract: A silicon nitride ceramic possessing excellent strength of the surface, including a silicon nitride and a rare earth oxide compound and being characterized in that the ratio of the transverse rupture strength, at room temperature, of the fired surface used as a tensile surface to the transverse rupture strength, at room temperature, of the worked surface used as a tensile surface subjected to working so as to have a surface roughness of R.sub.max 0.8 .mu.m or less is 0.7 or more, and the strength ratio is satisfied even when any portion besides the fired surface is utilized as the tensile surface to be worked to have a surface roughness of R.sub.max 0.8 .mu.m or less. The present invention also provides a process for producing a silicon nitride ceramic including the steps of: (1) mixing .alpha.-Si.sub.3 N.sub.4 powder and .beta.-Si.sub.3 N.sub.4 powder to obtain a raw material powder which satisfies the formula 0.05.ltoreq..beta./.alpha.+.beta..ltoreq.0.50, in which .alpha. refers to the weight of .alpha.-Si.

Abstract: Jigs usable in a method for manufacturing a joined ceramic structure having a plurality of tubes and perforated plates joined to both the end portions of these tubes which has the steps of inserting the tubes of sintered ceramics into through-holes of the perforated plates of unsintered ceramics having a plurality of the through-holes, thereby integrally joining both the members by the utilization of a difference between firing shrinkage ratios of both the members; the jigs having end portions which are inserted into jig fixation orifices beforehand formed through the perforated plates and which have an outer diameter slightly smaller than a diameter of the orifices, and stems having an outer diameter larger than the diameter of the jig fixation orifices, the end portions and the stems being constituted so as to be detachably combined at engagement portions where they are engaged with each other without mutual restriction, the jigs being integrally combined with the joined ceramic structure after the completi

Abstract: A silicon nitride powder containing .beta.-phase and .alpha.-phase at a ratio by weight (.beta./.alpha.) of from 0.018 to 0.032, and composed of crystallites 0.2 .mu.m or less in diameter.

Abstract: A process for producing a joined ceramic component having a plurality of parallel ceramic tubes and two perforated ceramic plates joined to the both ends of said ceramic tubes, which process comprises: arranging two unsintered ceramic plates each having a plurality of holes, in parallel to each other and also to the floor surface with a given distance provided between the upper plate and the lower plate; inserting a plurality of sintered ceramic tubes into the holes of the upper and lower plates so that the tubes are arranged vertically to the floor surface and in parallel to each other; and sintering the resulting material to join the tubes and the plates into one piece by utilizing the difference in sintering shrinkage factor between them, in which process the sintering is conducted in a state that each tube is hanged from the upper plate and that the lower end of each tube is in one hole of the lower plate placed on or above a setter, with a certain distance provided between the lower end of each tube and

Abstract: A jig for isostatic-pressing a ceramic feed powder to form a planar ceramic green body with a pressure of more than 300 kgf/cm.sup.2. The jig includes a mold in the form of a frame surrounding a cavity open at two sides and being made of a material with a Young's modulus greater than 5.times.10 kgf/cm.sup.2, a pair of pressure-medium diaphragms with each pressure-medium diaphragm arranged opposite one of the open sides of the cavity to seal the open sides of the cavity, and a pair of pressure-transfer plates with each pressure-transfer plate including at least one through hole and being placed on an outer surface of one of the pressure-medium diaphragms.

Abstract: A sealing member for use in a gas preheater is adapted to seal a gap between an outer peripheral portion of a rotor and a housing in the gas preheater or a gap between a side face of the rotor and a radial sealing member. At least a part of said sealing member is made of an inorganic glass and/or a wear resistive ceramic having a coefficient of thermal expansion of not more than 70.times.10.sup.-7 /.degree. C. A sealing member for use in a gas preheater may comprise a heat resistive ceramic, and a corrosion resistive steel, wherein the ceramic is substantially surrounded with the corrosion resistive steel, excluding a sliding surface of the ceramic.

Abstract: There is provided a thermal shock-resistant silicon nitride sintered material including silicon nitride and rare earth element compounds, which material contains at least 10 pore groups per mm.sup.2, each pore group consisting of pores of 10 or less in diameter and which material has a thermal shock resistance .DELTA.Tc (.degree.C.) of 1,000.degree. C. or more. The thermal shock-resistant silicon nitride sintered material can be produced by mixing and shaping starting materials consisting of silicon nitride powders of rare earth element oxides and carbide powder, and then firing the shaped material in a nitrogen atmosphere to decompose the carbide powders.

Abstract: The superconducting structure for magnetic shielding according to the present invention comprises at least two layers of a superconducting layer and a substrate. This superconducting structure for magnetic shielding can be formed in a plate-like shape or a cylindrical shape. When the structure is prepared in three-layers by providing an intermediate layer between the superconducting layer and the substrate, the three-layered structure has improved superconducting properties. When a protective layer is provided on the superconducting layer to protect the layer, the resulting structure has improved thermal shock resistance. The intermediate layer preferably consists of a ceramic or a noble metal and the ceramic preferably consists of a glass.

Abstract: Powders of carbides are mixed with a silicon nitride powder and powders of rare earth element oxides to obtain a mixture. The mixture is shaped and fired in a casing in a nitrogen atmosphere of 1,700.degree.-2,100.degree. C. under the conditions specified by the following formula:(0.025x-0.05)<y.ltoreq.0.1xwherein x is a firing time (hr) and y is the weight (g) of shaped material to be filled into casing divided by the internal volume (cc) of the casing.

Abstract: A sealing member for use in a gas preheater is adapted to seal a gap between an outer peripheral portion of a rotor and a housing in the gas preheater or a gap between a side face of the rotor and a radial sealing member. At least a part of said sealing member is made of an inorganic glass and/or a wear resistive ceramic having a coefficient of thermal expansion of not more than 70.times.10.sup.-7 /.degree.C. A sealing member for use in a gas preheater may comprise a heat resistive ceramic, and a corrosion resistive steel, wherein the ceramic is substantially surrounded with the corrosion resistive steel, excluding a sliding surface of the ceramic.

Abstract: There is provided a thermal shock-resistant silicon nitride sintered material consisting substantially of silicon nitride and rare earth element compounds, which material contains at least 10 pore groups per mm.sup.2, each pore group consisting of pores of 10 .mu.m or less and which material has a thermal shock resistance .DELTA.Tc (.degree.C.) of 1,000 .degree. C. or more. The thermal shock-resistant silicon nitride sintered material can be produced by mixing and shaping starting materials consisting of a silicon nitride powders of rare earth element oxides and carbide power, and then firing the shaped material in a nitrogen atmosphere to decompose the carbide powders.

Abstract: The present process for producing a Bi-based superconducting oxide includes the steps of molding a material powder and subjecting the molded article to partial melting and then to crystallization in the presence of oxygen. In that case, the molded article is annealed, after the partial melting, to the crystallization temperature and subjected to crystallization at that temperature. Also, the article after the crystallization is cooled and the cooled article is heat-treated in an inert gas atmosphere. According to the above process, there can be obtained a Bi-based superconducting oxide having excellent superconducting properties.