Abstract: Provided is a large-sized silicon nitride sintered substrate and a method for producing the same. The silicon nitride sintered substrate has a main surface 101a of a shape larger than a square having a side of a length of 120 mm. A ratio dc/de of the density dc of the central area and the density de of the end area of the main surface 101a is 0.98 or higher. The void fraction vc of the central area of the main surface 101a is 1.80% or lower, and the void fraction ve of the end area is 1.00% or lower. It is preferred that the density dc of the central area is 3.120 g/cm3 or higher, the density de of the end area is 3.160 g/cm3 or higher, and a ratio ve/vc of the void fraction vc of the central area and the void fraction ve of the end area is 0.50 or higher.

Abstract: Provided is a large-sized silicon nitride sintered substrate and a method for producing the same. The silicon nitride sintered substrate has a main surface 101a of a shape larger than a square having a side of a length of 120 mm. A ratio dc/de of the density dc of the central area and the density de of the end area of the main surface 101a is 0.98 or higher. The void fraction vc of the central area of the main surface 101a is 1.80% or lower, and the void fraction ve of the end area is 1.00% or lower. It is preferred that the density dc of the central area is 3.120 g/cm3 or higher, the density de of the end area is 3.160 g/cm3 or higher, and a ratio ve/vc of the void fraction vc of the central area and the void fraction ve of the end area is 0.50 or higher.

Abstract: A roll for use in a galvanizing pot, comprising a hollow body brought into contact with a steel strip, and shaft portions connected to the body, at least the body being made of a silicon nitride ceramic having thermal conductivity of 50 W/(m·K) or more at room temperature, and the body having an average surface roughness Ra of 1-20 ?m. The body is preferably shrink-fit to the shaft portions.

Abstract: A roll for use in a galvanizing pot, comprising a hollow body brought into contact with a steel strip, and shaft portions connected to the body, at least the body being made of a silicon nitride ceramic having thermal conductivity of 50 W/(m·K) or more at room temperature, and the body having an average surface roughness Ra of 1-20 ?m. The body is preferably shrink-fit to the shaft portions.

Abstract: A silicon nitride sintered body comprising Mg and at least one rare earth element selected from the group consisting of La, Y, Gd and Yb, the total oxide-converted content of the above elements being 0.6–7 weight %, with Mg converted to MgO and rare earth elements converted to rare earth oxides RExOy. The silicon nitride sintered body is produced by mixing 1–50 parts by weight of a first silicon nitride powder having a ?-particle ratio of 30–100%, an oxygen content of 0.5 weight % or less, an average particle size of 0.2–10 ?m, and an aspect ratio of 10 or less, with 99–50 parts by weight of ?-silicon nitride powder having an average particle size of 0.2–4 ?m; and sintering the resultant mixture at a temperature of 1,800° C. or higher and pressure of 5 atm or more in a nitrogen atmosphere.

Abstract: A silicon nitride sintered body comprising Mg and at least one rare earth element selected from the group consisting of La, Y, Gd and Yb, the total oxide-converted content of the above elements being 0.6-7 weight %, with Mg converted to MgO and rare earth elements converted to rare earth oxides RExOy. The silicon nitride sintered body is produced by mixing 1-50 parts by weight of a first silicon nitride powder having a ?-particle ratio of 30-100%, an oxygen content of 0.5 weight % or less, an average particle size of 0.2-10 ?m, and an aspect ratio of 10 or less, with 99-50 parts by weight of ?-silicon nitride powder having an average particle size of 0.2-4 ?m; and sintering the resultant mixture at a temperature of 1,800° C. or higher and pressure of 5 atm or more in a nitrogen atmosphere.

Abstract: A silicon nitride sintered body comprising Mg and at least one rare earth element selected from the group consisting of La, Y, Gd and Yb, the total oxide-converted content of the above elements being 0.6-7 weight %, with Mg converted to MgO and rare earth elements converted to rare earth oxides RExOy. The silicon nitride sintered body is produced by mixing 1-50 parts by weight of a first silicon nitride powder having a particle ratio of 30-100%, an oxygen content of 0.5 weight % or less, an average particle size of 0.2-10 ?m, and an aspect ratio of 10 or less, with 99?50 parts by weight of ?-silicon nitride powder having an average particle size of 0.2-4 ?m; and sintering the resultant mixture at a temperature of 1,800° C. or higher and pressure of 5 atm or more in a nitrogen atmosphere.

Abstract: A silicon nitride sintered body comprising Mg and at least one rare earth element selected from the group consisting of La, Y, Gd and Yb, the total oxide-converted content of the above elements being 0.6-7 weight %, with Mg converted to MgO and rare earth elements converted to rare earth oxides RExOy. The silicon nitride sintered body is produced by mixing 1-50 parts by weight of a first silicon nitride powder having a &bgr;-particle ratio of 30-100%, an oxygen content of 0.5 weight % or less, an average particle size of 0.2-10 &mgr;m, and an aspect ratio of 10 or less, with 99-50 parts by weight of &agr;-silicon nitride powder having an average particle size of 0.2-4 &mgr;m; and sintering the resultant mixture at a temperature of 1,800° C. or higher and pressure of 5 atm or more in a nitrogen atmosphere.

Abstract: There is disclosed a method of producing an aluminum composite material in which the content of silicon carbide can be made higher as compared with conventional methods, and the production cost is low, and the method can be carried out easily. An aluminum composite material of low-thermal expansion and high-thermal conductivity is produced by this method. A mixture of powder of aluminum metal or an alloy thereof and silicon carbide powder is pressurized and compacted to form a green compact. Subsequently, this green compact is charged into a mold, and is heated and compacted into a predetermined shape at a temperature not less than a melting point of the aluminum metal or the alloy thereof.