Abstract: In order to provide a manifold valve in which the overall height thereof can be lowered, a manifold base 10 is constituted by a fitting portion 18 with tube fittings 26, 28 being attached to output openings 22, 24 which open in a vertical direction on one side surface of the fitting portion 18, and a base portion 20 having a height lower than that of the fitting portion 18. A directional control valve 12 is constituted by a main valve 60 and a pilot valve 62 which is displaced upwardly from the main valve and attached at a height approximately equal to a difference in height between the fitting portion 18 and the base portion 20 from a lower surface of the main valve 60. The main valve 60 is disposed on the base portion 20, and the pilot valve 62 is disposed on or adjacent the fitting portion 18, wherein the directional control valve 12 is integrated with the manifold base 10.

Abstract: A method for preparing zircon powder, which comprises mixing (1) silica sol and (2) an aqueous zirconium oxychloride solution having a concentration which would be from 0.1 to 2 mols/l after mixed with the silica sol, in a SiO.sub.2 /ZrO.sub.2 molar ratio of from 0.95 to 1.10, heating the mixture to hydrolyze the zirconium oxychloride, followed by dehydration treatment to obtain a powder, heating the powder from room temperature to a calcination temperature over a period of from 0.7 to 30 hours and calcining the powder at a temperature of from 1,200.degree. to 1,400.degree. C. for a period of time satisfying the relation of:t.gtoreq.116-0.08Twhere t is the calcination time (hr) and T is the calcination temperature (.degree.C.), or heating the powder from room temperature to a calcination temperature over a period of from 0.8 to 70 hours and calcining the powder at a temperature higher than 1,400.degree. C. and not higher than 1,700.degree. C. for a period of time satisfying the relation of:t.gtoreq.18-0.

Abstract: A pollucite powder consisting essentially of a pollucite phase and having an Al.sub.2 O.sub.3 /SiO.sub.2 molar ratio of from 0.21 to 0.25 and a Cs.sub.2 O/SiO.sub.2 molar ratio of from 0.19 to 0.22.

Abstract: A silicon nitride sintered body having a composition of 1.5-3.0 weight % of Y.sub.2 O.sub.3, 0.1-1.0 weight % of Al.sub.2 O.sub.3 and balance substantially Si.sub.3 N.sub.4, a weight ratio of Y.sub.2 O.sub.3 /Al.sub.2 O.sub.3 being 2.5 or more, which has a density of 3.0 g/cm.sup.3 or more and has a structure in which the minor axes of grains are substantially 6 .mu.m or less. This silicon nitride sintered body is produced by preparing a powder mixture containing Y.sub.2 O.sub.3 powder, Al.sub.2 O.sub.3 powder and silicon nitride powder in the above proportions, the silicon nitride powder having an oxygen content of 1.2 weight % or less, a specific surface area of 9-11 m.sup.2 /g and a metal impurity content of 200 ppm or less; and sintering the powder mixture at a temperature of 1900.degree.-2100.degree. C. and a pressure of 5 kg/cm.sup.2 G or more in a nitrogen atmosphere.

Abstract: A preparation method for zircon powder, which comprises heating a feed powder mixture comprising:(1) silica and zirconia obtained by subjecting a liquid having a pH of not higher than 8 and containing silica and zirconia in a SiO.sub.2 /ZrO.sub.2 molar ratio of substantially 1/1, to liquid-removing treatment, and(2) zircon in an amount of at least 0.1% by weight based on the total amount of said silica and zirconia,at a heating rate of not higher than 5.degree. C./min from 1,200.degree. C. to a calcination temperature, and maintaining it at a calcination temperature of from 1,300.degree. to 1,700.degree. C. for from 1.0 to 24 hours.

Abstract: A silicon nitride sintered body comprised of 1.5 to 3.0% by weight of Y.sub.2 O.sub.3, 0.1 to 1.0% by weight of Al.sub.2 O.sub.3 and 96 to 98.4% by weight of Si.sub.3 N.sub.4 wherein the Y.sub.2 O.sub.3 /Al.sub.2 O.sub.3 weight ratio is at least 2.5, and having a density of at least 3.0 g/cm.sup.3, exhibits a high oxidation resistance and a high strength at a high temperature. This silicon nitride sintered body is prepared by sintering a powdery mixture consisting essentially of 1.5 to 3.0% by weight of Y.sub.2 O.sub.3 powder, 0.1 to 1.0% by weight of Al.sub.2 O.sub.3 powder, and 96 to 98.4% by weight of Si.sub.3 N.sub.4 powder, the Y.sub.2 O.sub.3 /Al.sub.2 O.sub.3 weight ratio being at least 2.5, the oxygen content in the Si.sub.3 N.sub.4 powder being less than 2.0% by weight and the total metallic impurity content in the Si.sub.3 N.sub.4 being less than 200 ppm, at a temperature of 1,850.degree. to 2,000.degree. C. in a non-oxidizing atmosphere.

Abstract: A method and an apparatus for grinding the surface of a semiconductor wafer by moving a holding table and a grinding wheel relative to each other in a predetermined direction substantially parallel to the surface of the semiconductor wafer held onto the holding table to cause the grinding wheel which is rotated to act on the surface of the semiconductor wafer held onto the holding table. The semiconductor wafer is placed on the holding table with its angular position being regulated so as to direct its crystal orientation in a predetermined direction with respect to the holding table, and thus the grinding direction of the surface of the semiconductor wafer by the grinding wheel is set in a predetermined relationship to the crystal orientation of the semiconductor wafer.

Abstract: A grinding apparatus comprising a supporting base and at least one grinding wheel assembly disposed to face to the supporting base. The supporting base includes at least one holding table and the surface of the holding table protrudes beyond the surface of the supporting base. The grinding wheel assembly includes a rotatably mounted supporting shaft and a grinding wheel mounted to the supporting shaft. At least the surface layer of the holding table is made of 2MgO.SiO.sub.2 -type ceramics.