Abstract: This invention relates to engine parts having high durability, which can be used at high operating temperatures. The engine parts comprise component members consisting mainly of the partially stabilized zirconia having high strength which is excellent in thermal insulation and mechanical strength. As the partially stabilized zirconia having high strength, use is made of ones in which thermal expansion hysteresis (difference of thermal expansion at an optional temperature in the thermal expansion during heating up and the thermal shrinkage during cooling down) is less than 0.4% and thermal expansion coefficient is more than 10.times.10.sup.-6 /.degree.C. The preferable engine parts having higher durability and reliability comprise component members consisting of a ceramic-metal composite body wherein the partially stabilized zirconia having a difference of thermal expansion coefficient being less than 3.times.10.sup.-6 /.degree.C. and a metal are bonded.

Abstract: A polycrystalline translucent alumina sintered body having high in-line transmission, which is suitable for an envelope for a high pressure vapor discharge lamp, is produced by adding to alumina powder having a purity of more than 99.8% MgO or a compound forming MgO in an amount of 0.01-0.1% by weight calculated as MgO, La.sub.2 O.sub.3 or a compound forming La.sub.2 O.sub.3 in an amount of 0.001-0.05% by weight calculated as La.sub.2 O.sub.3, and Y.sub.2 O.sub.3 or a compound forming Y.sub.2 O.sub.3 in an amount of 0.001-0.05% by weight calculated as Y.sub.2 O.sub.3, thoroughly mixing the resulting mixture, shaping the mixture into a desired form and firing the shaped article under vacuum or either atmosphere of hydrogen gas or dissociated ammonia gas under oxygen concentration of 10.sup.-15 -10.sup.-25 atm.

Abstract: A polycrystalline translucent alumina sintered body having high in-line transmission, which is suitable for an envelope for a high pressure vapor discharge lamp, is produced by adding to alumina powder having a purity of more than 99.8% MgO or a compound forming MgO in an amount of 0.01-0.1% by weight calculated as MgO, La.sub.2 O.sub.3 or a compound forming La.sub.2 O.sub.3 in an amount of 0.001-0.05% by weight calculated as La.sub.2 O.sub.3, and Y.sub.2 O.sub.3 or a compound forming Y.sub.2 O.sub.3 in an amount of 0.001-0.5% by weight calculated as Y.sub.2 O.sub.3, thoroughly mixing the resulting mixture, shaping the mixture into a desired form and firing the shaped article under vacuum or either atmosphere of hydrogen gas or dissociated ammonia gas under oxygen concentration of 10.sup.-15 -10.sup.-25 atm.

Abstract: A sealing composition consisting of 35-50% by weight of aluminum oxide, 35-50% by weight of calcium oxide, 1-10% by weight of yttrium oxide and 1-15% by weight of strontium oxide has a high wettability with alumina ceramics and refractory metal, and further has high heat resistance and resistance against sodium vapor. The sealing composition is excellent for sealing alumina arc tubes for high intensity discharge lamps with ceramics or refractory metal. Included within the scope of the invention is a composition consisting of 40-50% by weight of aluminum oxide, 35-43% by weight of calcium oxide, 3-10% by weight of yttrium oxide and 8-15% by weight of strontium oxide, as well as methods for using the compositions.

Abstract: Polycrystalline spinel sintered body consisting mainly of Al.sub.2 O.sub.3 and MgO in a molar ratio of Al.sub.2 O.sub.3 /MgO of ranging from 0.52/0.48 to 0.70/0.30 and containing 0.001-0.1% by weight of LiF has a high in-line transmission. The sintered body can be obtained by calcining a powdery mixture of Al.sub.2 O.sub.3 and MgO in a specifically limited molar ratio, molding the calcined mixture into a shaped article together with a specifically limited amount of LiF, and firing the shaped article under a specifically limited temperature condition.

Abstract: A high pressure metal vapor lamp and a transparent polycrystalline alumina tube therefor have been disclosed. The average crystal grain size at ends of the tube is selectively made smaller than that of the middle portion of the tube so that the mechanical strength and the thermal shock resistance of the end portions are made higher than those in the middle portion. Accordingly, the tube hardly causes cracks by a thermal shock when the both ends of the tube are sealed and when the lamp using the tube is switched on and off. Whereas middle portion of the tube has an excellent transparency so that the lamp has a high luminance efficiency.

Abstract: A sintered silicon nitride body consists of not more than 10% by weight in total of at least two metal oxides selected from the group consisting of beryllium oxide, magnesium oxide and strontium oxide (provided that each of the metal oxides is not more than 5% by weight) and the remainder of silicon nitride and may further contain not more than 10% by weight of at least one rare earth metal oxide, and is produced by preparing a mixture having the said composition range and then molding and sintering it at 1,600.degree.-1,900.degree. C. in nitrogen or inert gas atmosphere.

Abstract: A tubular discharge envelope and a high-pressure vapor discharge lamp using the same are disclosed. The envelope is composed of a polycrystalline transparent alumina having an average crystal grain size of 20-60 .mu.m and crystal grains of 20 .mu.m or less which occupy not more than 30% per unit area of the envelope.

Abstract: A polycrystalline alumina has at least 50% unit surface area provided by crystals of at least 60 .mu.m, and preferably 100 .mu.m size. This improves the in-line transmission value and hence lamp efficiency in a tube for a high pressure metal vapor lamp having an envelope of alumina.

Abstract: A sintered silicon nitride body consists of not more than 10% by weight in total of at least two metal oxides selected from the group consisting of beryllium oxide, magnesium oxide and strontium oxide (provided that each of the metal oxides is not more than 5% by weight) and the remainder of silicon nitride and may further contain not more than 10% by weight of at least one rare earth metal oxide, and is produced by preparing a mixture having the said composition range and then molding and sintering it at 1,600.degree.-1,900.degree. C in nitrogen or inert gas atmosphere.