Abstract: A single crystal of alkaline earth metal fluoride is produced by a single crystal pulling method, has a straight barrel part diameter of not less than 17 cm, preferably has a straight barrel part length of not less than 5 cm, and has a light transmittance, as measured at a wavelength of 632.8 nm, of not less than 80%, preferably 90 to 98%. Further, the main crystal growth plane of the single crystal is the {111} plane or the {100} plane. The single crystal of alkaline earth metal fluoride has a large diameter as described above, and in spite that it is in an as-grown state, the peripheral surface is not opaque and the visible light transmittance is high. Therefore, evaluation of bubbles or inclusions in the crystal becomes feasible without performing complicated machining of the crystal, and from the single crystal, a large-sized optical material having advantageous properties such as high quality and high uniformity can be cut out.

Abstract: The single crystal of alkaline earth metal fluoride of the invention is produced by a single crystal pulling method, has a straight barrel part diameter of not less than 17 cm, preferably has a straight barrel part length of not less than 5 cm, and has a light transmittance, as measured at a wavelength of 632.8 nm, of not less than 80%, preferably 90 to 98%. Further, the main crystal growth plane of the single crystal of the invention is the {111}plane or the {100}plane. The single crystal of alkaline earth metal fluoride of the invention has a large diameter as described above, and in spite that it is in an as-grown state, the peripheral surface is not opaque and the visible light transmittance is high. Therefore, evaluation of bubbles or inclusions in the crystal becomes feasible without performing complicated machining of the crystal, and from the single crystal, a large-sized optical material having advantageous properties such as high quality and high uniformity can be cut out.

Abstract: The object of the present invention is to provide an as-grown single crystal of calcium fluoride having a large diameter and small birefringence. The as-grown single crystal of calcium fluoride according to the present invention is obtained by a single crystal pulling method (Czochralski method), has a straight barrel part diameter of 17 cm or more, preferably has a straight barrel part length of 50 mm or more, and has a birefringence of not more than 3 nm/cm, preferably 0.1 to 2.0 nm/cm.

Abstract: A process for producing a sintered body of aluminum nitride, which comprises mixing an aluminum nitride powder with (A) an alkaline earth metal aluminate, or both of (A-1) an oxide or oxide-forming compound of aluminum, and (A-2) an oxide or oxide-forming compound of an alkaline earth metal, and (B) an oxide or oxide-forming compound of yttrium or an element of the lanthanide series, and firing the resulting mixture.

Abstract: A process for producing a sintered body of aluminum nitride, which comprises(1) forming a raw molded article from a homogeneous mixture of(A) a fine powder of aluminun nitride, and(B) a sintering aid composed substantially of (a) at least one halogen compound of at least one metal selected from the group consisting of alkaline earth metals, lanthanum group metals and yttrium, and (b) at least one halogen-free compound of at least one metal selected from the group consisting of alkaline earth metals, lanthanum group metals and yttrium; and(2) sintering the raw molded article at a temperature of 1600.degree. to 2100.degree. C. in a non-oxidizing atmosphere. A sintered body having a high thermal conductivity and a high density of at least 3.2 g/cm.sup.3 is prepared by the process.

Abstract: A process for producing a sintered body of aluminum nitride, which comprises mixing an aluminum nitride powder with (A) an alkaline earth metal aluminate, or both of (A-1) an oxide or oxide-forming compound of aluminum, and (A-2) an oxide or oxide-forming compound of an alkaline earth metal, and (B) an oxide or oxide-forming compound of yttrium or an element of the lanthanide series, and firing the resulting mixture.

Abstract: A composite nitride sintered body consisting essentially of aluminum nitride, boron nitride and at least one metal compound selected from the group consisting of compounds of metals of Groups IIa and IIIa of the periodic table.The composite nitride sintered body is produced by intimately mixing a powder of aluminum nitride, a powder of boron nitride and at least one metal compound selected from the group consisting of metal compounds of metals of Groups IIa and IIIa of the periodic table, and sintering the mixture under atmospheric or elevated pressures at a temperature in the range of 1600.degree. to 2400.degree. C.The sintered body has a good machinability.

Abstract: A fine powder of aluminum nitride having an average particle diameter of not more than 2 microns and comprising at least 94% by weight of aluminum nitride, at most 3% by weight of bound oxygen and at most 0.5% by weight as metal of metal compounds as impurities.The fine aluminum nitride powder is prepared from a fine alumina powder and a fine carbon powder as starting materials.The fine aluminum nitride powder provides a sintered body having a high purity and a high density such as at least 2.9 g/cm.sup.3.The fine aluminum nitride powder is also useful as a raw material for alpha-Sialon, beta-Sialon and AlN polytypes, as an addition aid in various ceramics.

Abstract: SIALON sintered product having the formulaSi.sub.6-z Al.sub.z O.sub.z N.sub.8-z(z is 0 to 4.2) is produced by sintering a molded product of the starting materials for SIALON in the condition of covering the surface of said molded product with a mixed powder of Si.sub.3 N.sub.4 and SiO.sub.2 as main components in nitrogen gas atmosphere.

Abstract: An electrolytic cell equipped with a cathode, said cathode comprising a supporting structure composed of iron, nickel or an alloy of such a metal and a nickel coating formed thereon by electroplating in the presence of at least one S/N substance selected from the group consisting of a thiocyanate ion, a thiosulfate ion, a dithiocarbamate ion, a thiocarboxylate ion, an amino acid ion, a thiocarbamoyl compound and thiourea.