Abstract: Glass ceramics used as dental material, artifical bone, etc. which contain 0.01 to 25 parts by weight of alkali metal oxides (R.sub.2 O), such as Li.sub.2 O, Na.sub.2 O, K.sub.2 O, Rb.sub.2 O, and Cs.sub.2 O, in 100 parts by weight of CaO-Al.sub.2 O.sub.3 -P.sub.2 O.sub.5 system material. During the casting for obtaining the glass ceramics, the molten fluid is sufficiently distributed to the fine corners of a mold, and the temperature for crystallization is low. Also, the time required for the crystallization is short and the crystalline formed shows no internal defects, and has high bending strength.

Abstract: Long potassium titanate fibers (100-3000 .mu.m) made by heat reaction in gas permeable calcination vessel, made of material containing at least 25 wt %, preferably at least 50 wt %, MgO to prevent plugging of the vessel during the reaction and maintain gas permeation.

Abstract: Calcium phosphate glass-ceramics of high strength and toughness is disclosed. These materials are excellent for artificial dental or bone materials. The strength and toughness of these materials are improved substantially in comparison with conventionally used calcium phosphate glass-ceramics by adding rare earth oxide in them. For dental materials, good aesthetic appearance to natural teeth is also obtained by adding one type, or two or more types of compounds selected from oxides of iron, manganese, cerium, titanium, nickel, zinc, cobalt, tungsten, chromium, and vanadium as color component. Also, if necessary, Al.sub.2 O.sub.3 and/or SiO.sub.2 is contained as coloring assistant agent in that composite. Moreover it is possible to adjust the color tone of each individual's teeth. The rare earth oxide, coloring component, and coloring assistant agent added are incorporated in crystals of calcium phosphate. Consequently, they cause no elution during use.

Abstract: Dental materials using calcium phosphate glass-ceramics and having the color tone with high approximation to that of natural teeth. In those dental materials, calcium phosphate composite, nickel oxide and one or more other type of compounds selected from oxides of iron, manganese, cerium, titanium and tungsten, are contained as coloring component. Also, if necessary, Al.sub.2 O.sub.3 and/or SiO.sub.2 is contained as a color assisting agent in that composite. The calcium phosphate glass-ceramic according to this invention consists of the same components as that of natural teeth. Besides, it is possible to adjust the color tone delicately to match with the color tone of each individual`s teeth. Moreover, the coloring components are incorporated in crystals of calcium phosphate. Consequently, they cause no elution during use and are therefore ideal as dental material.

Abstract: The present invention relates to silicon nitride composite refractories having silicon nitride bonds therein and having an increased thermal shock-resistance, an improved molten steel-resistance and an improved mechanical strength, which consists of silicon nitride at 20 to 60 wt %, refractory materials at 10 to 50 wt % and boron nitirde at 1 to 30 wt %, or additionally carbon fibers of 0.5 to 10 wt %. The above described characteristics can be realized because the silicon nitride bonds are bonding structures.