Abstract: A prefabricated part made of vitreous fused silica for use as a refractory, and in particular, for use in repairing coke ovens, which contains over 90% by weight of SiO.sub.2. The prefabricated part includes about 20 to 50% by weight of vitreous fused silica having 1 to 6 mm grain size, 20 to 40% by weight of vitreous fused silica having 0.1 to 1 mm grain size, 15 to 35% by weight of finely ground vitreous fused silica having grains less than 0.1 mm in size, 1 to 10% of finely ground vitreous fused silica having a specific surface area according to BET larger than 20 m.sup.2 per gram, 1 to 10% by weight of cement and 0.1 to 8% by weight of a phosphorous compound.

Abstract: A glass-ceramic sintered body comprising an SiO.sub.2 --Al.sub.2 O.sub.3 --MgO--ZnO--B.sub.2 O.sub.3 type crystalline glass and alumina, said sintered body containing at least 10% by weight of a spinel crystalline phase; and a substrate composed of the sintered material. There is also provided a process for producing the glass-ceramic sintered body which comprises adding a binder to a mixed powder of an SiO.sub.2 --Al.sub.2 O.sub.3 --MgO--ZnO--B.sub.2 O.sub.3 type crystalline glass and alumina, molding the mixture into a predetermined shape, and firing the mixture into a predetermined shape, and firing the molded mixture at a temperature of 925.degree. to 1000.degree. C. in a non-oxidizable atmosphere. The glass-ceramic sintered body and the substrate composed of it in accordance with the present invention have excellent mechanical strength and thereby have markedly increased metallizing adhesion strength.