Abstract: The present invention provides a process for producing fine flaky alumina particles which are suitable as a raw material for ceramics, a pigment for paint, etc., wherein aluminum hydroxide or alumina hydrate having a particle size regulated to the order of submicron is subjected to a hydrothermal treatment in water or an aqueous alkali solution at a temperature of 350.degree. C. or above and under a pressure of 200 kg/cm.sup.2 or below. The present invention further provides an alumina-based plastic material which is produced by kneading the aforesaid fine flaky particles with an organic water holding material and water. Methylcellulose, polyvinyl alcohol, carboxymethylcellulose, polyethylene glycol, etc. are preferably used as the organic water holding agent. The alumina-based plastic material has a high plasticity, so that there is no need of using a large amount of a binder. Thus a dense molded article having stable properties can be prepared.

Abstract: A heat-resistant inorganic pigment of the present invention comprises a composite metal oxide containing Ti and two divalent metals selected from the group consisting of Mg, Fe, Ni and Co, the content of said two divalent metals in said composite metal oxide being 0.95 to 1.05, in an atomic ratio, based on Ti, and the composition ratio of said two divalent metals being 95/5 to 5/95 in an atomic ratio. The pigment of the present invention is useful as a pigment for a heat-resistant coating material and is a novel heat-resistant inorganic pigment which does not pollute the environment.

Abstract: The present invention provides a process for producing fine flaky alumina particles suitable as a raw material for ceramics, a pigment for paint and etc., wherein aluminum hydroxide or alumina hydrate having a particle size regulated to the order of submicron is subjected to a hydrothermal treatment in water or an aqueous alkali solution at a temperature of 350.degree. C. or above under a pressure of 200 kg/cm.sup.2 or below. The present invention further provides an alumina-based plastic material which is produced by kneading the aforesaid fine flaky particles with an organic water holding material and water. Methylcellulose, polyvinyl alcohol, carboxymethylcellulose, polyethylene glycol, etc. are preferably used as the organic water holding agent. The alumina-based plastic material has a high plasticity, so that there is no need of using a large amount of a binder. Thus a dense molded article having stable properties can be prepared.

Abstract: A Bi-Pb-Sr-Ca-Cu-O system superconductor having a composition ofBi.sub.n Pb.sub.m Sr.sub.x Ca.sub.y Cu.sub.2 O.sub..delta.wherein n is a number from 0.76 to 1.05, m is a number from 0.01 to 0.20, x is a number from 0.85 to 1.35 and y is a number larger than 1.00 and not larger than 1.35; or n is a number larger than 1.06 and not larger than 1.15, m is a number from 0.12 to 0.25, x is a number from 1.20 to 1.35 and y is a number from 1.20 to 1.30; or n is a number larger than 0.75 and not larger than 1.15, m is a number from 0.25 to 0.35, x is a number from 1.20 to 1.35 and y is a number from 1.20 to 1.35, when they are normalized with the Cu mole number of 2, which has t.sub.c of at least 110 K.

Abstract: A Bi-Pb-Sr-Ba-Ca-Cu-O system superconductor having a composition of:Bi.sub.l Pb.sub.m Sr.sub.p Ba.sub.q Ca.sub.y Cu.sub.z O.sub.xwherein l, m, p, q, y and z satisfy the following inequalities:0.50<l<1.500.01.ltoreq.m.ltoreq.0.600.70.ltoreq.p.ltoreq.1.600.005.ltoreq.q.ltoreq.0.800.70.ltoreq.y.ltoreq.1.601.40.ltoreq.z.ltoreq.3.00which has the critical temperature of at least 77 K, and contains the high T.sub.c phase in a high fraction.