Abstract: The present invention relates to a zirconia-based sintered body comprising TiN, TiO.sub.2 and ZrO.sub.2 and having electric conductivity and a process for the production thereof. The present invention provides a zirconia-based sintered body which has, at normal temperature, a mechanical strength of not less than 50 kg/mm.sup.2, a fracture toughness of not less than 4 MPam.sup.1/2, a Vickers hardness of not less than 1,000 kg/mm.sup.2 and a volume resistivity of not more than 1 .OMEGA.cm, and which is sinterable under normal pressure at low temperature, and a process for the production thereof.

Abstract: Disclosed are zirconia ceramics superior in mechanical strength, hardness and toughness and a method for producing them. The zirconia ceramics contain ca. 7-12 mol % of cerium oxide and ca. 2-7 mol % of magnesium oxide and have an average crystal grain size of crystal grains thereof of 1 .mu.m or less, at least ca. 80 mol % of the crystal grains being tetragonal grains and the balance being monoclinic grains, and have a bending strength of at least 100 kg/mm.sup.2, a fracture toughness of at least 10 MNm.sup.-1.5 and a Vickers hardness of at least 1000 kg/mm.sup.2. The method comprises calcining a hydrate obtained by coprecipitation method from water-soluble salts of cerium and magnesium and a basic salt of zirconium or a hydrate obtained by adding water-soluble salts of cerium and magnesium to a zirconium hydrate and neutralizing the mixture of hydrates, further grinding the calcined hydrate to obtain zirconia powders of 1 .mu.

Abstract: A hollow catalyst carrier and hollow catalyst made of a transition-alumina (e.g. .gamma.-alumina) which comprises a calcined product having a pipe-like or multi-cell structure and having a very large void ratio (i.e. not less than 3%), a very large specific surface area (i.e. not less than 5 m.sup.2 /g), a bulk density of 0.8 to 1.8 g/cm.sup.3, a compressive strength in the extrusion direction of not less than 20 kg/cm.sup.2 and at least one hole in the extrusion direction, and a process for the production thereof by subjecting a powder containing a rehydratable alumina to an extrusion molding, rehydrating the molded product and followed by calcining. The hollow catalyst carrier and hollow catalyst have excellent properties for carrying the catalytically active components thereon and have an excellent mechanical strength.

Abstract: An electrode for aluminum reduction cells wherein an electrode base, at least in that portion which is brought into contact with a molten salt bath, is coated with a composition comprising at least 50% by weight of electronic conductive oxide ceramics, or said portion of the electrode is made of said composition.

Abstract: An electrode for aluminum reduction cells wherein an electrode base at least in its portion that is brought into contact with a molten salt bath is coated with a composition comprising at least 50% by weight of electronic conductive oxide ceramics, or said portion of the electrode is made of said composition.