Abstract: The invention relates to new refractories with a high content of alumina and the process for their production. The refractories are made up of alumina particles held by a binder capable of withstanding a reducing atmosphere at 850.degree. C. The refractories are characterized by low porosity and high mechanical strength and are also inert towards coal ashes and slags at these temperatures. The binder used in the refractories consists of a combination of aluminum nitride and aluminum oxycarbide. The carbon required to the formation of the carbon oxide may be introduced in a form of carbon black or graphite, or may originate from a decomposition of a provisional or organic binder.

Abstract: The invention relates to gas-permeable parts comprised, by weight, of (A) 60 to 90% of granules of a grain size from 5 mm to 0.2 mm formed from a material selected among the group consisting of a chamotte containing at least 42% of Al.sub.2 O.sub.3, mullite, fired gibbsite containing more than 90% Al.sub.2 O hd 3, sintered or fused cast corundum containing more than 95% Al.sub.2 O.sub.3, natural chromite, sintered MgO, zircon sand and stabilized zirconia, and (B) 10 to 40% of a bonding cement comprised a calcium aluminate, a material selected among SiO.sub.2, Al.sub.2 O.sub.3 and Cr.sub.2 O.sub.3 having a particle size between 100 A and 0.1 micron, and alumina having a particle size between 1 and 100 microns. These parts retain a high mechanical strength when heated between hydraulic setting and ceramization, and are useful for blowing a gas therethrough in order to stir molten steel and cast iron.

Abstract: The invention relates to produced refractory compositions comprising the four following particulate fractions:(1) 30-60% by weight of a coarse fraction at least 50% of which are greater than 0.5 mm;(2) 10-30% by weight of a fine fraction at least 50% of which are smaller than 75 microns;(3) 10-30% by weight of a very fine fraction at least 50% of which are smaller than 5 microns; and(4) 10-30% by weight of an ultra fine fraction at least 80% of which are smaller than 0.1 micron;the fractions being comprised of materials which are inert to water. The refractory compositions, when mixed with less than 10% by weight of water, give injectable pastes suitable for repairing refractory furnace linings.

Abstract: The invention is directed to a cement composition comprising (1) 10-30% of an alkaline-earth mineral substance such as a slag or cement having a base of calcium aluminate or a calcined alkaline-earth oxide, (b) 14-56% of a constituent of a grain size of 100 A to 0.1 micron selected from silica, chromium oxide, TiO.sub.2, ZrO.sub.2 and Al.sub.2 O.sub.3, and (c) 14-56% of an inert filler of a grain size from 1 to 100 microns, the sum of (b) + (c) representing from 70 to 90% of the cement. Concrete mixtures which employ the inventive cements display superior properties.