Abstract: Abrasive and/or refractory products comprising at least one compound from the group of oxynitrides of one or more metals or metalloids (such as Al, Mg, alkaline earth metals, Si, Ti or Zr) and obtained by melting and solidification.

Abstract: Process for direct nitriding of metals of relatively low melting point with the aid of a nitrogen-containing gas, in which a powder of at least one of the metals is mixed with a refractory powder, the mixture is heated under an atmosphere of nitrogen-containing gas at atmospheric pressure until the start of a rapid and exothermic nitriding reaction, and this reaction, which proceeds at a temperature generally higher than that of the melting point of the metals without apparent melting being observed, is allowed to proceed until all of the metals have been consumed, in order to obtain a highly porous solid mass which is easy to grind and is based on metal nitrides or metal oxynitrides.

Abstract: A device for obturating leaky tubes in heat exchangers, characterized in that it comprises a sleeve adapted to be sealingly mounted in an orifice, or port, of the upper wall of said heat-exchanger, a vertical stem provided, at the lower end thereof, with an arm of variable length at right angles to said stem, the free end of said arm being integral with an assembly carrying a deformable capsule with a vertical axis adapted to penetrate into one of said tubes and to obturate said tube after having been deformed, means integral with said assembly adapted to deform said capsule, means for dissociating said capsule from said assembly, means for carrying said arm to rotate about the vertical axis of said stem, means for vertically moving said arm and means for varying the length of said arm.