Abstract: In a method of manufacturing parts or powders made of a compound of silicon or of a metal by exothermally reacting parts or powders of silicon or a metal in the solid state with a gas, wherein the differential flow rate or the pressure variation of the reactive gas in contact with the part or the powder is sensed, and the reaction is performed at increasing temperatures as a function of the said differential flow rate or pressure of the reactive gas:the improvement wherein a maximum differential flow rate or a maximum speed of pressure drop of the reactive gas is predetermined as a function of the chemical nature of the parts or powders, and optionally as a function of the density and the size of the parts, and the rise in temperature is suspended when the differential flow rate or the speed of pressure drop of the reactive gas reaches the predetermined maximum value, beyond which the reaction would run away and prevent complete transformation of the parts or the powders being obtained.

Abstract: Rheometer for effecting measurement of rheological properties in a medium, comprising a hollow body (2) having an inner chamber (3) with a lower zone (3A) and an upper zone (3B) of enlarged diameter. An inner shaft (9) is located in the inner chamber (3) and is driven by a magnetic coupling (12A-13) through a cap (4) for hermetically sealing the hollow body (2). A rotor (18) is provided on the inner shaft (9) and is displaceable in a longitudinal direction between an upper position where it is located in the upper zone (3B) and a lower position where it is located in its position for measurement. A stirrer (10-11) is keyed to the lower part of the inner shaft (9) and is receivable within the rotor (18).

Abstract: Equipment (3) for centrifugal casting from a crucible (5) into a mold (8) is modified by the addition of agitation means (19) movable relative to the crucible (5) and a heating furnace (30) which is movable relative to the mold (8) in order to heat the latter, before casting, to a temperature close to that of the alloy in the thixotropic state.

Abstract: An enclosure (17) contains two ovens (18, 19) each containing a semiconductor metal oxide (SnO.sub.2 or NiO) sensor (13) previously activated using H.sub.2 S or SO.sub.2. The sensors (13) are heated to different temperatures the lower of which corresponds to a peak on the sensor conductivity curve characteristic of the gas. The signals produced are applied to a comparator (30). For many toxic gases this peak occurs at concentrations below their toxicity threshold in air.

Abstract: A process for the electrolytic deposition of chromium by means of a bath of trivalent chromium is characterized in that it uses, as electrolyte, a solution which is obtained by careful reduction of the chromic acid in a sulfuric medium by an excess of a reducing agent of the alcohol type, such as methanol. Subsequently this solution is diluted with water without indispensable addition of additional products. The electrolysis is effected without separation of the anodic and cathodic compartments at an anode-cathode potential difference greater than 6 volts, the cathodic current density being of the order of 10 to 40 amperes per dm.sup.2, the concentration of trivalent chromium ranging from 0,1 to 1 ion-gram per liter and the pH from 1 to 1,5.

Abstract: The invention relates to a process and apparatus for boronizing pieces made of metal or cermet and to surface-boronized pieces. The pieces are placed in a chamber at between 850.degree. and 1,150.degree. C. and they are subjected, in the presence of boron carbide, to a gaseous stream of trifluoroboroxole (BOF).sub.3. The boron carbide is advantageously pulverulent and out of contact with the pieces to be boronized.

Abstract: The invention relates to a process and apparatus for boronizing pieces made of metal or cermet and to surface-boronized pieces. The pieces are placed in a chamber at between 850.degree. and 1,150.degree. C. and they are subjected, in the presence of boron carbide, to a gaseous stream of trifluoroboroxole (BOF).sub.3. The boron carbide is advantageously pulverulent and out of contact with the pieces to be boronized.

Abstract: A method of manufacturing nitrided silicon parts which retain their mechanical properties after hot oxidation, said method consisting of sintering silicon powder in an atmosphere which is rich in nitrogen. 1% to 10% by weight of aluminium powder is added to the silicon before sintering thereof and preliminary hot oxidation is effected in conditions which allow acicular mullite to form by the direct action of the aluminium and of a complement of oxygen molecules supplied by the outside medium on the silicon formed.

Abstract: The invention relates to a process and apparatus for boronizing pieces made of metal or cermet and to surface-boronized pieces. The pieces are placed in a chamber at between 850.degree. and 1,150.degree. C. and they are subjected, in the presence of boron carbide, to a gaseous stream of trifluoroboroxole (BOF).sub.3. The boron carbide is advantageously pulverulent and out of contact with the pieces to be boronized.