Abstract: A pressure damping system for damping pressure perturbations incident to switching of switchable flow control means in a fluid flow circuit. The pressure surge damping system comprises a throttle valve in the circuit, with the throttle valve and switchable flow control means being constructed and arranged for selective adjustment of the throttle valve when the switchable flow control means is switched, to attenuate pressure perturbations incident to switching of the switchable flow control means. The pressure surge damping system of the invention may be employed in a multi-vessel oxidation system for the treatment of semiconductor effluent gas, or in other applications involving periodic or cyclic switched flows which generate an upstream-propagating pressure wave detrimental to an upstream process facility.

Abstract: Molybdenum trioxide in granular or powder form is reduced to molybdenum metal by stagewise fluid bed reduction wherein molybdenum trioxide is reduced to molybdenum dioxide using ammonia as the fluidizing-reducing gas at 400.degree. C. to 650.degree. C. and molybdenum dioxide is reduced to metal using hydrogen as the fluidizing-reducing gas at 700.degree. C. to 1400.degree. C. The content of impurities such as lead, zinc, bismuth and copper is reduced during the process.

Abstract: A method is disclosed for the intermediate reduction of a molybdenum compound selected from the group consisting of MoO.sub.3 and ammonium molybdate to MoO.sub.2. The molybdenum compound is fed to an indirectly fired inclined rotary calciner and uncracked ammonia caused to flow to the rotary calciner either concurrently or countercurrently to the flow of the molybdenum compound. The residence time and temperature are controlled to produce MoO.sub.2 at a conversion efficiency of at least about 80%.

Abstract: A process is provided for producing ammonium metatungstate comprising fluid bed roasting ammonium paratungstate at a temperature over the range of about 275.degree. C. to 305.degree. C. for a time at least sufficient to provide a roasted product in the form of a precursor of ammonium metatungstate, forming an aqueous slurry of the precursor and digesting the precursor at a pH of about 3 to 4 for a time at least sufficient to effect substantially complete dissolution of said precursor, filtering the digested slurry to produce a clear filtrate, and further processing the clear filtrate by evaporation to provide crystals of substantially pure ammonium metatungstate.