Modeling and Optimization of Jet Milling

The energy efficiencies of the acceleration nozzles of ejector and pneumatic jet mills are compared. Mathematical models are proposed for the acceleration of a two-phase mixture in the nozzle and the jet, and a procedure is put forward for optimizing subsonic nozzles and open-loop jet mills. The gas-dynamic perfection of the nozzles of pneumatic jet mills is assessed, and the initial particle-size range where the mill efficiency is highest is determined.     

Doping effects on the physicochemical and electrochemical properties of lanthanum manganite

The structural, thermal, electrical, and electrochemical properties of La_0.7Ca_0.3Mn_1-x(Co,Ni)_xO₃ and La_0.6Sr_0.4Mn_1-x(Co,Ni)_xO₃ (x = 0, 0.02, 0.05, 0.1) electrode materials were studied. Doping of the cubic perovskites with Co or Ni increases the fraction of Mn4+ ions, up to 49% in La_0.7Ca_0.1O₃ and 57% in La_0.6Sr_0.4Mn_0.95Co_0.05O₃. The 300-K conductivity of La_0.7Ca_0.3Mn_1-xNi_xO₃ passes through a maximum atx = 0.05, while that of La_0.6Sr_0.4Mn_1-xCo_xO₃ decreases steadily with increasingx. In the range 300–1100 K, the conductivity of the Ca-containing manganites exhibits semiconducting behavior, whereas that of the Sr-containing materials shows metallic behavior. No phase transformations were detected in this temperature range. In the four systems, the thermal-expansion coefficients are virtually independent ofx. In both undoped and doped electrode materials, the resistance parameterp/d of electrode layers on solid-electrolyte substrates shows semiconducting behavior at temperatures from 300 to 1100 K and oxygen partial pressures from 102 to 105 Pa. With increasing oxygen partial pressure or electrode-layer thickness (d = 15–100 mg/cm2),p/d decreases. The optimal electrode-layer thickness is found to be about 50 mg/cm2. The introduction of Co or Ni into the electrode materials decreases the polarization resistance of the electrode layer in gas/electrode/electrolyte systems. Compositions ensuring the lowest polarization resistance were found.     

Experience in the Introduction of Steam-Water-Oxygen Cleaning, Passivation, and Preservation at the TÉTs-23 Cogeneration Plant of the Mosénergo Company

Conditions of the process of steam-water-oxygen cleaning, passivation, and conservation (SWOC, P, and C) of internal heating surfaces of the boiler and the high-pressure feed heater (HPFH) piping over the steam side are presented. The process produces partial cleaning of the internal heating surfaces from scale and yields a corrosion-resistant protective film that hinders corrosion processes both in the operation of the boiler and in the idle period.     

Asymmetric rolling of metal powders and granules

The paper examines asymmetric rolling of aluminum powder and granules on driving rolls of different diameters at the same angular velocity. The ratio of roll diameters is 1.1 to 1.4. It is established that asymmetric rolling of powder material allows removing drawbacks peculiar to traditional asymmetric rolling. These drawbacks are roll camber and destruction caused by nonuniform distribution of contact stresses across the roll width. Thereby it is possible to substantially reduce rolling defects and improve the quality of roll. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 115–121, 2007.     

Oxidation of Silver by Atomic Oxygen

Oxidation of Metals - Interaction of silver with atomic oxygen has been studied at low incident-flux conditions (1015–1017 atoms?cm?2s??1, corresponding to a pressure of...     

The Structure and Properties of Precipitation-Strengthened Composites Produced From a Cast Alloy in the Al–Si–Mg System

Powder Metallurgy and Metal Ceramics - The properties of precipitation-strengthened composites produced from an aluminum alloy were studied. The composites were prepared by powder and casting...