Tape Casting and Sintering of Strontium-Doped Lanthanum Chromite for a Planar Solid Oxide Fuel Cell Bipolar Plate

Nonagglomerated strontium-doped lanthanum chromite powders were prepared by a modified Pechini resinintermediate process and tape cast to form bipolar plates for a planar solid oxide fuel cell. An air-sintering technique for the strontium-doped lanthanum chromite was developed, which involved placing the green tape between Cr₂O₃-fired plates. The sintering process was found to be diffusion controlled, with densification beginning at the surface and proceeding to the interior. A bipolar plate of 2-mm thickness was fired to more than 93.5% theoretical density when fired at 1670°C for 7 h.     

Plasma Spraying of Porous Electrodes for a Planar Solid Oxide Fuel Cell

Porous electrodes of Sr-doped lanthanum manganite in a planar solid oxide fuel cell were made by the plasma spray technique. Spherical carbon particles were utilized as an effective pore former. Spraying a mixture of annealed oxide powders sized between 50 to 200 μm and 15 wt% solid Carbospheres resulted in a uniform coating of 40% porosity. Porous coatings were also obtained when rigid resin intermediates were sprayed followed by annealing at 1000°C in air.     

A further analysis of the effectiveness of psychological warfare.

Standardized interviews with captured Malayan Communist Terrorists yielded data that support the hypothesis that psychological warfare is effective in changing behavior, but its effects are mainly of a precipitating nature that is differential for persons more sensitized to it by their morale and experiences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Controlled relative humidity storage for high toughness and strength of binderless green pellets

An equation was developed to predict fracture toughness of green powder compacts. The model combines crack tip toughness predicted by Kendall's model with crack tip shielding due to bridging of moisture meniscuses across the crack. The model predicts that crack tip shielding due to moisture should be dominant. Fracture tests on ceria green pellets verified that storing pellets at a high relative humidity (98% RH) for an extended period of time led to fracture strength more than double those stored at lower RH. However, at lower RH there is no significant increase in fracture strength with increased RH as predicted by the model. The lower strength at low RH is due to insufficient capillary and surface forces but may also be related to the lack of sufficient adsorbed moisture to form bridging meniscuses. The high green strengths achieved by storing pellets at a high RH suggest a method of strengthening green parts without adding binder.     

Thermal cycling of siliconized-SiC at high temperatures

Thermal cycling (between 1340 °C and 1480 °C) experiments were conducted using two types of reaction-bonded (siliconized) silicon carbide. A commercial material (Crystar^TM) and various silicon carbide pieces that had been joined together using electrophoretic deposition (EPD) followed by reaction bonding were evaluated. During the thermal cycling, residual free silicon metal rapidly vaporized from the Crystar^TM and cracks developed within its large SiC grains. In contrast, the EPD/reaction-bonded silicon carbide joints did not lose an observable amount of their residual silicon nor develop cracks. The reduced loss was attributed to reduced silicon content with the silicon residing largely in closed pores of the EPD layer. Reduced vaporization of the silicon that resided in surface-connected pores was engineered by applying a thick SiC surface coating. The morphology of the resulting coating was microscopically evaluated and two sequential growth mechanisms were postulated. An implication of this research is that hermetic (gas-tight) joints could be formed using EPD-derived SiC as a filler material.     

Dry bag isostatic pressing for improved green strength of surrogate nuclear fuel pellets

Dry bag isostatic pressing is proposed for mass production of nuclear fuel pellets. Dry bag isostatically pressed rods of a fuel surrogate (95% CeO₂-5% HfO₂) 200 mm long by 8 mm diameter were cut into pellets using a wire saw. Four different binders and CeO₂ powder obtained from two different sources were investigated. The strength of the isostatically pressed pellets for all binder systems measured by diametral compression was about 50% higher than pellets produced by uniaxial dry pressing at the same pressure. It was proposed that the less uniform density of uniaxially pressed pellets accounted for the lower strength. The strength of pellets containing CeO₂ powder with significantly higher moisture content was five times higher than pellets containing CeO₂ powder with a low moisture content even though they were 25% less dense. Capillary pressure of the moisture was thought to supply the added binding strength.