Suresh Baskaran

Effect of A-site cation nonstoichiometry on the properties of doped lanthanum gallate

Lanthanum gallate doped with Sr and Mg (LSGM) was synthesized using a combustion synthesis technique. The synthesized powders were sintered to high density in air, although excessively high sintering temperatures led to bloating of samples, possibly due to the volatilization of Ga2O from the perovskite structure. The electrical conductivity of sintered LSGM tended to decrease with increasing A/B cation nonstoichiometry. Under oxidizing conditions, the conductivity was almost completely ionic, but in reducing atmospheres a substantial electronic component was observed. It is likely that this electronic conduction resulted from the introduction of electronic charge carriers via the partial reduction of Ga from the trivalent to the divalent state. The flexural strength of LSGM with an A/B cation ratio of 1.00 was measured to be ∼150 MPa at room temperature; the strength decreased to ∼100 MPa at higher temperatures (600–1000°C). The fracture toughness, as measured by notched beam analysis, was ∼2.0–2.2 MPa√m at room temperature, decreasing to ∼1.0 MPa√m at 1000°C.

Mechanical properties of calcium- and strontium-substituted lanthanum chromite

Mechanical properties of acceptor (calcium and strontium)-substituted lanthanum chromites are reported as a function of composition, temperature and environment. The strength dependence on temperature for these perovskite conductors was found to depend on the acceptor type, with the calcium-substituted chromites showing a significant reduction in strength with increasing temperature, while the strength of strontium-substituted chromites was essentially invariant with temperature. The decrease in strength observed upon annealing in highly reducing environments was correlated to changes in lattice structure, stoichiometry and fracture morphology. A significant observation was the decrease in the cohesive strength of the grains relative to grain boundaries, beyond a critical oxygen vacancy concentration in the chromites. The structural changes in the chromite lattice upon reduction also resulted in decreased fracture toughness.

Mechanical properties of alkaline earth-doped lanthanum gallate

Lanthanum gallate doped with alkaline earths was prepared from combustion-synthesized powders. Mechanical properties of the doped gallates were evaluated as a function of composition and temperature. The indentation fracture toughness of Sr-substituted gallates was significantly better than the Ca- and Ba-substituted materials, but the toughness of all the doped gallates was significantly lower than yttria-stabilized zirconia, a typical electrolyte material. Small improvements in room temperature toughness and strength were measured in (La0.9Sr0.1)xGa0.8Mg0.2O3−δ, (“LSGM-1020”) samples with significant A-site cation non-stoichiometry (x = 0.9). The flexural strength of stoichiometric LSGM-1020 decreased from ≈150 MPa at room temperature, to ≈100 MPa at higher temperatures (600–1000°C). The notched-beam fracture toughness of LSGM-1020 decreased from ≈2.0–2.2 MPa√m at room temperature, to ≈1.0 MPa√m at 600°C. The decrease in mechanical properties over this temperature range was correlated to changes in crystal structure that have been identified by neutron diffraction. These crystallographic changes were also accompanied by significant changes in the thermal expansion behavior and elastic modulus. For off-stoichiometric LSGM-1020 with A/B cation stoichiometry of 0.90, strength and toughness also decreased with temperature, but the retained toughness (≈1.5 MPa√m) at elevated temperatures was higher than the toughness of the stoichiometric LSGM material.

Chemical sensors based on dielectric response of functionalized mesoporous silica films

Dielectric response of mesoporous silica films was monitored as a function of several gas-phase chemical species. The effects of humidity, ammonia, and methane on dielectric constant and dissipation factor of films subjected to different chemical treatments are described. Dielectric constant and dissipation factor of partially dehydroxylated films were found to be highly sensitive to both water vapor and ammonia in air. The capacitive devices based on mesoporous silica films show potential for use in chemical sensors.

Mechanical properties of calcium-substituted yttrium chromite

The interconnect in a solid oxide fuel cell (SOFC) is an electrical conductor that connects the individual cells in series. Therefore, the interconnect must be able to operate at high temperatures (800 to 1000 8C) in a large chemical potential gradient resulting from air (P(O2) 0:2 atm) on the cathode side and fuel, typically reformed natural gas (P(O2) 10 ˇ16 atm), on the anode surface. Due to the large chemical potential gradient, the interconnect must meet stringent electrical, environmental and thermo-mechanical requirements, and all properties must be stable in both reducing and oxidizing environments. Currently, only acceptor (calcium and strontium)substituted lanthanum and calcium-substituted yttrium chromite function adequately under these operating conditions, with lanthanum chromite receiving most of the attention as a potential

Application of Non-Thermal Plasma Assisted Catalyst Technology for Diesel Engine Emission Reduction

This paper presents an overview of a non-thermal plasma assisted catalyst system as applied to a small displacement diesel powered vehicle. In addition to effectively reducing NOx emissions, it has been found that a non-thermal plasma can also destroy a portion of the particulate matter (PM) that is emitted from diesel engines. Delphi Automotive Systems in conjunction with Pacific Northwest National Laboratories has been developing such an exhaust aftertreatment system to reduce emissions form diesel vehicles. The results of testing and system evaluation will be discussed in general, and the effectiveness on reducing oxides of nitrogen and particulate matter emissions from diesel vehicles. Published in Future Engines-SP1559, SAW, Warrendale, PA

Effect of solution chemistry and speciation on shelf-life of silica sols and characteristics of deposited mesoporous thin films

The effects of storage temperature and time on deposition characteristics of molecularly templated silica sols, used in synthesis of mesoporous silica films, were investigated by preparing acid catalysed water-ethanol-TEOS sols with surfactant and analysing by silicon-29 NMR spectroscopy over a period of multiple days, and by producing films after specific storage times corresponding to collection of NMR spectral data, and analysed for thickness and porosity.

Effects of trace metals and organic additives on porosity and dielectric constant of high purity mesoporous silica films

The beneficial effects that alkali metal and alkylammonium salt additions to molecularly templated silica sols have on the resulting mesoporous silica films formed from evaporative-coating methods with respect to porosity, elastic modulus, dielectric constant, and film surface uniformity were investigated and identified.