Shirley Weaver Lyons

Palladium metal and palladium oxide particle production by spray pyrolysis

Abstract Spray pyrolysis was used to produce dense, spherical palladium metal particles at and above 900 °C in air and 800 °C in nitrogen, well below the melting point of palladium (1554 °C). Palladium oxide particles were produced at lower temperatures. At 500 °C the PdO particles were composed of nanocrystalline grains 5 to 15 nm in diameter and had surface areas of 30.2 to 32.8 m2/g. The particles became less porous and less polycrystalline as temperature increased. At 800 °C the PdO particles were polycrystalline with grains of 20 to 50 nm and a surface area of 3.23 m2/g. The Pd particles produced at 900 °C by decomposition of the oxide were single-crystalline and fully-dense. These observations are consistent with the formation of porous but not hollow aggregates of PdO at lower temperatures, which can be densified in the gas phase to form solid particles of Pd above 900 °C.

Characteristics of Bi-Pb-Sr-Ca-Cu-O powders produced by aerosol decomposition and their rapid conversion to the high-Tc phase

Abstract Bi-Pb-Sr-Ca-Cu-O powders were produced by aerosol decomposition of nitrate solutions. The effects of reactor temperature and residence time on particle morphology and evaporative Pb loss from particles were demonstrated, and conditions necessary to control Pb loss established. Pb loss was roughly proportional to residence time, and minimal loss occurred with short residence times (3s) and T≤800°C. Particles produced at 700°C typically contained significant porosity, while those produced at T≥800°C were solid. Mixtures of the Bi2Sr2CuOy (2201) and Bi2Sr2CaCu2Oy (2212) phases were produced at 700–900°C in nitrogen and air. However, after hearing in air for 16 h at 850°C, pellets of powder produced at 700°C with nominal composition Pb0.44Bi1.8Sr2Ca2.2Cu3Oy converted to approximately 79 vol.% of the Bi2Sr2Ca2Cu3Oy (2223) phase and displayed a Tc (onset) of 110 K. Rapid conversion to 2223 was promoted by powder synthesis conditions, leading to controlled Pb loss and a homogeneous fine-grained dispersion of mixed-oxide precursor phases within particles.

Role of particle evaporation during synthesis of lead oxide by aerosol decomposition

The role of product evaporation during lead monoxide (PbO) powder generation by aerosol decomposition (spray pyrolysis) was investigated at various temperatures in a flow reactor. Particles consisting of phase pure litharge and a mixture of litharge and massicot were formed with the dominant phase changing from litharge to massicot as the pyrolysis temperature was increased. Scanning electron microscopy showed particles produced at lower temperatures had a lumpy surface morphology and at higher temperatures appeared to be solid, indicated by the faceted surfaces and a plate-like morphology. Evaporative losses of PbO x , to the reactor walls were observed due to the substantial vapor pressure of PbO x . A simple model was developed that accounts for particle evaporation and mass transfer of lead oxide vapor to the reactor walls. This model suggested that the loss of lead oxide to the reactor walls was limited by diffusional transport of lead oxide vapor to the reactor walls.

Nanophase oxide formation by intraparticle reaction

Abstract We have generated 0.1–0.5 μm aggregates that consist of nanocrystalline P d O and V 2 O 5 . The particles were generated by reacting aerosol particles that are composed of metal nitrates in a hot flowing gas stream. The microstructure of the particles was controlled by varying the temperature. Nanophase materials were formed at temperatures low enough to avoid grain growth in each particle, but sufficiently high to fully react the precursors. This process allows reasonable production rates of nanophase materials. Generation of multicomponent materials is also possible.

Synthesis of nanophase materials by intraparticle reaction routes

Abstract We have generated 0.1-0.5 μm particles that consist of nanophase PdO and V2O5. The particles were produced by an aerosol decomposition technique in which droplets containing precursors were passed through a hot-wall flow system in which the solvent evaporated and the precursors decomposed within the particles to form the product. By controlling the temperature and residence time, grain-growth in the particle could be minimized to allow formation of nanometer-sized crystallites. Advantages of this approach include the ability to form nanophase complex metal oxides with high purity at high production rates.

Wall losses of volatile metal oxides during spray pyrolysis

Abstract The role of product evaporation during lead monoxide (PbO) powder generation by aerosol decomposition (spray pyrolysis) was studied as a function of temperature in a flow reactor. The dominant phase of the particles formed changed from litharge to massicot with increasing temperature. Scanning Electron Microscopy analysis of the powders showed particles produced at lower temperatures had a lumpy surface morphology and at higher temperatures appeared to be solid, indicated by the faceted surfaces and a platelike morphology. There were significant evaporative losses of PbO X to the reactor walls due to the substantial vapor pressure of PbO X . A simple model was developed that takes into account particle evaporation and mass transfer of lead oxide vapor to the reactor walls. Model simulations suggested that the loss of lead oxide to the reactor walls was limited by diffusional transport of lead oxide vapor to the reactor walls.