7 - Powder Synthesis with Gas Phase Reactants

Abstract

This chapter discusses four methods of gas phase ceramic powder synthesis: by flames, furnaces, lasers, and plasmas. Different types of reactors are chosen due to considerations based on the enthalpy of reaction. A flame reactor must have an exothermic reaction, whereas in principle, the other reactors can operate with either exothermic or endothermic reactions. In each case, the reaction thermodynamics and kinetics are similar, but the reactor design is different. To account for the particle size distribution produced in a gas phase synthesis reactor, the population balance must account for nucleation, atomistic growth, and particle-particle aggregation. These gas phase reactors are real life examples of idealized plug flow reactors that are modeled by the dispersion model for plug flow. To obtain narrow size distribution ceramic powders by gas phase synthesis, dispersion must be minimized because it leads to a broadening of the particle size distribution. Finally, the gas must be quickly quenched or cooled to freeze the ceramic particles, which are often liquid at the reaction temperature, and thus prevent further aggregation.