Synthesis of core-shell mgal2o4/al2o3 composite powders via flame spray pyrolysis

The main objective of this thesis is the synthesis of composite powders in the form of MgA2O4/Al2O3 core/shell structure that are high in sintering activity and will improve microstructure significantly, by using flame spray pyrolysis method. Firstly, the precursor compositions and process parameters were determined which are required to achieve phase pure MgAl2O4 powders. In these studies, relatively low moisture sensitive and cost effective "trane" complex precursors are used to obtain oxide phases. However, it was showed that a widely used "trane" complex method for the synthesis of oxide powders via pyrolysis makes it difficult to obtain phase purity. A new hybrid method was proposed to achieve highly pure MgAl2O4 powders powders with controlled stoichiometry. Stoichiometry and phase analyzes were carried out by x-ray diffraction (XRD) method. Particle size control has been studied at different process parameters that affect the residence time of particles in the flame. The largest primary particle size measured with XRD-based Scherer formula was 17 nm, and the maximum aggregate size measured with Zetasizer was recorded as 180 nm. The coating of the core particles was studied by carrying AlCl3 vapor to the reactor with the N2 gas, feeding it into the reactor through the Torus ring and reacting it with the water vapor which is the combustion product in the reactor. The presence of the coating on the core particles were studied by transmission electron microscopy (TEM). Magnesium spinel powders were able to sintered to high densities that can provide optical transmission.