Coating of plate-like α-Al2O3 powders with TiO2 by flame spray pyrolysis and its characterization

While plate-like α-Al2O3 powders have a wide range of applications (eg, luster pigments) in which plate surfaces are coated with different metal oxide layers (TiO2, Fe2O3, etc.) are widely preferred in various industries (automotive, construction, cosmetics, safety applications, etc.). The production of metal oxide coated α-Al2O3 platelets is carried out by wet chemical methods and gas phase reaction techniques and various problems are encountered depending on the manufacturing process applied. In both methods, it is quite difficult to change the reaction kinetics to achieve the desired coating thickness and / or to control the respective coating thickness. As a result of this, it is attempted to control the coating (reaction) time in order to achieve the desired coating thickness. In wet chemical methods, coating time is tried to be controlled by suspending the coarse litter particles, while in the gas phase reaction methods, the suspending action can be achieved by means of a fluidized bed method using a turbulent air flow. However, these applications require an additional heat treatment step for both methods. In this thesis, it is aimed to perform a process design for achieving TiO2 coating on α-Al2O3 platelets. Furthermore, it is aimed to realize TiO2 coating on plate-like α-Al2O3 powders in a higher temperature range which cannot be reached by the current methods by using flame spray pyrolysis system, thus obtaining the desired coating phase on the respective substrate material without the need for an additional heat treatment step. For this purpose, plate-like α-Al2O3 powders were coated with TiO2 in the flame spray pyrolysis system and the microstructural properties and phase compositions of the obtained coatings were examined. The effects of various process parameters (such as suspension concentration and suspension flow rate) on the final coating phase were investigated. Keywords: Plate-like α-Al2O3 Powders, TiO2, Flame Spray Pyrolysis, Wet Chamical Methods, Gase Phase Reaactions, HeatTreatment