Investigation of Microstructure of Alumina Single-Splate Made By Solution Precursor High-Velocity Flame Spraying

Solution precursor thermal Spraying (SPTS) processes are suitable methods for producing nano-structured coatings. Due to the uncompleted reactions such as solvent evaporation and pyrolysis of the precursor, achieving coatings with controlled properties at a satisfactory precipitation rate remains an important challenge in these processes that needs to precise control of spray parameters. In this study, in order to investigate the effect of Solution precursor high velocity flame spraying parameters such as fuel and oxygen content, spraying distance and solution injection rate, single-scan spraying test was performed on glass substrates. The morphology of the formed splats and their structural characteristics were investigated using Scanning Electron Microscope (SEM). Structural comparison in the single-scan spraying test performed in two ratios of fuel to oxygen, showed that in the flame parameter with oxygen pressure of 6 bar and fuel 3 bar at the injection rate of Solution precursor 20 cm3/min and spray distance of 5 cm was selected as the optimal parameter. In this parameter, due to the low injection rate of the solution and higher heat transfer per drop of the solution precursor and completion of processes that resulting in melting and crystallization, the number of splats increased. Also, evaluation of single-scan spraying in the flame with oxygen pressure of 8 bar and fuel bar of 4 bar and spray distance of 5 cm showed that the injection rate of 40 cm3/min solution precursor would be more appropriate due to increasing the number of fine splats and improving coating efficiency.