Engineering zirconia coating microstructures by using saccharides in aqueous suspension plasma spraying feedstocks

This study aims to demonstrate the feasibility to develop columnar microstructures in zirconia coatings manufactured by suspension plasma spray, through the modification of the properties of the suspension feedstocks with different common monosaccharides: fructose, ribose and glucosamine. The research also pretends to relate the properties of the suspensions to the final coatings. For the study, the saccharides suspensions were characterised in terms of physical and rheological properties. Then, highly concentrated suspensions containing the saccharides were plasma sprayed under the same spraying conditions. The experimental study with optic and scanning electron microscopy was used to evaluate the microstructure of the coatings and their characteristics, while the confocal laser scanning microscope (CLSM) was used to carry out a precise study of the surface topography. Results showed that saccharides produce a strong influence on the proliferation of columnar structures in the coating cross-section visible as cluster (cauliflower-like) structures on the surface. This effect is due to the diminution of water surface tension as well as an extra energy input during combustion of the saccharides. CLSM has allowed a detailed examination of the topography of the coatings to clearly quantify the differences observed in relation to the development of columnar microstructure.