Plasma Sprayed Coatings for the Improvement of Chemical Resistance of Ceramic Refractories

Abstract

Plasma-sprayed ceramic coatings were deposited on refractory substrates to improve their chemical resistance to molten glass. Mullite, coarse and fine alumina powders were employed. Different layers with step-wise varying compositions were deposited in order to avoid dilatometric incompatibility troubles. In all the samples, the top coating consisted of plasma-sprayed fine alumina powders, to achieve low porosity and confer adequate chemical resistance, while mullite was used to match the low thermal expansion coefficient of the porous refractory substrates. The coatings were characterized by SEM, XRD, fracture toughness, abrasion resistance, thermal shock resistance and resistance to chemical attack. Since the overall thermo-mechanical and chemical behaviour is greatly affected by microstructural features, such as porosity amount, stacking sequence of layers and their composition, a FEM simulation of the thermo-mechanical properties (with particular regard to thermal stresses-induced cracking) has been conducted and compared to the experimental results.