This work deals with the flattening of alumina molten particles, called droplets, on stainless steel substrates either smooth or blasted and preheated at different temperatures. The blasted surface roughness has been limited to Ra= 1.4 µm to image the flattening droplet. Besides flattening and splat cooling, the wettability of melted millimeter-sized alumina drops on the same substrates was measured. The transition temperature, Tt, has been shown to be different between smooth and rough surfaces. For a smooth surface, Tt, is 170°C, and at 200°C 100% of disk shaped splats are obtained. For the rough surface, Tt is close to 300°C with porous splats, becoming almost dense at 450°C. Close to alumina melting temperature, wettability does not vary with the substrate preoxidation, which may not be the case when the temperature is much over the melting one as in plasma spray conditions.

Large (3 x 3 x 0.05 m 3 ) refractory pieces (as the ones used for examples in smelters or incinerators) do not sustain regular glazing in a kiln, mostly due to high associated costs. Still, glass coatings could find use on such pieces due to their physical properties (durability, chemical inertia, tightness, etc.). Thermal spraying, using oxyacetylenic flame in particular, appears as a cost-effective solution permitting to circumvent the aforementioned disadvantages. This study aims at evaluating the quality of two types of coatings in terms of permeability. The first type considered coatings (resulting from a previous optimization of the spray operating parameters) sprayed directly on the substrates whereas the second one considered an additional brass underlayer manufactured by twin-wire electric arc spraying. The wettability of the glaze on the refractory substrate and on the brass underlayer was studied to comprehend the coating structural attributes (thickness, porosity, crazing, etc.) as well as their effects on the permeability. A specific measuring device was developed to assess permeability.