Wetting of plasma-sprayed coatings of SrAl2Si2O8 (SrASi), BaAl2Si2O8 (BASi) and Sr4Al6O12SO4 (SAlSr) by Al-12Si alloy

The wettability of SrAl2Si2O8 (SrASi), BaAl2Si2O8 (BASi) and Sr4Al6O12SO4 (SAlSr) plasma-sprayed coatings on mullite substrates by an Al-12Si alloy at 1000 °C was studied using the sessile drop technique. All the coatings showed high adherence to the substrate. The SrASi and BASi coatings were mainly amorphous with some monoclinic crystallites of SrAl2Si2O8 and BaAl2Si2O8, respectively. The SAlSr coating was amorphous and contained Sr, Al and O, indicating a decomposition during the coating process. The average contact angles for BASi, SrASi and SAlSr coatings were 121, 122 and 124°, respectively, showing a non-wetting behavior. Coatings of BASi and SAlSr after the wetting experiments presented no reaction with aluminum, while the SrASi coating showed the formation of an alumina layer as a reaction product, indicating a slight reduction of the Sr-celsian by aluminum. In general, these coatings are suitable to enhance the corrosion resistance of aluminosilicate ceramics in contact with Al alloys.