Low surface energy ceramic coatings

The research aims to coat aluminium surfaces with a film composed by hybrid organic-inorganic network and an high metal oxide content. The coating must have acceptable mechanical strength, release characteristic and must be produced through a not toxic, low temperature process. The study is connected to the industrial production of food (cookwares) and rotating cylinders for paper and plastic shaping. Thin hybrid coating films with a contact angle of 100-140° were obtained with the sol gel process using methyl and/or ethyl alkoxy silanes. They were obtained enclosing colloidal silica, α-Al2O3, and other fillers and using HNO3 as catalyst. Several different formulations has been used and the film are obtained after an appropriate thermal treatment. The choice of inorganic fillers appear critical. The increase of the colloidal silica (CS) increases the contact angle and the hardness but decreases the abrasion resistance. SEM analysis indicate that a thin homogeneous layer, free of inorganic fillers, is formed on the surface probably due to rheology behaviour of the colloidal mixture during the application. Due to the relevance of the CS content and of the other fillers on the surface performance, we needed to analyse the total fillers distribution along the thickness with GDOES instrument and SEM analysis. The mechanical and morphological observations are discussed trying also to suggest some corrections in the ingredient content to optimise the formulation and the process parameters.