Sol Gel Alumina Coating on Fe–Cr–Al–Y Fibre Media for Catalytic Converters

Sol gel coating of γ-alumina was applied to Fe–Cr–Al–Y fine fibre media to examine the feasibility of using alloy fibres as a substrate for automobile catalytic converters. Two sol gel routes: aqueous based colloidal and alcohol based polymeric sol were used for coating. Prior to deposition, the fibre was oxidised in air to allow a dense α-alumina layer to form. The effect of several coating parameters such as withdrawal speed, sol concentration, soaking time and firing scheme on the coating quality and on the thickness were studied. The morphology of the coating was investigated with scanning electron microscopy (SEM) and the thickness of the coating was measured by the focused ion beam (FIB) technique. The crystal structures of the coating and the thermally grown oxide were studied with photo stimulated luminescence spectroscopy (PSLS). The coated fibre media exhibited different behaviour compared to the ordinary flat substrate. The performance of the alcohol based sol was better than that of the aqueous based sol with regard to the quality of the coating. PSLS was effective in differentiating the γ- and α-alumina.