Preparation of Boehmite Sol Employed for Formation of Alumina-Layer over Various Plates with the Dip-Coating

Abstract

Formation of boehmite sol from aluminum isopropoxide in aqueous solution was examined with XRD and solid state NMR to reveal that the hydrolysis of the isopropoxide was completed within a rather short reaction time of 1 h while a longer reaction time of 24 h had been employed in the typical preparation procedure. Although it had been mentioned that γ-alumina was formed from the calcination of boehmite at 1073 K, it was suggested that η-alumina, not γ-type, was obtained after the calcination, based on XRD analyses. In order to develop the employment of boehmite sol as the precursor material, the layer of active alumina and its precursor was formed with the dip-coating technique on glass, stainless steel, magnesia and α-alumina plates to show that approximately 1 μm layers were uniformly formed on glass and stainless steel plates while thickness of the layer formed on magnesia and α-alumina was not estimated due to the reflection of uneven plates of those oxides.