Influence of SiO2/Na2O ratio and temperature on the mechanism of interaction of soluble sodium silicates with porous anodic alumina

Porous anodized aluminum oxides were silicate-treated by dipping in a water-based sodium silicate solution. The surface modifications occurring on the oxide layer during immersion in solution are studied as a function of the SiO2/Na2O ratio and the temperature of the silicate solution. The anionic speciation in the silicate solution was studied by means of 29Si NMR.The reactions happening at the anodic alumina surface were studied by monitoring the open circuit potential as a function of time. The presence of silicate in the pores of the anodic layer is analyzed by means of GDOES and the morphological changes occurring on the oxide surface during immersion are observed by FE-SEM. The mechanism of the deposition is extended to silicate solutions with SiO2/Na2O = 1.

► Soluble Na silicate is used as pretreatment of metals or post-anodic treatment.
► Silicate-alumina interactions are studied by complementary surface analysis methods.
► The effect of SiO2/Na2O ratio and temperature are analyzed.
► The mechanism of interaction is extended to SiO2/Na2O = 1.