Sealing effect of surface porosity of Ti–P composite films on tinplates

Abstract

A novel chrome-free Ti–P composite film was prepared by casting a mixed solution containing titanium and phosphorus species, which is able to seal the pores on the tinplate surface. The obtained film was characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The surface porosity sealing effect on tinplates was verified by using a glow discharge spectrometer (GDS), porosity tests, and XPS. The results show that the film on the tinplates is composed of TiO₂, Ti₃(PO₄)₄·nH₂O, and FePO₄. Micropores on the tinplates are reduced apparently after film deposition, and the content of iron exposed in the pores is decreased significantly. An obvious concentration peak of phosphorus at a depth of around 0.75 μm infers that the film can penetrate into the micro-pores. The film lead to a 42.5% decrease in the surface porosity of the tinplates, exhibiting an outstanding surface porosity sealing effect in comparison with pure Ti or P films. Mechanistic analysis using XPS indicates that Ti₃(PO₄)₄·nH₂O and FePO₄ in the film play a role in sealing the surface porosity.