Influence of stabilizing agents on structure and protection performance of zirconium oxide films

We recently found that stabilizing agents have a strong effect on the interface structure of sol–gel deposited coatings. In this work we investigated the influence of the stabilizing agents hydroxypropyl cellulose (HPC) and acetylacetone (acac) on the protection performance and structure of protective zirconium oxide coatings which were deposited from zirconium–tetrapropoxide onto iron samples and heated at 675 K.The crystalline structure of the films was characterized with X-ray diffraction (XRD) and transmission electron microscopy (TEM). The element distribution and chemical composition was studied with energy dispersive X-ray spectroscopy (EDX) and secondary ion mass spectrometry (SIMS). Film porosity and protection performance were measured electrochemically with potentiodynamic scans. XRD measurements revealed a higher amount of crystalline zirconium oxide on the surface for acetylacetone coatings than for HPC. However, the SIMS depth profiles showed a thicker mixed iron–zirconium oxide layer in the case of HPC samples. Although the electrochemical results of acetylacetone films indicated a good protection with low film porosity, the dissolution currents of the HPC coatings were still two orders of magnitude lower than for acac. This means, with the use of HPC the protection ability of zirconium coatings on iron can be improved significantly.