Corrosion behavior of sol-gel coated amorphous alumina at different calcination temperatures

Abstract

In the current research, the effect of low-temperature calcination on the crystal structure, morphology and corrosion properties of sol-gel derived dip-coated amorphous Al2O3 on plain carbon steel with a nickel electrodeposited intermediate layer was investigated. Alumina sol suspension was prepared via Yoldas method and modified by the addition of polyvinyl alcohol (PVA). The coatings were calcinated at 300 °C and 500 °C, and the stability of sol suspensions was evaluated by zeta potential analysis. Phase transformation temperature and thermal properties of alumina sol were investigated using DSC analysis. The morphology and composition of coatings before and after potentiostatic test was studied using FESEM and EDS. XRD analysis were conducted to characterize the crystal structure and phase of synthesized alumina. FTIR spectroscopy were used to characterize obtained composites. Finally, the corrosion behavior of coatings was analyzed using OCP, potentiostatic polarization, and EIS. The results revealed that the calcined coating at 300 °C has a corrosion current density of 0.15 μA.cm−2, which is 15 times better compared to bare substrate (icorr = 2.3 μA.cm−2), and also 50 times better than the calcined coating at 500 °C (icorr = 7.8 μA.cm−2). This phenomena attributed to carbonaceous residues from PVA in the alumina coating calcined at 300 °C and its crack-free surface; thus, showed better corrosion resistance than those calcinated at 500 °C.