Corrosion inhibition of AISI 304-and AISI 316-type stainless steel coated with nickel oxide in H2SO4 as a function of annealing temperature

AISI 304 (SS(304))- and AISI 316 (SS(316))-type stainless steels were coated with 250 nm thickness Ni thin films and post-annealed at different temperatures (423 K, 623 K, 773 K and 923 K) with a constant flow of oxygen (600 sccm). This procedure was carried out to oxidize the Ni thin film which has excellent chemical stability and highly improved the corrosion resistance of steel in sulfuric acid medium. Corrosion behavior of the samples in 1.0 M H2SO4 solution was investigated by means of potentiodynamic technique. Both types of annealed samples (i.e., Ni/SS(304) and Ni/SS(316)) showed highest corrosion resistance at 623 K annealing temperature with corrosion inhibition efficiency factors of PE% = 99.60% and 97.87%, respectively. X-ray diffraction and atomic force microscopy were employed before corrosion measurements and scanning electron microscopy after corrosion test for obtaining the crystallography and physical morphology of the samples. A correlation is achieved between the structural variation of the films with the annealing temperature and the potentiodynamic corrosion results. Consistent results are obtained for two types of stainless steel (SS(304) and SS(316)), while better performance of SS(304) is attributed to the initially lower surface roughness of bare SS(304). It is shown that increased annealing temperature enhances the diffusion effect hence larger grains are formed with wider and deeper grooves between them which provide larger effective surfaces (thinner film areas). These regions react faster with the corroding media and initially may form pitted type corrosion which extends by time to form cracks.

Automated summary

The study utilized post-annealing with Ni thin film coatings at different temperatures to improve the corrosion resistance of stainless steel in sulfuric acid medium. The samples exhibited the highest corrosion resistance at the annealing temperature of 623 K, with Ni/SS(304) and Ni/SS(316) showing corrosion inhibition efficiency factors of 99.60% and 97.87% respectively.