Crack formation,exfoliation, and ridge formation in 500 °C annealed sol–gel silica coatings on stainless steel SUS304: Part II Spectroscopic and mechanical analyses and insights into mechanisms controlling coating characteristics

This report is a continuation of Part I of my studies of a non-aqueous sol–gel silica coating deposited on stainless steel SUS304. Part I discussed the microscopic observation of cracks, ridges and interlayers within the resulting silica coatings, and provided limited insight into their respective mechanisms of formation. This report provides further explanation for the mechanisms of these processes, as evidenced by spectroscopic and nano-indentation analyses of the coatings. Specifically, the coatings were analyzed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Auger electron spectroscopy. These results are discussed along with those obtained in Part I to further assess the mechanisms of crack formation in the coatings, and it was found that coating shrinkage and tension most likely caused crack formation. It seems that the O-deficient interlayers were formed under a mild oxidation condition existed around the silica/SUS304 interface during ～500 °C annealing. Additionally, nano-indentation analysis indicated that the coatings were compact, but the coatings’ hardness was intermediate. Suggestions for improvement of sol–gel silica coatings on stainless steel are also provided.