Facile chromaticity approach for the inspection of passive films on austenitic stainless steel

A chromaticity approach for the inspection of passive films on 304 stainless steel is explored by measuring the redness degree of the colouration reaction product of phenanthroline. The measurement exhibits good capability in evaluating film quality. The measured values are dependent on the structural integrity of the passive films. Based on the electrochemical examination and XPS spectra, this approach is discussed from the view point of the inhibition of the passive films on the release of ferrous from the matrix during its reaction with phenanthroline. The preferential dissolution of Fe-rich oxides in the films can affect the measurement.

► A passive film inspection composed of colouration reaction and colour measurement.
► This inspection is of good capability to evaluate the quality of passive films.
► The measured value consists well with electrochemical behaviour of passive films.
► The measurement is dependent on the barrier of passive film on colouration reaction.
► Reducing dissolution of Fe-rich oxides in passive film affects the measurement too.