Concentration measurement of chromium passivation solutions by an optical method

摘要

Chromium passivation solutions are widely used in the last step of plating process for improving metal surfaces. The appearance as well as corrosion resistance of the threated surface depend on the thickness of chrome layer which is controlled by many factors including the concentration of the solution. In this research, we study the relation of the light absorption and the concentrations of a chromium passivation solution. We prepare the solutions with five different concentrations and measure their absorbance by using an ultraviolet-visible spectrometer. The absorption spectrum non-monotonously changes with the wavelength of the incident light. However, the absorbance always linearly increases with the concentration at all wavelengths. We construct several calibration equations at different wavelengths and test them by using solution samples with other concentrations. The results show that the concentration of chromium passivation solution should be measured at wavelengths in the range of 420-700 nm because the errors are less than 5%.