engleski

ELECTROCHEMICAL OPTIMIZATION OF CITRIC ACID CLEANING PROCEDURE OF STAINLESS STEEL 316L

This investigation deals with electrochemical determination of parameters reflecting the corrosion resistance of stainless steel after the treatment of cleaning the iron contamination with a citric acid solution and subsequent passivation. The procedure of cleaning the iron contamination on surfaces of stainless steel with a citric acid solution is more acceptable for environmental, health and economic reasons compared to the commonly used nitric acid procedure. Since wrongly selected procedure conditions lead to application failure, the procedure required particularly accurate optimisation that may be conducted by electrochemical determination of corrosion resistance parameters. A major goal of this investigation was to optimize the conditions of citric acid cleaning procedure by determining the electrochemical parameters reflecting corrosion performance of treated stainless steel. The optimized conditions were concentration and temperature of the citric acid solution, time of exposure and subsequent passivation process. The optimisation of cleaning AISI 316L stainless steel with a citric acid solution was performed by immersion of steel plate into the citric acid of specific temperature and concentration for different times of immersion. After thorough rinsing of plate, passivation in air or NaOH was carried out. Electrochemical testing was conducted in 3, 5 % NaCl by measuring open circuit potential (EOC), following by electrochemical impedance spectroscopy and cyclic potentiodynamic polarisation. On the basis of the measurement results following corrosion resistance parameters were determined: open circuit potential (Eoc), pitting potential (Epit), passivation current (jpas) and polarization resistance (Rp). The optimal conditions of the citric acid cleaning procedure were found and it was determined that a combination of cleaning treatment with a citric acid solution and passivation either in air or in a NaOH solution improves the state of passivity and the appearance of the surface of stainless steel 316L.

stainless steel; passivation; citric acid

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