Corrosion Resistance of Decorative Chromium Films Obtained From Trivalent Chromium Solutions

Abstract

In this work, the resistance to corrosion of chromium films obtained from trivalent chromium solutions of different compositions and the influence of solution compounds on the coatings electrochemical behavior and the microstructure were studied. The chromium coatings were obtained from trivalent solutions in a chloride-based bath with different complexing agents adding also sodium hypophosphite and aluminum chloride. UV-vis spectroscopy was carried out on all solutions before and after plating to observe changes in the chromium complexes chemical state due to the plating process. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) were performed to examine the coatings surface morphology and composition; respectively. The coulometric method was used for measuring coating thickness. Electrochemical impedance spectroscopy (EIS) was done using 3% NaCl as electrolyte and using a three-electrode cell with a standard calomel electrode (SCE) as reference. Bright chromium films were obtained from all baths however, differences were observed concerning morphology, thickness and corrosion resistance depending on the composition of the forming solution.Keywords: Trivalent chromium, plating, microstructure, corrosion resistance. [9,11] have studied the effect of the operating conditions such as the pH, temperature, current density and adding agents on the cathodic efficiency, morphology and structure of deposits, obtaining a response variable dependence in all cases.Other authors have reported the effect of reaction conditions during Cr +3 complexation in previous works [2][3], as well as the effect of sodium formate and acetate present in the solution on the chromium film morphology and corrosion resistance. In this work sodium hypophosphite and aluminum chloride were added to the basic formate and formate plus acetate baths to study the electrochemical behavior of the chromium films. Electrochemical impedance spectroscopy (EIS) was used to study the electrochemical behavior of the chromium coatings. The coating morphology and composition were studied by Scanning electron microscopy (SEM) and Energy dispersive X-ray (EDX) and films thickness was measured by the coulometric method [12] which also allow us to calculate the cathode efficiency. EXPERIMENTAL DETAILS Experimental designThe underlying goal of this study was to correlate chromium coating corrosion resistance to a set of factors such as: complexing, addition agents and time exposition to a corrosive environment. The Minitab software was used for designing and analyzing the experiments; Variance analysis (ANOVA) was used for analyzing the experimental results. The experimental order was randomized to ensure against the effect of time-related variables and also to satisfy statistical requirements independence of the observations. Each experiment was carried out with two replicates, until experiments were completed according to the design layout. ElectroplatingAll chemicals used were Sigma Aldrich reagent grade. Solutions were formulated wit...

Unravelling the Fe Effect on the Corrosion of Chromium Coatings: Chemical Composition and Semiconducting Properties

“…It was also found that the presence of traces of Fe in the bath, generally in the range of 150 mg l −1 , could be beneficial to the final properties (including corrosion) of the Cr coatings. 18 There are studies evaluating the corrosion resistance of Cr(III)based electrodeposits 6,[19][20][21] where some of them claim a better corrosion resistance when using a proper amount of Fe 2+ ions in the bath. 22 However, such studies are mainly based on the overall performance of a multilayer nickel-chromium system 23 rather than evaluating the behaviour of a single chromium coating and its passive layer.…”