| Chromium coating has been widely used in decorative and functional film owing to its good hardness, wear resistance, corrosion resistance and decorative beautiful appearance. The traditional chrome exist problems such as low current efficiency, high energy consumption. As a new-style electrolyte, ionic liquids can avoid hydrogen evolution reaction, greatly improve the current efficiency, and reduce energy consumption. The study of environmental protection chromium electroplating using ionic liquids is increasing favored.The physical properties of ionic liquid stduy shows that ionic liquids have low viscosity, high conductivity, and have wider liquid range at low temperature when the molar ratio of ChCl/EG DESs ionic liquid is1:3,and CrCl3·6H2O concentration is0.3mol·L-1. A contrastive analysis of ionic liquids by infrared spectra and ultraviolet spectrum show that the chromium(III) complexes containing H2O and Cl-1as ligands change gradually from[Cr(H2O)4Cl2]+to [Cr(H2O)3Cl3] with the addition of CrCl3·6H2O ionic liquidsThe single factor experiment and response surface experimental results prove the effect of CrCl3·6H2O concentration and stirring speed is not significant. The current efficiency, deposit appearance quality respectively reached56.29%,4point when the CrCl3·6H2O concentration is0.3mol·L-1, stirring speed is300r·min-1, deposition temperature is319.3K, deposition time is26.57min, and current efficiency is55.89mA·cm-2. Chromium coating tests showed that, Chromium plating test showed that, in [ChCl-3EG] CrCl3·6H2O ionic liquid obtain black chromium coating which is about6～15μm thick, crack free and has good adhesion, and the corrosion resistance of the coating is is more excellent compared with trivalent chromium coating which is obtained from the conventional aqueous solution. As adding more LiCl, chromium coating has more refined grain and smoothness.The cyclic voltammety curves showed that the reduction of Cr(Ⅲ) to Cr in the ionic liquid occurs by a two-step process, from Cr(Ⅲ) to Cr(Ⅱ), then Cr(Ⅱ) to Cr, and the two steps are totally irreversible reaction controlled by diffusion. Diffusion coefficients of D changes small with step potential increasing, but decreases significantly with increasing LiCl concentration; Density of crystal nucleus number N0increases with increasing of electric potential and increases significantly with the increase of LiCl concentration, growth rate of crystal increases with a negative shift of step potential, and decreases with the addition of LiCl, all those show that the addition of LiCl take effect in improving Cr nucleation rate and have inhibitory action in crystal growth. Cathodic polarization curves show that the current density of the reduction peaks of C1and C2were decreased in different degree when adding LiCl. Cathodic polarization curves show, lower deposition temperature is helpful to get the good coating appearance. |
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