Electrochemical Oxidation And Reduction Of Chromium In Aqueous Solution & Preparation Of Chromium Materials

Traditional chromium salt manufacturing techniques cause serious environmental pollution problems.However,electrochemical methods of producing chromium salts performs more friendly to environment,but the mechanism of chromium electrochemical reduction and oxidation is still unclear and open to conjure.Electrochemical reduction of Cr???and electrochemical oxidation of Cr?0?in aqueous solution were studied through cyclic voltammogram?CV?,electrochemical impedance spectra?EIS?,linear polarization sweep voltammetry?LSV?,scanning electron microscope?SEM?,energy disperse spectroscopy?EDS?,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?.Superhydrophobic Cr₂O₃ surfaces respectively on iron and copper substrate were fabricated through electrodeposition in chromic acid aqueous solution,and the obtained surfaces performed well at superhydrophobicity and anti-corrosion property.Porous metal chromium was fabricated through pulse electrochemical etching in hybrid aqueous solution of sulfuric acid and ascorbic acid.The main parts of this work are shown as follows:?1?Electrochemical reduction of Cr???in sulfuric acid and chromic acid aqueous solution was studied,including the influences of sulfuric acid concentration,chromic acid concentration,electrode rotate speed and Cr3+ concentration to Cr???electrochemical reduction.Cr???tended to reduce into Cr3+ ions instead of insoluble Cr₂O₃ cathodic layer in the presence of sulfuric acid.The absorption on cathode surface and the gathering of electroactive substances in the near solution changed depending on chromic acid concentration.Increasing electrode rotate speed made Cr???reduction more easily,when Cr3+ ion played a negative role.?2?The electrochemical oxidation of Cr?0?in aqueous solution of sodium chloride,sodium sulfate,sodium hydroxide,ammonium hydroxide,sulfuric acid and ascorbic acid was studied.Cr?0?was easily electrochemically oxidized into Cr???and Cr?OH?3 in NaOH solution,and the Cr?OH?3 deposit on anodic surface was oxidized furtherly into Cr???at more positive potential.Cr?0?undergo a passivation-activation-repassivation process in sulfuric acid solution when electrode potential increasing,and the electrochemical oxidation from Cr?0?to Cr???would not happen until the passive film dissolved at over-passivation potential.Cr?0?could also be electrochemically oxidized in NaCl?Na2SO4 and high NH3·H2O concentration solutions,and could hardly be electrochemically oxidized in ascorbic acid or low NH3·H2O concentration solutions.It was discovered that a film formed on metal chromium surface in ascorbic acid solution at high potential.?3?Cr₂O₃ layer with micro-nano structure was electrodeposited on iron substrate from 1 mol·L-1 chromic acid aqueous solution at 6.1 V cell potential.After stearic acid modification,the prepared surface performed well at superhydrophobicity and corrosion resistance,and its water contact angle,sliding angle and corrosion protection efficiency was respectively 158.8°,2.1° and 99.94%.Cr₂O₃ layer was electrodeposited on copper substrate with addition of 0.05 g·L-1 NaNO3 and reduction of cell potential?from 6.1 V to 4.0 V?.The stearic acid modified surface showed excellent superhydrophobicity,and its water contact angle,sliding angle and corrosion protection efficiency was respectively 165.4°,1.8° and 99.9989%.?4?A method of preparing porous metal chromium was introduced.Taking advantage of the absorption and protection of ascorbic acid on Cr?0?surface,metal chroumium surface was pulse electrochemically etched in 0.1 mol·L-1 sulfuric acid and 0.01 mol·L-1 ascorbic acid hybrid aqueous solution,and the product showed good micro-nano porous morphology under SEM.