| A Study on Process and Fundamentals of Zn-MnAlloy Electrodeposition AbstractZinc deposit has been widely used to protect steel from corrosion for many years due to its good corrosion resistance and low cost. However, the corrosion resistance of the zinc-coatings can not fill with the demands of the development of industry and new technology. Not until the late 1970 s that alloyed zinc finishes have been suggested as excellent corrosion resistance coatings. Up to date, zinc-nickel, zinc-iron, zinc-cobalt, zinc-tin have received more attention and usage in industries such as automobile, electrical, home appliances, instruments, machines and so on. Zinc-manganese alloy deposit, a new alloy variant was appearing in zinc based alloy deposits, reporting to have even better corrosion resistance than other zinc alloys. Many countries such as America, Japan, British, Italy, Russia, India have made research in Zn-Mn electrodeposition. However, it quickly became apparent that this new alloy system had its drawbacks, particularly in terms of process control and current efficiency. In china, however, zinc-manganese alloy electroplating has not been reported by now. In this dissertation, based on current research through out the world, tries to study the electroplating process of zinc-manganese alloy and the concerned fundamentals .The main subjects of the dissertation are as fellows:First of all, the additive named ZM of zinc-manganese alloy electroplating was made, the main composite is op-10 as carrying agent brighter, benzalancetone as main brighter, polyethylene glycol, sodium benzoate as assistant brighter. The additive has wide bright current density region. Different anode materials, such as zinc, zinc-manganese composite, graphite, stainless steel were studied, stainless steel was the best in stability of bath. Ion exchange membrane is used to prevent Mn2+ from moving to anode and be oxidized to Mn3+.The process of zinc-manganese alloy electrodeposition based on zinc sulfate, manganese sulfate and sodium citrate bath has been studied. Through the analysis of the alloy electroplating solution in gradients, the process variables and their relationship between content of manganese in the alloy coating, the optimum process has been obtained, the additive to improve the cathode current efficiency was found ; it was found that the deposits with a manganese content 40-60% exhibit excellent corrosion resistance; the corrosion resistance of zinc-manganese alloy coating will be even better after "phosphated" and passivated.The electrochemical behavior of the Zn-Mn electrodeposition has been studiedIVrespectively by linear sweep Voltammetry and Cyclic Voltammetry and partial current method. The reasons that. cathode current efficiency is very low when Zn-Mn deposits is due to the H2 produce in cathode, It has been discovered that additive Na2SeO3 is efficient to increase the Mn% in coating and the cathode current efficiency.The mechanism which additive Na2SeO3 improve the cathode current efficiency was studied through several kinds of electrochemical methods, the mechanism is as fellow:M + xH+ + xSe032'+4e = MSe + nOH' (I)xad 1-0MSe3ad + 2e = MSe (II)The adsorption of Se32"can prevent the reducation of H+ and help the deposition of manganese.The anomalous co-deposition of Zn and Mn is studied by several electrochemical methods, the rule of transition from normal to anomalous co-deposition is unveiled. The transition current density is affected by exchange current density of Zn2+ and Mn2+when be reduced, the additive, anode ions do not reduce in cathode. The under-potential deposition of manganese is found when zinc is deposited ahead. For the first time the dissertation points out that the anomalous co-deposition of Zn-Mn results from the difference partial current density of Zn and Mn when they are reduced.A model of alloy deposition affected by interfacial state of electrode and solution is presented in this paper, the...
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