【作者】 符德学；

【导师】 舒余德；

【作者基本信息】 中南大学 ， 冶金物理化学， 2001， 博士

【摘要】 镀锌以其较好的抗蚀性和低廉的价格己被广泛地应用于各种钢铁制品的防腐，但是，随着工业和科技的发展，镀锌层远不能满足抗蚀性需要，20世纪70年代，人们发现锌基合金镀层具有耐蚀性高、延展性好、涂装性好、低氢脆性、内应力小等优点，必将取代锌镀层、铬镀层和镉镀层，在汽车、航空、航天、仪器、仪表、建筑和电子等工业中得到广泛应用。目前，Zn-Fe、Zn-Co、Zn-Ni、Zn-Sn已得到深入研究并己投入使用。锌锰合金镀层是新近引起人们注意的新型锌基合金镀层之一，由于其具有十分优良的抗蚀性而引起研究者的广泛关注，7.5微米厚的锌锰合金镀层盐雾实验2000小时后才生红锈，是同厚度锌镀层的7-8倍，而且具有优良的涂装性，研究发展前景十分广阔：目前美国、日本、英国、意大利、俄罗斯、印度等国都已开展锌锰合金电沉积的研究。但由于锌锰合金电沉积还存在一些问题如无合适阳极、阴极电流效率低、镀液不稳定等，国外对锌锰合金电沉积的研究处于实验室研究阶段。国内目前还未见这方面的研究报道。本文着重研究硫酸盐-柠檬酸体系Zn-Mn合金电沉积工艺及其基础理论。 通过配方优化首次研制出锌锰合金电镀添加剂ZM，经Hull Cell和扫描电镜研究表明该添加剂光亮电流密度区域宽，能够在0.9-4.2 A·dm^-2的电流密度范围内获得镜面光亮、结构致密的合金镀层。用该添加剂获得的镀层附着强度高，完全符合国家标准。 在国内首次研究了硫酸盐柠檬酸体系锌-锰合金电沉积的工艺条件，得出了含锰为50％左右的锌锰合金镀层的最佳镀液配方和工艺条件。首次采用阴离子膜技术和不锈钢阳极，防止了二价锰离子的氧化、保持了镀液中锌锰的平衡。研究发现了锌锰合金电沉积在高电流密度下存在异常共沉积的现象。首次探索了在使用惰性阳极的情况下，镀液循环使用的方法：用氢氧化钡除去硫酸根离子后，按比例加入硫酸锌、硫酸锰可使镀液各离子浓度恢复。通过控制合适的锌锰离子比(Zn²⁺/Mn²⁺为1：2.0～3)，使阴极电流密度降低至3.5A·dm^-2(为提高锰含量文献一般为30A.dm^-2左右，电流效率较低)。 稳态极化曲线和分电流曲线研究发现了锌、锰离子还原时电流值随阴极电势的负移先上升后下降的变化规律，发现檬酸钠可提高镀层中锰含量但却减低电流效率、Na₂SeO₃增大锌锰电沉积的沉积量，升温不利于锰离子的还原反应而有利于析氢，首次发现了pH升高到7，锌锰沉积量迅速下降的现象。 通过研究发现锌锰合金电流效率低的主要原因是锰沉积时阴极电势较负，造成阴极大量析氢，氢气的析出一方面消耗电量另一方面阴极析氢又使界面pH升高，使锌锰标准电极电势负移而阻碍锌锰合金的阴极沉积。研究发现Na₂SeO₃能显著提高锌锰合金电沉积电流效率。 首次用循环伏安法、恒电势电解法、恒电流阶跃法研究了Na₂SeO₃提高电流效率的作用机理。研究发现Na₂SeO₃在锌锰共沉积的条件下在阴极是分两步还中南大学博士学位论文摘要原，即:首先在一O.gV处被还原为单质硒，然后在一1 .25V处被还原为多硒阴离子。证明了多硒和多硒阴离子都在阴极存在特性吸附:、.2了.﹃、1尸护 了.压Z气丫.二 了.、M+xH++xse032·+4e=l一夕人少决二J+n0H’ 夕人试女3od+Ze=九爱沦孺用交流阻抗法证明了上述反应机理是正确的，NaZSeO3提高电流效率的机理是:NaZSeO3阴极还原物在金属阴极（锰）上产生吸附附，阻止了氢原子在金属阴极 （锰）上的吸附，因而阻止了氢离子的阴极还原，同时NaZSeO3阴极还原产物还与锰离子形成团簇离子而有利于锰离子的阴极还原因而提高了阴极电流效率。 通过稳态极化曲线和分电流曲线，揭示了锌锰合金共沉积由正常到异常的转变规律，锌分电流值达到极限电流后随阴极电势的负移而下降，锰的分电流值也存在这种现象，但当锌分电流处于低谷时锰的分电流值处于高峰值此时便发生了锌锰异常共沉积。发现锌锰的交换电流密度、锌锰离子摩尔比、锌锰离子总浓度、添加剂及其它沉积条件都对转换电流密度有影响。研究发现锰存在欠电势沉积。发现了惰性阳离子降低锌锰分电流曲线的峰值的现象。 首次提出了合金电沉积的界面层作用模型，主要内容为: （1）、OHP面上的配位离子在阴极电子云的推斥下，脱去配位体，脱去配位体后的金属离子受阴极电子的作用进入IHP面与金属阴极电子云形成电子配物，继而被还原为吸附原子，在结晶力的作用下吸附原子进入金属晶体，放出晶格能。 （2）、金属阴极/溶液界面状态的变化影响合金电沉积的行为，即各还原组分在阴极面上的位置分率和OHP面上金属离子浓度的分布对合金电沉积行为产生显著的影响，这些影响是造成异常共沉积、欠电势沉积、电流效率高低、合金组成等的主要因素。惰性阳离子在OHP面上的分部对合金共沉积有阻碍作用。 （3）、运用界面层作用模型观点，建立了合金共沉积动力学方程。‘k:二nFK’阴:〔C备，:二】二exp（一ZF丫- RT）一△C乱2:二，一△C井r“:expl_丝鲤二兰与 RT用该方程推导出的锌、锰、氢分电流曲线与实验事实更多还原

【Abstract】 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更多还原