【作者】 张晓伟；

【导师】 何湘柱；

【作者基本信息】 广东工业大学 ， 化学工程， 2011， 硕士

【摘要】 随着高新技术产业的发展,市场上对于电子产品需求欲望的增加,特别是液晶技术的成熟与普及,LCD液晶产品的研究与应用日益广泛,但在加工与生产过程中对应用于切割LCD的刀具材料的工艺研究还不完善。当前在市场条件下所使用的材料,主要是通过电铸的方法使金属镍与金刚石复合形成切割材料,其具有硬度高、耐磨性好等优点,同时也呈现出一些问题,如结合力不佳、出现缝隙,严重影响产品的使用寿命。考虑到金刚石微粒价格昂贵,但其与石墨粉均属于C元素,结构性质相差不大,因此用石墨粉代替金刚石微粒探讨金属镍与石墨复合镀层的性能。本文将超细石墨粉加入到镍镀液中,用复合电沉积的方法制备出性能良好的Ni-石墨复合镀层。系统地研究了超细石墨粉在水溶液及镍镀液中的分散情况,Ni-石墨复合电沉积工艺对性能的影响以及运用电化学工作站分析电结晶过程中的机理研究；用XRD和SEM研究了镀层的成分、结构与表面形貌,并对Ni-石墨复合镀层的硬度、结合力、耐蚀性等性能进行测试。具体的研究内容与工作如下：(1)在水溶液中,研究超细石墨粉颗粒的团聚现象,超细石墨粉的等电点在pH=6.30左右,加入分散剂CMC后,等电点变化不大,但在pH为4.00～4.50范围内有较高的Zeta电位,分散比较稳定。同时,通过沉降实验,超声分散30分钟,从不同类型的分散剂中选择了分散效果较好的阴离子型分散剂CMC,合适用量为10%即CMC的用量为超细石墨粉的10%,得到分散效果较好的溶液；将分散剂CMC应用于镀液中,仍具有一定的分散效果,但略差于在水溶液中的情况,同时比较了分散剂对镀层表面形貌的影响,发现加入分散剂可以使超细石墨粉比较均匀的分散于整个镀层中。(2)通过单因素实验方法,研究了Ni-石墨复合电沉积的主要影响因素,即电流密度、镀液pH、搅拌转速、镀液温度、电沉积时间、石墨粉浓度以及主盐浓度,确定了工艺条件为：电流密度为8A/dm2、镀液pH为4.00、温度T为40℃、搅拌转速为200r/min.电沉积时间为10min。采用正交表L18(3’),研究得到了Ni-石墨复合电沉积最佳的工艺参数：300g/L主盐,5g/L NiCl2·6H20,35/L H3BO3,0.2/L表面活性剂,1gL糖精,0.4g/L 1,4-丁炔二醇,60g/LAN-1,20g/LAN-2,3g/L石墨粉,0.36g/L分散剂CMC。在最优工艺条件下所得的Ni-石墨复合镀层呈亚光色,SEM检测表明镀层中石墨粉比较均匀的分散于镀层中,镀层的显微硬度达到372.6HV,复合镀层中的主要元素为Ni85.03%(wt)、C14.86%(wt),石墨与Ni实现了共沉积。(3)采用扫描电镜(SEM)和XRD对Ni-石墨复合镀层的表面形貌与组分进行分析,结果表明,超细石墨粉与Ni实现共沉积形成Ni-石墨复合镀层。镀层中的石墨颗粒粒径均一,均匀弥散分布于整个镀层,强化镀层的微观组织结构,提高了镀层的显微硬度,通过测试镀层的显微硬度,发现Ni-石墨复合镀层的显微硬度高达372.6HV,明显高于纯镍层的175.2HV；在复合镀层XRD谱图中,2θ=27°出现了石墨的特征峰,这说明复合镀层中存在石墨成分；从Tafel曲线中可知,复合镀层在不同的介质中,其耐蚀性不同：在5%HCl和5%NaCl溶液中,其耐蚀性明显优于未加络合剂的,而在5%NaOH溶液中,其耐蚀性差于未加络合剂的。(4)为了了解Ni-石墨复合电沉积的电极过程,采用线性扫描伏安法、循环伏安法和交流阻抗谱技术对Ni-石墨复合的电沉积与镍的电沉积进行了对比性研究。结果表明,随着扫描速度的增大,Ni的析出电势向负方向偏移,阴极极化增强；在含有络合剂的复合镀液中,阴极极化曲线向负方向移动,同时析氢电位减小,抑制析氢反应的发生,提高了电流效率,而且相同电位下阴极电流密度减小,有利于镀层细化晶粒,提高镀层的耐蚀性能。通过循环伏安曲线,了解了镍及Ni-石墨的电化学成核机理,深入认识电沉积过程；从动电位极化曲线及交流阻抗试验,发现石墨粉明显改变了镀层的微观结构,镀层耐蚀性均有所提高,与纯镍层相比,Ni-石墨复合镀层在中性和酸性溶液中具有较好的耐蚀性,在碱性条件下其相对较差。更多还原

【Abstract】 With the development of high-tech industries and the higher requirement of electronic product, the LCD technology is widely used in various areas. However, the LCD materials which are used as LCD cutting tools in the processing and manufacturing process are still imperfect. Most of the cutting tools are obtained by means of electroforming. The electroformed nickel-diamond composite coating is of high hardness and well wear-resistance but poor binding force and cracked morphology which shortens the service life of LCD product. Given the high cost of diamond particles and the same element and similar structure with graphite, graphite particle is used to study the electrodeposition of Ni-graphite composite coating instead of diamond in this work. The dispersion of graphite particle in water and nickel electrolyte is systematically researched. Moreover, the preparation of composite electroplating bath and the influence of process parameters such as current density, bath pH, bath temperature, plating time and graphite concentration etc on the properties of Ni-graphite composite coating are researched in detail. Analysis of the mechanism of the distillation process with electrochemical workstations; X-ray diffraction(XRD) and SEM are used to analyze the structure and surface morphology of the composite coating. The microhardness, binding force, corrosion resistance of composite coating are tested. The main results are as follows:(1) The agglomeration of graphite particle in aqueous solution is studied. Results reveal that the Zeta potential of graphite is zero when the pH is about 6.30; with the addition of dispersant CMC, the Zeta potential changes very little but get higher when pH is about 4.00-4.50, and then the graphite particle disperses very well. Meanwhile, sedimentation experiment shows that CMC has the best dispersion effect among the used kinds of dispersants. The graphite particle has better dispersing ability by thirty-minute ultrasonic waves and adding CMC with the mass fraction of CMC to graphite is 10%. The dispersion of the graphite particle with CMC in nickel electrolyte is also discussed. Results show that it disperses well in nickel electrolyte but not better than in aqueous solution. Graphite particle distributes more uniformly throughout the composite coating with the addition of dispersant agent. (2) Effects of current density, bath pH, stirring speed, bath temperature, plating time, concentration of graphite and main salt are studied to obtain suitable process parameters by single-factor experiment. Results show that the optimum process parameters are as follows: current density 8A/dm2, pH 4.00, temperature 40℃, stirring speed 200 r/min, and deposition time 10min. And the optimum bath composition is as follows:nickel sulfaminate 300g/L, nickel chloride 5g/L, boric acid 35g/L, surfactant 0.2g/L, saccharin lg/L,1,4-butynediol 0.4g/L, AN-160g/L, AN-220g/L, graphite particle 3g/L and CMC 0.36g/L. The Ni-graphite composite coating is grayish white and graphite particle is uniformly distributed throughout the composite coating. The microhardness of the coating is up to 372.6HV, mass fractions of the main elements in the coating are as follows:Ni 85.03%, C 14.86%, it is demonstrated that graphite particle has been deposited with nickel.(3) The surface morphology and structure of Ni-graphite composite coating are characterized by Scanning Electron Microscopy (SEM) and XRD. It can be further confirmed that the graphite particle is embedded into the deposit to form the Ni-graphite composite coating. Graphite particle contained in the coating distributes evenly throughout the coating. The graphite particle that evenly dispersed in the coating can significantly intensify the microstructure of composite coating for the uniform diameter of particle. The micro-hardness of the Ni-graphite composite coating is 372.6 HV, higher than that of the pure nickel coating 175.2HV. XRD analysis indicates that characteristic absorption band appears at the 20 of 27°which belongs to the graphite; this is to say that graphite particle exists in the coating. Analysis of Tafel curves demonstrates that corrosion resistance of the coating prepared from bath containing complex agents is better than that prepared from bath without complex agents in the 5%NaCl and 5%HC1 solution, but worse in the 5%NaOH solution.(4) The electrochemical behavior of Ni-graphite composite electrodeposition are investigated by analyses of potentiodynamic polarization, cyclic voltammetry(CV) and electrochemical impedance spectroscopy(EIS) and compared with that of the nickel deposition. Results show that the potential of Ni shifts towards to negative side and the cathodic polarization increases with the increasing scanning speed. When the complex agents are added into composite electrolyte, cathodal polarization curve moves toward to the negative side, improving the current efficiency and reducing hydrogen evolution potential; furthermore, the coating has a more flat morphology and compact microstructure since the current density decreasing at the same potential, resulting in better corrosion resistance compared with that of pure nickel coating. The nucleation mechanisms of pure nickel and Ni-graphite composite electrodeposition are discussed by cyclic voltammetry. Results of polarization curves and impedance method reveal that corrosion resistance of composite coating is better than pure nickel coating both in neutral and acidic solution due to the presence of graphite particle, which not only make the metal matrix grains finer, but also improve corrosive potential.更多还原