Ni-SiC复合沉积电极过程动力学及镀层电化学腐蚀行为研究

【作者】 赵旭山；

【导师】 谭澄宇；

【作者基本信息】 中南大学 ， 材料学， 2008， 硕士

【摘要】 本课题主要对复合电沉积的机理进行了研究,特别是第二相粒子的引入对晶粒成核和生长机理的影响。应用扫描电镜,X-射线衍射,对SiC粉体的形貌、结构进行分析,借助精密pH计就SiC粉体在镀液中吸附特性进行了检测。在此基础上,利用CHI660C电化学工作站对纯镍体系、Ni-SiC复合体系和加入促进剂的复合体系电沉积过程进行了循环伏安、计时安培和交流阻抗谱测试。论文还就三类镀层在3.5%NaC1和3.5%NaCl+0.3%H₂O₂腐蚀体系中的电化学行为采用极化曲线、交流阻抗等电化学手段进行了监测分析。试验结果表明,SiC粉体呈不规则多边形,平均粒径约7μm,其晶型主要为6H即六方结构。SiC颗粒加入到Watts镀液中,将会吸附镀液中H⁺离子而使表面荷正电,在镀液pH为3.70左右,其吸附量最大。恒电位阶跃分析表明,复合沉积镍电结晶形核经历两相继过程,第一过程沉积伊始形核遵循BFT模型连续成核机制,而后随电位负移过渡到BFT瞬时成核机制,第二过程随电位负移先后吻合BFT瞬时成核或SH瞬时成核理论曲线;无论Ni-SiC复合镀层还是纯Ni镀层,形核弛豫时间t_m随负电位的增大,呈现规律性递减趋势,相应的L_m值基本相近;SiC粉体的引入导致Ni形核过电位正移和t_m的显著减小。交流阻抗表明,非法拉第电位区,SiC粉体的表面吸附（或附着）改变了电极表面的荷电状态,打破了内Helmholtz面大分子和水化离子对电极的屏蔽,大幅降低了复合体系的电荷传输电阻。而在临近及此后沉积电位区,纯镍表面双电层被击穿,复合体系SiC增大导纳的优势不复存在,表现为与纯镍体系阻抗相当。三类镀层在两种体系中呈现了不同的腐蚀规律,在3.5%NaCl体系中,纯镍镀层的耐腐蚀能力强于复合镀层;而在强氧化性介质中腐蚀规律发生了很大的变化,复合镀层的耐蚀性又高于纯镍镀层。SiC粉体在镀层中引入的大量的错综复杂的网状结构,造成表界面的电荷转移电阻R_t和蚀孔电阻R_L大幅增加,有效分散了腐蚀极化电流,阻碍了腐蚀的发生和发展。更多还原

【Abstract】 The electrodeposited mechanism was studied, especially the influence of SiC particles. The SEM and X-ray were performed in order to study the morphology and microstructure of the SiC powder. And the adsorption action of SiC particles in the solution was characterized by precision pH apparatus. On this condition, cyclic voltammetry （CV）, chronoamperometry （CA） and electrochemical impedance spectroscopy （EIS） at cathodic potentials were performed in the pure nickel system （PN）, Ni-SiC codeposition system （NS） and Ni-SiC codepositon system with accelerant （NSA）, all these experiments were tested by the CHI660C instrument. Furthermore, we also have studied the corrosion behaviors of these three types of coatings immersing in the 3.5%NaCl and 3.5%NaCl+0.3%H₂O₂ solution by Tafel plots and electrochemical impedance spectroscopy.The results show that SiC particles make for the polygon morphology, and the mean diameter is 7μm . From the X-ray reflection, we find most of the SiC particles have the 6H crystal structure. When these powders were added into the deposition solution, they would be packed by lots of H⁺ and Ni²⁺ or other ions. As a result, they will present negative potential. Under the pH value of 3.70, ions adsorpotion is most obviously.In order to make clear the nucleation and growth process, we performed the potentiostatic I-t transients tests for the above three kind of solution systems. The results show that, the electrocrystallization of nickel prefer to two step. In the initial of the first process, the codeposition of compound systems follow a 3-D progressive nucleation/growth mechanism of Bewick-Fleshmann-Thrisk model, along with the increase of negative potential, this process passes through a transformation between BFT progressive mechanism and BFT instanstaneous mechanism. The second stage, along with the increase of negative potential, the nucleation/growth process follow the BFT instanstaneous mechanism and SH instanstaneous mechanism successively. However, either Ni-SiC codeposition coatings or pure nickel coationgs, the nucleation relaxation time t_m decreases regularly with the increasing of the negative potential, while the corresponding current I_m were almost in the same quantity. Obviously, because of the addition of the SiC powders, the nucleation potential of nickel turns to positive direction. And the nucleation relaxation time t_m decreases clearly.The results of electrochemical impedance spectroscopy show that, outside the farady potential zone, the adsorption character of SiC powders will change the surface charge arrangement. It destroys the shield effects of hydrate and large molecules adsorpped on the working electrode surface, and decreases the transfer resistance largely. When the voltages near or exceed the electrodeposited potential, the double lays capacitance microstructure was dropped, the advantages of SiC were destroyed too. The impedance will as same as the pure nickel solution.In the 3.5%NaCl and 3.5%NaCl+0.3%H₂O₂ solution, these three types lays shows the different corrosion behaviors. In 3.5%NaCl solution, pure nickel coatings display a greater corrosion resistance value than codeposition coatings. However, in the strong oxidable solution, codeposition coatings obtain more protection than pure nickel coationg. A great deal of complex three dimension net structures were imported to layers. It causes a great increase of charge transfer resistance, seperates the corrosion current efficiently, and protects the matrix from destroyed environment.更多还原