核—壳结构钴包碳化钨复合粉体的间歇电沉积制备研究

发布时间：2018-05-16 14:50

本文选题：钴包碳化钨粉体 + 间歇电沉积　；参考：《湖南大学》2016年硕士论文

【摘要】：间歇电沉积是一种新兴的合成金属-粉体复合材料的技术。在电沉积溶液中加入不溶性固体颗粒,通电时由于粉体颗粒覆盖在阴极表面,金属离子在向阴极移动的同时在粉体表面得到电子而还原成金属,形成具有优异性能的核-壳结构的金属包覆粉体复合材料。本文在间歇电沉积方式下,选取WC颗粒为内核,钴为金属外壳,在铌板基体上制备Co包WC复合粉体。主要研究了电流密度、表面活性剂、pH值等参数与粉体性能之间的关系,确定了电沉积Co包覆WC复合镀层的最佳工艺参数；利用光学显微镜、扫描电镜(Scanning Electron Microscopy)、能谱仪(Energy Dispersive Spectroscopy)和X射线衍射仪(X-ray diffraction)等手段对复合镀层的表面形貌、化学成分和相结构进行了观察和分析。结果表明,Co能够均匀地包覆在WC颗粒表面上,且结合紧密；复合镀层均为晶态结构。当镀液中沉积电流密度为16A·dm-2时,电沉积复合粉体的电流效率和钴含量均达到最大,分别为47.50%和89.81%,得到了包覆均匀的钴包碳化钨复合粉体。主要结果如下：(1)通过简单的混酸处理方法对WC粉体进行前处理,利用SEM观察前处理前后的WC粉体表面形貌,以EDS和XRD图对简单前处理过后电沉积的WC/Co复合粉体表征和分析,结果表明混酸是通过在WC表面形成阶梯状的缺陷来活化WC粉体的表面的。(2)利用电流效率、表面形貌复合粉体的钴含量、电沉积速率等结果来优化电沉积钴包碳化钨粉体的最佳电流密度、单次电沉积时间、pH值等工艺条件。pH值对WC粉体的钴的晶体结构有着极大的影响,保持镀液pH值为4-5时,能够得到沉积速率快,电流效率高,均匀分散的钴包碳化钨复合粉体。(3)利用恒电位暂态阶跃法研究在大电流密度下,钴在碳化钨上沉积的三维成核机理。(4)加入适当表面活性剂,吸附在阴极表面,能够改变钴的沉积电势,增大阴极表面极化。根据红外图谱,PEG-2000极易吸附于WC粉体表面,通过本身长链的空间位阻效应来得到均匀分散的钴包碳化钨复合粉体。
[Abstract]:Intermittent electrodeposition is a new technology for synthesizing metal-powder composites. An insoluble solid particle is added to the electrodeposition solution. When the powder particles are covered in the cathode surface, the metal ions are reduced to metal while moving toward the cathode and obtaining electrons on the powder surface. Metal coated powder composites with core-shell structure with excellent properties were formed. In this paper, Co-coated WC composite powder was prepared on niobium substrate with WC particles as core and cobalt as metal shell under intermittent electrodeposition. The relationship between the parameters such as current density, surfactant pH value and powder properties was studied. The optimum technological parameters of Co coated WC composite coating were determined. The surface morphology, chemical composition and phase structure of the composite coating were observed and analyzed by scanning electron microscope (SEM), scanning electron microscope (SEM) and scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that Co can be uniformly coated on the surface of WC particles and bonded tightly, and the composite coatings are of crystalline structure. When the deposition current density is 16A dm-2, the current efficiency and cobalt content of electrodeposited composite powders reach the maximum, which are 47.50% and 89.81%, respectively. The Co coated tungsten carbide composite powder with uniform coating is obtained. The main results are as follows: (1) WC powder was pretreated by simple mixed acid treatment. The surface morphology of WC powder before and after pretreatment was observed by SEM, and the electrodeposition of WC/Co composite powder after simple pretreatment was characterized and analyzed by EDS and XRD diagrams. The results show that the mixed acid activates the surface of WC powder by forming a step defect on the surface of WC. The optimum current density of cobalt coated tungsten carbide powder was optimized by the results of electrodeposition rate. The technological conditions such as single electrodeposition time and pH value had great influence on the crystal structure of cobalt in WC powder. When the pH value of plating solution was 4-5, The cobalt coated tungsten carbide composite powder with fast deposition rate, high current efficiency and uniform dispersion can be obtained. The three-dimension nucleation mechanism of cobalt deposited on tungsten carbide at high current density is studied by potentiostatic transient step method. Adsorption on the cathode surface can change the deposition potential of cobalt and increase the polarization of the cathode surface. According to the infrared spectra, PEG-2000 is easily adsorbed on the surface of WC powder. Through the steric resistance effect of its own long chain, the uniformly dispersed cobalt coated tungsten carbide composite powder can be obtained.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TB383.3

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