不同荷电类型表面活性剂对WC-10Ni粉体表面化学镀镍包覆影响和机制

Effect of Surfactants with Different Charge Types on Electroless Nickel Deposition on WC-10Ni Powders and Its Mechanism

采用金属层包覆硬质合金喷涂粉体是抑制热喷涂粉体中碳化物硬质相脱碳、提高沉积粒子浸润性、减少涂层孔隙缺陷的一种有效手段,然而如何获得连续致密且厚度可控的金属包覆层仍缺乏系统研究。对比研究阳离子型十六烷基三甲基溴化铵(CTAB)和溴代十六烷基吡啶(HPB)、非离子型Triton X-100以及阴离子型十二烷基磺酸钠(SDS)等三种荷电类型表面活性剂对WC-10Ni粉体表面化学镀镍包覆层形成的影响作用。采用场发射扫描电子显微镜(FE-SEM)和能谱仪(EDS)对镀镍前后WC-10Ni粉体的表面形貌和元素分布进行表征,基于EDS元素分布图像的统计方法定量评价粉体表面镍包覆层的完整性和均匀性;分析三类表面活性剂对WC-10Ni粉体表面化学镀镍的固-液界面吸附行为、粉体表面电荷状态及其对Ni^(2+)还原过程的影响。研究结果表明,适当浓度的阴离子型表面活性剂SDS或非离子型表面活性剂Triton X-100改善了WC-10Ni粉体表面镀层的完整性和均匀性,而阳离子型CTAB和HPB则阻碍Ni^(2+)的迁移、吸附和金属Ni的形核和生长,不利于WC-10Ni粉体表面Ni层的均匀沉积。在较低的沉积温度下,Ni层的沉积速度与沉积均匀性之间达到平衡,进一步促进了WC-10Ni粉体表面完整均匀Ni层的形成。

It is recently recognized that coating of a stable metallic layer onto cemented carbides powders for thermal spray processes is a potential method to effectively suppress decarburizing of the powders and improve wettability between the splats toward a defect-free coatings.There is still lack of systematic study on how to achieve a continuous,dense and thickness controllable metallic layer on the powders.Effect of three types of surfactants,cationic CTAB(Cetyltrimethyl ammonium bromide)and HPB(Hexadecyltrimethylammonium bromide),non-ionic Triton X-100 and anionic SDS(Sodium laurylsulfonate)are comparatively investigated during electroless deposition of nickel layer on WC-10Ni powders at various process temperatures.The surface morphology and the elemental distribution of Ni-coated WC-10Ni powders are characterized with field emission scanning electron microscopy(FESEM)and energy dispersive spectroscopy(EDS),respectively.A statistical method based on EDS elemental mapping images is employed to quantify the overall nickel coverage ratio of the powders for a comprehensively quantitative evaluation of the integrity and homogeneity of the deposited nickel layers.The underlying influential mechanism of the various types of surfactants is discussed concerning the corresponding solid/liquid interface adsorption,powder surface charge state and its role in affecting Ni^(2+) reduction.The results indicate that anionic SDS and non-ionic Triton X-100 at a suitable,low concentration can improve the homogeneity and integrity of deposited nickel layers on the WC-10Ni powders,whereas cationic CTAB and HPB deteriorate the integrity and homogeneity of the deposited nickel layers by hindering the migration,adsorption as well as the reduction of nickel ions.Furthermore,low deposition temperature is beneficial to homogenous nickel layer formation on the powders due to relatively good balance between nucleation and growth rates of the nickel layer.