材料期刊网

利用多孔结构的表面活性, 采用以硫酸镍(NiSO₄?7H₂O)为主盐, 次亚磷酸钠(NaH₂PO₂?H₂O)为还原剂且无其它特殊组分的常用化学镀Ni溶液, 经无敏化活化预处理直接在微弧氧化形成的多孔MgO薄膜表面制备出化学镀Ni层, 并对Ni层的相组成、显微结构、导电性和耐蚀性进行了表征. 结果表明: 平均厚度约5 μm的化学镀Ni层颗粒均匀, 组织致密; Ni层进入MgO薄膜的孔洞, 形成交错咬合状态. XRD分析表明, Ni层由晶态Ni与非晶态Ni--P组成. 四探针和极化曲线测试结果说明 Ni层的导电性良好, 同时由于Ni层的存在, 试样的腐蚀电位显著提高. 化学镀Ni过程中, 溶液中的Ni²⁺在还原剂离子的作用下首先在多孔MgO薄膜的微孔处还原沉积生成微小的初生Ni颗粒, 初生Ni颗粒进而长大并扩展, 最终形成完整的化学镀Ni层. 多孔结构以其特有的活化作用实现了氧化物表面无敏化活化预处理的化学镀.

Generally, the surface pretreatments such as sensitization and activation are necessary for depositing a nickel metal layer on oxide surface by electroless plating, however, for an oxide surface with porous structure it is possible that the pretreatment is not necessary. In this paper, only by use of the surface activity of porous structure, an electroless plated nickel layer can be prepared on the surface of microarc-oxidation-fabricated porous magnesium oxide film in a conventional electroless nickel plating solution, consisted of nickel sulfate as main salt and sodium hypophosphite as reducing agent. Furthermore, the phase, microstructure, electrical conductivity and corrosion resistance of the obtained nickel layer were characterized. The results indicate that the 5 μm-thick nickel layer is composed of fine and homogeneously distributed nickel particles, at the same time the microstructure of nickel layer is dense. Nickel layer spreads into the micropores on the surface of porous magnesium oxide film, so that an interleaving interface is formed at nickel/oxide interface. XRD results reveal that the nickel layer contains crystalline Ni and amorphous Ni-P. Four-point probe measurement indicates that the nickel layer exhibits well electrical conductivity. Meanwhile, polarization curve reveals that corrosion potential elevates notably due to the presence of nickel layer. During electroless nickel plating the nickel ions in solution were reduced and deposited in the micropores of porous magnesium oxide film under the action of reducing agent ions, so as to generate tiny primary nickel particles, subsequently, these primary nickel particles continuously grew and spread, and finally formed an entire nickel layer on oxide surface.