摘要
ZrO_2是一种耐高温、耐磨损、耐腐蚀的无机非金属材料，目前广泛地应用于电子陶瓷、功能陶瓷和结构陶瓷等高科技领域。化学镀是实现非金属材料表面金属化的一种重要手段，镀镍后进一步扩展其用途，使其在集成电路、电力电容器、压电陶瓷和装饰材料等方面得以应用。
本文用原子氢理论和电化学理论解释了化学镀镍的机理，系统介绍了化学镀镍溶液的组成及各组分的作用，讨论了影响化学镀镍溶液的稳定性因素，在此基础上成功地实现了在ZrO_2陶瓷表面化学镀镍。同时，对镀层进行了外观、结合力和耐蚀性测试，并用SEM、EDXA、X射线衍射和XPS等测试方法对镀层结构和成分进行了分析，结果表明：
镀层与基体结合力的好坏，关键是粗化处理的效果。高温烧结后的ZrO_2陶瓷的化学稳定性很高，除HF外不溶于任何酸碱，传统的粗化液对它没有粗化作用，笔者通过大量的实验，找到了ZrO_2陶瓷粗化液的配方，它能在ZrO_2表面腐蚀出大量均匀的微坑和凹槽。在化学镀镍的工艺中，研究了次亚磷酸钠和络合剂乳酸的浓度、pH值、稳定剂和温度等工艺参数等对沉积速度和镀镍层含磷量的影响，找出了合理的化学镀镍工艺：还原剂的浓度为25g／l～30g／l，络合剂乳酸的浓度为8ml／l～12ml／l，pH值的范围为4.6～4.9，选择(NH_4)_2MoO_4作稳定剂，温度为85℃左右。
从外观上观察，ZrO_2陶瓷表面的化学镀镍层光滑、致密、细腻、光泽度好，没有任何针孔、麻点、起皮、卷皮等现象发生。用不同的方法对镀层进行结合力和耐蚀性试验，结果表明其结合强度高，耐蚀性良好。通过对不同沉积时间的试样进行SEM、EDXA和X射线衍射分析，发现镍的沉积过程是：先是镍原子的沉积，再是P在镍催化作用下发生Ni与P的共沉积，形成晶核，随着溶液中的Ni、P的不断沉积，晶核长大成一个个的胞体，最后连成一片，成为排列紧密的胞状体结构。比较不同陶瓷基体镀镍后的表面形貌，发现基体表面状况也是影响镀镍层结构的重要因素，基体粗糙度越小，镀层的胞体结构越小，且越致密平整。化学镀镍的工艺参数也对镀镍层的结构也产生一定的影响，一般来说，镀速越快，胞体结构越大。X射线衍射表明，化学镀镍层的X射线衍线图谱为非晶的“馒头包”状的散漫峰，XPS分析结果显示镀层的表面成分与内部成分存在较大的差距，表面层存在镍、磷的氧化态，内部氧化态成分的镍、磷均降低，这说明了镀镍层耐蚀性好的原因是表面生成氧化保护膜的缘故。
ZrO2 is one of the inorganic nonmetallic materials which have excellent heat resistance, wear-resistance, corrosion resistance. At present, it is widely applied in Hi-Tech fields, such as electronic ceramics, function ceramics and structure ceramics, etc. Electroless plating is a kind of important means to realize surface metallization of nonmetallic materials. Through electroless nickel plating on ZrO2, it can apply in such aspects as integrated circuit, electric condenser, piezoelectric ceramic and ornament materials.
In this paper, the mechanism of electroless nickel plating is explained with atom hydrogen theory and electrochemical theory. The composition and the function of the electroless nickel plating solution and the factors that influences the stability of the plating solution are introduced. At this basis, Ni-P alloy coating was successfully plated on ZrO2 ceramic surface. The appearance, adhesion and corrosion resistance of the coating were tested .And the samples were detected and analysed by SEM, EDXA, X-ray diffraction and XPS.
The coarsened quality of ZrO2 ceramic will decide the cohesion between Ni-P coating and substrate. Heat sintered ZrO2 ceramic does not react with any acids and bases except HF. It can't be coarsened by the traditional pretreatment process. Through a great deal of experiments, author found a kind of coarsened prescription which can corrode ZrO2 ceramic, forming many holes and troughs on its surface. In order to obtain reasonable processing parameter of electroless nickel plating, the influences of the concentration of reductants NaH2PO2 and complex agents DL-lactic acid, stabilizers ,pH value and temperature on the deposition rate , the content of P and stability of the plating solution were studied. It was found that the concentration of both NaH2PO2 H20 varied from 25 g/1 to 30g/l, the concentration of DL-lactic acid varied from 8ml/l to 12 ml/1, pH value varied from 4.6 to 4.9, (NH4)2MoO4 was chose as stabilizers, and the reaction temperature was about 85℃
Observing the appearance of the Ni-P coating, you will find it is very smooth, homogeneous, compact and has metal luster without small hole, grey dot and curly skin. The results of adhesion and corrosion resistance experiment show that it can meet the requirement for use. The different samples which were deposited during different times were analyzed by SEM, EDXA and X-ray diffraction. The depositing process of electroless nickel plating is that nickel atoms first deposit, then the crystal nuclei emerge after phosphor and nickel co-deposit under nickel catalyzing, the crystal nucleus will grow up and become larger global particles with continual phosphor and nickel co-depositing, at end global particles will join together each other. By comparing surface morphologies of electroless Ni-P plating on different substrates, it was found that the substrate surface state influence the structure of global particles. Coarser the substrate is, larger the global particles are. Process parameters also influence on the structure of global particles. Generally, faster the depositing speed is, larger the global particles are. X-ray diffraction patterns of Ni-P coating look like steamed bread with amorphous structure characteristics. The oxidized nickel and phosphorous contents in surface are higher than in internal. It explains why the Ni-P coatings have stronger corrosion resistance.
引文
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