镍磷化学镀层的耐蚀性及其与磷含量的关系

用极化曲线法和交流阻抗法研究了磷含量为16.2%至23.4% (x)的不同镍磷(Ni-P)化学镀层在5%(w) NaCl溶液中的耐蚀性, 发现磷含量为21%～22% (x)时镀层的极化阻抗(Rp)出现极大值. 差示扫描量热测定也发现Ni-P合金的峰值晶化温度(Tp)在此P含量范围内存在极大值. XRD实验表明镀层呈非晶态结构. 利用描述非晶态的菱面体单元结构模型(RUSM)解释耐蚀性能和峰值晶化温度的极大值现象, 耐蚀性随P含量的变化与镀层中金属元素(Ni)和类金属元素(P)之间形成的键数有关. 通过比较镀层密度的测量值和基于RUSM的计算值, 证明了采用RUSM的合理性.

Corrosion Resistance of Electroless Ni-P Deposits and Its Relation to P Contents

By measuring polarization curves and alternating-current impedances, the corrosion resistance of electroless Ni-P deposits with P contents from 16.2% to 23.4%(x) was investigated in 5% (w) NaCl solution. It was found that there was a maximum of polarization resistance (Rp) when the P content was at 21%～22%(x) and the peak temperature of crystallization(Tp) of electroless Ni-P alloys, determinated by differential scanning calorimetry (DSC), also showed a maximum at such a P content. X-ray diffraction (XRD) experiments indicated that the electroless Ni-P deposits were amorphous. The maxima for both polarization resistance (Rp) and the peak temperature of crystallization(Tp) were explained in terms of the rhomb unit structure model (RUSM) for amorphous structures. The corrosion resistance of electroless Ni-P deposits was related to the changes of the bond numbers formed between metal (Ni) and metalloid element (P) with the P contents. The rationalization to adopt RUSM was also discussed by comparing the measured and theoretically calculated densities for electroless Ni-P deposits with various P contents.