化学镀镍过程中丙酸作用的机理研究

利用循环伏安法和红外漫反射光谱法研究化学镀镍过程中丙酸的作用机理. 不同丙酸浓度下的循环伏安曲线表明,丙酸能同时促进Ni^2＋的还原和H₂PO^-₂的氧化.根据丙酸分别与NaH₂PO₂和NiSO₄共存时镍基体上吸附物的红外漫反射光谱变化,推断丙酸是通过与NaH₂PO₂和Ni^2＋形成表面络合物来促进化学沉积的. 丙酸能与NaH₂PO₂形成分子间氢键,促使P-H键断裂并生成·PHO^-₂中间物,从而提高H₂PO^-₂的氧化速度; 同时,丙酸以其-OCO-官能团与Ni^2＋生成桥式配合物,有利于加速Ni^2＋的沉积. H₂PO^-₂氧化速度的提高有助于磷的沉积,从而增大了化学镀层中的磷含量.

Mechanistic Studies on Mechanism of Propionic Acid Action in Elecroless Nickel Plating

Propionic acid as an additive in electroless nickel plating will accelerate chemical deposition and raise P contents in the deposits.  In this work, the action mechanism of propionic acid in the electroless plating were studied by cyclic voltammetry and infrared reflection spectroscopy.  The voltammetric curves at various concentrations of propionic acid indicate that propionic acid will promote both cathodic Ni2＋ reduction and anodic NaH2PO2 oxidation.  According to the differences between the infrared reflection spectra of adsorbed propionic acid on Ni substrates and that of the adsorbed species when propionic acid co-exists with NaH2PO2 or NiSO4, it was proposed that the acceleration of chemical deposition was attributed to the formation of surface complexes of  propionic acid with NaH2PO2 and NiSO4,respectively.  Propionic acid could form intermolecular hydrogen bonds with NaH2PO2, which promotes splitting of P-H bond in the reductant and producing  PHO-2 intermediates, hence facilitates the oxidation of NaH2PO2.  At the same time, propionic acid is coordinated with Ni2＋ via   its  —OCO— group to form bridge complexes so as to promote NiSO4 reduction.  The accelerating oxidation of NaH2PO2 in turn helps the deposition of P, as a result, P contents in the deposits increase with accelerating NaH2PO2 oxidation.