化学镀镍-高磷合金晶化行为的现场XRD研究

In situ XRD Investigation on the Crystallization Behaviors of Electroless High-Phosphorous Ni-P Alloys

从柠檬酸-酒石酸-乳酸-EDTA混合体系中得到含P12%(质量比)的化学镀高磷Ni-P合金,其差热曲线显示,在350和420℃出现两个放热过程.现场XRD分析结果显示,镀层在300℃以下保持非晶态结构,在320℃之后开始晶化,首先析出介稳的Ni5P2和Ni12P5相,在360℃后开始有稳定的Ni3P和Ni相的衍射峰出现,400℃以上只有Ni3P和Ni相.325℃恒温时,镀层在4min内保持非晶态的衍射特征,随即析出Ni5P2和Ni12P5相,并在2h内基本保持不变.350℃恒温时,析出的Ni5P2和Ni12P5介稳相只存在40min.实验结果表明,DTA曲线上350℃的放热峰不仅有非晶相转变为介稳相的过程,也包含部分介稳相转化为稳定相的过程.

Crystallization behaviors of electroless Ni-P deposits with 12% (w) P were studied by differential thermal analysis(DTA), thermogravimetry(TG) and in situ X-ray diffraction (XRD). The Ni-P alloys were prepared from a bath containing NiSO4 28 g.L-1, NaH2PO2.3H(2)O 32 g.L-1, C6H8O7.H2O 16 g.L-1, EDTA [CH2N(CH2COOH)(2)](2) 7 g.L-1, C4H4O6 6 g.L-1, NaAc 18 g.L-1, C3H6O3 6 g.L-1, KIO3 0.001 g.L-1, with pH 4.5similar to5.0, at 90degreesC. The DTA curves of the alloys indicate that there were two exothermic processes at 350 and 420degreesC, respectively, which could be related to, the processes of phases change of the alloys as the mass change is less than +/-1% as revealed by the TG curves. The results of in situ XRD show that the structure of the alloy is amorphous when the temperature bellows 300degreesC. The XRD pattern of metastable Ni5P2 and Ni12P phases initially appeared at the temperature over 320degreesC, and disappeared completely at 400degreesC. The XRD peaks belonging to Ni3P and Ni stable phases emerged at 360degreesC. The metastable Ni5P2 and Ni12P5 remained during the testing period of 2 h at 325degreesC, and lasted just for 40 min at 350degreesC before transferring into the stable phases of Ni3P and Ni. According to the results, the exothermic peak of the DTA curves for the deposits at 350degreesC should result from the two processes, i.e., the amorphous Ni-P alloys crystallized into metastable Ni5P2 and Ni12P5 phases, and then the metastable phases partially turned into the stable phases of Ni3P and Ni.