Electrolytical obtaining and characterization of composite layers Ni-P+W and Ni-P+NiO+W in an alkaline environment
Magdalena Popczyk, Antoni Budniok Uniwersytet Śląski, Instytut Fizyki i Chemii Metali, ul. Bankowa 12, 40-007 Katowice
Annals 3 No. 6, 2003 pages 17-22
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abstract Electrodeposited Ni-P+W and Ni-P+NiO+W composite layers were obtained in the galvanostatic conditions at the current density jdep = 0.200 A • cm−2 with the following electrolyte: 28 g • dm−3 NiSO4 • 7H2O, 32 g • dm−3 NaH2PO2 • H2O, 5 g • dm−3 NH4Cl, 9 g • dm−3 H3BO3, 8 g • dm−3 CH3COONa, 29 g • dm−3 C6H5O7Na3 • 2H2O + 40 g • dm−3 powder of W (Ni-P+W) and + 100 g • dm−3 powder of NiO (Ni-P+NiO+W). For comparision the Ni-P layer was also obtained and investigated in the same manner. Reagents of analytical purity and distilled water were used for preparation of electrolytes. The phase composition of the layers was performed using a Philips diffractometer and the chemical composition - by the atomic absorption method using a Perkin- Elmer spectrometer. Stereoscopic and scanning microscope, and X-ray microanalyser were used for surface characterisation of the layers. Electrochemical corrosion investigations were carried out in the 5 M KOH, using voltammetry method. All Ni-P, Ni-P+W and Ni-P+NiO+W layers, show good adhesion to the substrate. In contradistinction from smooth Ni-P layer, Ni-P+W and Ni-P+NiO+W composite layers to characterize of a mat and rough surface, with visible grains of embedded powder. The surfaces of Ni-P+W and Ni-P+NiO+W composite layers are more developed in comparision to Ni-P layer, with proportionate of distribution grains of nickel oxide and tungsten (Fig. 1A). Changes of surface morphology of the layers after corrosion resistance researches to show considerably of corrosion in 5M KOH. Particularly, this is visible in the case of Ni-P layer (Fig. 1B). Surface and linear analysis of distribution of nickel and tungsten in the Ni-P+W and Ni-P+NiO+W composite layers, show o local differentiation of chemical composition of the elements. In the places, where to observe a minimum of capacity of nickel, to observe maximum of capacity of tungsten and inversely (Figs. 2, 3). On the base of carry corrosion resistance researches it was found, that Ni-P+W and Ni-P+NiO+W composite layers are more resistible on aggressive activity an alkaline environment in comparison to the Ni-P layer. The most resistible on corrosion is Ni-P+W composite layer. Results of this with least value of corrosion current and rate, and greatest value of corrosion potential and polarization resistance (Tab. 1). The reason of this is probably presence of tungsten as composite component, which to cause large development real surface of this layer. Key words: amorphous nickel matrix, tungsten, nickel oxide, composite layers, corrosion resistance