Production of electrolytic nickel composite layers containing titanium
Andrzej Serek, Antoni Budniok Uniwersytet Śląski, Instytut Fizyki i Chemii Metali, ul. Bankowa 12, 40-007 Katowice
Annals 2 No. 3, 2002 pages 63-67
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abstract Electrolytic nickel layers are typified by good corrosion resistance and electrochemical activity in the processes of cathodic hydrogen evolution and anodic oxygen evolution. In order to improve of utilizable properties of the nickel layers, the coatings were co-deposited from baths containing metal oxides (TiO2, Sc2O3 NiO), carbide, nitrides or PTFE. Incorporating into a metallic matrix of metal of composite component in powder form and its embedding into the matrix structure follows us to obtain a new kind of composite material. Therefore, the present study was undertaken in order to obtain the galvanic composite layers on a nickel matrix containing embedded titanium grains. Composite Ni+Ti and Ni-P+Ti layers were prepared by simultaneous electrodeposition of nickel and titanium on a steel substrate from a Watts bath in which 4, 12, 20, 28 and 40 g/dm3 of Ti powder were suspended. The electrodeposition was carried out under galvanostatic conditions at a temperature of 343 K and current density of jD = 0.1 A/cm2 for 0.5 h. The phase composition of the layers was investigated by the X-ray diffraction method (Fig. 1). It was found that the phase structure of obtained layers depends on phosphorous content in the layer only. The surface morphology of the coatings was examined by means of a stereoscopic microscope with a morphometric computer system (Fig. 2). It was ascertained that obtained layers are of mat, rough metallic surface with a visible titanium grains of embedded Ti powder. The surface of Ni+Ti layers are comparatively homogenous that point out an uniform distribution of Ti grains in the layer. Atomic absorption spectroscope was used for chemical characterization of the layers. The influence of titanium powder content in an electroplating bath on the chemical composite of Ni+Ti and Ni-P+Ti layers was examined (Fig. 3). In the layers of Ni+Ti a linear increase of Ti content in the layer from 9% to about 25% was observed. In the layers of Ni-P+Ti a linear increase of Ti content in the layer from 5% to about 17% was observed. Chemical and phase analysis of the Ni+Ti and Ni-P+Ti layers confirms the co-deposition of Ni and Ti, and the formation of a homogeneous materials. It was also ascertained that the increase of titanium powder amount in the bath causes the rise in Ti content embedded into the composite layers. The presence of NaH2PO2 in the basic bath reduces Ti content in the layers. Mass increase of the deposited layers depends on the amount of titanium powder in the bath and points out on nickel adsorption effects (Fig. 4). Using the microscopic method the thickness of the layers from cross-sections was evaluated (Fig. 5). The thickness of composite layers increase linearly with the increasing of Ti content in the bath (Fig. 6). It is equal 290 and 170 micrometers for Ni+Ti and Ni-P+Ti layers respectively. As conclusions it was state that the Ni+Ti and Ni-P+Ti obtained layers exhibit the composite structure based on a nickel matrix. Those layers are typified by the crystalline or amorphous Ni-P system containing embedded crystalline titanium phase. The percentage increase of Ti content and Ni content decrease in the layers were observed along with the increase of Ti powder amount in the bath. It was assumed that mechanism of Ti embedding into the layer based on the adsorption phenomena and migration of the charged suspension micelles towards the cathode. The result of that process is possibility to obtain considerable thickness and good adhesivity of those composite layers