| Popis: |
The induced deposition of W in the presence or iron-group metals has been known for a long time without a proper understanding of the mechanism of the codepostion. Hints were made by several authors, concerning primarily a similar case of codeposition of Mo, which were not sufficiently substantiated by proper kinetic investigations, as the research was oriented mainly toward practical aims. In the present investigation the induced deposition of W with Ni was studied primarily from the viewpoint of the composition and phase structure of the resulting NiW alloy. The method of anodic linear sweep voltammetry was used to analyze the deposits obtained at a rotating disc electrode, as this has proved to be a good tool for the analysis of thin-layer deposits. The polarization diagram was found to exhibit a sharp current maximum and a subsequent decay at potentials at which Ni deposition starts. As some W oxide was found to deposit at less negative potential, the sharp rise of current and the maximum are acribed to the catalytic effect of the oxide on hydrogen evolution, larger than that of the depositing NiW alloy. The deposit was found to exhibit two peaks upon anodic dissolution, both at significantly more positive potentials than that of Ni dissolution. The first peak is of a limited quantity of electricity, independent on the amount of the deposit which is reflected in the second peak only. An aging effect was found, rendering an alloy requiring much more positive potentials for dissolution than those for dissolution of freshly deposited alloys. |
