Estudo dos parâmetros operacionais e de composição para o enriquecimento de tungstênio na liga Ni-W.

Abstract

The electroplating of metal alloys is a more sophisticated process than that of pure metals, therefore, requires a further refinement of the operational parameters to obtaining it. In the codeposition of alloys, the characteristics of the constituents are united to obtain better quality deposits. The excellent properties physical and chemical properties of tungsten added to nickel contribute to the increase in the nobility of Ni-W alloys. The solutions used to obtain deposits were prepared with distilled and deionized water, using high-quality reagents analytical purity. As complexing agents, tartrate and oxalate were used associated sodium The operational and composition parameters were evaluated for the enrichment of tungsten in the Ni-W alloy. The pH of the solution was adjusted to three values ​​studied in this work: 7, 5 and 3. Sulfuric acid was added to promote the solubilization of reagents and to evaluate the influence of pH on chemical composition of the alloy. It was observed that the proportion between the metals Ni and W vary according to the decrease in the pH value of the electrolyte solution. Being the pH the only variable in the electrodeposition process, it is noted that the decrease in even favors the increase in the mass percentage proportion of tungsten in the obtained deposit. The heat-treated alloy at a temperature of 600 BC an inversion in the mass percentage ratio between Ni and W, this fact can be explained by the possible migration of nickel to the copper substrate in this temperature. A considerable increase in alloy hardness was noted when subjected to the treatment of 600 BC. The results obtained from the polarization, obtained in 0.1 M NaCl medium, demonstrate the characteristics of corrosion resistance of the studied alloys. An increase in the potential is observed corrosion with decreasing pH, and consequently an increase in polarization resistance. This behavior is associated with a higher content of W in the alloy obtained in the lowest studied pH value.