Electrochemical dissolution of simulated "white inclusions". Kinetics and material balance for Mo, Re, Ru metals and their alloys during electrochemical dissolution in nitric acid

Abstract

Abstract The kinetics of pure Mo, Re and Ru metals, as well as their alloys 52.5at. Mo – 47.5at. Re and 90at. Mo – 10at. Ru electrochemical dissolution during potential controlled electrolysis at a temperature T=25 °C in 0.5–6.0M HNO3 solutions were studied. The dissolution kinetics for all metal and alloy electrodes under study were found to be of zero order vs. metal concentration in the electrolyte. Rate constants for Mo electrochemical dissolution increased from 1.68×10-3 to 5.99×10-3mol cm-2h-1 with the growth of HNO3 concentration in the electrolyte from 0.5 to 4.0M. Further increase of the acid concentration in the solution to 6.0M did not result in the acceleration of Mo electrochemical dissolution. Rate constants of Re and Ru metals electrochemical dissolution increased monotonously from 4.27×10-4 to 1.7×10-3mol cm-2 h-1 for Re and from 1.28×10-4 to 1.61×10-3mol cm-2 h-1 for Ru with the rise of HNO3 concentration from 0.5 to 6.0M. Dissolution of Mo-Re and Mo-Ru alloys was congruent. With the increase of HNO3 concentration in the electrolyte from 0.5 to 6.0M, the dissolution rate constant of Mo-Re alloy was increasing from 1.33 to 7.60×10-3mol(Mo+Re)cm-2h-1. Maximum rates of Mo-Ru alloy electrochemical dissolution from 2.21×10-3 to 3.28×10-3mol(Mo+Ru)cm-2 h-1 were observed in 2.0–4.0M HNO3 at the electrolysis potential E=1.6V/SCE. The main electrochemical and chemical processes occurring at the metal and alloy electrodes and resulting in the metals dissolution are pointed out.