Critical Pitting Potentials of Tungsten in lithium chloride‐methanol‐water solutions

Abstract

The critical pitting potentials of tungsten were determined in 0.5 M LiCl ‐ X M H2O ‐ methanol solutions where X ranged from 0 to 55. They were obtained from potentiostatic current time curves measured by two different methods: (1) The potential of the electrode in solution was brought to the desired value at a definite rate of potential change (2) Dry electrodes were immersed into the solution under applied potential. At water concentrations up to 11. M the cpp's obtained by (1) and (2) are less than 2 V vs Ag/AgCl/0.5 M LiCl(aq). The cpp's obtained by method (1) are 52 V, 62 V (maximum value) and 33 V for solutions having 14. M, 28. M and 55. M H2O, respectively. The cpp's obtained by method (2) are about as half as large as those of (1) with the exception of the values for 14. M and 17. M H2O, which are about 4/5 as large. The shape of the cpp‐water concentration curve is similar to that of the viscosity‐concentration curve of 1 M LiCl–H2O‐methanol solutions given in the literature. A mechanism for chloride ion attack of the film involving the formation of WO2Cl2 is proposed.

Effect of Sulfuric Acid on Corrosion and Passivation of 316 SS in Organic Solution

“…The corrosion performance of metals (Fe, Ni, Zn, Ta, W etc.) and Ti alloys in methanol solutions has been studied extensively by many researchers, [6][7][8][9][10][11][12][13][14][15][16][17][18] which is broadly based on the effect of water concentration on corrosion, passivation and pitting processes. According to these investigations, the materials exhibit enhanced corrosion resistance in presence of water in the methanolic solution; and the minimum water content required for passivation is dependent on the type of material.…”