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

The critical pitting potentials of tungsten were determined in 0.5 M LiCl ‐ X M H 2 O ‐ 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 H 2 O, 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 H 2 O, 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–H 2 O‐methanol solutions given in the literature. A mechanism for chloride ion attack of the film involving the formation of WO 2 Cl 2 is proposed.