Electrochemical behaviour of molybdenum electrodes in various aqueous and buffered solutions and their use in titrations

Abstract

Electrochemical behaviour of molybdenum electrodes in various aqueous and buffered solutions and their use in titrations T he open circuit potential of Mo electrodes has been followed as a function of time in H. A. EL SHAYEB various aqueous solutions until steady state values E st were obtained. T hese varied with the F. M. ABD EL WAHAB logarithm of the molar concentration C as E st =a+b log C. T he rate of oxide film thicken-E. A. ABD EL MEGUID ing was determined from the linear relationship between the open circuit potential of Mo E and the logarithm of immersion time t as E=a 1 +b 1 log t. A plot of the final steady state potential of Mo as a function of the pH of buVered solutions fits the linear relationship E st =a 2 −b 2pH. T he oxide film formed on Mo provides the opportunity to use the metalmetal oxide as an indicator electrode for potentiometric acid-base and precipitation titrations. In the case of redox titrations, the Mo electrode could not be used successfully on its own, but when coupled with platinum as a bimetallic pair electrode, excellent results were obtained when used as an indicator electrode for oxidation-reduction reactions.

Kinetics of oxide film growth on cobalt in neutral aqueous solutions

“…The open circuit potential of the Co electrode was found to vary with the logarithm of the immersion time t until reaching the steady state values, according to 12,14,16,17 (Fig. 4), b 1 increases with an increase in anion concentration.…”

“…3a, 3b and 4, and the like, the rate of oxide film thickening d, on Co surface in solutions of the different anions studied have been calculated. 12,14,16,17 In Table 1, the values of the rate of oxide film thickening on Co surface, in solutions of Cl 2 , Br 2 , SO 22 4 , NO From the data in Table 1, two different types of behaviour can be recognised. Thus, in solutions of the first five anions, irrespective of the anion type, the rate of oxide film growth decreases gradually with increasing solutions concentration.…”

Kinetics of oxide film growth and destruction on iron surface in carbonate solutions

“…As can be seen from the curves of Fig. 1b, E varies linearly with the logarithm of the time of immersion, where t is in minutes, in all the solution concentrations, according to [20][21][22] E~a 1 zb 1 log t…”

“…The thickness of the passivating oxide film depends primarily on the type and concentration of the anions present in the solution, [1][2][3] the time at which the metal is held in solution 4 and the presence of foreign ions. [2][3][4][5][6][7][8] Owing to the extensive use of iron and steel in CO 2 containing environments, such as sweet oil and gas fields, many studies have been carried out in HCO 3 2 and CO 3 22 solutions free from and containing various aggressive anions. [9][10][11][12][13][14][15][16] Since most of these studies made use of accelerated polarisation techniques which are not, however, in line with the natural corrosion conditions, one objective of the present work is to follow up the behaviour of iron in carbonate containing solutions by measuring the open circuit potential of the metal as a function of the immersion time and solution concentration.…”

“…. The ennobling of the Fe electrode potential when immersed in strongly oxygenated solutions of CO 3 22 denotes that the preimmersion air formed oxide film carried by the metal surface is not sufficient to impart passivity in this environment. 17 Thus, further thickening of the oxide film continues until steady state is reached.…”