The behavior of indium in dilute sodium tetraborate containing bromide ions in the presence of some ethoxylated surfactants

Abstract

The potentiometric technique was used to study the oxide film repair and destruction on indium electrodes in 0.01 M Na2B4O7 containing various amounts of Br- ions. Higher amounts of Br- ions, ≥5 × 10−2 M, reduces the oxide film growth and initiate the destruction of oxide film by inducing pitting corrosion. The initiation of pitting corrosion is raised with the addition of more concentrations of Br- ions and raising the temperature. Some freshly prepared ethoxylated surfactant molecules, ETO I, ETO II, and ETO III were utilized as inhibitors to resist the oxide film destruction and sustain the oxide film repair with the formation of a layer of surfactant molecules. The protection efficacy of such molecules is found to rely on the concentration of the surfactant besides the number of ethylene oxide monomers per molecule. The inhibition efficacy reaches 87.8 %, 83.1 %, and 79.5 % with ETO III, ETO II, and ETO I, successively, at 0.01 M inhibitor concentration and 25 ºC. The inhibition mechanism relies on an adsorption process obeying Langmuir's model. The thermodynamic adsorption functions. Viz, Kads, and ∆G°ads are computed and explained. The inhibition efficacy of such compounds decreases in the order, ETO III> ETO II> ETO I.