Schiff bases of ethylenediamine/triethylenetetramine with benzaldehyde/cinnamic aldehyde/salicylaldehyde as corrosion inhibitors of zinc in sulphuric acid

Purpose A survey of technical literature indicates that there is a shortage of excellent corrosion inhibitors for zinc in non‐oxidizing acids, particularly sulphuric acid. This paper aims to describe the behaviour of ethylenediamine‐N‐N′‐dibenzylidene, ethylenediamine‐N‐N′‐disalicylidene, ethylenediamine‐N‐N′‐dicinnamylidene, triethylenetetramine tribenzylidene and triethylenetetramine trisalicylidene as corrosion inhibitors for zinc in sulphuric acid solutions. The objective of this research work also is to have an insight into the action mechanism of these inhibitors. Design/methodology/approach The effect of the various parameters affecting the action of the above‐mentioned corrosion inhibitors has been studied using weight‐loss data and polarisation measurements. Adsorption data also were utilized. Findings The inhibitors showed excellent corrosion inhibition (>99 per cent) at effective inhibitor concentrations. The two salicylidenes were better corrosion inhibitors than were corresponding benzylidenes. It appeared from this study that an efficient inhibitor is characterised by a relatively greater decrease in free energy of adsorption, lower entropy of adsorption and relatively lower heat of adsorption. Basically, these inhibitors were cathodic, as was revealed by polarisation data, and the inhibitors followed Langmuir adsorption isotherm behaviour. In general, the conjoint action of the inhibitor and the cathodic current was synergistic. Research limitations/implications Powerful Schiff bases still need to be synthesized so as to be effective at extremely low concentrations. The behaviour with other metals and alloys in diverse media also requires to be investigated. Originality/value Very few inhibitors demonstrate such excellent corrosion inhibition of zinc in aggressive corrosive media. Such detailed investigations on corrosion inhibitors are unusual.