Cashew Nut Testa Tannin: Assessing its Effects on the Corrosion of Aluminium in HCl

Abstract

Cashew nut testa tannin [CASTAN] has been found to inhibit the corrosion of aluminium in hydrochloric acid solutions using gravimetric, thermometric and UV/visible spectrophotometric techniques. CASTAN inhibition was by adsorption on aluminium following Temkin isotherm in 0.1 M HCl and Langmuir isotherm in 0.5 M and 2.0 M HCl at 303 Kelvin. Physical adsorption on aluminium has been proposed in studied HCl solutions; therefore, CASTAN is a cathodic inhibitor. Earlier reports [1] showed CASTAN to contain quercetin, azaleatin, catechin, epicatechin, cyanidin and delphinidin. However, UV/visible spectrophotometric analysis of CASTAN in ethanol reveals quercetin as its major component. This work therefore investigated the correlation between computed molecular parameters and inhibitive properties of CASTAN and adsorption sites on its components. Calculated quantum chemical parameters namely: E HOMO (highest occupied molecular orbital energy), E LUMO (lowest unoccupied molecular orbital energy), energy gap (∆E) and dipole moment ( µ ) suggest that CASTAN is a soft inhibitor and it's components inhibited aluminium corrosion in protonated forms. Calculated Mulliken charges implicated some electron rich sites, namely: the aromatic and conjugated C=C, C=O and O-H as adsorption sites on the inhibitor molecules. Proposed kinetic model reveals complex reaction mechanism, parallel reactions, for aluminium corrosion inhibition by CASTAN.

Green corrosion inhibitors for aluminium and its alloys: a review

“…43 The inhibition effectiveness of all studied extracts increased with increasing concentration, independently of their type, corrosive environment, or material. However, Nnaji et al 44 Arora et al, 46 Li and Deng, 47 Chauhan et al, 48 and Jain et al 49 investigated the inhibition effectiveness of extracts as a function of the corrosive environment. Arora et al 46 tested the extracts of Capparis decidua fruits, stem bark, and root bark in ethyl alcohol as inhibitor in the corrosion of aluminium in 0.5-5.0 N HCl and 0.5-5.0 N H 2 SO 4 solutions, at room temperature.…”

“…The extracts tested as corrosion inhibitors were obtained from different parts of the plants, including leaves, 41,43,45,[47][48][49][50][51][52][53][54][55][56][57] stem and root bark, 42,46,49 fruits 45,46,54,58 and fruit peel, 59 seeds, 48,49,57 owers, 60 husks, 61 and nuts. 44 Wan Nik et al 39 gave no clear indication as to which part of Lawsonia inermis was selected to prepare the extract. The distribution of active compounds in different parts of plants, such as such as leaves, stems, roots, and fruit, shows qualitative and quantitative variations.…”

“…Furthermore, no clear distinction as to the inhibition performance of ethanolic extracts of Cola acuminate leaves and fruits was reported by Loto and Popoola. 45 The inhibition effectiveness of the tested extracts was investigated in a temperature range from 20 C to 60 C. [40][41][42]44,47,[50][51][52][53]55,56,58,59,61 In the majority of the abovementioned studies it was reported that the inhibition effectiveness of the respective extracts decreased with increasing temperature, apart from the works of Ating et al 51 and Umoren et al 40 Ating et al 51 studied the inhibition effectiveness of the extract of Ananas sativum leaves in ethanol as an inhibitor for AA1060 aluminium alloy in 0.1 M and 2.0 M HCl solutions at 30-60 C. Umoren et al 40 tested the inhibition effectiveness of coconut (Cocos nucifera) coir dust extract in acetone as a corrosion inhibitor for Al 3SR (98.60% aluminium) aluminium alloy in 1 M HCl solution at 30 and 60 C. According to the authors, coconut coir dust extract contains a mixture of alkaloids, avonoids, and organic acids, without identifying any compound in particular.…”

“…Nnaji et al 44 reported that quercetin, azaleatin, catechin, epicatechin, cyaniding, and dephinidin are among the main components of cashew nut (Anacardium occidentale) testa extract in acetone. Based on the quantum chemical parameters, the authors suggested that the extract adsorbed on the aluminium surface through the aromatic C]C, C]O, and O-H sites contained in the protonated forms of the extract components.…”

“…Lower extraction temperatures and the omission of large amounts of organic solvents will certainly contribute to a higher yield of phenolic compounds in the nal product. Some authors [43][44][45][46][47]50,52,56,61 report easy, economically feasible extraction procedures carried out at low temperatures with a low consumption of chemicals. Modern extraction techniques certainly represent a green solution to obtain extracts of high quality.…”