Marjoram Extract as Corrosion Inhibitor for Dissolution of Zinc in 1.0 M HCl

In this study, water marjoram (Origanum marjorana L.) extract was evaluated as corrosion inhibitor for zinc in 1.0？M HCl solution. The polarization measurements showed that this inhibitor is acting as mixed inhibitors for both anodic and cathodic reactions. The results showed that the inhibition efficiency was increased by increasing the inhibitor doses and reached the maximum at 500？ppm. The adsorption of marjoram extract on zinc surface was found to obey Langmuir type isotherm. The efficiency obtained from the impedance measurements was in good agreement with those obtained from the gravimetrical, thermometric, and polarization techniques which prove the validity of these tolls in the measurements of the tested inhibitor. 1. Introduction Corrosion inhibitors are widely used in industry to reduce the corrosion rate of metals and alloys in contact with aggressive environment. Most of the corrosion inhibitors are synthetic chemicals, expensive and very hazardous to environment. Therefore, it is desirable to source for environmentally safe inhibitors [1–4]. It has been shown that natural products of plant origin contain different organic compounds (e.g., alkaloids, tannins, pigments, and organic and amino acids, and most are known to have inhibitive action [5, 6]). Other authors have also shown that the inhibitive effect of some plant extract solutions was due to the adsorption of photochemical molecules present in the plant on the metal surface [7], which blocks the metal surface and thus does not permit the corrosion process take place. The main components of marjoram (Origanum marjorana L.) oil extract are thymol (38.4%) and cis-sabinene hydrate (25.3%). Other components detected in lower amounts in oil sample were sabinene and p-cymene (up to 7.4% and 13.9% in), and alpha-terpinene (up to 13.3%) in addition to some active phytochemicals like terpines, flavonoids, and rosmarinic acid is found in big quantities [8, 9]. The objective of the present work is to study the effect of dry plant extracts of marjoram as a corrosion inhibitor for the corrosion of zinc in 1.0？M HCl. Moreover, the effect of temperature on the dissolution of zinc as well as on the inhibition efficiency of the extracted compound was also investigated. 2. Experimental 2.1. Medium The acid solution of 1.0？M HCl was prepared by dilution of analytical grade HCl (37%) with double distilled water and all experiments were carried out in unstirred solutions. 2.1.1. Extract Preparation Marjoram plant used in this study was collected and washed to remove impurities such as dust and then dried