article · Molecules
Marjoram essential oil, sourced from Morocco, acts as an effective natural corrosion inhibitor for mild steel exposed to hydrochloric acid. Laboratory testing using weight loss measurements alongside potentiodynamic polarisation and electrochemical impedance spectroscopy demonstrated that the extract significantly curbs metal degradation. At a concentration of 500 parts per million, the oil achieved an inhibition efficiency of 87.1 per cent, cutting the corrosion rate to 0.11 milligrams per square centimetre per hour. The evaluation categorised the extract as a mixed-type inhibitor with cathodic supremacy, operating predominantly through a charge transfer mechanism. Microscopic and elemental analyses confirmed that functional phytochemicals in the oil physically adsorb onto the metal surface in line with the Langmuir isotherm, creating a protective barrier against corrosive species.
Industrial acid cleaning and processing often cause severe corrosion to steel infrastructure, necessitating chemical inhibitors that are frequently toxic. Evaluating natural extracts like marjoram oil provides evidence for bio-based, less hazardous alternatives. Such sustainable inhibitors can help reduce reliance on synthetic chemicals while maintaining the protection of steel equipment exposed to acidic working environments.
This work presents early-stage laboratory evidence for formulating plant-based anti-corrosion additives for acidic industrial media, such as those used in pickling or acid washing. Potential end users include industrial chemical formulators and plant operators maintaining mild steel systems. The research remains at an exploratory laboratory stage, having assessed coupon performance under controlled conditions without dynamic flow or long-term operational testing.
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In recent years, the anti-corrosive properties of natural extracts as environmentally friendly inhibitors have gained considerable interest. This study evaluates the potential of Marjoram (Origanum majorana L.) essential oil (OML), collected from Salé, Morocco, as a corrosion inhibitor for mild steel in 1 M HCl medium. The protection performance of OML was assessed using various electrochemical techniques, including potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS), as well as the weight loss method. The influence of OML concentration and temperature on the inhibition performance were investigated. OML demonstrated pronounced inhibitory benefits via increasing the corrosion resistance of mild steel in the corrosive HCl solution, thus reducing the corrosion rate to 0.11 mg cm−2 h−1 and increasing the inhibition efficiency to 87.1% at an inhibitor concentration of 500 ppm. PDP confirmed that the inhibitor works as a mixed-type inhibitor with cathodic supremacy. EIS revealed that the charge transfer mechanism is the main controlling factor for the corrosion process. The thermodynamic parameters suggested a key role of OML physisorption in inhibition, following the Langmuir isotherm. Importantly, SEM and EDX analyses suggested the formation of a protective layer of the extract onto the steel surface, which shields the surface from corrosive species. This is owed to the functional group-rich phytochemicals of OML. Therefore, the development of bio-based corrosion inhibitors is not only a step towards more eco-friendly industrial practices, but also meets the growing demand for sustainable materials in a world with constrained resources.
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DOI: 10.3390/molecules30020272
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