Submit Manuscript | http://medcraveonline.com Introduction Corrosion is the natural process that occurs when native metals are transformed into undesirable substances when they react with substances like water or air. 1 This process undergoes a redox reaction whereby metals act as the reducing agent, losing electrons, and the oxygen (in water and air) act as the oxidizing agent, receiving electrons, causing the reaction to be spontaneous and electrochemically favoured. The damage to the metals caused by this reaction begins from the tiny part of the metal exposed to a corrosive environment which then leads to rusting. 2 When the metal is subjected to the rusting, hydroxyl ions (OH) occur when the electrons on the oxygen, and the hydrous iron oxide Fe(OH) 3 is formed through the reaction of hydroxyl ions and Fe 3+ : Fe 3+ + 3OH - → Fe (OH) 3 (Overall equation). Corrosion has been identified as a major problem in olefin applications due to the loss of materials such as pipes, especially in oilfields. Oil and gas-producing industries are negatively affected by corrosion worldwide every year, which results in a great loss of costs and a negative impact on the economy. 3 The economic loss of corrosion worldwide is estimated to be greater than $2.5 trillion, while in South Africa it is R130 billion. 4 This was conducted by the University of Witwatersrand and the Corrosion Institute of Southern Africa. Most companies transport the products through pipelines and tanks, which get into contact with water and interact with air. After the reaction of oxygen and water, the rust is generated which then flows with the compressed air inside the steel pipes, attacking them from the small portion to the entire metal. The use of inhibitors has been identified as the method for preventing corrosion. Corrosion inhibitors are substances that prevent or decrease the rate of corrosion on metals. 5 This is done by coating, plating, cathodic protection, and anodic protection of the surface of the metal or by immersing the metal inside the inhibitor solution. In addition, sodium hydroxide (NaOH) and sodium carbonate (Na 2 CO 3 ) are the most used inhibitors; since they increase pH near metals which reduces the transportation of oxygen to the metal surface. Other organic compounds such as heterocyclic compounds are effective and form a hydrophobic film on the metal surface. In this study, the use of the glycerol stearate in Figure 1 is reckoned as a part of the green chemistry inhibition method. The concentrations of the inhibitor decrease the rate of corrosion, especially the higher concentrations than the lower ones. The prevention occurs by immersing the metal inside the inhibition solution. 6 The metal absorbs the inhibitor on its surface, forming a protective film and preventing oxygen or water to attack. Furthermore, temperature has been identified as one of the factors affecting the rate of corrosion. Figure 1 Molecular structure of glycerol stearate. Materials and methods Glycerol stearate was purchased from Prestige laboratory supplies, South Africa. Zinc metal sheets were prepared and purchased from the University of Northwest, South Africa, and 32% Hydrochloric acid (HCl) was purchased at Rochelle Chemicals, South Africa. Gravimetric method Three zinc metals with the specimen of 3 cm x 4 cm were weighed and immersed inside 100 ml beakers containing a blank solution of J Anal Pharm Res. 2023;12(2):60‒65. 60 ©2023 Pesha et al. 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Inhibition of zinc corrosion by glycerol stearate in 1.0M hydrochloric acid medium with experimental, theoretical, and electrochemical techniques Volume 12 Issue 2 - 2023 Thabo Pesha, 1 Vusimuzi L Mulaudzi, 1 Peace P Mkhonto, 2 Mmaphefo P Mothapo, 1 Terrence Mothlathlo 1 1 Department of Chemistry, School of Physical and Mineral Sciences, Faculty of Science and Agriculture, University of Limpopo (Turfloop Campus), Private Bag X1106, Sovenga 0727, South Africa 2 Department of Physics, Materials Modelling Centre, School of Physical and Mineral Sciences, Faculty of Science and Agriculture, University of Limpopo (Turfloop Campus), Private Bag X1106, Sovenga 0727, South Africa Correspondence: Vusimuzi Ludwig Mulaudzi, School of Physical and Mineral Sciences, Faculty of Science and Agriculture, University of Limpopo (Turfloop Campus), Polokwane, Private Bag X1106, Sovenga 0727, South Africa, Tel 0152683240, Email Received: April 15, 2023 | Published: May 02, 2023 Abstract Glycerol Stearate (GS) was investigated as a corrosion inhibitor via weight loss on zinc (Zn) metal inside 1.0M hydrochloric acids (HCl). Different electrochemical techniques such as potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) and characterization methods were used in the study. Weight loss measurements and inhibition efficiency (IE) were used to calculate the amount of weight loss and to scrutinize the effect of inhibition concentration on the metal in HCl, and it demonstrated that weight loss decreased as the inhibition concentration increased, and percentage inhibition efficiency increased with increasing inhibition concentration. The Corrosion rate ( ρ ) was calculated, and it was observed that it decreased with the increasing inhibition concentration but increased with an increase in temperature. The compound of inhibitor effectively prevented corrosion by becoming adsorbed to the metal surface and was confirmed by Fourier transform infrared spectroscopy (FTIR). Free Gibbs energy (FGE) demonstrated a spontaneous corrosion process at the metal surface of zinc and the scanning electron microscope (SEM) was used to investigate the surface morphology of the protective layer and confirmed that the adsorption of glycerol stearate was via physisorption adsorption. The adsorption of glycerol stearate on the metal surface was found to follow the Langmuir adsorption isotherm model. Keywords: zinc metal, glycerol stearate, corrosion inhibition, weight loss, corrosion rate, adsorption, inhibitor concentration, inhibition efficiency Journal of Analytical & Pharmaceutical research Research Article Open Access OH HO O O