المستخلص
Corrosion is the detrimental effect of various corrosive environments on metals and alloys. Sulfuric acid is one of the most common types of these environments due to its widespread use in the chemical industry. Several strategies are used to prevent and control corrosion. Plant extract inhibitors are the most common and widely used of these strategies because they are inexpensive, readily available, sustainable and environmentally friendly.
In this investigation, Okra Leaf Extract (OLE) was used as an inhibitor for corrosion of mild steel (N80) in acidic solution (1M H2SO4), the solvent extraction method which is the most widely used to separate plant components, where by the Soxhlet device, solid organic compounds were extracted from okra leaves using distilled water as a solvent. Optimizing the effect of extraction time, solvent volume, and dried okra leaf powder mass on the yield percentage. Two mathematical models were proposed, the polynomial and the power model. It was found that the highest correlation coefficient (0.9707) was obtained from the polynomial model and the highest extraction yield was obtained at the ideal values of time 200.0 min and 29.07 g for the powder mass and 290 mL for solvent volume.
The metal corrosion rate in the absence and presence of the inhibitor at concentrations (0, 25, 50, 75, 100 mL\L) and temperatures (30, 40, 50, 60 °C) was evaluated using mass loss technique and electrochemical polarization technique with the highest efficiency of 96%, 95% respectively. The electrochemical measurements showed that the inhibitor is of a mixed type, providing both cathodic and anodic protection. The corrosion inhibition process was modeled mathematically and statistically by proposing two models, the first is polynomial and the second is power model. Levenberg-Marquardt estimation and nonlinear estimation using least squares were used. The correlation coefficient for the first polynomial model was 0.9421 and the second is power model 0.9487. The force model had the highest correlation coefficient and was more accurate.
Measurements of FTIR, HPLC and UV were used to confirm and support the results of the weight loss technique and electrochemical polarization technique. To study the surface morphology, Optical Microscopy (OM), Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) were used, all of which showed the formation of a protective layer on the metal surface. The thermal stability of the inhibitor molecules was studied using Thermogravimetric Analysis (TGA), which showed that the OLE molecules are thermally stable up to a temperature of 85 °C.
