Fenugreek seed and cape gooseberry leaf extracts as green corrosion inhibitors for steel in the phosphoric acid industry

Phosphoric acid is the core material for the fertilizer industry; however, it is incredibly corrosive to manufacturing plants' structures, mainly steel. Corrosion is one of the most severe problems encountered during phosphate fertilizer manufacturing. Recently, plant extracts have been commonly used as corrosion inhibitors because they are cheap and environmentally friendly. Steel corrosion in a 20% aqueous phosphoric acid solution in the absence and presence of fenugreek seed (Fen) or cape gooseberry leaf (CgL) extracts was investigated using the electrochemical impedance spectroscopy technique, potentiodynamic polarization measurement, scanning electron microscope, and quantum chemical calculations. Fourier Transform Infrared, FTIR, was used to identify the functional groups in Fen and CgL extracts. The inhibition efficiency for steel in 20% aqueous phosphoric acid was roughly equal to 80% for 0.4 g/L CgL and 1.2 g/L Fen extracts. A scanning electron microscope showed that the chemical constituents of extracts block the surface roughness of steel, decreasing the corrosion rate. The activation parameters indicated the effectiveness of the extracts at a higher temperature. Measurements of the potential of zero charges showed that the steel surface is positively charged in the phosphoric acid solution. Quantum chemical computations were also employed to examine the corrosion inhibition mechanisms of the natural extracts.

Automated summary

Phosphoric acid, a core material in the fertilizer industry, shows high corrosiveness to manufacturing plants' structures, especially steel. In this study, plant extracts, such as fenugreek seed and cape gooseberry leaf, were investigated as corrosion inhibitors due to their cheap and environmentally friendly properties. Experimental and computational methods were used to study the corrosion inhibition effects of these extracts in 20% aqueous phosphoric acid solution. The results showed that fenugreek seed and cape gooseberry leaf extracts can effectively reduce the corrosion rate of steel.