Anticorrosion potential of mangrove tannins on aluminium alloys AA6061 in NaCl solution has been studied using potentiodynamic polarisation method and scanning electron microscopy (SEM). The study was carried out in different pH of corrosive medium in the absence and presence of various concentrations of tannin. The corrosion inhibition behaviour of the mangrove tannin on AA6061 aluminium alloy corrosion was found to be dependant on the pH of NaCl solution. Our results showed that the inhibition efficiency increased with increasing tannins concentration in chloride solution at pH 6. Treatment of aluminium alloy 6061 with all concentrations of mangrove tannins reduced the current density, thus decreased the corrosion rate. Tannins behaved as mixed inhibitors at pH 6 and reduction in current density predominantly affected in cathodic reaction. Meanwhile, at pH 12, addition of tannins shifted the corrosion potential to more cathodic potentials and a passivating effect was observed in anodic potentials. SEM studies have shown that the addition of tannins in chloride solution at pH 12 reduced the surface degradation and the formation of pits.
The effect of scan rate on the accuracy of corrosion parameter in evaluating the efficiency of rice straw extract as corrosion inhibitor has been studied via potentiodynamic polarization measurement. Scan rate in the range of low (0.1- 0.25 mV s-1), medium (0.5-1.0 mV s-1) and high (1.5-2.0 mV s-1) scan were carried out on the carbon steel in 1 M HCl. The corrosion parameters such as corrosion rate, polarization resistance and corrosion current density have been analyzed through Tafel polarization curve. High scan rate gave poor accuracy of corrosion parameter compared to medium and low scan. Medium scan at 1.0 mV s-1 has been chosen as the optimum scan rate due to the approached steady-state and small disturbance of charged current. As a result, the addition of rice straw extract in 1 M HCl has reduced the values of corrosion current density in both cathodic and anodic reactions signified the corrosion has been inhibited. The efficiency of rice straw extracts as a corrosion inhibitor offer good result as much as 86%.
Anticorrosive properties of nano silicate from paddy husk in salt medium was investigated via weight loss method, Tafel
polarization and impedance techniques. Prior to the corrosion test, the silica powder was obtained from burning the
rice husk and extended with a chemical treatment process. The size of silica powder was characterized via zeta sizer and
showed the amount of micro silica particle appear more than the nano size particle. Nano silica powder was produced
from the refluxing process of micro silica to enhance the good properties of silica particle. The corrosion inhibition
efficiency of nano silicate showed good inhibition with increased in inhibitor concentrations. Weight loss test exhibits
high inhibition as more than 80% even, immersed in the corrosive medium until 14 days. The nano silicate inhibitor
affected the anodic reaction as showed by Tafel plot analysis. Impedance results also correlated with other test as shown
by the large size of Nyquist semicircle which represents as high resistance of charge transfer. The surface morphology
of inhibited specimen showed a smooth surface after nano silicate inhibitor applied in the NaCl medium as observed
through scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX).