AZ31 magnesium alloy was subjected to corrosion tests in a 0.9% NaCl containing 0 to 5 g/L D-glucose at 37°C. Potentiodynamic measurements were performed in corrosive environments with natural pH and with the pH set to 7.4. The results show that glucose in the range of 0.1 to 5 g/L led to a deterioration of the corrosion resistance of AZ31 alloy in 0.9% NaCl at an initial pH of 7.4. If the corrosive environment did not have a set pH, then a slightly different behavior was observed. Addition of 0.1 g/L glucose to 0.9% NaCl resulted in inhibition of corrosion, while higher concentrations accelerated corrosion. The corrosion aggravation was related to the oxidation of glucose to gluconic acid, which together with chlorides degraded the Mg(OH)2 layer on the AZ31 alloy surface. Surface analysis revealed that the corroded AZ31 alloy was covered with fine crystals in the absence of glucose.

The effect of lignitic humic acid in 0.1 M NaCl at pH 7 on low carbon steel was investigated using potentiodynamic polarization and immersion test. The morphology and elemental composition of the corrosion products were characterized using scanning electron microscopy with energy dispersive spectroscopy. The results showed that humic acid accelerated the corrosion of low carbon steel in 0.1 M NaCl. The negative effect of humic acid was attributed to the complexation of the molecules with iron ions. After seven days, immersion tests revealed that steel in 0.1 M NaCl was covered with the discontinuous black corrosion products, whereas humic acid in 0,1 M NaCl induced the formation of a continuous layer of brown corrosion products with low adhesion to the surface. The elemental composition of the black and brown corrosion products corresponded to Fe3O4 and FeOOH, respectively.