In this work, the phosphatizing process of steel is investigated using open circuit potential and Tafel curves as well as scanning electron microscopy and energy dispersive X-ray spectroscopy. The results reveal that a pH of 2.57 in the phosphatizing solution promotes the dissociation of phosphoric acid which assists the formation of the manganese tertiary salt (Mn₃(PO₄)₂), which is deposited on the substrate. It was also observed that an increase in the temperature from 25 to 90°C and the presence of HNO₃ as catalyst enhances the manganese phosphatizing kinetics. On the other hand, the generation of iron phosphates and oxides is predominant at a pH of 1 and 90°C. These observations are supported by species distribution and Pourbaix thermodynamic diagrams.

No abstract

No abstract

No abstract

In this investigation a kinetic study of the HER was carried out employing a steel rotating disk with different aqueous solutions containing Phosphoric Acid (H3PO4) with or without metallic manganese (Mn) and Nitric Acid (HNO3). Furthermore, the HER was evaluated on iron and manganese phosphate coatings. Analyses of Tafel plots and the charge transfer coefficients, revealed one electrical potential zone where the monoatomic hydrogen can be recombined electrochemically to H2 as the rate determining step, with charge transfer coefficients similar to an activationless process (α→0). On the other hand, an increase in the concentration of H3PO4 promotes a higherexchange current for the HER. The Mn in the aqueous solutions has a catalytic effect on the hydrogen generation rate at room temperature. However, the precipitation of Mn3(PO4)2 on steel decreases the HER kinetics at high temperatures. These observations are also supported with SEM (Scanning Electron Microscopy) characterizations.