Jean Steinmetz

The tin effect in lead-calcium alloys

Abstract The effect of tin in the depassivation of lead-calcium alloys under conditions of deep discharge (0.7 V versus Hg/Hg2SO4 in 0.5 M H2SO4) is investigated by measurements of the polarization resistance, the oxidation rate of ferrous ions added to the electrolyte, the potential decay with/without applied cathodic current, and surface analysis and visual inspection. The results may help to choose the optimal level of tin in the alloys.

Mangrove (Rhizophora apiculata) tannins: an eco-friendly rust converter

Abstract Rust converters are chemical formulations that can be applied to corroded surfaces to convert residual rust on iron/steel surfaces into harmless and adherent chemical compounds. The known hazardous effects of most synthetic rust converters have led to a search for safer, more environmentally friendly natural products. Tannins, a class of natural, non-toxic and biodegradable polyphenolic compounds, extracted from plant sources have been proposed as an alternative. The transformation of rust in the presence of 5 g L−1 tannins extracted from mangrove (Rhizophora apiculata) barks was studied. Three different methods of pre-rusted sample preparations were tested. The rust composition of the steel was dependent of sample preparation. The pre-rusted samples prepared formed predominantly lepidocrocite and magnetite. Transformation of rust components to ferric-tannates, particularly lepidocrocite, in the presence of mangrove tannins that could be observed via Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy analysis indicated their potential as rust converters.

Rust Phase Transformation in the Presence of Mangrove Tannins

The transformation of rust in the presence of 5 g L � 1 tannins extracted from mangrove barks was studied. Pre-rusted samples prepared resulted in the formation of predominantly lepidocrocite and magnetite. Partial transformation of rust components, particularly lepidocrocite in the presence of mangrove tannins was found to occur when observed via infrared spectroscopy, X-ray diffraction and SEM analysis. The anti-corrosive properties of the mangrove bark extracts seem to be related to the tannins which are capable of chelating with Fe 3+ giving a highly stable, and insoluble ferric-tannate complexes. A molecular modeling study of the reaction of catechin, a flavanoid of mangrove tannins with Fe 3+ to form a ferric- tannate complex was performed to explain the adsorption mechanism of tannins on iron. The correlation between the electronic density of the catechin molecule and the inhibiting properties is reported.