No abstract

No abstract

The ubiquitous use of plain and low-alloy steels in neutral, chloride bearing environments presents an everyday challenge for corrosion protection professionals. This paper explores the possibility of developing a non-toxic and environmentally friendly synergistic inhibitor mixture made of propolis, tannin, sodium benzoate, PEG400 and starch that could be applied into the solution to induce the formation of a persistent protective layer on steel. Components of the mixture were chosen based on the references giving their characteristics relevant to their possible action in the solution and/or at the surface of the steel. The efficiency of the protective layer formed under the influence of the inhibitor mixture, and then measured by the LPR probe in the inhibitor-free solution, was the lowest under quiescent conditions (75%) and the highest (95%) under flow conditions. Both, LPR and EIS data indicate that the inhibitor modified layer presents a barrier for diffusion of oxygen that acts as a primary corrosion reaction depolarizer in the investigated neutral chloride solution. The demonstrated persistence of the inhibitor modified layer is of primary interest as it gives possibility batch application.

Three different forms of Ag/TiO 2 composite layers, which have whisker-, dot-and island-like distribution of silver were obtained on a mechanically polished titanium surface by adjusting the conditions of silver deposition from an aqueous AgNO 3 solution. The deposit morphology was the result of both the program of electrode polarization and the template action of the simultaneously formed TiO 2 layer. The catalytic activity of the composite layers toward the oxygen reduction reaction was studied in aqueous 0.1 M NaOH solutions and found to be a function of both the surface loading of silver and the type of silver distribution within the Ag/TiO 2 composite layers. The reaction path of oxygen reduction on the composite layers was found to be always a 4e -one, characteristic otherwise of polycrystalline silver electrodes.

This paper studies the corrosion inhibition of X52 5L carbon steel in 0.51 mol dm-3 sodium chloride solution in the presence of propolis extract. The inhibition efficiency of propolis extract in a chloride solution was tested by its adding to the working solution and by making a solid propolis coating on the electrode surface. The possibility of corrosion inhibition in the presence of propolis in flow conditions as well as at different temperatures was investigated by electrochemical methods: potentiodynamic polarization method and electrochemical impedance spectroscopy. It was shown that propolis extract acts as a corrosion inhibitor of anodic type whose efficiency increases with increasing of temperature and with stirring of solution. The best protection is achieved by applying propolis coating in flow systems. The EIS method confirmed formation of a protective layer by adsorption of propolis extract on the electrode surface. The results of the FTIR, SEM and EDX surface tests are consistent with the results of electrochemical testing and suggest that propolis extract acts as a corrosion inhibitor of steel by forming a protective film on the electrode surface.

Biosorption of cadmium from aqueous solutions using fermented grape marc is investigated in this paper as well as influence of the most important factors, such as: contact time, granulation of biosorbent and the initial concentration of metal ions, is investigated in this paper. The equilibrium sorption of cadmium ions is achieved after 15-20 min., depending on the initial concentration of metal ions. Such a short time needed to achieve the equilibrium indicates that mass sorption is dominate process. Langmuir, Freundlich and Dubinin-Radushkevich isotherm were used to describe the equilibrium sorption process, while Langmuir model was found to be the most conveniente. Maximum of sorption capacity is 20 mg g1. EDS spectrum analysis showed that the process of ion exchange is one of the main sorption mechanism. Minor changes observed in the FTIR spectrum of grape marc after the sorption of Cd(II) ions indicate forming a band between metal ions and partially ionized carboxyl and phenol groups from the biomass. The results of this study confirmed that the fermented grape marc, due to the porous structure and characteristic chemical composition, is good sorption material.

Cyclic voltammetry was used to examine the kinetics of degradation of ascorbic acid (AA) at different temperatures. It has been shown that the reduction of the concentration of AA in all temperatures follow the kinetics of the first order reaction. The rate constant of the oxidation reaction increases with temperature as follows: 5x10-5; 2x10-4; 1x10-3 and 3x10-3 min-1 at temperatures of 25?C, 35?C, 65?C and 90?C, respectively. The temperature dependence of the rate constant follows Arrhenius equation, and the value of activation energy of the reaction degradation is 48.2 kJ mol-1 . The effect of storage time at a temperature of 90 ?C on AA content in fresh juice of green peppers was investigated. It was shown that AA oxidation reaction in the juice is also the first order reaction, while the lower rate constant in relation to the pure AA (5x10-3 min-1) indicates the influence of other substances present in peppers.

No abstract