Sanja Martinez

Inhibitory mechanism of low-carbon steel corrosion by mimosa tannin in sulphuric acid solutions

Mimosa tannin was investigated as inhibitor of low-carbon steel sulphuric acid corrosion in concentrations from 10−5 to 10−1 mol L−1, at the temperature of 298 K in the solutions of pH 1, 2 and 3. The inhibitor effectiveness increases with increase in concentration. The adsorptive behaviour of mimosa tannin in solutions of pH 1 and 2 may be approximated, both by Temkin and Frumkin type isotherms, probably due to the chemisorption of tannin molecules on the metal surface. The free energies of adsorption are in the range from −35.1 to −39.5 kJ mol−1. At pH 3, a Freundlich type isotherm is obeyed, probably due to the physisorption of ferric-tannate that forms at this pH, both on the metal surface and in the bulk electrolyte. The free energy of adsorption at pH 3 is −11.8 kJ mol−1. The activation energy of the iron dissolution process at pH 1 was found to be 51.4 kJ mol−1 and decreased to 48.0 kJ mol−1 on the addition of 1.25 × 10−2 mol L−1 mimosa tannin. The addition of the same amount of mimosa tannin into solutions of pH 2 and 3, increased the activation energy of iron dissolution from 15.6 to 34.3 kJ mol−1 and from 12.0 to 19.2 kJ mol−1, respectively.

Modelling of the cathodic protection system with dynamic non-linear polarization characteristics

Cathodic protection (CP) is a technique that is used for protection of underground and underwater metallic structures from corrosion. Design of cathodic protection system requires defining of protection current density and potential. These parameters must meet given criterions during the exploitation of cathodic protection system. This paper deals with problem of modelling of the cathodic protection systems with dynamic non-linear polarization characteristics. Firstly, paper describes dynamic non-linear polarization characteristics. Mathematical model based on combined Boundary Element Method and Finite Difference Time Domain Method with assumptions on which is based are explained in the following part. Finally, application of the presented mathematical model was done on one geometrically simple example.

Determination of anionic surfactants in real samples using a low-cost and high sensitive solid contact surfactant sensor with MWCNTs as the ion-to-electron transducer

Multi-walled carbon nanotubes (MWCNTs) were used as a conducting substrate for construction of an all solid contact anionic surfactant sensor, which used the 1,3-didecyl-2-methylimidazolium–tetraphenylborate (DMI–TPB) ion pair as the sensing element implemented in PVC membranes. Scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) were used for morphological and electrochemical characterisation of the sensor. The investigated sensor showed a Nernstian response for lauryl sulfate (LS), 57.1 mV per decade of activity between 2.0 × 10−7 and 1.1 × 10−3 M; and a sub-Nernstian response for dodecylbenzenesulfonate (DBS), 51.1 mV per decade of activity between 3.6 × 10−7 and 6.6 × 10−4 M. For each ten-fold concentration change, the response time was 7 s (in the range from 1 × 10−6 M to 5 × 10−4 M). The detection limits for LS and DBS in water were 1.2 × 10−7 and 2.6 × 10−7 M, respectively. The sensor revealed a stable potentiometric response at pH 3–13 with a signal drift of 1.9 mV h−1 and exhibited outstanding selectivity performances for LS toward the majority of organic and inorganic anions that are most frequently employed in commercial formulations based on surfactants. The new sensor was applied for end-point location at potentiometric anionic surfactant titrations. Cetyltrimethylammonium bromide (CTAB) was used as a standard cationic titrant in all titrations. Ethoxylated non-ionic surfactants (EONSs) with a higher content of ethoxylated groups in the molecule and higher concentrations of EONSs reduce the magnitude of inflexion of titration curves and may cause a remarkable distortion during anionic surfactant (AS) determination. The sensor was tested by determination of ASs in commercial detergent products. The standard two-phase titration method and a conventional PVC liquid membrane surfactant sensor (PVCSS) showed satisfactory mutual agreement. The low-cost surfactant sensor developed had an operational lifetime of ca. six months.

Molecular and cellular approach in the study of antioxidant/pro-oxidant properties of Micromeria croatica (Pers.) Schott

Phytochemical composition and antioxidant activity of three wild populations of endemic Illyric-Balcanic species Micromeria croatica (Pers.) Schott have been evaluated with respect to plant organ and growing location. Multivariate analysis (principal component analysis) was performed to visualise (dis-)similarity among samples and identify the correlations between phytochemical variables that explain the most variability. The tested leaf extract from BaČić kuk locality exhibited protective effects against reactive oxygen species-induced damage of DNA and inhibition of lipid peroxidation, while it caused oxidative degradation of protein in the bovine serum albumin assay at higher concentrations. This extract also exhibited cytotoxic activity and facilitated the formation of reactive oxygen species in the HEp2 cell line, in a dose-dependent manner.

Passivity of Nitrogen-Bearing Stainless Steel in Acidic Solution

The mechanism and kinetics of the passivation process, the mechanisms of charge transfer and potential distribution in the system NTR50 steel | passive film |0.5 M H 2 SO 4 , were studied using transient electrochemical techniques in combination with cyclic voltammetry and the earlier results of XPS analysis. It has been established that the point defect model, that takes into account the interfacial kinetic effects, presents the best fit to the experimental data yielding physically reasonable parameters. The model has been applied to quasi-stationary experimental data to determine: (i) the transfer coefficient for the metal dissolution reaction through the barrier film, α 11 = 0.017 (ii) the proportionality coefficient between the barrier film | solution potential and the applied potential, α = 0.446 and (iii) the electric field strenght, ∈ = 4.4 ×10 6 V cm −1 . Cation vacancies, V Cr 3- represent the main charge carriers under quasi -stationary conditions of formation and growth of the barrier Cr 2 O 3 film. The barrier layer on NTR50 stainless steel is essentially a cation conductor. The outward migrating species are presumed to be the Fe 3+ ions and the molybdenum Mo 4+ and Mo 6+ ions, in concordance with the film composition comprised of an inner Cr 2 O 3 barrier layer and a Fe-rich outer hydrated layer.

Application of the coupled BEM/FEM method for calculation of cathodic protection system parameters

Cathodic protection (CP) is a technique that prevents corrosion of underground metallic structures. Design of any CP system first requires defining the protection of current density and potential distribution, which should meet the given criterion. It also needs to provide, as uniform as possible, current density distribution on the protected object surface. Determination of current density and potential distribution of CP system is based on solving the Laplace partial differential equation. Mathematical model, along with the Laplace equation, is represented by two additional equations that define boundary conditions. These two equations are non-linear and they represent the polarization curves that define the relationship between current density and potential on electrode surfaces. Nowadays, the only reliable way to determine current density and potential distribution is by applying numerical techniques. This paper presents efficient numerical techniques for the calculation of current density and potential distribution of CP system based on the coupled boundary element method (BEM) and finite element method (FEM).

On the Use of Boundary Element Method for Cathodic Protection System Modeling

Metallic installations placed in the soil or sea water (such as metallic pipelines) are submissive to the processes of corrosion. Corrosion is the destruction of the metal which is placed in electrolytes. One of the most often used technique for protection of underground or underwater metallic infrastructures against corrosion is cathodic protection systems. Design of any cathodic protection system requires determination of the electric potential and current density distribution on the electrode surfaces. This paper presents numerical method based on the direct boundary element method for calculation of distribution of electric potential and current density on electrode surfaces with nonlinear polarization characteristics. Presented numerical method was used to calculate parameters of one illustrative example of cathodic protection system.