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1.
Inhibition properties of TRITON-X-100 on ferritic stainless steel in sulphuricacid at increasing temperature
Regina Fuchs-Godec, Gregor Žerjav, 2009, izvirni znanstveni članek

Opis: The inhibiting action of a non-ionic surfactant of the TRITON-X series (TRITON-X-100) on stainless steel type X4Cr13 in 1.0 M H2SO4 solution at five different temperatures was investigated by the potentiodynamic polarisation measurements. The inhibition efficiency has been calculated in the presence and in the absence of the inhibitor. The experimental data suggest that the inhibition efficiency increases with increasing concentration of the TRITON-X-100, and decreases with the increasing temperature. Adsorption of the non-ionic surfactant used here obeys the Flory- Huggins isotherm. The thermodynamic parameters, such as, the heat of adsorption, adsorption entropy, and the adsorption free energy, have been calculated by employing thermodynamic equations. Kinetic parameters, also been evaluated.
Ključne besede: non-ionic surfactants, corrosion inhibitors, sulphuric acid, Flory-Huggins adsorption isotherm
Objavljeno: 31.05.2012; Ogledov: 1039; Prenosov: 39
.pdf Celotno besedilo (332,60 KB)
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2.
An impedance study of two types of stainless steel in Ringer physiological solution containing complexing agents
Mojca Slemnik, Ingrid Milošev, 2006, izvirni znanstveni članek

Opis: The effect of complexing agents EDTA and citric acid on the electrochemical behaviour of AISI 304 and orthopaedic stainless steels in Ringer physiological solution was investigated by potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS). The content of Mo has a pronounced effect on the corrosion resistance, as evident by the broader passive range of the orthopaedic stainless steel containing Mo. The addition of complexing agents induces significant changes in polarization and impedance characteristics, i.e., the shift of corrosion and breakdown potentials in a more negative direction, an increase in current density, and a significant decrease in charge transfer resistance. The results were interpreted by the formation of soluble complexes of metal ions with chelating agents, especially EDTA, which suppressed the formation of the outer Fe(III) layer of the passive film. The impact of complexing agent on the electrochemical parameters was found to be related to its concentration in electrolyte and the stability constant of the complex formed with the related metal ion.
Ključne besede: resistance, corrosion resistance, stainless steel, orthopedy, potentiodynamic polarization emthod, electrochemical impedance spectroscopy
Objavljeno: 31.05.2012; Ogledov: 817; Prenosov: 23
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3.
The adsorption, CMC determination and corrosion inhibition of some N-alkyl quaternary ammonium salts on carbon steel surface in 2 M H2SO4
Regina Fuchs-Godec, 2006, izvirni znanstveni članek

Opis: Electrochemical measurements were performed to investigate the effectiveness of cationic surfactants of the N-alkyl quaternary ammonium salt type, i.e. myristyltrimethylammonium chloride (MTACl), cetyldimethylbenzylammonium chloride (CDBACl), and trioctylmethylammonium chloride (TOMACl), as corrosion inhibitors for type X4Cr13 ferritic stainless steel in 2 M H2SO4 solution. Potentiodynamic polarization measurements showed that these surfactants hinder both anodic and cathodic processes, i.e. act as mixed-type inhibitors. It was found that the adsorption of the N-alkyl ammonium ion in 2 M H2SO4 solution follows the Langmuir adsorption isotherm. Plots of log ▫$[/theta$▫/(1-▫$/theta$▫)] versus log▫$c_{inh}$▫ yielded straight lines with a slope, which changed drasticallyat the critical micelle concentration (CMC) of the surfactants studied. Accordingly, the CMC could be accurately determined from these measurements. The calculated values of the free energy of adsorption ▫$/Delta$▫▫$G_{ads}$▫ are, in cases when the charge on the metal surface is negative with respect to the PZC, relatively high what is characteristically for the chemisorption. On the other hand, for positive metal surfaces it is assumed that ▫$SO_4^{2-}$▫ anions are adsorbed first, so the cationic species would be limited by the surface concentration of anions. Accordingly ▫$/Delta$▫▫$G_{ads}$▫ values were lower in this case and the adsorption is due to merely electrostatic attraction, which is characteristically of physisorption.
Ključne besede: electrochemistry, corrosion inhibitors, cationic surfactants, Langmuir isotherm, corrosion kinetic parameters, critical micelle concentration, sulphuric acid
Objavljeno: 30.05.2012; Ogledov: 1193; Prenosov: 32
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4.
Localized dissolution kinetics of low carbon steel
Aljana Petek, Valter Doleček, 2007, izvirni znanstveni članek

Opis: Localized dissolution of low carbon steel in saturated calcium hydroxide with different amount of sodium chloride has been investigated, using a dc technique. Potentiokinetic polarization curves indicated that pitting potentials ($E_{pit}$) decrease linearly with the log of chloride concentration. The rate of pit nucleation (1/$t_i$), and the rate of pits growth increases with increasing concentration of $Cl^-$ ions. Initiation of pitting attack could be ascribed to the adsorption of $Cl^-$ ions on the oxide surface. Adsorption of $Cl^-$ ions is physisorption and follow the Langmuir isotherm with $Δ_{ads}G^0$ = -21.1 kJ/mol.
Ključne besede: pitting corrosion, adsorption isotherm, low carbon steel, simulated interstitial solution
Objavljeno: 31.05.2012; Ogledov: 1239; Prenosov: 31
.pdf Celotno besedilo (105,67 KB)
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5.
Characterization of corrosion processes by current noise wavelet-based fractaland correlation analysis
Peter Planinšič, Aljana Petek, 2008, izvirni znanstveni članek

Opis: Electrochemical noise data in the presence of pitting, general corrosion and passivity were analyzed using the discrete wavelet transform. The registered current noise was decomposed into a set of band-limited details, which contain information about corrosion events occurring at a determined time-scale. It has been observed that the signal variance and variances of details depend on the intensity of processes. Distribution of the signal energy among different details was characteristic for the particular type of corrosion. The characterization of corrosion processes on the basis of in the wavelet domain calculated Hurst parameter H and fractal dimension, D, of electrochemical noise signals has been established. It is concluded that general corrosion is a stationary random process with a weak persistence and D= 2.14, whereas pitting corrosion is a non-stationary process with a long memory effect and D = 1.07. Passivity is a non-stationary process near to the Brownian motion with D = 1.56. The persistence features of electrochemical noise signals were explained also by correlation coefficients calculated between signals obtained by discrete wavelet multiresolution decomposition.
Ključne besede: elektrokemijski šum, valčki, Hurstov parameter, fraktalna dimenzija, korelacijski koeficient, korozija, electrochemical noise, wavelets, Hurst parameter, fractal dimension, correlation coefficients, corrosion
Objavljeno: 31.05.2012; Ogledov: 1075; Prenosov: 30
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6.
Protection of copper and its alloys using corrosion inhibitor-literature review
Milorad V. Tomić, Miomir Pavlović, Milovan Jotanović, Regina Fuchs-Godec, 2010, izvirni znanstveni članek

Opis: A review of the literature dealing with the electrochemical corrosion of copper and its alloys with purpose to find the most suitable inhibitor for its protection has been done. According to their chemical composition of corrosion inhibitors are divided into inorganic and organic inhibitors. Inhibition of alloying metals are possible (such as the addition of arsenic alloy components in brass, preventing its unzincanization). The paper reviews the theoretical basis of application of inhibitors to protect metals from corrosion as well as an overview of current research application of inhibitorsto protect copper and copper alloys. Benzotriazole (BTA) is most often used corrosion inhibitor for copper and its alloys in acidic and alkaline solution, because of its high inhibition efficiency. The lowest concentration of inhibitor for protection of copper in various solutions was 0.05%, and for the protection of copper in contact with steel is 0.1%. On the surface of copper and brass BTA forms a protective Cu-BTA film. However, BTA is like many other synthesized organic inhibitors is very toxic and if used invery small concentrations. It turnedout that the AETD, AETDA and PTAT good corrosion inhibitors of copper mixed type with the efficiency of inhibition increases with concentration. Due to the adverse effects on the environment, health and other bodies in recent times the focus of researchis transferred to the inhibiting action of biological molecules or mixtures of natural compounds called "Green inhibitors".
Ključne besede: corrosion inhibitors, protection of metals, inorganic inhibitors, organic inhibitors, alloys elements, green inhibitors
Objavljeno: 31.05.2012; Ogledov: 1234; Prenosov: 35
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7.
Use of a stable carbon isotope to assess the efficiency of a drinking water treatment method with CO[sub]2
Mojca Poberžnik, Albrecht Leis, Aleksandra Lobnik, 2012, izvirni znanstveni članek

Opis: CO2 gas with a special isotopic signature (?13C = -35.2% vs. VPDB) was used as a marker to evaluate the efficiency of a drinking water treatment method and the effect of an ultrasonic (US) stirrer. This treatment was developed to prevent precipitation and corrosion effects in water-supply systems. The research work was performed using a laboratory-scale pilot plant that was filled with tap water. The stable isotope analyses of ?13C-DIC (Dissolved Inorganic Carbon) in the water samples indicated that the maximum content of added CO2 gas in DIC was in the range of 35 to 45%. The use of the US stirrer during the entire experiment decreased the method's overall efficiency by 10%, due to degassing at a late stage of the experiment but accelerated the dissolution process in the early experimental stage.
Ključne besede: 13C stable isotope, carbon dioxide, carbonate equilibrium, corrosion, drinking water, limestone
Objavljeno: 01.06.2012; Ogledov: 1489; Prenosov: 18
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8.
Effects of surfactants and their mixtures on inhibition of the corrosion process of ferritic stainless steel
Regina Fuchs-Godec, 2009, izvirni znanstveni članek

Opis: The corrosion inhibition characteristics regarding mixtures of cationic/zwitterionic types of surfactant (Myristyltrimethylammonium bromide/Palmitylsulfo-betaineas), and non-ionic surfactant TRITON-X-405 mixed with 1 mM of KBr, as corrosion inhibitors for stainless steel (SS) (type X4Cr13) in aqueous solutions of 2 M H2SO4 were investigated using potentiodynamic polarisation measurements. The polarisation data showed that mixtures of the surfactants used in this study acted as mixed-type inhibitors, adsorbing on the stainless steel surface in agreement with the Flory-Huggins adsorption isotherm. The tensiometric results of this study suggest the existence of a second state of aggregation for zwitterionic/cationic surfactant mixtures. From these values of the free energy of adsorption, which in both mixtures decreased with respect to a single surfactant, we concluded that the adsorption in mixtures was stronger. The mixtures studied here showed good inhibition properties for ferritic stainless steel type X4Cr13 in 2 M H2SO4 solution.
Ključne besede: corrosion inhibitor, cationic surfactant, Zwitterionic surfactant, Flory-Huggins isotherm, Sulphuric acid
Objavljeno: 01.06.2012; Ogledov: 764; Prenosov: 39
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9.
Effect of testing temperature on corrosion behaviour of different heat treated stainless steels in the active-passive region
Mojca Slemnik, 2008, izvirni znanstveni članek

Opis: Purpose - This paper aims to focus on the effects of temperature of the immersion media on the corrosion behaviour of differently heat-treated X20Cr13 stainless steel. Design/methodology/approach - Specimens, quenched on air, quenched in oil and quenched in oil and then tempered, were tested during exposure in 0.1?M H2SO4 at 30, 40 and 50°C. The results were interpreted on the base of potentiodynamic and impedance measurements. Findings - From the impedance spectra a reaction mechanism can be determined: after samples had reached and passed the active peak, expressed as the highestpeak on the potentiodynamic curve, corrosion products at interfaces, which were adsorbed at metal surface, led to an increase in the charge transfer resistance. Elevated temperature of immersion media has had appreciable influence on the corrosion rate and adsorption of products, but atthis temperature level did not affect the principle of corrosion reactions. Activation energies were calculated to exhibit temperature dependence of current density, which was the highest for the oil- and the lowest for the air-quenched sample. Originality/value - The paper provides further research on stainless steel, the corrosion behaviour of which can be controlled already by heat treatment.
Ključne besede: corrosion, stainless steel, heat treatment, temperature
Objavljeno: 01.06.2012; Ogledov: 722; Prenosov: 39
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10.
Inhibitory effect of non-ionic surfactants of the TRITON-X series on the corrosion of carbon steel in sulphuric acid
Regina Fuchs-Godec, 2007, izvirni znanstveni članek

Opis: The corrosion inhibition characteristics of non-ionic surfactants of the TRITON-X series, known as TRITON-X-100 and TRITON-X-405, on stainless steel (SS) type X4Cr13 in sulphuric acid were investigated by potentiodynamic polarisation measurements. It was found that these surfactants act as good inhibitors of the corrosion of stainless steel in 2 mol L-1 H2SO4 solution, but the inhibition efficiency strongly depends on the electrode potential. Thepolarisation data showed that the non-ionic surfactants used in this study acted as mixed-type inhibitors and adsorb on the stainless steel surface, in agreement with the Flory-Huggins adsorption isotherm. Calculated Gads values are -57.79 kJ mol-1 for TRITON-X-100, and -87.5 kJ mol-1 for TRITON-X-405. From the molecular structure it can be supposed that these surfactants adsorb on the metal surface through two lone pairs of electrons on the oxygen atoms of the hydrophilic head group, suggesting a chemisorption mechanism.
Ključne besede: electrochemistry, corrosion inhibitors, non-ionic surfactants, Flory-Huggins isotherm, critical micelle concentration, sulphuric acid
Objavljeno: 01.06.2012; Ogledov: 1009; Prenosov: 41
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