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1.
Electrochemical and surface analysis of 2-phenylimidazole adsorbed on copper from chloride solution
Matjaž Finšgar, Klodian Xhanari, 2018, original scientific article

Abstract: The electroanalytical and surface characterization of copper immersed in 3 wt.% NaCl solution containing 1 mM of 2-phenylimidazole (2PhI) is presented. It was proven that 2PhI can be employed as corrosion inhibitor for copper using various electrochemical analyses, such as cyclic voltammetry, chronopotentiometry, electrochemical impedance spectroscopy, and potentiodynamic curve measurements. The adsorption of 2PhI on copper was further analyzed by 3D-profilometry, attenuated total reflectance Fourier transform infrared spectroscopy, contact angle measurements, and scanning electron microscopy equipped with an energy dispersive X-ray spectrometer. This system was therefore comprehensively described by various analytical approaches.
Keywords: corrosion inhibitor, copper, electrochemical impedance spectroscopy, EIS, cyclic voltammetry, attenuated total reflectance Fourier transform infrared, ATR-FTIR
Published: 17.01.2019; Views: 747; Downloads: 259
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2.
Corrosion mechanisms for cemented soils in three different sulfate solutions
Pengju Han, Chao Ren, Xiaohong Bai, Frank Chen, 2015, original scientific article

Abstract: In order to simulate and study the corrosion effects on the compressive strength of cemented soils that could be exposed in a polluted environment, a series of tests were conducted on cemented soil blocks cured with different concentrations of H2SO4, MgSO4, and Na2SO4 solutions. The test results show that the corrosion degree generally increases with the corrosion time and the solution concentration, while the compressive strength decreases with the increasing corrosion degree. The corrosion degree is highest for the Na2SO4 solution, followed by the MgSO4 and H2SO4 solutions. Namely, when the SO4 2- ion exists in a solution, the corrosion degree for the positive ions follows this descending order: Na+, Mg2+, and H+. X-ray diffraction (XRD) phase analyses were performed for the cemented soil samples after corrosion and ionic concentrations. The results show that the compressive strength decreases with an increase of the Mg2+ concentration in the MgSO4 solution and the Na+ concentration in the Na2SO4 solution. At the same time, the strength increases with an increase of the pH value of the H2SO4 solution. Based on the chemical analysis results, the corrosion of H2SO4 or MgSO4 solutions on cemented soils is deemed as a composite action involving the combined resolving and crystallizing corrosion processes. Furthermore, the corrosion of the Na2SO4 solution of cemented soil is a composite action consisting of dissolving and crystallizing.
Keywords: cemented soil, compressive strength, corrosion mechanism, sulfate, pollution, solution
Published: 15.06.2018; Views: 722; Downloads: 48
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3.
The influence of $Ce^{3+}$ ions on the corrosion rate of stainless steel in acidic solutions of different pH-values
Aljana Petek, Sebastijan Kovačič, 2014, original scientific article

Abstract: The corrosion resistance of AISI 420 stainless steel in 0.1 mol $L^{−1}$ $H_2SO_4$ + 0.1 mol $L^{−1}$ $Na_2SO_4$ solutions at different pH-values and the inhibiting effect of $Ce^{3+}$ ions was studied using electrochemical polarization methods. The results reveal decreasing of the corrosion rate with an increasing the pH of the solution, which demonstrates the progressive protective character of the inhibitor used. At pH lower than 3.33, the corrosion inhibition was most probably a result of the competitive adsorption of $Ce^{3+}$ with $H^+$ ions on the cathodic sites of the electrode surface, and it was found to be dependent on the relative concentration of $H^+$/$Ce^{3+}$. The peroxide generated from the oxygen reduction reaction at pH 3.33 was found to be capable oxidize trivalent cerium (Ce) to the tetravalent state. As obtained hydroxide precipitates act as diffusion barrier hindering the corrosion processes, whereafter a spontaneous passivity occurs on the steel surface at this pH.
Keywords: acid corrosion, green corrosion inhibitor, stainless steel, electrochemical techniques
Published: 24.07.2017; Views: 593; Downloads: 251
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4.
Novel chitosan/diclofenac coatings on medical grade stainless steel for hip replacement applications
Matjaž Finšgar, Amra Perva-Uzunalić, Janja Stergar, Lidija Gradišnik, Uroš Maver, 2016, original scientific article

Abstract: Corrosion resistance, biocompatibility, improved osteointegration, as well the prevention of inflammation and pain are the most desired characteristics of hip replacement implants. In this study we introduce a novel multi-layered coating on AISI 316LVM stainless steel that shows promise with regard to all mentioned characteristics. The coating is prepared from alternating layers of the biocompatible polysaccharide chitosan and the non-steroid anti-inflammatory drug (NSAID), diclofenac. Electrochemical methods were employed to characterize the corrosion behavior of coated and uncoated samples in physiological solution. It is shown that these coatings improve corrosion resistance. It was also found that these coatings release the incorporated drug in controlled, multi-mechanism manner. Adding additional layers on top of the as-prepared samples, has potential for further tailoring of the release profile and increasing the drug dose. Biocompatibility was proven on human-derived osteoblasts in several experiments. Only viable cells were found on the sample surface after incubation of the samples with the same cell line. This novel coating could prove important for prolongation of the application potential of steel-based hip replacements, which are these days often replaced by more expensive ceramic or other metal alloys.
Keywords: corrosion, corrosion resistance, chitosan, biocompatibility, biomaterials, biomedical materials, coatings, stainless steel
Published: 23.06.2017; Views: 954; Downloads: 290
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5.
Morphology and corrosion properties PVD Cr-N coatings deposited on aluminium alloys
Darja Kek-Merl, Ingrid Milošev, Peter Panjan, Franc Zupanič, 2011, original scientific article

Abstract: The attempt to find an alternative coating for corrosion protection of Al- alloys was made. PVD coatings are one of the possible alternatives for replacement of ecological unfriendly chromate coatings. Chromium-nitride (Cr-N) and Ni/Cr-N coatings were sputtered on aluminium substrates (AA7075 and cladded AA2024). Surface and sub-surface characterizations were performed by AFM and SEM. Special attention was given to defects incorporated into coatings, since they play important role in the corrosion protection of the coating/substrate systems. The cross-sections through the typical defects were performed by ion beam milling incorporated into the SEM. The Vickers hardness of the Cr-N with and without layer of Ni on both substrates was determined. After the coatings deposition, the values of Vickers hardness (10 mN load) increase for 10 to 100-fold compared to the substrates. The corrosion behaviour of Cr-N and Ni/Cr-N thin films was investigated in near neutral 0.1 M solution of NaCl using potentiodynamics electrochemical measurement. Cr-N and Ni/Cr-N coatings shift the corrosion potentials to more positive values. The best corrosion resistance among the tested coating/substrate systems were found for Ni/Cr-N on AA7075 substrate.
Keywords: Al-alloys, corrosion properties, CrN films, FIB, PVD coatings
Published: 17.03.2017; Views: 601; Downloads: 59
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6.
Modified surface of Cu, Zn, Cu10Zn and Cu40Zn with expression of hydrophobic properties for the purpose of corrosion protection
Gregor Žerjav, 2015, doctoral dissertation

Abstract: Copper and its alloys are soft and malleable metals and are often used for fabricating structures and monuments open to the atmosphere where they are subject to corrosion attack. There are many ways to protect metal against corrosion: corrosion inhibitors, protective layers, hydrophobic layers. He aim was to develop a simple technological process for forming hydrophobic, protective coatings for protection of Cu, Cu10Zn, Cu40Zn and Zn under conditions of atmospheric corrosion as tested in simulated urban rain. Carboxylic acids form self-assembled hydrophobic layers by adsorption to the positively charged metal surfaces via their carboxylic group. Corrosion inhibitors are often used to protect metals against corrosion in closed system. Most used corrosion inhibitors to protect Cu and its alloys is benzotriazole (BTAH) which showed good results in different environments. 2-mercaptobenzimidazole (2-MBI) is a derivative of BTAH with stronger affinity to adsorb on the Cu surface and showed good corrosion protection results in acidic solutions. Corrosion protection properties of the layers were tested with the use of electrochemical methods: potentiodynamic polarization and electrochemical impedance spectroscopy. The results were complement with immersion test where the weight loss was obtained. The properties of the layers were explored with surface-analytical methods: measurement of the contact angles, X-ray photoelectron spectroscopy, scanning electron microscopy with a chemical analysis and glow discharge optical emission spectroscopy. First the optimal conditions to produce hydrophobic coatings with the use of carboxylic acids were explored. The inhibition efficiency increased with increasing carbon chain length, longer preparation time in ethanol solution and increasing concentration of carboxylic acid. The inhibition of corrosion of Cu, Cu10Zn, Cu40Zn and Zn in simulated urban rain was further studied using the self-assembly of BTAH, 2-MBI and SA in ethanol solution, as individual inhibitors and in combinations. The morphology of layers differed greatly. The results of electrochemical measurements and weight loss immersion test ruled out BTAH as a possible inhibitor, unless combined with stearic acid. In the cases of Cu40Zn and Zn it even promoted corrosion. In contrast, 2-MBI gave good results, and even better in combination with stearic acid. SA layers provided the best long term corrosion protection of all tested inhibitors and exhibited the highest contact angles. 2-MBI provided less protection than SA. Combining organic inhibitor and stearic acid improves the corrosion protection properties of the self-assembled layers compare to individual layers. To make the procedure of layer preparation more appropriate for industrial application the time of immersion was decreased. Layers prepared on Cu with 1 min immersion time showed adequate corrosion protection of Cu in simulated urban rain. We also studied the possibility of combining SA with vitamin E in the layer preparation procedure. The modified layers formed with combination of Vitamin E and SA showed better corrosion inhibition properties for Cu and Cu40Zn in simulated urban rain as individual layers. Combining inhibitor and carboxylic acid together to prepare corrosion protective layers has a positive effect on the corrosion properties of the layers. Layers made combining corrosion inhibitor and carboxylic acid showed better corrosion protection than individual layers. The self-assembling process is a fast process shown by the tests made on the Cu layers with shorter immersion time. The addition of Vitamin E in the preparation of layers with carboxylic acids shows a positive effect on the corrosion properties of layers.
Keywords: copper, brass, corrosion, simulated urban rain, inhibitors, carboxylic acid, benzotriazole, 2-mercaptobenzimidazole
Published: 30.11.2015; Views: 930; Downloads: 105
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7.
Nucleation and growth of a passive film on AISI 420 martensitic stainless steel under potentiostatic conditions
Regina Fuchs-Godec, Aljana Petek, Valter Doleček, 2002, original scientific article

Abstract: The kinetics of the early stage s of passive film formation on AISI stainless stell in mixtures of 0.1M ▫$H_2SO_4$▫ and 0.1M ▫$Na_2SO_4$▫, with pH-values of 2.42, 2.85 and 3.33, were studied at different anodic potentials. The potentiostatic step method was used as an electrochemical technique in which the anodic current density was measured as a function of time. For analysis of the measured data, the theory of "topochemical reaction" was applied for the charcterization of the exponent n in that part where the steepest current decay was observed. Through this theory, which includes the Erofeev equation, the number of conversion steps could be obtained, as well as the number of directions in which the nuclei grow. It was found that this theory can be successfully applied to the passivation process of AISI 420 stainles steel.
Keywords: corrosion, corrision resistance, martensitic stainless steels, passive films, potentiostatic step method, topochemical reactions
Published: 10.07.2015; Views: 948; Downloads: 61
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8.
The effect of nitrogen-ion implantation on the corrosion resistance of titanium in comparison with oxygen- and argon-ion implantations
T. Sundararajan, Zdravko Praunseis, 2004, original scientific article

Abstract: Commercially pure (CP) titanium was surface modified with nitrogen-, argon- and oxygen-ion implantations in order to investigate the material's corrosion resistance in a simulated body fluid. Five doses were chosen for the ions, ranging from 5.1015 cm-2 to 2.5-1017 cm-2. In-vitro open-cyclic potential-timemeasurements and cyclic polarization studies were carried out to evaluate the corrosion resistance of the modified surface in comparison to an unmodified surface. Specimens implanted at 4.1016 cm-2 and 7.1016 cm-2 showed the optimum corrosion resistance, higher doses showed a detrimental effect on the corrosion resistance. Argon- and oxygen-ion implantation at these doses did not show any improved corrosion resistance, indicating the beneficial role of nitrogen on the corrosion resistance of titanium in the simulated body-fluid environment. Grazing-incidence X-ray diffraction (GIXD) was employed on the implanted specimens to determine the phases formed with the increasing doses. X-ray photoelectron spectroscopy (XPS) studies on the passive film of the implanted samples and on the unimplanted samples were analyzed in order to understand the role of nitrogen in improving the corrosion resistance. The results of the present investigation indicated that nitrogen-ion implantation can be used as a viable method for improving the corrosion resistance of titanium. The nature of the surface and the reason for the variation and the improvement in the corrosion resistance are discussed in detail.
Keywords: metallurgy, ion implantation, orthopedic implants, corrosion, titanium, nitrogen, oxygen, argon
Published: 10.07.2015; Views: 1656; Downloads: 71
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9.
Determination of the critical pitting temperature and the critical ion ($Cl^-$) concentration inducing pitting of AISI 304L stainless steel in 0.5 M $H_2SO_4$
Regina Fuchs-Godec, Valter Doleček, 2004, original scientific article

Abstract: Corrosion of AISI 304L stainless steel in aqueous solutions of 0.5 M $H_2SO_4$ + 0.01 M KCNS + x M NaCl was studied at different temperatures (25, 40, and 50 °C). The critical ion ($Cl^-$) concentration (CIC) and the critical pitting corrosion temperature (CPT) were determined on the basis of characteristic corrosion parameters ($i_{crit}$, $i_{pass}$, $E_{pp}$), which were obtained through potentiodynamic scanning experiments. The activation energy of the process wasfound to be equal to -42.0 (1 ± 0.08 ) kJ $mol^{-1}$. As the temperature increased, the pitting potential, $E_{pp}$, was shifted towards more negative values linearly with the reciprocal of temperature, when the concentration of added NaCl was above the CIC. In contrast, at concentrations very close to the CIC, the straight lines changed slopes. This result may indicate of the approximate boundary between metastable pitting and the beginning of stable pitting.
Keywords: austenitic stainless steel, critical ion ($Cl^-$) concetration, critical pitting corrosion temperature, metastable pitting
Published: 10.07.2015; Views: 673; Downloads: 68
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