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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: 902; Prenosov: 47
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Modelling and parameter comparison of equivalent circuits on the basis of impedance measurements of stainless steels
Mojca Slemnik, 2006, izvirni znanstveni članek

Opis: In our former work [1] we have discussed the impedance of differently heat treated steels X20Cr13 in 0.1 M H2SO4, undergoing an active passive transition. Impedance spectra were interpreted in terms of a model by Armstrong [2, 3], describing the electrochemical reaction at interfaces with adsorbed intermediates. The present work was performed in order to study this phenomenon in more detail, with computer simulations of a new created and more convenient equivalent circuit in comparison with the former model. Computer simulations of equivalent circuits were also made in the region of passivity which was also continuation of our earlier work [4]. In this sense the entire study for these steels was completed by collating distinctive parameter values, demonstrating electrochemical characteristics of steel X20Cr13, undergoing different heat treatments in the active-passive and passive region.
Ključne besede: electrochemical impedance spectroscopy, equivalent circuits, stainless steel, heat treatment of steel
Objavljeno: 30.05.2012; Ogledov: 1153; Prenosov: 46
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Study of crosslinking efficiency of cotton cellulose by different physical-chemical methods and genetic programming
Olivera Šauperl, Miran Brezočnik, 2006, izvirni znanstveni članek

Opis: We have investigated the crosslinking effect of unmercerized and mercerized cotton celluose crosslinked with different BTCA mass fractions in the impregnation bath. Crosslinking efficiency was analyzed using FT-IR spectroscopy, water retention capacity method, tensiometry and the methylene blue method. On the basis of the experimental data which was obtained with theseparate physical-chemical methods, different prediction models for crosslinking efficiency was developed. Modelling was taken out with the genetic programming method. Research shows good accordance of the experimentaldata with the genetic models.
Ključne besede: textile fibres, cotton, cellulose, crosslinking, FTIR spectroscopy, methylene blue method, water retention capacity, tensiometry, genetic programming
Objavljeno: 30.05.2012; Ogledov: 1242; Prenosov: 37
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Electrochemical impedance studies of corrosion protected surfaces covered by epoxy polyamide coating systems
Saša Skale, Valter Doleček, Mojca Slemnik, 2008, izvirni znanstveni članek

Opis: Electrochemical impedance spectroscopy (EIS) was used to study the corrosion behavior of different types of commercial quality epoxy polyamide dry coatingson mild steel, with thickness between 150 and 250 ▫$/mu$▫m, which were previously weather accelerated in a wet chamber. The following data were established on the basis of impedance curves and corresponding equivalent circuits: the coating capacity that relates to the coating dimension, the pore resistance that represents conductive paths through the pores, and Warburg coefficients, which are the measure of ion diffusion through the coating. EIS data were compared with a criterion in the European standard, and samples were classified on the basis of their quality, also receiving a final ranking by summing-up all the individual rankings. Suggestions have been made, namely that the use of anticorrosive active pigments is obsolete, when the thickness of the coatings exceeds 200 ▫$/mu$▫m.
Ključne besede: electrochemical impedance spectroscopy, metal-coatings, epoxy polyamide coatings, weathering, ISO 12944
Objavljeno: 31.05.2012; Ogledov: 1448; Prenosov: 59
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Use of AFM force spectroscopy for assessment of polymer response to conditions similar to the wound, during healing
Uroš Maver, Tina Maver, Andrej Žnidaršič, Zdenka Peršin, Miran Gaberšček, Karin Stana-Kleinschek, 2011, izvirni znanstveni članek

Opis: Force spectroscopy is a very promising technique for the evaluation of interactions within different environments. Knowledge about them is especially important during the design and preparation of those modern wound dressings in contact with a changing wound-environment over a prolonged time. Such exposure can cause a drastic decrease in the materialćs mechanical performance, and can lead to degradation, thus lowering the success of any healing process. Our study tries to establish a model system, which would enable us to assess the applicability of the mentioned technique for the evaluation of any interaction changes between polymer molecules and a chosen surface, after exposure to different environments. Our proposed experimental setup consists of two representative polymers, a model silicon surface, and two solutions of various pHs and ionic strengths, respectively. Within the chosen range of parameters, we are confident that we can prove the usefulness of force spectroscopy for further research into polymer suitability, for the development of novel wound dressings.
Ključne besede: force spectroscopy, AFM, wound dressings, polymer materials, model system
Objavljeno: 01.06.2012; Ogledov: 1072; Prenosov: 50
.pdf Celotno besedilo (316,48 KB)
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Optical properties of plastically deformed copper : an ellipsometric study
Nebojša Romčević, Rebeka Rudolf, J. Trajić, M. Romčević, B. Hadžić, Dana Vasiljević-Radović, Ivan Anžel, 2011, izvirni znanstveni članek

Opis: In this paper the results of optical properties investigations on plastically deformed copper are presented. The optical properties of the plastically deformed copper were studied using spectroscopic ellipsometry in the ultraviolet-visible (UV-VIS) range. Chemically pure copper was deformed by applying the Equal Channel Angular Pressing (ECAP) technique. During the last decade, equal-channel angular pressing procedure was used for the fabrication of ultrafine-grained metals and alloys. The plastic deformation of metallic materials leads to the production of bulk nano-scale structures with ultrafine grains and cross-sections, which remain about equal before and after deformation. The parameters of the sample were calculated using a two-film model together with the Bruggeman effective medium approximation.
Ključne besede: ellipsometric spectroscopy, atomic force microscopy, copper, amorphisation
Objavljeno: 01.06.2012; Ogledov: 1106; Prenosov: 39
.pdf Celotno besedilo (354,12 KB)
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Analysis of the oxidation of cellulose fibres by titration and XPS
Lidija Fras Zemljič, Leena Sisko Johansson, Peer Stenius, Janne Laine, Karin Stana-Kleinschek, Volker Ribitsch, 2005, izvirni znanstveni članek

Opis: The purpose of this study was to evaluate the effect of selective oxidation on the surface properties of cotton cellulose fibres. Four different methods to evaluate the accessibility, nature and content of ionisable acidic groups (charge) in the fibres were applied: potentiometric and conductometric titrations, polyelectrolyte adsorption and X-ray photoelectron spectroscopy (XPS). The results from this combination of methods show that two processes take place when the oxidation method is applied: elimination of low molecular mass non-cellulosic compounds and formation of new acidic groups in the cellulose chains. Which of these processes is predominating depends on oxidation time, but the first one is initially more important. Polyelectrolyte adsorption and XPS show that the surface concentration of acidic groups is considerably lower than the bulk concentration, i.e. during oxidation the content of carboxyl groups in the surface region decreases, while it increases in amorphous regions. The decrease is due to the dissolution of low molecular weight compounds; the increase is due to the formation of new acidic groups. The use of titration methods in combination with XPS appears to be a very useful tool for identification of the formation and distribution of ionic groups in cotton fibres and their surfaces.
Ključne besede: textile fibres, cotton fibres, cellulose fibres, oxidation, X-ray photoelectron spectroscopy, XPS, acid groups in fibres
Objavljeno: 01.06.2012; Ogledov: 1284; Prenosov: 63
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Substitution of the constant phase element by Warburg impedance for protective coatings
Saša Skale, Valter Doleček, Mojca Slemnik, 2007, izvirni znanstveni članek

Opis: This paper proposes an alternative model for fitting electrochemical impedance spectra of protective coatings. It describes broadening of the semicircle in the complex plane, in the absence of corrosion reactions. In addition the infinite Warburg impedance circuit element is represented, which bridges existing parallel elements of the plate capacitor and resistor of a classical equivalent electrical circuit. The Warburg impedance element is the result of the Fick's second law on partial differential equation solution. The proposed model and, for comparison the model with the CPE element, are used on our epoxy protective system to describe EIS measurements. The proposed model shows a better quality of fitting for our EIS data in comparison to the model with CPE.
Ključne besede: metal-coatings, electrochemical impedance spectroscopy, Nyquist charts, constant phase element, Warburg impedance
Objavljeno: 01.06.2012; Ogledov: 1290; Prenosov: 69
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Crystal-structure and Mössbauer studies of Li[sub]1.746]Nd[sub]4.494FeO9[sub]9.493
Mihael Drofenik, Irena Ban, Darko Makovec, Darko Hanžel, Amalija Golobič, Ljubo Golič, 2007, izvirni znanstveni članek

Opis: The ▫$Li_1.746Nd_4.494FeO_9.493$▫ (LNF) ternary phase, located in the ▫$Li_2O$▫-rich part of the ▫$Li_2O-Nd_2O_3-Fe_2O_3$▫ system, crystallizes with a cubic unit cell of dimension and the space group Im3m. Refinement on F resulted in R=1.9%. The structure is comprised of a network of corners, edges and faces sharing the coordination polyhedra of neodymium. In between this skeleton the regular octahedra of oxygen-coordinated iron and trigonal prisms of lithium are located. The Mössbauer spectra revealed the presence of ▫$Fe^3+$▫, ▫$Fe^4+$▫ and ▫$Fe^5+$▫ ions distributed on two symmetry-independent lattice positions.
Ključne besede: crystal structure, ternary compounds, single-crystal X-ray diffraction, Mössbauer spectroscopy, iron oxidation state, kristalna struktura, ternarne spojine, rentgenska difrakcija, Mössbauerjeva spektroskopija, rentgenska strukturna analiza
Objavljeno: 01.06.2012; Ogledov: 1191; Prenosov: 24
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Hydroxylammonium fluorogermanates
Irena Ban, Matjaž Kristl, Mihael Drofenik, Arkadije Popović, 2004, izvirni znanstveni članek

Opis: A new hydroxylammonium compound (NH3OH)2GeF6, has been synthesized by the addition of solid NH3OHF to a solution of GeO2 dissolved in 20% HF. The compound was characterized by chemical analysis and X-ray powder diffraction, the thermal decomposition was studied by thermal analysis and mass spectrometry. (NH3OH)2GeF6 crystallizes monoclinic. Two endothermic and two exothermic peaks have been observed on the DSC curve, the decomposition product at 500 °C is GeO2.
Ključne besede: inorganic chemistry, synthesis, characterisation, hydroxylammonium fluorogermanates, x-ray powder diffraction, mass spectroscopy, thermal analysis
Objavljeno: 01.06.2012; Ogledov: 1441; Prenosov: 47
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