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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, izvirni znanstveni članek

Opis: 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.
Ključne besede: acid corrosion, green corrosion inhibitor, stainless steel, electrochemical techniques
Objavljeno: 24.07.2017; Ogledov: 614; Prenosov: 260
.pdf Celotno besedilo (463,32 KB)
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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, izvirni znanstveni članek

Opis: 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.
Ključne besede: corrosion, corrosion resistance, chitosan, biocompatibility, biomaterials, biomedical materials, coatings, stainless steel
Objavljeno: 23.06.2017; Ogledov: 985; Prenosov: 299
.pdf Celotno besedilo (2,73 MB)
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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, izvirni znanstveni članek

Opis: 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.
Ključne besede: austenitic stainless steel, critical ion ($Cl^-$) concetration, critical pitting corrosion temperature, metastable pitting
Objavljeno: 10.07.2015; Ogledov: 690; Prenosov: 69
.pdf Celotno besedilo (334,40 KB)
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Fracture behaviour of thin sheet stainless steel
Nenad Gubeljak, Darko Jagarinec, Jožef Predan, John Landes, 2012, objavljeni znanstveni prispevek na konferenci

Opis: The differences in fracture behavior between the compact tension C(T) and the middle tensile M(T) specimens make structure integrity assessment uncertain. Two different types of specimens C(T) and M(T) specimens made from stainless steel have been used for fracture toughness testing at the room temperature by the principles of the ASTM 1820-05 standard procedure. Stable crack initiation and crack propagation occurred for the C(T) specimens at lower values of crack driving force than for the M(T) specimens. Crack tip opening displacement-CTOD has been directly measured on the surface of specimens by using a stereo-optical grading method. The critical crack tip opening displacement at crack initiation CTODi has been measured as a plastic Stretch Zone Width (SZW) during a post test fractographic inspection. Comparison between the CTOD-R curves of both types of specimens shows some difference between the C(T) and the M(T) specimens, but a more significant difference appeared in the crack driving force, as consequence of different constraint (triaxiality) of the C(T) versus the M(T) specimens. Therefore, the result obtained by test on laboratory C(T) specimens cannot be directly used as fracture toughness material properties in a structure integrity assessment, except as a conservative lower bound estimate.
Ključne besede: stainless steel, compact tension specimen, middle tension specimen, CTOD-R curves
Objavljeno: 10.07.2015; Ogledov: 771; Prenosov: 67
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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: 1173; Prenosov: 90
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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: 1256; Prenosov: 73
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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: 1521; Prenosov: 74
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