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Prague, Czech Republic

Rapouch J.,Institute of Chemical Technology Prague | Bystriansky J.,Institute of Chemical Technology Prague | Sefl V.,Institute of Chemical Technology Prague | Svobodova M.,UJP Prague
Materiali in Tehnologije

A correct prediction of the remaining lifetime of the components for power plants requires an evaluation of the material structural stability. In this work, the possibility of a non-destructive evaluation of the structural changes in 9 % Cr creep-resistant steel P92 after a long-term annealing was investigated using the electrochemical-polarization technique. Aging at 650 oC caused a significant precipitation and coarsening processes resulting in a redistribution of some alloying elements in the structure. The structural changes confirmed by scanning-electron-microscopy observations and a hardness measurement affected the shape of the measured potentiodynamic curves. Significant local peaks on this curve, in the active-to-passive transition area and in the transpassive region, were evaluated. Characteristic current densities in these regions showed very good correlation with the results of the structure observation and hardness testing. Source

Fojt J.,Institute of Chemical Technology | Joska L.,Institute of Chemical Technology | Malek J.,UJP Prague | Sefl V.,Institute of Chemical Technology
Materials Science and Engineering C

Abstract To increase an orthopedic implant's lifetime, researchers are now concerned on the development of new titanium alloys with suitable mechanical properties (low elastic modulus-high fatigue strength), corrosion resistance and good workability. Corrosion resistance of the newly developed titanium alloys should be comparable with that of pure titanium. The effect of medical preparations containing fluoride ions represents a specific problem related to the use of titanium based materials in dentistry. The aim of this study was to determine the corrosion behavior of β titanium alloy Ti-39Nb in physiological saline solution and in physiological solution containing fluoride ions. Corrosion behavior was studied using standard electrochemical techniques and X-ray photoelectron spectroscopy. It was found that corrosion properties of the studied alloy were comparable with the properties of titanium grade 2. The passive layer was based on the oxides of titanium and niobium in several oxidation states. Alloying with niobium, which was the important part of the alloy passive layer, resulted in no significant changes of corrosion behavior. In the presence of fluoride ions, the corrosion resistance was higher than the resistance of titanium. © 2015 Elsevier B.V. Source

Fojt J.,Institute of Chemical Technology Prague | Joska L.,Institute of Chemical Technology Prague | Malek J.,UJP Prague
Corrosion Science

The presented work was aimed to describe the effect of porosity on the corrosion behaviour of Ti-39Nb alloy produced by the powder metallurgy technology, which represents a prospective material for medical applications. Corrosion properties of specimens with a porosity ranging from 0% to 33% were studied in simulated body environments, using electrochemical techniques and exposure tests. The results of measurements proved the occurrence of a localized form of corrosion in the material with a porosity of 24% and 33%. Distinct localization of the corrosion process was recorded in an environment containing fluoride ions. © 2013 Elsevier Ltd. Source

Joska L.,Ict In Prague | Fojt J.,Ict In Prague | Cvrcek L.,HVM Plasma | Brezina V.,Masaryk University | Malek J.,UJP Prague
METAL 2012 - Conference Proceedings, 21st International Conference on Metallurgy and Materials

Properties of DLC (diamond-like carbon) layers provide for their broad use in medical applications. Their tribological properties are frequently utilized in big joint implants. Another benefit is offered by their barrier effect. In the frame of presented work the corrosion behavior of DLC-Ti alloyed coatings formed on TiNbTa alloy in environments to which dental implants may be exposed was studied. Electrochemical impedance spectroscopy, XPS and a cell colonization test were employed in the study. Influence of DLC alloying by titanium was tested on samples with 3 levels of titanium amount. According to results of XPS analysis, surface concentration of titanium was 3.4, 10.2 and 23.6 at.%. Unambiguous and marked peak of titanium carbide was detected only in the case of highest concentration of titanium. Corrosion resistance of TiNbTa/Ti/DLC and TiNbTa/Ti/DLC-Ti was in low-aggressive physiological solution slightly different nevertheless very high in both cases. Electrochemical behaviour of carbon was significantly suppressed by titanium; character of EIS spectra was more capacitive than in the case of pure DLC. Decrease of pH did not influence the level of charge transfer resistance (polarization resistance). The main disadvantage of titanium - sensitivity to fluorides - was emphasized by alloying. Colonization by cells was slightly increased on alloyed samples in comparison with unalloyed DLC. Source

Polarization curves measured in a sufficiently aggressive environment (e.g. 0.5 mol dm-3 of H2SO4) may help to assess corrosion resistance of stainless steels. New phases precipitate in steel exposed long-term to high temperatures, which may affect the corrosion resistance. Potentiostatic polarization curves were measured on austenitic steel Super304H in a solution annealed state (from the producer) and in a state aged for 15 000 hours at temperatures of 650, 675 and 700 °C. The higher level of current density in passivity (worse corrosion resistance) was reported after aging at 650 °C. © 2016 Chmela T., published by De Gruyter Open. Source

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