UJP Prague

Prague, Czech Republic

UJP Prague

Prague, Czech Republic

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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 | Year: 2015

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.


Rapouch J.,Institute of Chemical Technology Prague | Bystriansky J.,Institute of Chemical Technology Prague | Svobodova M.,UJP Prague
METAL 2012 - Conference Proceedings, 21st International Conference on Metallurgy and Materials | Year: 2012

This work is focused on evaluation of material changes of heat and creep strained steel Cr-W (P92) using electrochemical methods. Samples were exposed at temperatures 600-650 °C for different times (up to 20,000 h) and by application of various strain. Structural changes were evaluated by polarization methods, structure of steels was characterized using light and scanning electron microscope. On measured polarization curves significant local peaks in the passive/transpassive area were observed. Correlation between curve characteristic parameters and time of heating was determined. It is also shown, that electrochemical method could be used for detection of structural instability and creep damage of material.


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 | Year: 2012

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.


Fojt J.,Institute of Chemical Technology Prague | Joska L.,Institute of Chemical Technology Prague | Malek J.,UJP Prague
Corrosion Science | Year: 2013

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.


Fojt J.,Institute of Chemical Technology Prague | Joska L.,Institute of Chemical Technology Prague | Hnilica F.,UJP Prague
Kovove Materialy | Year: 2012

Titanium exhibits high corrosion resistance in biological environments. The main objective of its alloying with beta-stabilizing elements is to decrease modulus of elasticity. It is important to preserve corrosion resistance. The presented study was aimed at corrosion properties of Ti15Ta and Ti30Ta alloys in comparison with titanium. Measurements were performed on titanium, both alloys and tantalum in the physiological solution without or with fluoride ions. Electrochemical study was based on electrochemical impedance spectroscopy. Corrosion behavior of the studied alloys was significantly influenced by titanium. In the physiological solution, both alloys displayed stable passivity. Titanium is highly sensitive to the presence of fluoride ions. Its alloying with tantalum had a positive effect under the given conditions, which applied particularly to the Ti30Ta alloy. Titanium-tantalum binary alloys are not considered for direct use, yet the knowledge of their behavior may contribute to a more rational design of alloy systems applicable in dental practice.


PubMed | UJP Prague and Institute of Chemical Technology Prague
Type: | Journal: Materials science & engineering. C, Materials for biological applications | Year: 2015

To increase an orthopedic implants 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 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.


Koncek O.,Czech Technical University | Krivonoska J.,UJP Prague
Radiation Physics and Chemistry | Year: 2014

The MCNP Monte Carlo code was used to simulate the collimating system of the 60Co therapy unit to calculate the primary and scattered photon fluences as well as the electron contamination incident to the isocentric plane as the functions of the irradiation field size. Furthermore, a Monte Carlo simulation for the polyenergetic Pencil Beam Kernels (PBKs) generation was performed using the calculated photon and electron spectra.The PBK was analytically fitted to speed up the dose calculation using the convolution technique in the homogeneous media. The quality of the PBK fit was verified by comparing the calculated and simulated 60Co broad beam profiles and depth dose curves in a homogeneous water medium.The inhomogeneity correction coefficients were derived from the PBK simulation of an inhomogeneous slab phantom consisting of various materials. The inhomogeneity calculation model is based on the changes in the PBK radial displacement and on the change of the forward and backward electron scattering. The inhomogeneity correction is derived from the electron density values gained from a complete 3D CT array and considers different electron densities through which the pencil beam is propagated as well as the electron density values located between the interaction point and the point of dose deposition.Important aspects and details of the algorithm implementation are also described in this study. © 2014 Elsevier Ltd.


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 | Year: 2015

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.


Fojt J.,ICT in Prague | Smatova S.,ICT in Prague | Joska L.,ICT in Prague | Hnilica F.,UJP Prague
METAL 2012 - Conference Proceedings, 21st International Conference on Metallurgy and Materials | Year: 2012

The porous materials are able to improve osseointegration leading to strong connection of implant with the bone. However, presence of pores in material may result in corrosion problems. Samples of Ti-39Nb alloy prepared by powder metallurgy technique with porosity up to 33 % were studied. Exposure environments were phosphate buffered saline solution and physiological solution with fluoride ions. Reason is the possible use of studied material in dentistry. Measurements according to the ASTM F2129 standard were used for determination of the susceptibility to crevice corrosion. Time dependencies of the open circuit potential and electrochemical noise were analysed in environment containing fluoride ions. Influence of the pores was detected on materials with the porosity 24 % and 33 %. Porosity has a clear effect on the corrosion behavior of this type of material. Sensitivity to crevice corrosion attack of the Ti-39Nb alloy increased with increasing porosity as well. Localized corrosion damage was observed in areas of pore clusters, while the more compact areas were undamaged. Corrosion resistance of the low porous Ti-39Nb alloy was comparable with compact material. Nevertheless, the higher amount of pores led to the initiation of a localized corrosion attack. This may limit the use of this porous material in applications where it came into contact with highly corrosive environment.


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.

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