| 1. |
- Bassani, Carlos L., et al.
(author)
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Nanocrystal Assemblies : Current Advances and Open Problems
- 2024
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In: ACS Nano. - 1936-0851. ; 18:23, s. 14791-14840
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Research review (peer-reviewed)abstract
- We explore the potential of nanocrystals (a term used equivalently to nanoparticles) as building blocks for nanomaterials, and the current advances and open challenges for fundamental science developments and applications. Nanocrystal assemblies are inherently multiscale, and the generation of revolutionary material properties requires a precise understanding of the relationship between structure and function, the former being determined by classical effects and the latter often by quantum effects. With an emphasis on theory and computation, we discuss challenges that hamper current assembly strategies and to what extent nanocrystal assemblies represent thermodynamic equilibrium or kinetically trapped metastable states. We also examine dynamic effects and optimization of assembly protocols. Finally, we discuss promising material functions and examples of their realization with nanocrystal assemblies.
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| 2. |
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| 3. |
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| 4. |
- Cunha, M. S., et al.
(author)
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Rotation and pulsation in Ap stars : first light results from TESS sectors 1 and 2
- 2019
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In: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 487:3, s. 3523-3549
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Journal article (peer-reviewed)abstract
- We present the first results from the Transiting Exoplanet Survey Satellite (TESS) on the rotational and pulsational variability of magnetic chemically peculiar A-type stars. We analyse TESS 2-min cadence data from sectors 1 and 2 on a sample of 83 stars. Five new rapidly oscillating Ap (roAp) stars are announced. One of these pulsates with periods around 4.7 min, making it the shortest period roAp star known to date. Four out of the five new roAp stars are multiperiodic. Three of these and the singly periodic one show the presence of rotational mode splitting. Individual frequencies are provided in all cases. In addition, seven previously known roAp stars are analysed. Additional modes of oscillation are found in some stars, while in others we are able to distinguish the true pulsations from possible aliases present in the ground-based data. We find that the pulsation amplitude in the TESS filter is typically a factor of 6 smaller than that in the B filter, which is usually used for ground-based observations. For four roAp stars we set constraints on the inclination angle and magnetic obliquity, through the application of the oblique pulsator model. We also confirm the absence of roAp-type pulsations down to amplitude limits of 6 and 13 mu mag, respectively, in two of the best characterized non-oscillating Ap (noAp) stars. We announce 27 new rotational variables along with their rotation periods, and provide different rotation periods for seven other stars. Finally, we discuss how these results challenge state-of-the-art pulsation models for roAp stars.
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| 5. |
- Diment, Daryna, et al.
(author)
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A New Methodology to Elucidate Lignin Structure-Properties-Performance Correlation
- 2022
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Conference paper (peer-reviewed)abstract
- Unveiling the interrelation between the lignin structure, its properties and performance inspecific applications is of primary importance for lignin engineering for high-value products.Herein, we suggest a new efficient methodology to quantitatively evaluate the roles of ligninspecific functionalities in selected applications. The method is based on changing only onestructural variable at a time, while keeping all others constant prior to performance evaluation.Indulin AT (a softwood Kraft lignin) was subjected to a set of chemical modifications byselectively masking its aliphatic (AlipOH), phenolic OH (PhOH), carboxyl (COOH) andcarbonyl (CO) groups. The property-performance correlation was demonstrated by measuringthe glass transition temperatures (Tg) of the modified lignins. The effect of the modificationson the adsorption performance of the modified lignins was evaluated towards methylene blue.This approach clearly demonstrated that PhOH and AlipOH groups have about equalcontribution (50% each) to the lignin adsorption capacity, while the role of the other functionalgroups is insignificant.
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| 6. |
- Diment, Daryna, et al.
(author)
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Study toward a More Reliable Approach to Elucidate the Lignin Structure–Property–Performance Correlation
- 2024
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 25:1, s. 200-212
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Journal article (peer-reviewed)abstract
- The correlation between lignin structure, its properties, and performance is crucial for lignin engineering in high-value products. Currently, a widespread approach is to compare lignins which differ by more than one parameter (i.e., Kraft vs organosolv vs lignosulfonates) in various applications by attributing the changes in their properties/performance specifically to a certain variable (i.e., phenolic −OH groups). Herein, we suggest a novel approach to overcome this issue by changing only one variable at a time while keeping all others constant before investigating the lignin properties/performance. Indulin AT (Ind-AT), a softwood Kraft lignin, was chosen as the model substrate for this study. Selective (analytical) lignin modifications were used to mask/convert specific functionalities, such as aliphatic (AliphOH) including benzylic −OH (BenzOH) and phenolic −OH (PhOH) groups, carboxyl groups (−COOH) and carbonyl groups (CO) via methylation, acetylation, and reduction. The selectivity and completeness of the reactions were verified by comprehensive NMR analysis (31P and 2D HSQC) of the modified preparations together with state-of-the-art molar mass (MM) characterization. Methylene blue (MB) adsorption, antioxidant activity, and glass transition temperature (Tg) were used to demonstrate and compare the properties/performance of the obtained modified lignins. We found that the contribution of different functionalities in the adsorption of MB follows the trend BenzOH > −COOH > AlipOH > PhOH. Noteworthy, benzylic −OH contributes ca. 3 and 2.3 times more than phenolic and aliphatic −OH, respectively. An 11% and 17% increase of Tg was observed with respect to the unmodified Indulin by methylating benzylic −OH groups and through reduction, respectively, while full acetylation/methylation of aliphatic and phenolic −OH groups resulted in lower Tg. nRSI experiments revealed that phenolic −OH play a crucial role in increasing the antioxidant activity of lignin, while both aliphatic −OH groups and −COOHs possess a detrimental effect, most likely due to H-bonding. Overall, for the first time, we provide here a reliable approach for the engineering of lignin-based products in high value applications by disclosing the role of specific lignin functionalities.
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| 7. |
- Dudarko, Oksana, et al.
(author)
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Removal of Poly- and Perfluoroalkyl Substances from Natural and Wastewater by Tailored Silica-Based Adsorbents
- 2024
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In: ACS ES&T Water. - : American Chemical Society.
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Journal article (peer-reviewed)abstract
- Per- and polyfluoroalkyl substances (PFAS) are very stable and ubiquitously distributed in terrestrial and aquatic environments, and treatment and remediation techniques for the removal of PFAS are urgently needed. In this study, mesoporous silica matrix SBA-15 grafted with alkyl amino groups was used to remove perfluorooctanoate (PFOA) from aqueous solutions. The amino groups were grafted onto SBA-15 by the condensation of alkyl amino silanes. The synthesized adsorbents were studied by SEM, TEM, IR, low-temperature nitrogen sorption, and XRD. The solid-state and liquid 19F NMR spectroscopy, EDX, and LC-MS/MS results showed high adsorption efficiency and rapid reaction kinetics. In freshly prepared solutions and on the surface of the sorbents, the presence of PFOA micelles was observed. Furthermore, the introduction of amine-containing groups into the structure of the sorbent allows the sorption of up to 649 mg/g of PFOA from solutions. Results showed that the protonated surface amino groups and PFOA interacted electrostatically. The obtained results open perspectives for producing adsorbents for facile extraction of PFAS.
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| 8. |
- Kochukhov, Oleg, et al.
(author)
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V772 Cas : an ellipsoidal HgMn star in an eclipsing binary
- 2021
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 500:2, s. 2577-2589
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Journal article (peer-reviewed)abstract
- The late B-type star V772 Cas (HD10260) was previously suspected to be a rare example of a magnetic chemically peculiar star in an eclipsing binary system. Photometric observations of this star obtained by the TESS satellite show clear eclipses with a period of 5.0137 d accompanied by a significant out-of-eclipse variation with the same period. High-resolution spectroscopy reveals V772 Cas to be an SB1 system, with the primary component rotating about a factor two slower than the orbital period and showing chemical peculiarities typical of non-magnetic HgMn chemically peculiar stars. This is only the third eclipsing HgMn star known and, owing to its brightness, is one of the very few eclipsing binaries with chemically peculiar components accessible to detailed follow-up studies. Taking advantage of the photometric and spectroscopic observations available for V772 Cas, we performed modelling of this system with the PHOEBE code. This analysis provided fundamental parameters of the components and demonstrated that the out-of-eclipse brightness variation is explained by the ellipsoidal shape of the evolved, asynchronously rotating primary. This is the first HgMn star for which such variability has been definitively identified.
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| 9. |
- Mikhraliieva, Albina, et al.
(author)
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Carbon Nanodots with Solvatochromic Photoluminescence for the Electrochemical Determination of Estrogenic Steroids
- 2022
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In: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 5:8, s. 10962-10972
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Journal article (peer-reviewed)abstract
- Herein, we utilized carbon nanodots (R-CNDs) for the electrochemical detection of estrogens in tap and natural water samples and simulated effluents from Swedish waste water treatment plants (WWTPs). R-CNDs were prepared from 2-aminophenol by solvothermal synthesis and used as a modifier for chitosan-based selective membranes. The data obtained from atomic force microscopy and transmission electron microscopy suggest a spherical morphology of the R-CNDs with lateral size in the range of 3–8 nm and the height of 1–8 nm. In contrast to most other known carbon nanodots, R-CNDs are soluble in various organic solvents, including apolar, and less soluble in water. Small nanodots (3 nm) are more hydrophilic than large ones (6–8 nm) and can be separated from the bulk suspension of R-CNDs in heptane by their extraction into a water/ethanol mixture. Suspensions of large R-CNDs in apolar solvents exhibit green photoluminescence, while small R-CNDs in polar solvents have orange. This phenomenon was attributed to a solvatochromic rather than to a quantum effect. The R-CNDs were embedded on a chitosan-modified pencil electrode and the electrode was applied for voltammetric determination of four abandoned estrogens: estrone, estradiol, estriol, and ethynyl estradiol. The sensor demonstrates a group-selective response to the estrogens with a detection limit of 17.0 nmol L–1. It can be applied to determine the estrogens in the range of 0.05–4.6 μmol L–1 in the presence of typical interfering bioactive compounds, such as paracetamol, uric acid, progesterone, sulfamethoxazole, trimethoprim, ibuprofen, and caffeine. The developed sensors show repeatability and reproducibility values of 1.8–3.4% and 4.3%, respectively. The efficiency was proved by application for tap and lake water samples, where the recovery range was found to be 93–100%. The low cost, stability, and high sensitivity and selectivity of fabricated sensors make R-CNDs a perspective modifier for electrochemical sensors for the detection of estrogen microquantities in variable water samples.
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| 10. |
- Polishchuk, Liliia M., et al.
(author)
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In Situ Ring-Opening Polymerization of L-lactide on the Surface of Pristine and Aminated Silica : Synthesis and Metal Ions Extraction
- 2022
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In: Polymers. - : MDPI. - 2073-4360. ; 14:22
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Journal article (peer-reviewed)abstract
- The development of functional materials from food waste sources and minerals is currently of high importance. In the present work, polylactic acid (PLA)/silica composites were prepared by in situ ring-opening polymerizations of L-lactide onto the surface of pristine (Silochrom) and amine-functionalized (Silochrom-NH2) silica. The characteristics of the ring-opening polymerization onto the surface of modified and unmodified silica were identified and discussed. Fourier transform infrared spectroscopy was used to confirm the polymerization of lactide onto the silica surface, and thermogravimetric analysis determined that PLA constituted 5.9% and 7.5% of the composite mass for Silochrom/PLA and Silochrom-NH2/PLA, respectively. The sorption properties of the composites with respect to Pb(II), Co(II), and Cu(II) ions were investigated, and the effect of contact time, initial metal ion concentration, and initial pH were evaluated. Silochrom-NH2/PLA composites were found to have a higher adsorption capacity than Silochrom/PLA for all chosen ions, with the highest adsorption value occurring for Pb2+ at 1.5 mmol/g (90% removal efficiency). The composites showed the highest performance in the neutral or near-neutral pH (created by distilled water or buffer pH 6.86) during the first 15 min of phase contact. The equilibrium characteristics of adsorption were found to follow the Langmuir isotherm model rather than the Freundlich and Temkin models. Perspective applications for these PLA/silicas include remediation of industrial wastewater or leaching solutions from spent lead-acid and Li-ion batteries.
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| 11. |
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| 12. |
- Tkachenko, A., et al.
(author)
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Denoising spectroscopic data by means of the improved least-squares deconvolution method
- 2013
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 560, s. A37-
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Journal article (peer-reviewed)abstract
- Context. The MOST, CoRoT, and Kepler space missions have led to the discovery of a large number of intriguing, and in some cases unique, objects among which are pulsating stars, stars hosting exoplanets, binaries, etc. Although the space missions have delivered photometric data of unprecedented quality, these data are lacking any spectral information and we are still in need of ground-based spectroscopic and/or multicolour photometric follow-up observations for a solid interpretation.Aims. The faintness of most of the observed stars and the required high signal-to-noise ratio (S/N) of spectroscopic data both imply the need to use large telescopes, access to which is limited. In this paper, we look for an alternative, and aim for the development of a technique that allows the denoising of the originally low S/N (typically, below 80) spectroscopic data, making observations of faint targets with small telescopes possible and effective.Methods. We present a generalization of the original least-squares deconvolution (LSD) method by implementing a multicomponent average profile and a line strengths correction algorithm. We tested the method on simulated and real spectra of single and binary stars, among which are two intrinsically variable objects.Results. The method was successfully tested on the high-resolution spectra of Vega and a Kepler star, KIC 04749989. Application to the two pulsating stars, 20 Cvn and HD 189631, showed that the technique is also applicable to intrinsically variable stars: the results of frequency analysis and mode identification from the LSD model spectra for both objects are in good agreement with the findings from literature. Depending on the S/N of the original data and spectral characteristics of a star, the gain in S/N in the LSD model spectrum typically ranges from 5 to 15 times.Conclusions. The technique introduced in this paper allows an effective denoising of the originally low S/N spectroscopic data. The high S/N spectra obtained this way can be used to determine fundamental parameters and chemical composition of the stars. The restored LSD model spectra contain all the information on line profile variations present in the original spectra of pulsating stars, for example. The method is applicable to both high- (>30 000) and low- (<30 000) resolution spectra, although the information that can be extracted from the latter is limited by the resolving power itself.
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| 13. |
- Tkachenko, Oleg, et al.
(author)
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Kraft Lignin-Derived Microporous Nitrogen-Doped Carbon Adsorbent for Air and Water Purification
- 2024
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In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 16:3, s. 3427-3441
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Journal article (peer-reviewed)abstract
- The study presents a streamlined one-step process for producing highly porous, metal-free, N-doped activated carbon (N-AC) for CO2 capture and herbicide removal from simulated industrially polluted and real environmental systems. N-AC was prepared from kraft lignin─a carbon-rich and abundant byproduct of the pulp industry, using nitric acid as the activator and urea as the N-dopant. The reported carbonization process under a nitrogen atmosphere renders a product with a high yield of 30% even at high temperatures up to 800 °C. N-AC exhibited a substantial high N content (4–5%), the presence of aliphatic and phenolic OH groups, and a notable absence of carboxylic groups, as confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Boehm’s titration. Porosity analysis indicated that micropores constituted the majority of the pore structure, with 86% of pores having diameters less than 0.6 nm. According to BET adsorption analysis, the developed porous structure of N-AC boasted a substantial specific surface area of 1000 m2 g–1. N-AC proved to be a promising adsorbent for air and water purification. Specifically, N-AC exhibited a strong affinity for CO2, with an adsorption capacity of 1.4 mmol g–1 at 0.15 bar and 20 °C, and it demonstrated the highest selectivity over N2 from the simulated flue gas system (27.3 mmol g–1 for 15:85 v/v CO2/N2 at 20 °C) among all previously reported nitrogen-doped AC materials from kraft lignin. Moreover, N-AC displayed excellent reusability and efficient CO2 release, maintaining an adsorption capacity of 3.1 mmol g–1 (at 1 bar and 25 °C) over 10 consecutive adsorption–desorption cycles, confirming N-AC as a useful material for CO2 storage and utilization. The unique cationic nature of N-AC enhanced the adsorption of herbicides in neutral and weakly basic environments, which is relevant for real waters. It exhibited an impressive adsorption capacity for the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) at 96 ± 6 mg g–1 under pH 6 and 25 °C according to the Langmuir–Freundlich model. Notably, N-AC preserves its high adsorption capacity toward 2,4-D from simulated groundwater and runoff from tomato greenhouse, while performance in real samples from Fyris river in Uppsala, Sweden, causes a decrease of only 4–5%. Owing to the one-step process, high yield, annual abundance of kraft lignin, and use of environmentally friendly activating agents, N-AC has substantial potential for large-scale industrial applications.
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| 14. |
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| 15. |
- Tkachenko, Oleg, et al.
(author)
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Unveiling the Nature of lignin’s Interaction with Molecules : A Mechanistic Understanding of Adsorption of Methylene Blue Dye
- 2024
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In: Biomacromolecules. - : American Chemical Society. - 1525-7797 .- 1526-4602. ; 25:7, s. 4292-4304
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Journal article (peer-reviewed)abstract
- The valorization of lignin into advanced materials for water and soil remediation is experiencing a surge in demand. However, it is imperative that material research and manufacturing be sustainable to prevent exacerbating environmental issues. Meeting these requirements necessitates a deeper understanding of the role of lignin’s functional groups in attracting targeted species. This research delves into the interaction mechanisms between lignin and organic molecules, using the adsorption of the cationic dye Methylene Blue (MB+) as a case study. Herein, we aim to quantitatively estimate the contribution of different interaction types to the overall adsorption process. While carbonyl groups were found to have no significant role in attraction, carboxylic groups (−COOH) exhibited significantly lower adsorption compared with hydroxyl groups (−OH). Through alternately blocking aliphatic and phenolic −OH groups, we determined that 61% of the adsorption occurred through hydrogen bonding and 38% via electrostatic interactions. Performance studies of modified lignin along with spectroscopic methods (XPS, FTIR) confirmed the negligible role of π–π interactions in adsorption. This study offers fundamental insights into the mechanistic aspects of MB adsorption on lignin, laying the groundwork for potential modifications to enhance the performance of lignin-based adsorbents. The findings underscore the importance of hydroxyl groups and provide a roadmap for future studies examining the influence of steric factors and interactions with other organic molecules.
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| 16. |
- Tkachenko, Serhii, et al.
(author)
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The Effect of Al Addition on the Tribological Behavior of Ti-Si-Zr Alloys
- 2019
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In: Journal of tribology. - : ASME International. - 0742-4787 .- 1528-8897. ; 141:4
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Journal article (peer-reviewed)abstract
- While commercial biomedical titanium alloys present excellent biocompatibility and corrosion resistance, their poor wear resistance remains a major limitation. In this study, alloying with aluminum was used to improve the tribological performance of an experimental Ti-Si-Zr alloy. The effect of Al content on the alloy's microstructure and mechanical properties was evaluated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Vickers hardness measurements. Sliding wear testing was performed in a ball-on-disk setup, using stainless steel and silicon nitride counterparts and serum solution lubrication. Microstructural examinations showed that an increase in Al content induced a change from eutectic cell microstructure to regular near-equiaxed particles and produced a solid solution strengthening, increasing alloy's hardness. The adhesive tendencies of the alpha-Ti matrix to the counterpart dominated the frictional response, and a lower friction coefficient was found against silicon nitride compared to stainless steel. In wear tests against stainless steel counterparts, the alloys showed significantly higher wear rates than the CoCr and Ti-6Al-4V references due to severe abrasive wear, induced by the adhesion of titanium matrix to the counterpart. The Al addition had a positive effect on the wear resistance against silicon nitride due to the solid solution strengthening and the change in microstructure, which reduced the risk of brittle delamination. However, while this gave a trend for a lower wear rate against silicon nitride than the Ti-6Al-4V alloy, the wear rate was still approximately three times higher than that of CoCr.
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| 17. |
- Tkachenko, Serhii, et al.
(author)
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Wear and friction properties of experimental Ti-Si-Zr alloys for biomedical applications
- 2014
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In: Journal of The Mechanical Behavior of Biomedical Materials. - : Elsevier BV. - 1751-6161 .- 1878-0180. ; 39, s. 61-72
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Journal article (peer-reviewed)abstract
- Titanium alloys are widely used in biomedical applications due to their higher biocompatibility in comparison to other metallic biomaterials. However, they commonly contain aluminum and vanadium, whose ions may be detrimental to the nervous system. Furthermore, they suffer from poor wear resistance, which limits their applications. The aim of this study was to evaluate the tribological performance of experimental Ti-1.25Si-5Zr, Ti-2.5Si-5Zr, Ti-6Si-5Zr and Ti-2.5Si-5Zr-0.2Pd alloys as compared to that of control Ti-6Al-4V, CoCr F75 and CoCr F799 alloys. Friction and wear tests were performed using a standard ball-on-disc rig in serum solution at ambient temperature with Si3N4-balls as counterparts. The alloys microstructure and hardness were investigated using optical microscopy, XRD, scanning electron microscopy (SEM) and Vickers indentation. The coefficients of friction of the experimental Ti-Si-Zr alloys were generally lower than the commercial ones with Ti-6Si-5Zr presenting the lowest value (approx. 0.1). Their wear rates were found to be 2-7 times lower than that of the commercial Ti-6Al-4V alloy, but still higher than those of the CoCr alloys. SEM analysis of worn surfaces showed that abrasion was the predominant wear mechanism for all studied materials. Wear and friction were influenced by the formation and stability of transfer layers, and while commercial Ti-6Al-4V as well as the experimental Ti-Si-Zr alloys demonstrated extensive material transfer to the ceramic counterparts, the CoCr alloys did not show such material transfer.
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