Papers by Author: Jef Vleugels

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Authors: Bram Neirinck, Ferdinand Singer, Annabel Braem, Sannakaisa Virtanen, Jef Vleugels
Abstract: Magnesium and magnesium alloys are gaining considerable attention for use in biomedical applications due to their capability to completely resorb in the human body without noticeable side effects. For structural biomedical applications however, the resorption rate is too large. In order to decrease this rate researchers are investigating magnesium alloys with an increased corrosion resistance and/or biodegradable coatings, such as dense protein layers, which retard the resorption.In this work, we demonstrate the electrophoretic deposition of Bovine Serum Albumin (BSA) directly onto pure magnesium substrates using unbalanced alternating fields (AC-EPD). The effect of the obtained coatings on the corrosion behavior of the substrates was evaluated by potentiodynamic polarization. The results show that an albumin layer deposited by AC-EPD from a 50/50 ethanol/H2O medium significantly reduces the corrosion rate.
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Authors: Bram Neirinck, Jan Fransaer, Jef Vleugels, Omer Van der Biest
Abstract: From an environmental, safety and economic perspective water should be the solvent of choice for electrophoretic deposition under industrial circumstances. However, because of the electrolytic decomposition of water under the influence of direct current, the majority of EPD is carried out in non-aqueous solvents. In this work, experiments prove that deposits can be obtained from aqueous alumina suspensions while avoiding electrolysis of the medium by using unbalanced alternating current fields [1]. In addition it is shown that the formed deposits have a green density which is intrinsically higher than those formed by traditional DC EPD from ethanol based suspensions. A theoretical basis for both electrophoretic deposition by means of unbalanced alternating fields and the higher density of deposits formed by application of such fields is provided.
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Authors: Bram Neirinck, Dimitri Soccol, Jan Fransaer, Omer Van der Biest, Jef Vleugels
Abstract: The surface chemistry of a suspended particle greatly affects it behavior during electrophoretic deposition. The type and amount of surface groups determines whether the particles can be charged by interaction with the solvent. Furthermore, it is suspected that the surface chemistry plays a prominent role in the mechanisms governing the actual deposition of the particles. In the present work the surface chemistry of as-received and surface modified alumina powder is characterized by means of contact angle measurements and Diffuse Reflectance Infrared Fourier Transform spectroscopy. The wetting is measured using a modified Washburn method which yields quantitative contact angle values. The acid-base and dispersive surface energy components are calculated from these values using the surface tension component theory. Infrared spectroscopy was used to compare the surface groups of the treated and untreated powders and confirm the trends in surface properties as calculated from the contact angles.
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Authors: Shui Gen Huang, Omer Van der Biest, Jef Vleugels, Kim Vanmeensel, Lin Li
Abstract: In this study, 2 mol% Y2O3 (2Y), 1 mol% Y2O3+6 mol% CeO2 (1Y6Ce) and 12 mol% CeO2 (12Ce)-doped tetragonal ZrO2 ceramics were made by spark plasma sintering (SPS) for 2 min at 1450°C under a pressure of 60 MPa. The influence of stabilizers on microstructure, phase and mechanical properties of the ZrO2 ceramics was investigated. After sintering, the 2Y and 1Y6Ce were intact, containing full tetragonal ZrO2 phase on the polished cross-sectioned surface, whereas the 12Ce exhibited macro-cracks, corresponding to a large amount of monoclinic ZrO2 phase. Graded microstructure and mechanical properties were observed in the 1Y6Ce, showing a gradually decreased fracture toughness from sample edge towards centre, together with the slight decreased hardness. The 2Y had a uniform microstructure and mechanical properties. The formation of the graded structure and toughness profile was explained in terms of the gradual CeO2 reduction to Ce2O3 in the Y2O3+CeO2 doped ZrO2 ceramics.
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Authors: Jef Vleugels, Omer Van der Biest
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Authors: Bram Neirinck, Lieve Van Mellaert, Omer Van der Biest, Jozef Anné, Jef Vleugels
Abstract: The recent development of the alternating current electrophoretic deposition (AC-EPD) technique has rendered it possible to deposit material from aqueous suspensions while preventing the electrochemical reactions associated with the application of high voltages on such systems. This does not only allow for more economical and ecological processes but also opens up electrophoretic deposition as a processing technique to a whole range of materials sensitive to either electrochemical reactions or non-aqueous solvents. Living cells can be considered as one class of such materials. In this paper the deposition of two types of bacteria, the Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli, and one type of yeast cells, Saccharomyces cerevisiae, is demonstrated.
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Authors: Michael M. Gasik, Bao Sheng Zhang, Omer Van der Biest, Jef Vleugels, Guy Anné, Stijn Put
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Authors: Koenraad Bonny, Patrick de Baets, Omer Van der Biest, Jef Vleugels, Bert Lauwers
Abstract: A trend in the development of WC based cemented carbides and zirconia based ceramic composites is grain size refinement and more narrow grain size distributions of the starting powder, in order to accomplish higher hardness and abrasive wear resistance. The current work reports the results of dry sliding wear experiments on laboratory-made electrically conductive ZrO2-WC composites and commercially available WC-Co based cemented carbides, which have been manufactured and finished by rough cutting wire EDM with consecutive execution of gradually finer EDM regimes. Tribological data are obtained using a small-scale pin-on-plate test rig. Wear tracks are analyzed by surface scanning topography and scanning electron microscopy, revealing that the outer extensions of the wear tracks exhibit some differences in wear behavior compared to the central parts.
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Authors: Melis Arin, Jef Vleugels, Kim Vanmeensel, Gultekin Goller
Abstract: Fully dense ZrO2-TiN composites containing 1.75-2 mol %Y2O3, 1 mol% Y2O3 and 1 mol% Nd2O3 stabilizers, small amounts of Al2O3, and electrical conductive TiN particles (40-70 vol%) have been produced by hot pressing and spark plasma sintering at 1550°C. Although the intrinsic hardness of TiN (1400 kg/mm²) is higher than that of t-ZrO2 (1200 kg/mm²), the decreasing hardness trend can be attributed to the larger TiN grain size with the higher TiN content. Since TiN is more brittle, the fracture toughness decreases with increasing TiN content. Transformation toughening has been attributed as the main toughening mechanism as a result of fracture toughness decreasing with the transformability. Spark Plasma sintering temperature was too high for mechanical properties and hydrothermal stability of the mixed stabilized composites. The transformability decreases so hydrothermal stability increases linearly with increasing TiN content as a result of smaller volume fraction of t-ZrO2 grains becoming susceptible to hydrothermal transformation due to the shielding effect of the present TiN grains.
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Authors: Dongtao Jiang, Jef Vleugels, Omer Van der Biest, Wei Dong Liu, Raf Verheyen, Bert Lauwers
Abstract: Electrically conductive and wear resistant Si3N4-based composites were developed in order to facilitate electrical discharge machining (EDM). The microstructural and mechanical properties of Si3N4-based composites with different amounts of TiC0.5N0.5, fabricated by hot pressing at 1650°C for 1 hour, are investigated and evaluated. The hardness of the micron-sized TiC0.5N0.5 powder based composites increased with increasing TiC0.5N0.5 content from 20 up to 40 vol. %, whereas the bending strength decreased. The fracture toughness reached a maximum at 30 vol. % TiC0.5N0.5 and exhibits a strong anisotropy with respect to the hot-pressing direction. The EDM behaviour of the composites is strongly influenced by the TiC0.5N0.5 content. The composites with a higher TiC0.5N0.5 content have a lower material removal rate but a better surface quality.
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