Fachgebiet 17: Keramische Werkstoffe und Bauteile
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Item-typ:Veröffentlichung, Combined effect of magnesia and zirconia on the bioactivity of calcium silicate ceramics at C\S ratio less than unity(Elsevier, 2016-09-01); ; ; ; This paper describes the effect of magnesia in the presence of zirconia on the bioactivity, microstructure and physico-mechanical properties of calcium silicate composition adjusted at calcia/silica ratio(C/S) of 0.5. A mixture from calcium carbonate and silica was conducted at C/S of 0.5. 20wt.% of magnesia and 5-25wt.% of ZrO2 were added. Each mixture was mixed with ethanol in a planetary ball mill, dried, formed and fired at a temperature of 1325±5°C. Phase composition, FE-SEM, and physico-mechanical properties of the fired specimens were determined and explained. The in vitro bioactivities of these specimens were investigated by analysis of their abilities to form apatite in the simulated body fluid (SBF) for a short time (7days) using SEM-EDS. The findings indicated that the surface of the specimens containing 5 and 15wt.% ZrO2 were completely covered by single and multilayered hydroxyapatite (HA) precipitate typical to "cauliflower" morphology, respectively. The surface of the specimen containing 25wt.% ZrO2 did not cover, but there are some scattered HA precipitate. The differences among the results were rationalized based on the phase composition. Vickers hardness and fracture toughness of the specimens of highly promised bioactivity were 2.32-2.57GPa and 1.80-1.50MPa. m1/2, respectively. The properties of these specimens are similar to the properties of human cortical bone. Consequently, these composites might be used as bone implant materials.Wissenschaftlicher ArtikelBand:70111 77 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Fatigue behavior and damage analysis of PIP C/SiC composite(Elsevier Science, 2022-10-01); ; ; ; In this work, we study the fatigue behavior of a C/SiC composite produced by several cycles of polymer infil- tration and pyrolysis (PIP). Fatigue tests were performed with maximum stresses corresponding to 60–90% of the tensile strength of the composite. During the fatigue tests, acoustic emission (AE) monitoring was performed and the measured AE energy was utilized to quantify the damage and distinguish possible damage mechanisms. Most of the fatigue damage in the form of matrix cracking, interface damage and fiber breakage occurs in the first cycle. As loading cycles proceeded, damage in form of matrix crack re-opening and interfacial friction constantly accumulates. Nevertheless, all samples survived the run-out of 1,000,000 cycles. After the fatigue tests, an in- crease of the tensile strength is observed. This phenomenon is associated with the relief of process-induced in- ternal thermal stresses and the weakening of the fiber-matrix interface. In general, the studied material shows very high relative fatigue limit of 90% of its tensile strengthWissenschaftlicher ArtikelBand:42Heft:1370 73 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, A new silicon oxycarbide based gas diffusion layer for zinc-air batteries(Elsevier {BV}, 2020-06-05); ; ; ; Rational material designs play a vital role in the gas diffusion layer (GDL) by increasing the oxygen diffusion rate and, consequently, facilitating a longer cycle life for metal-air batteries. In this work, a new porous conductive ceramic membrane has been developed as a cathodic GDL for zinc-air battery (ZAB). The bilayered structure with a thickness of 390 μm and an open porosity of 55% is derived from a preceramic precursor with the help of the freeze tape casting technique. The hydrophobic behaviour of the GDL is proved by the water contact angle of 137.5° after the coating of polytetrafluoroethylene (PTFE). The electrical conductivity of 5.59 * 10-3 S/cm is reached using graphite and MWCNT as filler materials. Tested in a ZAB system, the as-prepared GDL coated with commercial Pt-Ru/C catalyst shows an excellent cycle life over 200 cycles and complete discharge over 48 h by consuming oxygen from the atmosphere, which is comparable to commercial electrodes. The as-prepared electrode exhibits excellent ZAB performance due to the symmetric sponge-like structure, which facilitates the oxygen exchange rate and offers a short path for the oxygen ion/-electron kinetics. Thus, this work highlights the importance of a simple manufacturing process that significantly influences advanced ZAB enhancement.Wissenschaftlicher ArtikelBand:577195 160 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Arsenic and sulfur nanoparticle synthesis mimicking environmental conditions of submarine shallow-water hydrothermal vents(2022-01); ; ; Arsenic and sulfur mineralization is a natural phenomenon occurring in hydrothermal systems where parameters like temperature and organic matter (OM) can influence the mobilization of the toxic metalloid in marine environments. In the present study we analyze the influence of temperature and OM (particularly sulfur-containing additives) on As and S precipitation based on the recent discovery of As-rich nanoparticles in the hydrothermal system near the coast of the Greek island Milos. To this end, we experimentally recreate the formation of amorphous colloidal particles rich in As and S via acidification (pH 3-4) of aqueous precursors at various temperatures. At higher temperatures, we observe the formation of monodisperse particles within the first 24 h of the experiment, generating colloidal particles with diameters close to 160 nm. The S:As ratio and particle size of the synthetized particles closely correlates with values for AsxSy particles detected in the hydrothermal system off Milos. Furthermore, organic sulfur containing additives (cysteine and glutathione, GSH) are a key factor in the process of nucleation and growth of amorphous colloidal AsxSy particles and, together with the temperature gradient present in shallow hydrothermal vents, dictate the stabilization of As-bearing nanomaterials in the environment. Based on these findings, we present a simple model that summarizes our new insights into the formation and mobility of colloidal As in aquatic ecosystems. In this context, amorphous AsxSy particles can present harmful effects to micro- and macro-biota not foreseen in bulk As material.Buch136 105 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Microstructure and properties of Cu-Ti alloy infiltrated chopped Cf reinforced ceramics compositesNovel friction composites (C/C-Cu5Si-TiC) were prepared via reactive melt infiltration (RMI) of Cu-Ti alloy into porous C/C-SiC composites. The microstructure, physical properties and tribological behaviors of the novel material were studied. Results were compared to conventional C/C-SiC composites produced by liquid silicon infiltration(LSI). The resultant composite showed the microstructure composed of Cu5Si matrix reinforced with TiC particles and intact C/C structures. Most importantly, the composite did not present traces of free Si. As a result, the C/C-Cu5Si-TiC composite showed higher flexural strength, impact toughness and thermal diffusivity in comparison to C/C-SiC composites. Tribological properties were measured using 30CrSiMoVA as a counterpart. In general, the C/C-Cu5Si-TiC composites showed lower coefficient of friction(COF), but higher wear resistance and frictional stability. The improved wear resistance of the C/C-Cu5Si-TiC composites is credited to the formation of friction films from Cu5Si matrix. Other deformation and wear mechanisms are also described considering the microstructural observations.Wissenschaftlicher ArtikelBand:43Heft:1879 94 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Preparation of novel adsorbents based on combinations of polysiloxanes and sewage sludge to remove pharmaceuticals from aqueous solutions(Elsevier {BV}, 2016-03-19); ; ; Novel adsorbents were developed by varying the ratios of polysiloxanes and sewage sludge. The adsorbents were synthesized by mixing various polysiloxanes with methyl (MK), methyl/phenyl (H44) or without functional groups with sewage sludge in a solvent and pyrolyzed under an inert atmosphere. The adsorbents were characterized using several analytical and functional techniques, and used for adsorption of diclofenac (DCF) and nimesulide (NM) from aqueous solutions. Nitrogen adsorption/desorption measurements showed type I isotherms, which are typically for microporous materials, and the specific surface areas (SBET) were found to be in the range of 48 m2 g−1 and 631 m2 g−1. The sludge content was the major determinant for a decrease in SBET and hydrophobicity, as compared with pure polysiloxane samples. Among the composite materials, H67S33-500 (sample with 67% of polysiloxane H44 and 33% of sludge pyrolyzed at 500◦C) had the highest SBET value of 487 m2 g−1 while M40T60-600 (sample with 40% of polysiloxane MK and 60% of TEOS and pyrolyzed at 600◦C) exhibited the highest SBET value of 631 m2 g−1 among the hybrid materials. Experimental variables such as initial pH of the adsorbate solutions was optimized for adsorptive characteristics of the novel adsorbents. The optimum pH for adsorption of DCF and NM onto the adsorbents were 7.0 and 9.0, respectively. The equilibrium of adsorption was investigated using Langmuir, Freundlich and Sips models. Sips isotherm model gave the best fit of the equilibrium data. DCF showed better affinity for adsorbents than NM—suggesting that hydrophobic sites on the surfaces played a key role in the adsorption process.Wissenschaftlicher ArtikelBand:49792 169 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Evaluation of mechanical properties of a dense SiC/SiCN composite produced via PIP process(2022-03-01); ; ; ; The material behavior of Polymer Infiltration and Pyrolysis based SiC/SiCN composites is studied and the characteristic thermal and mechanical properties in on- (0/90 °) and off-axis (±45 °) direction are summarized. The tensile properties are determined at room temperature and 1300 °C. Based on the ratio of Young’s modulus and strength between on- and off-axis loading, a new approach for the classification of Weak Matrix Composites (WMC) and Weak Interface Composites (WIC) is proposed, which seems to be reasonable for various CMCs. Even without fibre coating mechanical behavior of SiC/SiCN is similar to that of WIC. In order to explain this, a microstructure model is developed and confirmed by analysis of fracture surface. The effect of temperature on the tensile properties is investigated through analysis of residual thermal stresses. Even though at 1300 °C the strength is slightly lower, the fracture strain increased significantly from RT to 1300 °C.Wissenschaftlicher Artikel110 121 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Novel tape-cast SiOC-based porous ceramic electrode materials for potential application in bioelectrochemical systemsOne alternative to improve electrochemical performance and long-term applicability in microbial bioelectrochemical systems (BESs) is the use of porous ceramic electrodes. In this work, electrodes of polymer-derived ceramics based on poly(silsesquioxanes) are synthesized, tailoring the properties by varying pyrolysis temperatures and incorporating conductive phases. Carbon (graphite, carbon black) and metal-based (stainless steel/Cu grids, Co/Ni particles) materials are incorporated into the silicon oxycarbide (SiOC) matrix. The influence of pyrolysis temperature and incorporation of conductive materials on functional properties and electrical conductivity is discussed. Furthermore, this study provides the first investigation of biofilm development on SiOC-based ceramic surfaces with Escherichia coli and Bacillus cereus. SiOC-based ceramics with DC conductivity values at room temperature in the semiconductor range (0.044–0.385 S cm-1) were obtained, with the highest values achieved by Co and Ni particles incorporation and in situ formation of CNTs. Adjustment in hydrophilicity and specific surface areas (6.21–263.45 m2 g-1) is realized by the pyrolysis. The biofilm studies reveal adhesion in the first 2 h for most of the surfaces, with higher bacterial adhesion and biofilm formation with the E. coli. The biocompatibility in terms of bacterial attachment and conductivity values comparable to a commercial carbon felt support the applicability of the developed SiOC-based materials as promising new class of electrodes for BES.Wissenschaftlicher Artikel106 103 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Edible high internal phase Pickering emulsion with double-emulsion morphology(Elsevier {BV}, 2020-10-24); ; ; ; Food-grade high internal phase Pickering emulsions (HIPPEs) unify the stability of Pickering emulsions and the advantages of detergent-based high internal phase emulsions (HIPEs), making them attractive as nutritional products. However, as oral delivery systems, HIPPEs are usually prepared in the form of o/w emulsions, which are suitable mainly for oleophilic active ingredients and may suffer from leakage during gastric digestion. To better protect and deliver hydrophilic cargo molecules, we developed a HIPPE-based w/o/w double emulsion system. Zein nanoparticles and soybean lecithin are found to have a synergistic effect in stabilization — using both natural emulsifiers together results in the formation of w/o/w double emulsions with improved stability, which is further confirmed by the interfacial tension and rheology of zein- and/or lecithin-laden oil-water interfaces. A combination of zein nanoparticles and lecithin achieves the fastest interfacial tension decrease, indicating an improved interfacial activity. Besides, lecithin contributes to the strong surface elasticity of the interfacial films, which makes the formed emulsions even stabler. Simulated digestion experiments suggest that the inner aqueous droplets can be strongly protected from gastric fluids. This edible HIPPE with double emulsion morphology provides new ideas for designing healthy foods for nutrients delivery.Wissenschaftlicher ArtikelBand:111111 205 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Antibacterial active open-porous hydroxyapatite/lysozyme scaffolds suitable as bone graft and depot for localised drug deliveryAn engineered synthetic scaffold for bone regeneration should provide temporary structural support and a medium for controlled and localised release of bioavailable medical drugs. In this work, a method is proposed to incorporate biologically active agents without impairing agent activity into open-porous resorbable hydroxyapatite scaffolds. Scaffolds are obtained by a one-pot freeze gelation process and loaded with different amounts of lysozyme, a model macromolecular drug with antibacterial activity. The antibacterial activity is tested by submerging hydroxyapatite scaffolds with 0.5 to 2.5 wt.% lysozyme into two different bacteria stock solutions. A complete dieback of M. luteus bacteria when in contact with the scaffolds is observed. Higher lysozyme amount in the scaffold leads to faster dieback. In contact with scaffolds containing 2.5 wt.% lysozyme after 30 min, no viable bacteria can be observed. An amount of 0.5 wt.% lysozyme in the scaffolds is sufficient to kill all bacteria after a contact time of 24 h. For L. innocua, a bacteriostatic effect is observed. The scaffolds have spongiosa-like stability and are suitable bone implant substitutes. As agents are released from the scaffolds by degrees over a time period of at least 9 days, they are particularly attractive as depot for localised drug delivery of bioactive macromolecular drugs.Wissenschaftlicher ArtikelBand:31Heft:8130 124