Open Ceramics最新文献

This study investigated the impact of La₂Zr₂O₇ (LZ) and different types of glass on the performance of polymer-derived ceramic (PDC) coatings on AISI 441 stainless steel substrates. Four double-layer PDC-based glass-ceramic coatings containing LZ and different glass fillers were prepared by dip coating. The LZ powder was synthesised by solid-state reaction (SSR): powder morphology, crystal structure, and thermal stability were analysed. X-ray diffraction (XRD) detected a LZ pyrochlore phase after annealing at 1300 and 1400 °C with a trace of t-ZrO₂. Four different glass compositions, namely BaO-Al₂O₃-SiO₂ (BAS), BaO-Al₂O₃-La₂O₃-B₂O₃-SiO₂ (BALBS), CaO-B₂O₃-SiO₂ (CBS), and BaO-ZnO-MgO-B₂O₃-SiO₂ (BZMBS), were also synthesised as fillers for PDC coatings. The glass transition and crystallisation temperatures of the glasses were determined using differential scanning calorimetry (DSC). The coating systems, consisting of a Durazane 2250 bond coat and a top coat (Durazane 1800 + LZ filler + different glass sealants), were prepared. After pyrolysis of the coatings at 900 °C, some of the glasses partially crystallised. Scanning electron microscopy (SEM) revealed that the layers containing BAS, BALBS and CBS glass were dense, with good adhesion to the substrate, and with occasional presence of larger pores and cracks. Delamination of the upper layer was observed in the coating with the BZMBS glass filler.

An immiscible glass system consisting of a continuous silica-rich phase and a discontinuous droplet phase enriched in phosphorus form the glassy framework for a novel magnetite glass-ceramic. Upon cooling from the molten state, the material phase separates into the droplet-in-matrix structure and magnetite precipitates spontaneously within the phosphorus-enriched droplet phase. Magnetic hysteresis curves of an exemplary magnetite glass-ceramic show a saturation magnetization of ∼20 emu/g and magnetic remanence of 2.6 emu/g for a maximum externally applied field of 30 kOe. This novel material space provides a simple and economical means to produce magnetite glass-ceramics with potential suitability for a variety of biomedical applications.

In this work, refractory components based on alumina were produced by binder jetting using a large-scale 3D printer. The formulation contained several particle fractions up to a grain size of 3 mm, equal to the printer resolution. The binder system contained fine dead burnt magnesia, milled citric acid and reactive alumina, which were added to the aggregate mixture to create the powder bed. Deionized water was deposited from the printer's nozzles and triggered the binding reaction between the magnesia and citric acid. After 24 h, the printed samples were removed from the powder bed, dried and sintered at 1600 °C for 5 h. Reactive alumina contributed to the in situ creation of magnesium aluminate spinel at high temperature. The samples were characterized in terms of Young's modulus of elasticity, bending and compressive strength in 2 directions (parallel and perpendicular to the printing direction). The broken parts were used to investigate physical properties such as the open porosity and bulk density. The microstructure was studied by means of computed tomography. Finally, powder samples were used to determine the phase composition at different stages of production by means of XRD.

Global warming necessitates efficient new batteries, with Zn-O₂ batteries standing out due to their high theoretical energy density, safety, and long cycle life, making them ideal for large-scale use. However, their industrial application faces challenges such as rapid energy density decline after initial cycles, limited cathode efficiency, and high overpotential between discharge and charge. This study focuses on synthesizing and characterizing ceramic iron compounds as catalysts for the cathode of Zn-O₂ aqueous batteries. The findings revealed that obtained catalysts presented surface active areas beyond 220 m²/g after calcination at 800 °C, which removed organic templates. Various thermal treatments have been analysed to measure their impact on the final product. XRD, FTIR, and Raman spectroscopy confirmed sample nitridation, while SEM showed macro–meso-porosity. The electrochemical evaluation demonstrated a significant enhancement in the material's catalytic properties for ORR/OER in alkaline Zn-O2 batteries, surpassing 140 h of satable cyling with catalytic activity for ORR and OER. This improvement, coupled with optimized electrode design, resulted in a substantial increase in the batteries' operational life, achieving stable cycling for over 120 h.

In “London Underground” stations, a high concentration of dust particles containing organic and inorganic matter of varying chemical composition. “London underground dust” is created from train wheels and brakes grinding against steel tracks and collected in filtration systems. The experiment will focus on using “London Underground Dust” to colour the ceramic facing tiles intended for re-use in newly built London Underground stations. The phase composition, particle size distribution surface area, morphology, and thermal behavior of collected dust were studied by XRD, XRF, SEM-EDS, BET, heating microscopy, STA-MS, UV–VIS spectroscopy. The substrate tiles for glazing experiments were prepared from local London clay. The mixtures of glazes and collected or milled dust were sprayed on the substrate tile's surface, dried and finally fired at 1060 °C. The influence of used materials weight ratio and dust milling time were shown as crucial parameters to obtain optimal final glaze colour.

Zirconia is a ceramic material with fine properties for dental restorations, but the color of zirconia does not match natural teeth color. In this study, the effect of zirconia doped with different rare earth oxides on the color of denture manufactured by Digital Light Processing (DLP) method was investigated. Experimental results showed that the color of the ceramic parts after sintering could cover Vita 3D colorimetric plate for natural teeth, and the color accuracy was within 1.5 NBS. Meanwhile, the forming accuracy of the denture reached 67.7 μm, and the three-point bending strength was 520.32 ± 35.44–649.10 ± 42.31 MPa, which met the requirements of triple crown in dentistry. This study establishes a method to achieve colors of natural teeth using DLP technology, and the results of this study have important leading implications for the use of additive manufacturing technology to fabricate natural-color ceramic dentures for dental applications.

In manufacturing of UHTCMC components machining is often one of the ultimate process steps and have then important objectives, including dimensional tolerances and surface roughness. Additionally, the prevention of any damage to high-value components is very important. In this study, the machining of 0/90°-C/ZrB₂ composite is investigated to understand some fundamental mechanisms involved. Specifically, the material removal mechanisms of the heterogeneous and anisotropic material structure through scratch tests are explored. Grinding experiments are conducted to evaluate surface quality, measuring surface roughness and grinding forces. This allows an interpretation of machining induced damage mechanisms of UHTCMCs. 0/90°-C/ZrB₂ shows generally brittle removal mechanisms and influence of fiber cutting direction. Scratching depth and speed influences less on damage. This was also found in the grinding experiments, where roughness remains almost constant.

TiC features an interesting combination of mechanical properties, high-temperature resistance, and lightness, making it an excellent candidate for several applications in harsh environments. However, its sintering to obtain bulk components is extremely challenging. Herein, we show that titanium aluminide is a promising sintering aid for TiC (5, 10, and 20 vol% were investigated). The aluminide allows the formation of a nearly fully dense component at 1350 °C by spark plasma sintering under 80 MPa. The aluminide forms a grain boundary secondary phase that promotes the Ti diffusion: Ti from TiC can be dissolved within the TiAl_y at the neck center and precipitate at the neck surface, while C can easily diffuse through the TiC lattice. Higher temperatures cause the extrusion of the aluminide out of the SPS die and its reaction with oxygen impurities. The final microstructure is constituted by nearly pure TiC with isolated alumina pockets at the triple points.

Y₂O₃ transparent ceramics with different amounts of ZrO₂ were obtained by reactive vacuum sintering at a relatively low temperature of 1735 °C for 22 h. The influence of ZrO₂ concentration within the 0–15 mol.% range on the microstructure, phase composition, microhardness, and optical properties of ceramics in the visible and IR ranges was investigated. SEM and XRD results indicate the absence of secondary phases in the studied concentration range, indicating the formation of single-phase solid solutions. It was shown that doping by ZrO₂ considerably decreases the average grain size of ceramics, while microhardness has the opposite behaviour. 15 mol.% ZrO₂-doped Y₂O₃ ceramics demonstrated the highest transmittance in the visible wavelength range. On the other hand, 5 and 7 mol.% ZrO₂-doped Y₂O₃ could be considered promising materials for the first atmospheric window (3–5 μm).