Open Ceramics最新文献

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).

Magneto-optical and thermo-optical characteristics of transparent Tb₂Ti₂O₇ ceramics were investigated. The dependence of the index of refraction on the wavelength in the 0.29–2 μm range, the wavelength and temperature dependence of the Verdet constant, as well as the dependence of thermally induced depolarization on laser radiation power were measured. The value of the Verdet constant in Tb₂Ti₂O₇ surpasses that in Tb₃Ga₅O₁₂ by more than 1.68 times. The thermo-optical characteristic Q_eff was estimated to be (1.8–3.7)∙10⁻⁸ 1/K, which is record small compared to Q_eff of the known magneto-optical materials. The small value of Q_eff makes Tb₂Ti₂O₇ a highly promising magneto-optical material for Faraday isolators and rotators for high average power lasers.

In this research, B₄C-TiB₂ composites were successfully fabricated via the spark plasma sintering method. First, the TiB₂ source effect on the B₄C-TiB₂ composites was investigated using commercially available TiB₂ and in-house synthesized TiB₂. Subsequently, the effect of Si/B co-doped B₄C on composite ceramics was studied, followed by examining the samples' microstructure and elastic and mechanical properties. The results showed that B₄C-TiB₂ composites made with in-house TiB₂ powder obtained higher relative density and more desirable elastic and mechanical properties than samples made with commercial TiB₂. In-house TiB₂ and Si/B-B₄C composites provided more properties improvement overall. The elastic modulus, Vickers hardness, and fracture toughness values of Si/B co-doped samples were 493 GPa, 30.09 ± 1.97 GPa, and 4.31 ± 0.74 MPa m^1/2, respectively. Additionally, the amorphization of the TiB₂-B₄C composite decreased with Si/B co-doping.

The aim of this work was to gain an initial impression of the surface quality that can be achieved with additively manufactured ceramic components. For this purpose, an assessment body was generated, which has partially double-curved surfaces that can be scanned using a confocal microscope. After manufacturing using Vat Photopolymerization for ceramic components (CerAM VPP) with a commercial alumina suspension (Lithalox 350, Lithoz, Vienna, AUT) and thermal processing, the respective surface was measured at four different geometric areas. For evaluation, line sections were extracted to calculate R_a values as well as to determine S_a values for surfaces. R_a and S_a values were determined in all areas, reaching always values below 2.5 μm. The surface quality is therefore an order of magnitude lower than that of typical metallic AM components.

The reuse of waste to promote manufacturing processes that are respectful of the environment is a fundamental requirement in circular economy practices. In this work, it is assessed the feasibility of manufacturing ceramic proppants from a commercial red clay, sodium and potassium feldspars, and significant amounts of green bottle glass recovered from urban wastes.

Different ceramic mixtures were formulated, and the sintering conditions were defined considering optical dilatometric, differential thermal, and thermogravimetric analysis. The obtained granules were characterised following the international standard for proppants, and also using X-ray diffraction, scanning electron microscopy, and individual diametral compression tests.

The results show that competitive proppants are obtained, due to their low-density (2.5 g/cm³) and good breakage ratio (7.8 % at 5000 psi, or 34.5 MPa), but also considering the involved low-cost processing route and raw materials.

Silica refractories are promising materials for high-temperature thermal energy storage (HT-TES), because they exhibit excellent thermal cycling properties, unless cooled below a critical temperature (usually assumed to be 600 °C). When cooling down to room temperature severe damage can occur, which can be conveniently monitored via the impulse excitation technique (IET). This damage is most severe when the cycling maximum temperature is low. The question is whether this damage can be healed again. In this short contribution we show that severe damage in silica refractories, caused by heating from room temperature to 300 °C and back again to room temperature, can indeed be healed by thermal cycling to 1300 °C. The healed material is actually better than the pristine material.

Spark plasma sintering (SPS) is the most straightforward way to rapidly sinter nanoceramics, but the applied pressure prevents sintering of additively manufactured ceramics. Therefore, fast firing techniques such as “pressureless” SPS and ultra-fast high-temperature sintering, based on intense thermal radiation, are gaining interest. Here we compare pressure/current-assisted and pressureless SPS techniques for the rapid heating (∼300 °C/min, 5 min) of nanocrystalline zirconia with high sintering activity. The applied pressure and current indeed contributed to the lowestr temperatures needed for full densification of nanocrystalline zirconia, retaining very fine grain size, but also induced tetragonal phase transformations in the final sintering stages. When the radiative heat transfer was “decoupled” (pressureless SPS), a pronounced temperature difference between graphite crucible wall and simulated specimen temperature along with non-steady-state conditions during dwell were observed. Nevertheless, high heating rates facilitated fine and dense microstructures even in the absence of pressure/current.