Open Ceramics最新文献

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.

Advanced ceramics printed with photon-based additive manufacturing deals with anisotropic mechanical properties from the layer-by-layer manufacturing. Motivated by the success in using highly filled transparent slurries containing nanoparticles for powder-based two-photon-polymerization (2PP) for advanced ceramic printing, this works approach is the transfer to Xolography, a volumetric additive manufacturing technology based on linear two-photon excitation and without recoating steps. This paper reports the results of a preliminary investigation optimizing the photocurable slurry to the requirements of Xolography in terms of transparency, over a significantly larger mean free path, compared to 2PP. A feedstock filled with 70 % weight fraction of ceramic particles (∼30 vol%) exhibiting an exceptionally high degree of transparency in the relevant wavelength range of 400–800 nm was prepared from 5 nm zirconia nanoparticles. The high transparency of the photocurable slurry is attributed to the near-monomodal particle size distribution of the zirconia nanoparticles used.

A study has been carried out to examine the influence of augmented intra-bundle spacing achieved through innovative pre-treatment (heat treatment or ultrasonication) of carbon fibre (C_f) fabric, on mechanical properties of C_f-ZrB₂-SiC composites processed by ZrB₂–SiC slurry infiltration and hot pressing. Significantly enhanced C_f fabric intra-bundle spacing has facilitated homogeneous slurry infiltration, but has lowered elastic modulus, flexural strength, and fracture toughness compared to the composite with as-received C_f, because of fibre disorientation introduced during pre-treatment and its partial degradation by formation of interfacial ZrC during sintering. Notably, the composite with heat-treated C_f has shown superior fracture toughness (7.78 ± 0.4 MPa√m) and work of fracture (3043.25 ± 24.2 J/m²) compared to that containing ultra-sonicated C_f by 52.5 % and 95.7 %, respectively. Despite these variations, all the composites have exhibited non-catastrophic fracture behaviour during testing owing to the role of fibre pull-out, crack bridging, and crack deflection operating as toughening mechanisms.

Achieving full-spectrum lighting is a major challenge for phosphor-converted light-emitting diodes (pc-LEDs), which are crucial for solid-state lighting. This study presents the synthesis of polycrystalline Eu-doped Y₃Al₅O₁₂ (YAG) phosphors through a sol-gel method and flame synthesis process, leading to XRD amorphous microspheres. The amorphous nature of the microspheres allows the reduction of Eu³⁺ to Eu²⁺ at a significantly lower temperature (800 °C) than the reduction of crystalline samples described in the literature (1400 °C). The presence of Eu²⁺ in the YAG lattice was confirmed by X-ray photoelectron spectroscopy (XPS). The X-ray diffraction (XRD) of samples annealed in reducing atmosphere confirmed partial crystallization of pure YAG in all examined samples. The Eu-doped YAG phosphor embedded in residual glass microspheres exhibited a broadband emission spectrum over the wavelength range 450–800 nm peaking at 565 nm, corresponding to the 4f⁶5d¹→ 4f⁷ electron transition within the Eu²⁺ ions.

In this study, functionally graded ZrB₂–B₄C–SiC–LaB₆ composite materials (FGMs) with potential applications in hypersonic aircraft thermal protection systems were fabricated using spark plasma sintering. A systematic study of the thermal conductivity of the FGM, the conductivity of respective FGM layers, and the equivalent non-graded composites, was performed from room temperature up to 450 °C. The results suggest that the thermal conductivity of the FGMs (in the through-thickness direction) and their equivalent non-graded composites ranged between 25 and 34.9 W/mK, which was ∼60 % less than ZrB₂. While the overall thermal conductivity of the FGM and equivalent non-graded composites were similar, in the FGM, the topmost layer with high ZrB₂-content displayed up to 245 % higher thermal conductivity than the bottom layer with high B₄C content. A systematic comparison between experimentally determined conductivity and relevant thermal conductivity models was conducted.

Granite extraction waste represents an interesting alternative material for porcelain stoneware production, but information on its influence presents several gaps. For this reason, two different wastes were selected: a coarser iron-rich material from magnetic separation and a finer one from conveyance and abatement systems. Both were physically and chemically characterized. Batches were formulated by partial substitution of feldspar and technological behaviour of bodies was assessed by simulating the industrial manufacture at laboratory scale. Tiles were shaped by uniaxial pressure and fired by fast firing in electric roller kiln. The effect of waste addition was evaluated during the whole production process. Fired samples were characterized in terms of technological properties, mineralogical composition and microstructure evolution. The formulation optimization reduces firing temperature getting commercial technological constraints. A further increase of finer waste content affects compaction and mechanical strength. The presence of micaceous particles after the firing process may act as cracks initiation.

One significant hurdle in additively manufacturing polymer-derived ceramics lies in reconciling the lower mechanical properties of additively manufactured parts compared to traditionally manufactured ceramics and PDCs. Here, a methodology is presented for evaluating the influence of layer thickness and exposure on polymer-derived ceramics within the constraints of commercially available software and hardware. Maximizing exposure within printable limitation of DLP processes, produced green bodies with the highest conversion, and resulted in improved pyrolysis outcomes, manufacturability, and most importantly ceramic strengths comparable to traditionally manufactured SiOC PDCs. Decreasing layer thickness and increasing total dwell time had a dramatic impact on mechanical properties, increasing flexural strength by more than 6x from 18 MPa at 100 μm layer thickness to 111 MPa at 10 μm layer thickness. Density of resultant ceramic also increased from 1.62 ± 0.03 g/cc to 2.3 ± 0.05 g/cc. This represented a large increase in mechanical strengths of PDCs produced via DLP in literature.

Kitchen and bathroom countertop is a demanding application, where high aesthetic standards must combine with durability, ease of maintenance, and resistance to heat, stain, scratch and chipping. The hard materials and composites used for high-end countertops usually contain crystalline silica phases that can be inhaled by workers during drilling and cutting operations. The occurrence of silicosis and other respiratory diseases in machining workers makes it important to know exactly how much crystalline silica is present in countertop materials. This paper collects over 300 quantitative determinations of quartz and cristobalite in porcelain stoneware products and compare these contents with other countertop materials. The sum of crystalline silica phases in porcelain stoneware is on average 21 ± 5 % by weight (mostly quartz). This content is lower than granite (∼30 %) and much lower than engineered stone (∼90 %). Possible ways to reduce the amount of crystalline silica phases in ceramic slabs are overviewed and critically discussed.