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Porous Si 3 N 4 ceramics were fabricated via pressureless sintering employing ternary lithium oxides (LiScO 2 , LiYO 2 , LiYbO 2) derived from various Re 2 O 3 as sintering additives under nitrogen atmosphere at the temperature of 1400–1700 °C. The study studied how sintering temperatures andternary lithium oxide additives affect the phase, microstructure, and material properties of Si 3 N 4. The results show that as the amount of sintering aids increases, the bulk density of samples increases. At the same time, the apparent porosity diminishes, leading to enhancements in flexure strength and dielectric constant. The Si 3 N 4 -based porous ceramic sample containing 5 wt% LiYbO 2 sintered at 1600 °C exhibits a volumetric weight of 1.828 g/cm3, an apparent porosity of 35.14 %, an average flexure strength of 114.8 MPa, a dielectric constant of 3.95, a loss tangent of 5.457 × 10−3, and a low thermal conductivity of 8.241, offering insights into the preparation of radome materials. [ABSTRACT FROM AUTHOR]

Maintaining high surface area and porosity at high temperatures is important when considering aerogels for use in thermal management systems. The mesoporous structure of aerogels results in extremely low thermal conductivity, making them lightweight, high performance insulating materials. Maintaining these properties requires innovative routes to suppress sintering and pore collapse as use temperatures rise. The current work aims to improve the pore structure stability of yttria‐stabilized zirconia aerogels by the addition of a SiO2 coating. The functionalization of surface hydroxyl groups by the addition of SiO2 is hypothesized to mitigate condensation reactions, which are a driving force for shrinkage and pore structure collapse. Zirconia aerogels with 0, 10, and 30 mol% yttria (YO1.5) additions were coated in a tetraethyl orthosilicate (TEOS) solution and exposed to temperatures up to 1200°C. Crystal structure, pore structure, and aerogel morphology were investigated to understand changes in aerogel thermal stability. The SiO2 coating exhibited a greater influence on pore stability over yttria concentration, with specific surface area of the coated aerogels being twice that of the uncoated aerogels up to 1000°C. However, the presence of the SiO2 coating promoted rapid sintering and densification at 1200°C, establishing an upper use temperature for SiO2 and a need to develop other coating chemistries. [ABSTRACT FROM AUTHOR]

Porous mullite ceramics exhibit exceptional mechanical and thermal properties in high-temperature environments, making them suitable for applications in thermal insulation. However, a notable challenge associated with high porosity is the tendency for increased sintering shrinkage during the sintering process. The sintering shrinkage can lead to unpredictable cracking and deformation, negatively impacting the final properties of the porous ceramics. In this study, porous mullite ceramics were fabricated using aluminium powder, alumina powder, and silica sol through foam-gelcasting and freeze-drying methods. The oxidative expansion of the aluminium powder was employed to offset the sintering shrinkage. The influence of alumina powder content on the microstructure and properties of porous mullite ceramics was investigated. Particularly, at the alumina content of 50 wt%, the porous mullite ceramics exhibited near-zero sintering shrinkage (0.3%). These ceramics demonstrated high porosity ranging from 78.9% to 83.3%, accompanied with low thermal conductivity (0.24-0.29 W/(m·K)) and great mechanical properties (0.51-1.02 MPa). The temperature difference over 750 °C revealed porous ceramics get excellent thermal stability as ideal lightweight high-temperature thermal insulation materials. This innovative approach presents a novel idea for fabricating complex net-shape porous mullite ceramic components with enhancing yield and low cost. • Near-zero sintering shrinkage porous mullite ceramics were prepared by foam-gelcasting combined with freeze-drying. • The microstructure and properties of porous mullite ceramics was tailored by the ratio of alumina and aluminium. • High porosity, low thermal conductivity and excellent thermal insulation performance were achieved. [ABSTRACT FROM AUTHOR]

Preparation of ultralight ceramic foams via aqueous-based direct foaming method for practical application is a challenging task owing to Ostwald ripening of wet foam and unsatisfied mechanical strength of final products. To tackle these issues, the current work demonstrates the construction of alumina-mullite ceramic foams via gelation-assisted dual-phasic nanoparticle stabilized foams using boehmite sol and nanosilica as the raw materials. The gelation process of boehmite sol inhibits the Ostwald ripening and pore enlargement during drying. The highly active alumina powder derived from boehmite sol and nanosilica enables the reaction by forming mullite at 1200 °C. Consequently, the resultant products demonstrate a compressive of 3.9 MPa at a porosity level of 95.9 %, a bulk density of 0.18 g/cm3 and an ultralow thermal conductivity of 0.1043 W m−1 K−1 after firing at 1200 °C. The current strategy provides new insight for fabricating high-performance ceramic foams for multiple applications. [ABSTRACT FROM AUTHOR]

This work reports the preparation and characterization of a 3D-printed porous 3 mol% yttria-stabilized zirconia (3YSZ) inert-supported micro-tubular solid oxide fuel cell (MT-SOFC) with high cell performance. For the first time, the impacts of pore-former particle size and mass fraction on the microstructure of 3D-printed porous 3YSZ, along with the influences of debinding atmosphere and pre-sintering temperature on the flexural strength and the shrinkage rate, were comprehensively explored. Optimal results were achieved using a particle size of 3 μm and a mass fraction of 30 wt%, facilitating the preparation of a printable 3YSZ photocurable slurry with a relatively low apparent viscosity of 4.2 Pa s at a shear rate of 30 s−1. Notably, 3D-printed porous 3YSZ debound in nitrogen and sintered in air at 1400 °C exhibited the highest flexural strength of ∼80.2 MPa compared to debinding in air or vacuum. Based on flexural strength and shrinkage rate considerations, the 3D-printed porous 3YSZ debound in nitrogen and pre-sintered at 1150 °C was deemed suitable as an inert support for SOFC. Cells prepared using this optimized approach demonstrated exceptional performance, achieving a maximum power density of 876.8 mW cm−2 at 850 °C, surpassing inert-supported MT-SOFCs fabricated using traditional methods. The outstanding cell performance underscores the successful application of 3D printing technology in preparing porous 3YSZ inert supports for SOFCs, offering an attractive approach for cell preparation and porous ceramics. [ABSTRACT FROM AUTHOR]

In this work, the deformation behavior of porous ceramics ZrO2–5.5 wt.% Y2O3 with different morphology of the pore space under axial quasi-static compression is studied by the digital image correlation (DIC) method. Two stages of the deformation behavior of the ceramics have been identified, namely, the controlled accumulation of microcracks and the formation of block structures. It has been found that an increase in the average pore size leads to a decrease in the tensile strength, a decrease in the effective elasticity modulus, and an increase in the ultimate deformation, while the nature of the deformation macrolocalization changes from ordered to chaotic one. It is shown that the rate of accumulation of local deformations in the central part of the deformable sample with a pore size of 68 μm is several times higher than in the sample with a pore size of 29 μm. [ABSTRACT FROM AUTHOR]

The current study introduces porous ceramic materials fabricated from cenospheres through spark plasma sintering. The investigation delves into the impact of sintering temperature, mould diameter (20 and 30 mm), and cenosphere size on the resulting material properties. Notably, sample shrinkage initiates at 900 °C and demonstrates an upward trend with temperature escalation, while a larger mould diameter contributes to sample shrinkage. Elevated sintering temperature leads to increased apparent density across various sample series, such as CS 63–150 µm in a 20 mm mould (0.97 to 2.3 g/cm³ at 1050–1300 °C), CS 150–250 µm in a 20 mm mould (0.93 to 1.96 g/cm³ at 1050–1200 °C), and others in different mould sizes. Total porosity decreases from 61.5 % to 3.9 % with a rising sintering temperature (1050 to 1250 °C), while open porosity starts decreasing at lower temperatures. Closed porosity peaks in samples sintered at 1150 °C. Furthermore, an increase in sintering temperature from 1050 to 1300 °C boosts the compressive strength of CS 63–150 samples in a 20 mm mould from 11 MPa to 312 MPa. These findings align with the Rice model, illustrating an exponential relationship between compressive strength, material porosity, and fully dense material compressive strength. [ABSTRACT FROM AUTHOR]

The porous TiC ceramics with different porosity were fabricated by hot-press sintering using CaO as pore-forming agent, which opened a new field to explore pore ceramics. Then a serious of porous TiC were fabricated and investigated the microstructure, porosity and mechanical properties of pore TiC. The porosity and bulk density of TiC depend on CaO content, which significantly affects the microstructure, mechanical properties and fracture behaviors. With the CaO content increasing, the porosity and pore size of TiC are increased, while the bulk density is decreased. Compressive strength and specific compressive strength exhibit a trend of monotone variation, and the maximum compressive strength is 51.3 MPa when CaO content is 40 vol%. A high porosity condition leads to a loose structure with low load-bearing capacity. As CaO content increases from 40vol% to 55vol%, porosity of TiC increases from 32.9 to 52.6%, and the compressive strength of porous TiC decreases from 51.3 MPa to 9.7 MPa. Additionally, it was concluded that porosity determine the bulk density and strength of porous TiC. However, the thermal conductivity of pore TiC increases with rising of porosity. This is attributed to the total number of pores is decrease owing to CaO agglomeration. [ABSTRACT FROM AUTHOR]

Porous sound absorption ceramic is one of the most promising materials for effectively eliminating noise pollution. However, its high production cost and low mechanical strength limit its practical applications. In this work, low-cost and in situ mullite whisker-reinforced porous sound-absorbing ceramics were prepared using recyclable construction waste and Al2O3 powder as the main raw materials, and AlF3 and CeO2 as the additives, respectively. The effects of CeO2 content, AlF3 content, and sintering temperature on the microstructure and properties of the porous ceramics were systematically investigated. The results showed that a small amount of CeO2 significantly promoted the growth of elongated mullite crystals in the resultant porous ceramics, decreased the growth temperature of the mullite whiskers, and significantly increased the biaxial flexural strength. When 2 wt.% CeO2 and 12 wt.% AlF3 were added to the system, mullite whiskers were successfully obtained at a sintering temperature of 1300 °C for 1 h, which exhibited excellent properties, including an open porosity of 56.4 ± 0.6%, an average pore size of 1.32–2.54 μm, a biaxial flexural strength of 23.7 ± 0.9 MPa, and a sound absorption coefficient of >0.8 at 800–4000 Hz. [ABSTRACT FROM AUTHOR]

MXenes, a large family of two‐dimensional carbides and/or nitrides, are among the most studied materials worldwide due to their great diversity of structures and compositions. Their unique properties find use in several applications. Typically, they are manufactured by selective wet‐chemical etching of layered MAX phase ceramics, which are produced nowadays primarily for MXene synthesis. However, the synthesis of MAX phases has not been changed since the time of their use in structural and high‐temperature applications, and it has not been optimized for MXene manufacturing. The main purpose of this study is to develop a porous Ti3AlC2 MAX phase that can be easily ground into individual grains without time‐consuming, harsh, and tedious crushing and milling steps. Moreover, we also demonstrate the synthesis of highly porous Ti3AlC2 from an inexpensive titanium sponge instead of a highly pure titanium powder and explain the mechanisms of reaction sintering and formation of porous MAX phase. MXene obtained from this MAX phase, Ti3C2Tx, shows larger flake size and higher electrical conductivity in thin films, compared to the materials produced from the costly fine titanium powder. The proposed approach may apply to the synthesis of other MAX phases as well. [ABSTRACT FROM AUTHOR]

Porous SiC ceramics with three different pore sizes (∼7, ∼45, and ∼98 μm) and two different porosities (∼54% and ∼63%) were prepared to investigate the effects of pore size on electrical and thermal properties of the porous ceramics. With an increase in pore size from ∼7 to ∼98 μm at the same porosity (∼54%), the electrical and thermal conductivities of the porous ceramics increased from ∼1.01 to ∼2.30 Ω−1·cm−1 and ∼14.3 to ∼26.2 W·m−1K−1, respectively. Similar trends have been obtained in the ceramics with ∼63% porosity. The porous SiC ceramic with larger pore size has smaller pore/strut interface area at the same porosity, which leads to less carrier scattering and phonon‐pore scattering at the pore/strut interfaces, resulting in higher electrical and thermal conductivities, respectively. These results suggest that the electrical and thermal properties of porous SiC ceramics can be successfully tuned by adjusting the pore size and porosity depending on the application. [ABSTRACT FROM AUTHOR]

SiAlON ceramics is a unique material used in various applications. Producing porous SiAlON material from available industrial waste by combustion is of great interest. In this work, a porous SiAlON composite was synthesized by the combustion of a mixture of aluminum ferrosilicon powder and aluminosilicate hollow microspheres in nitrogen. Aluminosilicate hollow microspheres were used as a pore-forming agent. The addition of aluminosilicate hollow microspheres to aluminum ferrosilicon powder increased the total porosity from 34.1 to 90.3%, the open porosity from 16.4 to 88.2%, and the maximum pore size from 53 to 413 μm in the final product. The porosity of the synthesized samples was predominantly open. [ABSTRACT FROM AUTHOR]

Through an activation reaction sintering method, porous (Mo2/3Y1/3)2AlC ceramics were prepared by Mo, Y, Al, and graphite powders as raw materials. The phase composition, microstructure, element distribution, and pore structure characteristics were comprehensively studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Archimedes method, and bubble point method. A detailed investigation was conducted on the influence of sintering temperature on the phase composition. Possible routes of phase transition and pore formation mechanisms during the sintering process were provided. The experimental results reveal that at 650–850 °C, transition metals react with aluminum, forming aluminum-containing intermetallics and a small amount of carbides. At 850–1250 °C, transition metals collaborate with graphite, producing transition metal carbides. Then, at 1250–1450 °C, these aluminum intermetallics interact with transition metal carbides and remaining unreacted Y, Al, and C, yielding the final product (Mo2/3Y1/3) 2AlC. Simultaneously, the pore structure alters correspondingly with the solid-phase reaction at different reaction temperatures. [ABSTRACT FROM AUTHOR]

In this paper, a kind of geopolymer porous ceramic was prepared using the physical foaming method combined with the gel casting process. The effect of sintering temperature on phase composition and physical properties of samples was studied. Fe2O3/geopolymer porous ceramic samples were prepared by Fe2O3 loaded on the surface of geopolymer porous ceramic samples through the impregnation-calcination method. The Fe2O3-loaded geopolymer porous ceramic samples were characterized by SEM-EDS, FTIR, and XPS. The adsorption experiments were employed to investigate the effect of testing conditions on the adsorption of Pb(Ⅱ) from the Pb(NO3)2 solution. The results show that the porosity of geopolymer porous ceramic samples decreased while the compressive strength increased, and the proportion of pores with a pore size range of

To meet the emerging demands for thermal protection materials for hypersonic aircraft, developing porous ultrahigh-temperature ceramics with both robust mechanical properties and superior thermal insulation performance is a critical challenge. Herein, we report novel porous (Ta0.2Nb0.2Ti0.2Zr0.2Hf0.2)C high-entropy carbide (PHEC) ceramics fabricated by a self-foaming method using commercially available metal chloride and furfuryl alcohol (FA) as precursors. The PHEC ceramics are constructed of microspheres with a size of 2 µm, leading to a high porosity of 91.3% and an interconnected frame. These microspheres consist of high-entropy carbide grains (20 nm), resulting in abundant interfaces and nanosized pores in the PHEC ceramics. Due to its unique hierarchical structure, the prepared PHEC ceramics have outstanding compressive strength (28.1±2 MPa) and exceptionally low thermal conductivity (κT, 0.046 W·m−1·K−1) at room temperature. This makes it a promising thermal insulation materials for ultrahigh temperature applications. This work provides a cost-effective and facile strategy for producing porous ultrahigh-temperature ceramics.

Al2TiO5 porous ceramics with high density and excellent thermal stability were prepared by the replica template method. MgO was introduced into Al2TiO5 by adding magnesite (MgCO3) to the slurry during the preparation process. The density and compressive strength of Al2TiO5 porous ceramics with varying MgCO3 content were studied. Additionally, the atomic-scale microstructure, thermal stability, and thermal shock resistance of the Al2TiO5 porous ceramics with 2 wt% MgCO3 were investigated. The results show that the Al2TiO5 porous ceramics doped with 2 wt% MgCO3 exhibit the highest density and compressive strength. The crystallographic orientation relationships of Al2TiO5 (ATO) - Mg0.3Al1.4Ti1.3O5 (MATO) and Mg0.3Al1.4Ti1.3O5 (MATO) - MgAl2O4 (MAO) are observed as (1 1 3) ATO//(1 1 2) MATO and [1‾ 2‾ 1] ATO//[1‾ 2‾ 1] MATO, (1 1 2) ATO//(2 2 0) MAO and [1‾ 2‾ 1] MATO//[1‾ 1 0] for the first time. In addition, the Al2TiO5 porous ceramics with 2 wt% MgCO3 remain phase stable after annealing at 1200 °C for 20 h, and the residual compressive strength is still higher than 88% after 20 cycles of the heating-cooling process at 1400 °C. These results indicate that the Al2TiO5 porous ceramics containing 2 wt% MgCO3 have potential applications in the porous media combustion (PMC) field.

Using a mixture of TiH 2 , Al, B 4 C, and graphite powders with a molar ratio of 3+2 m/1.2/m/2-m (where m ranges from 0 to 0.25, with increments of 0.05), porous Ti 3 AlC 2 -TiB 2 composite ceramics were successfully synthesized through activated reaction sintering. The effect of B 4 C content on the phase composition, volumetric expansion, microstructure, and pore structure parameters (including pore size, porosity, and permeability) was systematically studied. When the molar ratio of B 4 C was less than 0.1, the volumetric expansion rate, average pore size, and permeability increased with the addition of B 4 C, reaching maximum values of −5.46 %, 2.23 μm, and 92.4 m3 m−2·10 kPa−1 h−1, respectively. Conversely, when the B 4 C molar ratio exceeded 0.1, the parameters related to the pore structure of the porous Ti 3 AlC 2 -TiB 2 composite ceramics decreased, with minimum values of −10.40 %, 1.46 μm, and 68 m3 m−2·10 kPa−1 h−1, respectively. In addition, the pore formation mechanism of the porous Ti 3 AlC 2 -TiB 2 composite ceramics was systematically explored. The revolution tendency of pores is related to the decomposition of TiH 2 , Kirkendall partial diffusion, diffusion between B and C, and the transition process of the final phase Ti 3 AlC 2 -TiB 2. This research work could provide a reference for the preparation of the MAX phase composite porous materials. [ABSTRACT FROM AUTHOR]

High flight speed of hypersonic vehicles will push thermal insulation composites to achieve balanced enhancement of high porosity with increasing load-bearing capability. Herein, hierarchically porous SiC(rGO) polymer-derived ceramics (PDCs) with lightweight, heat-insulating, anti-ablative and tough engineered merits, are designed from polycarbosilane-vinyltriethoxysilane-graphene oxide precursors by re-pyrolysis/graphite-assisted decarburization. Graphite pore-forming agents tightly coupled with SiO x C y /C free (rGO) by C-dangling bonds, can inhibit SiO x C y decomposition, increase ceramic network disorder and expedite concurrent removal of C free. SiO 2 generated from Si-dangling oxidation bonding, efficiently densifies framework to retain mechanical performances, and meanwhile creates more interfaces to enhance phonon scattering. Such structure similar to nodular cast iron confers low thermal conductivity (0.11 W·m-1·K-1), particularly, fully preserves good compressive strength (5.4 MPa) for SiC(rGO) 40%. Under both cyclic butane flame ablation (∼1300 °C) and long-term oxidation for 7200 s, self-healing effect of SiO 2 imbues products with good structural integrity, shedding light on the opportunity to apply any thermal protection system. [Display omitted] • Hierarchically porous SiC(rGO) PDCs were ingeniously in-situ constructed. • Re-pyrolysis/graphite-assisted decarburization is a new structural design strategy. • The obtained products own well-balance between thermal insulation and load bearing. • Graphite-assisted interfacial interactions aims at strengthening ceramic framework. • Self-healing effect of SiO 2 can be promptly activated under flame scouring. [ABSTRACT FROM AUTHOR]

The Al 2 O 3 –SiO 2 porous ceramics (ASPC) prepared from phosphorus tailings usually showed a large fluctuation in material properties due to the complex composition of the raw material, which required extensive experimental exploration to optimize their properties. To solve the above problem, a novel deep learning strategy for automatically adjust hyperparameters had been proposed to predict the property of ASPC based on the small experimental datasets in this work. Initially, phosphate tailings and bauxite were used as raw materials. Active carbon, ranging from 0 to 15 wt%, was added as a pore-forming agent. After mixing the raw materials, they were shaped under a pressure of 5 MPa and sintered in the temperature range of 1000–1200 °C to produce ASPC, the density and compressive strength of the ASPC were measured to train the artificial neural network (ANN). An exhaustive search was conducted to identify the optimal combination of hyperparameters suitable for small datasets, then the influence of each hyperparameter on the training performance of ANN was analyzed. Subsequently, the trained model was used to predict the feature space of ASPC, and the key processes for regulating ASPC performance were explored, thereby the experimental schemes that meet target performance (density and compressive strength) were identified. Three groups of experimental schemes were predicted, whose properties were compared with the experimental ones. The results showed that the mean squared errors (MSE) of 0.03 and 0.85 for density and compressive strength, respectively. Furthermore, the ASPC exhibited excellent comprehensive properties when 70 wt% phosphorus tailings and 30 wt% bauxite were added, whose apparent porosity was 59.11 %, density was 1.16 g/cm3 and cold compressive strength was 6.49 MPa. And the predicted data trend influence of the pore-forming agent content and sintering temperature on the performance of ASPC is the same as the experimental data. This research provides valuable guidance for addressing the limited controllability of traditional experimental design processes and accelerate the preparation of ASPC from solid waste. [ABSTRACT FROM AUTHOR]

ABSTRACTLow thermal conductivity and excellent high-temperature stability make lanthanum zirconate (La2Zr2O7, LZO) a very promising material for high-temperature insulation applications. In this study, LZO porous ceramics with ultra-high porosity and an open-pore structure were prepared by the replica method using a polyurethane template. The flowability and coating quality of the ceramic slurry were optimized. When the dispersant content of the slurry was 0.6 wt% and the alcohol to water ratio was 1:1, the slurry had low surface tension and low viscosity, leading to good coating quality of the ceramic slurry on the sponge template. The pore size between hollow skeletons was 100–500 μm with the hollow structure of the skeletons forming secondary pores. LZO porous ceramics showed high porosity of 87.6%-96.0%, low thermal conductivity of 0.048–0.126 W/(m·K), and compressive strength of 0.13–0.74 MPa by adjusting the ceramic content. A high temperature insulation performance test showed that the temperature difference between the cold side and the hot side of the sample was over 1000°C, indicating the excellent thermal insulation properties of LZO porous ceramics. LZO porous ceramics had good high-temperature stability without sintering shrinkage at heat treatment temperatures below 1500°C.

This is an article in the field of ceramics and composites. In order to improve the performance of fly ash-based porous ceramic materials, the samples were surface-treated using Al2O3 modifying liquid, and physical and mechanical properties, adsorption effects and microscopic experiments were carried out on them. The results showed that the higher the sintering temperature, the smaller the porosity and water absorption of the porous ceramics, and the greater the strength and apparent density. Optimal sintering and molding of porous structures at a temperature of 1100 °C. When the concentration of Al2O3 modifying liquid was increased from 0 to 50 mol/L, the saturated adsorption rate of the porous ceramics increased about 6 times, and at the same time, the densities and strengths were also significantly increased. The surface modification effect of the Al2O3 modifying liquid promotes the formation of the caliche feldspar crystals, which results in a significant increase in the strength and adsorption properties of the porous ceramics. strength and adsorption performance were significantly improved.

Porous mullite ceramics have good properties for high‐temperature applications, but porosity gives place to ceramics with low mechanical strength, which restricts the service life in their potential applications. Therefore, performing modifications at the microscale to increase the mechanical strength has become a current challenge to expand its application fields. This work describes the properties of a porous mullite–zirconia composite produced by ceramic processing, using industrial kaolin and stabilized zirconia as raw materials. The growth of mullite needle‐like grains to reinforce the ceramic was promoted by the addition of a molybdenum oxide precursor. The effect of zirconia on the composite was analyzed through an experimental multi‐technique approach and considering a pure mullite sample, identically processed, as a reference. The novel composite has a porosity of about 50%, and presents a homogeneous microstructure, with interlocked mullite needle‐like grains and dispersed rounded zirconia grains. This morphology restricts the mullite tendency to shrink during sintering, giving the material a higher stiffness. In particular, the presence of zirconia in the composite improves both the flexural strength and the apparent Young modulus of the material (about 20% and up to 600%, respectively). These results encourage further investigations to establish this composite for different technological applications. [ABSTRACT FROM AUTHOR]

Porous ceramics hold the great potential in the field such as bone tissue engineering, superinsulation material, and energy storage. However, it is quite challenging to fabricate them with arbitrary shape using conventional processes. Herein, a method to fabricate arbitrary‐shaped porous ceramic structure is presented by combining traditional freeze‐casting process and indirect three‐dimensional printing technology. Various polydimethylsiloxane (PDMS) soft molds are prepared for freeze‐casting, and diverse‐shaped porous ceramics are fabricated. It proves that PDMS molds are ideal choices for freeze‐casting of porous ceramics with complex geometries. The freeze‐casting process of a complex‐shaped model with PDMS is simulated by finite element analysis. The effect of the solid loading of the alumina suspension on the microstructure and compressive strength of the as‐fabricated porous ceramics are investigated. The present study provides a strategy to fabricate complex‐shaped porous ceramic structure that can be used in a wide variety of applications. [ABSTRACT FROM AUTHOR]

Phase change material (PCM) is an ideal heat storage material with huge latent heat and nearly constant phase change temperature, but there are serious problems in application such as leakage and low thermal conductivity. Porous ceramic is widely used in PCM packaging because of its advantages of controllable porosity and high thermal conductivity. Porous Al 2 O 3 ceramics were prepared by foaming injection coagulation method. In order to improve the thermal conductivity of porous ceramic matrix, Porous Al 2 O 3 @Graphite Ceramics (PAGC) were prepared by sucrose decomposition. Form-Stable Phase Change Materials (FSPCMs) were prepared by adsorption of Lauric Acid/Myristic Acid (LA/MA) in PAGC by vacuum impregnation method. SEM showed that the prepared PAGC had a three-dimensional interpenetrating structure and high porosity. TEM and XPS showed that alumina skeleton were uniformly coated with graphite. After PAGC impregnated by LA/MA, the maximum PCM storage reached 62.11 wt %. The maximum latent heat of FSPCMs reaches 83.33 J/g. Thermogravimetric analysis, thermal cycling test and Fourier transform infrared spectroscopy show that the prepared FSPCMs has good thermal stability, thermal reliability, chemical stability and compressive strength. More importantly, the thermal conductivity of the prepared FSPCMs is greatly improved, reaching up to 3.73 W/mK. It is 20.72 times the original PCM, mainly due to the synergistic effect of the Al 2 O 3 skeleton and the graphite coating to build a continuous highway for heat transfer. This study provides a practical means to greatly improve the thermal conductivity of FSPCMs, which will promote the practical application of FSPCMs. [ABSTRACT FROM AUTHOR]

The deformation behavior of ZrO2 under compression of cylindrical and three point bending of V-notched beam-shaped samples has been investigated. The ceramics possess 50% porosity and the average pore size varying from 10 to 300 μm. It is shown that the formation of stochastic porosity and further increase in the average pore size lead to a multiple strength decrease relative to a non-porous sample. At the same time, the deformation behavior changes from elastic to pseudoplastic one reflected by the appearance of many local minima in the deformation curves and the increase in the relative ultimate strain. A plateau is found in the fracture toughness dependence on the pore size due to the increase in the main crack trajectory running mainly between the pores. In addition, the formation of multiple microcracks is found, also preventing the development of the main crack. [ABSTRACT FROM AUTHOR]

Low thermal conductivity and excellent high-temperature stability make lanthanum zirconate (La2Zr2O7, LZO) a very promising material for high-temperature insulation applications. In this study, LZO porous ceramics with ultra-high porosity and an open-pore structure were prepared by the replica method using a polyurethane template. The flowability and coating quality of the ceramic slurry were optimized. When the dispersant content of the slurry was 0.6 wt% and the alcohol to water ratio was 1:1, the slurry had low surface tension and low viscosity, leading to good coating quality of the ceramic slurry on the sponge template. The pore size between hollow skeletons was 100–500 μm with the hollow structure of the skeletons forming secondary pores. LZO porous ceramics showed high porosity of 87.6%-96.0%, low thermal conductivity of 0.048–0.126 W/(m·K), and compressive strength of 0.13–0.74 MPa by adjusting the ceramic content. A high temperature insulation performance test showed that the temperature difference between the cold side and the hot side of the sample was over 1000°C, indicating the excellent thermal insulation properties of LZO porous ceramics. LZO porous ceramics had good high-temperature stability without sintering shrinkage at heat treatment temperatures below 1500°C. [ABSTRACT FROM AUTHOR]

The application temperature and exposure time of lightweight, high performance aerogel insulation is limited by the thermal stability of the aerogel system used. Elevated temperatures cause rapid densification of the porous structures accompanied by increases in thermal conductivity and density. Previous studies have demonstrated the importance of doping concentration to thermal stability in doped metal oxide aerogel systems. The compositional route remains insufficient for stabilizing the pore structures of yttria-stabilized zirconia aerogels at elevated temperatures above 1100 °C. Non-compositionally, modifying synthetic parameters in the aerogel synthesis have been known to change the as dried pore structures. However, few studies have investigated the microstructure evolution of these pore structures under heat treatment. The current work investigates YSZ aerogels prepared via a sol-gel method at 30 mol% YO1.5, varying solids loadings and water contents. The results inform the ways in which the aerogel pore structure at high temperatures is sensitive and insensitive to the variation in synthetic parameters. An improved understanding of the relationships between synthetic parameters, as dried structure, and thermal stability will inform future efforts in the design and synthesis of aerogels with thermal stability in extreme environments. Highlights: Synthetic parameters of solids loading and water content modify the pore structure of YSZ aerogels. Microstructural evolution of a full factorial set of aerogels is characterized to 1200 °C. Higher specific surface areas contribute to significantly greater densification to 1000 °C. The change in densification with synthetic parameters is small compared to change with composition. [ABSTRACT FROM AUTHOR]

To address the difficulties of continuous adjustment of visible transmittance of amorphous porous ceramics and their anti-fogging without treatment, this paper delicately combined "hydrochromism" and porous ceramics, and prepared water-induced SiO 2 transparent porous ceramics (TPCs) with high strength and adjustable transparency. The effects of adding solvents to the silica sol on their visible transmittance, integrity and porosity were studied, and their multifunctional applications were also investigated. Results showed that the addition of EG, ammonia and acetonitrile mainly affected the gel integrity, the porosity of amorphous TPCs, and their gelation time and light transmittance, respectively. The compressive strength, porosity, visible transmittance after drying and water absorption of the optimal TPCs prepared at 600 °C by adding the above three solvents were 23.95 MPa, 54.7 %, 43 % and 81 %, respectively. The transparency of TPCs could be adjusted from 3 % to 81 % by controlling their water content, and they had excellent thermal insulation and anti-fogging ability without any treatment, and the excellent anti-fogging performance is related to their hydrophilicity and uniform nanopore structures. Overall, this paper provides new strategies for lightweighting, anti-fogging, and continuous adjustment of visible transmittance of transparent ceramics, and the resulting lightweight TPC is an ideal candidate for applications in daylighting design, as well as thermal insulation and anti-fogging in high humidity environments. [Display omitted] • Water-induced highly transparent SiO 2 -based TPCs were prepared for the first time. • Controlling water content in TPCs has realized its continuous cycle from transparent to opaque. • TPCs possess the anti-fogging ability without any treatment. • TPC is an ideal candidate for applications in daylighting design, thermal insulation and anti-fogging. [ABSTRACT FROM AUTHOR]

This work discusses ceramic filter materials used as substrates to study biological objects by electron microscopy. The composition, structure, pore sizes, and morphology of ceramic substrates made of foamed silicate prior to and following the application of inverse silicon oxide opals were evaluated by x-ray diffraction analysis and SEM method. Adescription of the use of the obtained filtering substrates in an experiment with biological objects is given. The substrates seem promising for electron microscopy, since they can be used for sample preparation of biological objects with the use of metal spraying or ionic liquid. This technique, together with the filtering porous material and the technical capabilities of the microscope, preserves the physical characteristics of biological objects. [ABSTRACT FROM AUTHOR]

Polycrystalline metal‐organic framework (MOF) membrane films prepared on ceramic supports can separate gases with high energy efficiency. They generally exhibit very high permeance and selectivity but suffer from cost issues through the required ceramic supports. Increasing the area and reducing the ceramic component to a minimum can be a strategy to enabling neat membranes of MOFs. In a rapid prototyping approach using 3D‐printed porous scaffolds with a double‐helical channel geometry, an increased active membrane area‐to‐volume ratio is shown. Following stereolithographic printing and debinding of a ceramic slurry, an adapted sintering protocol is employed to sinter commercially available alumina slurries into porous scaffolds. The 3D‐printed scaffolds are optimized at a porosity of 40%, with satisfying mechanical stability. Furthermore, synthetic procedures yielding omnidirectional, homogeneous coatings on the outside and inside of the tubular scaffolds are developed. Membrane films of zeolitic imidazolate framework 8 and Hong Kong University of Science and Technology 1 covering a huge 50 cm2 membrane area are produced in this way by applying a counter‐diffusion methodology. Gas‐separation performance is evaluated for H2, CO2, N2, and CH4, in single‐gas measurements and on their binary‐gas mixtures. [ABSTRACT FROM AUTHOR]

In this study, 0.57(Bi0.8La0.2)FeO3‐0.43PbTiO3 (BLF‐PT) porous ceramics were fabricated by the burnable plastic sphere method using polymethyl methacrylate (PMMA) as a pore forming agent. X‐ray diffraction results reveal that BLF‐PT porous ceramics mixed with tetragonal and rhombohedral phases display the single perovskite structure, changing little for different porosities. Scanning electron microscope images show that porosity of BLF‐PT ceramics increases with the increase of PMMA content with average grain size of 3.2–3.5 μm. Different from the continuous decrease of dielectric constant εr and remnant polarization Pr, piezoelectric constant d33 of BLF‐PT porous ceramics increases initially but then drops with the increase of porosity that reaches to the maximum of 230 pC/N at porosity of 8.5 vol.%. The abnormal enhancement of piezoelectric property is attributed to the unique three‐dimensional grid porous ceramic skeleton and uniformly distributed grain size. Moreover, acoustic impedance Z of BLF‐PT porous ceramic is 11.2 MRayls at porosity of 24.3 vol.% comparing with that of 17.7 MRayls for bulk ceramics, which reduces by 58%. BLF‐PT porous ceramics at lower porosity with enhanced piezoelectric and acoustic matching performances have a great potential in the fields of underwater acoustic transducers and medical ultrasonic diagnosis. [ABSTRACT FROM AUTHOR]

In order to improve filtering efficacy, nanoparticles are often deposited as photocatalytic degrading agents onto porous ceramics. This study aimed to deposit ZnO nanoparticles on ceramic substrates produced from fly ash and red mud with adjustable porosity and investigate their photocatalytic properties. To achieve this goal, at first porous ceramics were produced and sintered at various temperature/time intervals. It was observed that sintering at 800°C for 120 min provided a proper structure and porosity. In addition, MgO replacement with MgCO3 lowered the water absorption of the samples from 25.63% to 11.45%. The samples were then coated with ZnO nanoparticles using the sol–gel method and the ZnO structures obtained were micron‐sized plates. It was observed that increasing porosity increased the ZnO amount and accordingly the photocatalytic properties of the products. During the adsorption tests conducted in the dark, the coated ceramic samples were stained with MB with a maximum MB adsorption ratio of ∼14%. On the other hand, no visible MB stain was observed on the samples that were exposed to UV irradiation, and the MB removal after the UV irradiation was 93.6%; therefore, it was concluded that the dominant MB removal mechanism was photocatalytic. [ABSTRACT FROM AUTHOR]

In this study, the effect of porosity on the structural and functional (dielectric, ferroelectric, nonlinear, and piezoelectric) properties in Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics was investigated. Various levels of microporosity in the range of 3% to 31 vol.% have been produced using poly(methyl methacrylate) microspheres as sacrificial templates. The structural investigation indicates a phase coexistence, as expected for this composition at room temperature. The maximum permittivity decreases with increasing porosity, from around 7000 (ceramic with 3 vol.% porosity) down to 3500 (ceramic with 31 vol.% porosity), and the Curie temperature shifts from 47 to 67°C when increasing porosity, related to the possible porosity‐induced structural and internal stress modifications. An enhanced piezoelectric response was found in the Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramic with intermediate porosity around 18 vol.%, with the highest value of piezoelectric response of 470 pC/N and a figure of merit of 7.3 pm2/N. The optimum piezoelectric properties at the intermediate porosity level are related to the microstructural changes (pore shape and connectivity) and possible field‐induced structural modifications. The piezoelectric energy harvesting measurement results have shown the possibility of using Pb‐free porous ferroelectric materials in devices for energy harvesting applications. [ABSTRACT FROM AUTHOR]

In order to solve the problem of metal-organic framework MTL-100(Fe) powder which was difficult to be recycled and reused in industrial applications, this paper synthesized MTL-1 OO(Fe) powder by a hydrothermal method. The MTL-1 00(Fe)©porous ceramic composites were prepared by loading the powder on alumina porous ceramic using vacuum filtration method. The structure and properties of the MTL-1 00(Fe) and composites were characterized by using field emission scanning electron microscope-energy spectrometer (FE-SEM-ET)S), X-ray diffractometer (XRD), specific surface area analyzer (BET), and ultraviolet-visible spectrophotometer (UV-VTS). The photo-Fenton-degradation abilities in the H2O2 reaction system were investigated by simulating the dye wastewater with rhodamine B (RhB) solution. Results showed that the MTL-1 OO(Fe) presented an octahedral structure with a specific surface area as high as 1 152.75 m²/g. When the reaction temperature was 60 °C, the initial concentration of was 0.5 g/L and the initial concentration of RhB solution was 20 mg/L the degradation rate of RhB solution reached 99.26%. When the MTL-100(Fe)@porous ceramic composites were recycled for 5 times, the degradation rate of RhB solution still reached more than 98%. The composites present excellent recyclability and had promising for commercialization application. [ABSTRACT FROM AUTHOR]

Mullite-bonded SiC porous ceramics are of potential in hot gas infiltration while the insufficient mechanical performance limits its application. In-situ mullite whisker reinforcement is a potential solution but the formation temperature mismatch between mullite whisker and bonding layer is a challenge. In that case, mullite whiskers massively form ahead of the bonding layer excessively consuming alumina leading to poor bonding layers between SiC particles and thus, the mechanical performance. Herein, the mismatch was solved by using CaF 2 as a temperature-controlled reaction switch. As a result, both the bonding layer and whisker synchronously formed. The material showed significant reinforcement effects, and exhibited a flexural strength of 124.8 MPa and a fracture toughness of 1.53 MPa·m1/2 with an open porosity of 36.6 vol%, realizing a breakthrough in the mechanical performance. Interestingly, an increase in oxygen vacancy concentration with the sintering temperature was first reported, which may benefit the whisker growth. [ABSTRACT FROM AUTHOR]

The effect of addition of various metal carbides on the electrical, thermal, and mechanical properties of porous SiC ceramics was investigated. The results showed a decrease in the electrical resistivity from 1.2 × 102 to 1.3 × 10−3 Ω‧cm and thermal conductivity from 14.2 to 3.6 W.m−1K−1 whereas the compressive strength increased from 12.7 to 21.1–81.1 MPa at ∼60.2% porosity. The decrease in electrical resistivity and thermal conductivity was caused by the introduction of conductive carbides and multiple heterophase interfaces, respectively, in the porous ceramics. The electrical and thermal conductivities and compressive strength of porous SiC-based ceramics, processed with a SiC-B 4 C-VC-ZrC-NbC composition, were 8.0 × 102 Ω−1‧cm−1, 3.6 W‧m−1K−1, and 58.0 MPa, respectively. Therefore, it is proven that the electrical, thermal, and mechanical properties of porous SiC ceramics can be tuned over a wide range by adding a suitable combination of metal carbides. [ABSTRACT FROM AUTHOR]

In order to obtain ceramic materials for high-temperature gas-solid separation, the cordierite-mullite-corundum porous ceramics were prepared by particle stacking and pore-forming agent method, with bauxite as aggregate and in-situ synthesized cordierite as binder. Designed four-factor four-level orthogonal experiments for the first time to improve the porosity of the samples. The phase composition and microstructure of the samples were studied by XRD, SEM and other testing methods. The results show that: X6 sample (firing temperature of 1340 °C, 50 wt% binder, aggregate coarse, medium and fine mass percentage 30:50:20, plus 20 wt% charcoal powder, 10 wt% graphite) has the best comprehensive performance, with porosity of 41.51 % and bending strength of 17.88 MPa. Pore size distribution range from 10 to 40 μm. Corundum and mullite, with excellent high-temperature properties formed by the aggregate, are tightly bonded together by cordierite, contributing to the strength of the porous ceramics. The addition of pore-forming agent improves the porosity and forms a stable and uniform pore structure in the porous ceramics. The high porosity and large connected pore size reduce the viscous resistance of the porous ceramics to the gas, improve the filtration performance of the material, and make it expected to be applied in the field of hot gas clean-up. [ABSTRACT FROM AUTHOR]

Calcium hexaaluminate (CaO·6Al 2 O 3 , CA 6) porous ceramics possess excellent properties, including low density and high surface area. However, their inherent brittleness presents challenges in traditional fabrication methods, especially in terms of on-demand molding of macroscopic geometries and modulation of pore structures at the micro and nano scales. In this study, a novel approach was developed for producing CA 6 porous ceramics by employing in-situ gelation-assisted direct ink writing with sodium alginate. This method allows for the precise molding of macroscopic geometries and incorporates reaction sintering to prepare hierarchical porous features with macroscopic and microscopic pores. During the slurry printing process, the sodium alginate present in the ceramic slurry undergoes gelation upon contact with the calcium chloride expelled from the atomizer, thus facilitating in-situ curing and shaping. The optimal formation temperature for CA 6 is 1550 °C, resulting in grains with a lamellar structure. The ceramics display predominant pore sizes of 346 nm, 5.59 μm, and 8.25 μm, with an apparent porosity of 70.72 %. This printing strategy employs a slurry that offers excellent compatibility and design flexibility, opening up possibilities for tailoring porous structures to precisely meet specific application requirements. [ABSTRACT FROM AUTHOR]

This paper describes the fabrication and characterization of porous SiC ceramics derived from highly-filled preceramic papers. The SiC ceramics were obtained by spark plasma sintering of stacked preceramic papers at temperatures of 2100 and 2200 °C under pressures of 5–60 MPa for 10 min. The microstructure and phase composition were analyzed by scanning electron microscopy and X-ray diffraction, respectively. Gas permeation tests were performed using hydrogen permeation cell at room temperature. It is revealed that the porosity of sintered SiC can be varied from 9 to 45 % depending on the sintering parameters. The shrinkage of the materials during spark plasma sintering occurs in four stages. The linear shrinkage value of the material increases from 7 to 47 % at 2100 °C and from 20 to 50 % for the samples sintered at 2100 and 2200 °C, respectively. Correlation dependencies between porosity and mechanical properties of the fabricated SiC were established. The obtained porous SiC ceramics exhibit high bending strength of 165 MPa and gas permeation flux of 78 molH 2 /m2/s at the porosity of 36 % that make it suitable for ceramic-based membranes. [ABSTRACT FROM AUTHOR]

Porous anorthite (CaAl2Si2O8) ceramics, suitable for thermal insulation in buildings, were obtained using waste seashells as a source of CaO, kaolin as a source of Al2O3 and SiO2 and banana peel as a pore former. Changing the volume of banana peel as well as the processing temperature was found to be an effective approach to control the thermo-mechanical properties of the obtained anorthite ceramics. The sintering of powder compacts containing up to 30 wt% banana peel at temperatures ranging from 1100 to 1200 °C resulted in anorthite ceramics possessing up to 45% open porosity, a compressive strength between 13 and 92 MPa, a bulk density between 1.87 and 2.62 g/cm3 and thermal conductivity between 0.097 and 3.5 W/mK. It was shown that waste materials such as seashells and banana peel can be used to obtain cost-effective thermal insulation in buildings. [ABSTRACT FROM AUTHOR]

Reaction-bonded silicon carbide porous ceramics (SCPCs) are increasingly employed as membrane supports for the high-temperature filtration. However, the inevitable expansion of cracks limits their application. Herein, we studied the crack propagation behavior of SCPCs and discovered the commendable self-healing properties at high temperatures. Results show that the optimal healing conditions are 1200 °C for 2 h, which can recover the strength from 41.9% to 88.4%, and maintain the initial pore structure and permeance. This is mainly attributed to the infiltration of the multi-phase oxide melt that healed the cracks rather than the oxidation of SiC. Neck cracks are more prone to healing than surface cracks on SiC particles due to the residual compressive stress and a high proportion of melt volume. Nonetheless, the recovery of residual compressive stress and the crack width constrain the upper limit of strength recovery. These insights lay the groundwork for the high-temperature industrial application of SCPCs. [Display omitted] • Reaction-bonded SiC ceramics exhibit self-healing behavior at high temperatures. • The optimum healing condition is 1200 °C for 2 h. • The infiltration of multiphase oxides plays a dominant role in the healing process. • Neck cracks are more prone to healing than surface cracks on SiC particles. • The recovery limit of residual stress restricts the restoration of strength. [ABSTRACT FROM AUTHOR]

In order to improve the filtration performance, silicon carbide porous ceramics with network cell wall were fabricated via the polyurethane foaming method using silicon carbide powder, alumina powder, polyether polyol, polymethylene polyphenyl polyisocyanate, dibutyltin dilaurate, triethylenediamine and silicone oil (foam stabilizer) as raw materials. The effects of the solid loadings of the slurry (45%, 50%, 55% and 60%, by mass) on the microstructure, physical properties and their filtration properties towards particu-late matters were studied. The result shows that: (1) with the increasing solid loading, the bulk density and cold compressive strength gradually increase, and the apparent porosity decreases; (2) the micropores generated during the polyurethane foaming process are distributed on the ceramic pore wall to form a network cell wall structure, which increases the collision probability between particles and the wall pores and improves the filtration efficiency; meanwhile, the network cell wall structure also improves the pore interconnectivity and reduces the press drop; (3) when the solid loading is 55%, the silicon carbide based porous ceramics have the bulk density of 0.57 g · cm-3, apparent porosity of 79.2%, cold compressive strength of 3.7 MPa, and the filtering efficiency of the paniculate matter of 91.2%, achieving good regeneration performance. [ABSTRACT FROM AUTHOR]

To achieve the low temperature synthesis of cordierite, according to its theoretical ratio, porous cordierite ceramics were prepared using calcined kaolin (≤0.044 mm), sintered magnesia (≤0.074 mm) and silica micropowder (d50 =2.6 µm) as main raw materials, analytically pure zirconia and lanthana as sintering aids, and polyvinyl alcohol (PVA) solution as the binder, pressing to samples of Φ30 mm x30 mm at 60 MPa, drying and calcining. The effects of the extra additions of zirconia (0 and 8%, by mass) and lanthana (0, 0.2%, 0.4%, 0.6% and 0.8%, by mass) and calcination temperatures (1 200, 1 250 and 1 300 °C) on the cold physical properties, phase composition and microstructure of the porous cordierite ceramics were studied. The results show that: (1) the sample fired at 1 300 °C and introduced with 8% zirconia and 0.6% lanthana shows good physical properties; (2) the co-doping of zirconia and lanthana can improve the mechanical properties of the sample while maintaining the apparent porosity, and promote the formation of cordierite; (3) the co-doping of zirconia and lanthana can reduce the synthesis temperature of cordierite and improve the comprehensive performance of the sample. [ABSTRACT FROM AUTHOR]

ABSTRACTCalcium hexaluminate (CA6) porous ceramics were prepared by foaming and pore-forming agent methods, with Al2O3 and calcium aluminate cement (CAC) as raw materials and magnesium aluminum spinel hollow spheres (MASHSs) as pore-forming agent. The effects of the amount of magnesium aluminum spinel hollow sphere on the phase composition, bulk density, apparent porosity, flexural strength, microstructure, and thermal conductivity of CA6-based porous ceramics were systematically studied. The pores of such porous ceramics are mainly formed by the enhanced amount of MASHSs and the generation of CA6 phase. The results demonstrate that with the elevation of MASHSs content, the microstructure of the samples transforms from a uniform distribution of closed pores to an interconnected micro-pore arrangement. Notably, the fracture paths transition from cohesive to interfacial interactions between MASHSs. This intricate interplay culminates in a remarkable outcome – our ceramics exhibit thermal conductivities ranging from 0.210 to 0.451 W/(m/k), an augmented gas permeability of 25.96 × 10−11m2, and exceptional compressive strengths reaching up to 22.3 MPa. Overall, this study provides insights into the influence of MASHSs content on the microstructure and thermal-mechanical properties of porous materials, which may contribute to the development of advanced ceramic materials with tailored properties.

The microstructure and properties of porous ceramics are severely affected by volume shrinkage during the sintering process. Therefore, reducing sintering shrinkage while maintaining the properties of porous ceramics is a serious challenge. Herein, near-net-size porous mullite ceramics with tuneable sintering shrinkage were prepared by the foam-gelcasting method using kyanite as raw material and aluminum fluoride and aluminum powders as additives through the volume expansion generated by the sintering reaction. The effects of Al powder content on the sintering shrinkage, porosity, compressive strength and thermal conductivity of porous mullite ceramics were investigated. The results show that the sintering shrinkage gradually decreases with increasing Al powder content, and expansion is even produced. When the Al powder content was 5 wt%, the sintering shrinkage of porous mullite ceramics was −0.21 %, with porosity of 84.2 %, compressive strength of 2.45 ± 0.15 MPa, and thermal conductivity of 0.19 W/(m·K) at room temperature. The results of the high-temperature fire resistance test showed that the temperature difference between the front and back sides of the sample under the flame gun reached 800 °C, indicating good thermal insulation performance. The near-net-size sintering process of porous ceramics can effectively reduce the subsequent processing cost, open new paths for their production, and broaden the application fields of porous mullite ceramics. [ABSTRACT FROM AUTHOR]

A simple and scalable approach to fabricate monodispersed Si 3 N 4 hollow microspheres (Si 3 N 4 HMs) with uniform spherical structures is proposed in this study. This approach involves spray drying of Si 3 N 4 precursor, followed by carbothermal reduction nitridation. The homogeneous Si 3 N 4 precursor was first obtained by mixing phenolic resins and silicon resins, which are carbon and silicon sources, respectively. The spray drying process was then tuned by regulating the viscosity of the precursor by adding polyvinyl butyral in an appropriate ratio. Next, the hollow precursor microspheres were pyrolyzed at 1500 °C for 6 h, while ensuring that the shells of the obtained Si 3 N 4 HMs remained intact. Porous Si 3 N 4 ceramics with different contents of Si 3 N 4 HMs were then prepared using the gel-casting method. It was observed that the densities and dielectric constants of the porous Si 3 N 4 ceramics decreased with an increasing Si 3 N 4 HMs content. Thus, the proposed approach can be used for the synthesis of Si 3 N 4 HMs, that can be further processed into ceramic materials with both low densities and dielectric constants. [ABSTRACT FROM AUTHOR]