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Porous ceramics are demanded in a wide range of high‐temperature, biological and energy‐related applications, but may show conflicting properties or suffer from poor mechanical properties. Introducing pores at different length scales has been shown to be a promising design strategy to combine antagonistic performance parameters and reach high porosity without severely compromising strength. Herein, a cost‐effective and simple process to create strong, highly porous ceramics via direct ink writing of suspensions of hollow microspheres into cellular architectures with pores at three hierarchical levels is reported. X‐ray diffraction, rheological measurements, scanning electron microscopy, and mechanical tests are conducted to thoroughly study the processing steps and morphology of the printed hierarchical porous ceramics. The presence of pores at multiple length scales increases significantly the mechanical strength of the porous structure, providing a useful platform for the manufacturing of lightweight ceramics from inexpensive and widely available feedstock materials. [ABSTRACT FROM AUTHOR]

Porous materials are useful as lightweight structures, bone substitutes, and thermal insulators, but exhibit poor mechanical properties compared to their dense counterparts. Biological materials such as bone and bamboo are able to circumvent this trade‐off between porosity and mechanical performance by combining pores at multiple length scales. Inspired by these biological architectures, a manufacturing platform that allows for the fabrication of Al2O3 foams and Al2O3/Al composites with hierarchical porosity and enhanced mechanical properties is developed. Macroscale pores are formed through the assembly of aluminum particles around templating air bubbles in wet foams, whereas the thermal oxidation of the metal particles above 800 °C generates porosity at the micrometer scale. After elucidating the mechanism of pore formation under different sintering conditions at the microscale, the mechanical performance of the resulting hierarchical foams using compression experiments and finite element simulations is evaluated. Porous materials manufactured via this simple approach are found to reach unparalleled mechanical properties with near‐zero sintering shrinkage and minimum loss in mechanical strength. The ability to produce macroscopic objects with ultrahigh strength at porosities up to 95% makes this an attractive manufacturing technology for the fabrication of high‐performance lightweight structures or advanced thermal and acoustic insulators. [ABSTRACT FROM AUTHOR]

In situ coagulation for yttria‐stabilized zirconia (YSZ) suspension via polyvinyl pyrrolidone (PVP) crosslink is reported. PVP is used to prepare sterically stabilized YSZ suspension. Influence of PVP on the dispersion of YSZ suspension was investigated. It indicates that well disperse YSZ suspension with 0.3 wt % PVP can be prepared. Dimethyl sulfate (DMS) was added at 40 °C to coagulate the suspension after degassing. Influence of DMS content and coagulation temperature on coagulation process and properties of green bodies were investigated. It indicates that sufficiently high viscosity to coagulate the suspension is achieved with the addition of 1 vol % DMS at 60~80 °C. The coagulation mechanism is proposed that the YSZ suspension is destabilized by the self‐crosslink of PVP. Coagulated samples with the highest wet compressive strength of 6.34 MPa could be demolded without deformation by treating 50 vol % YSZ suspension at 60 °C. Dense YSZ ceramics with relative density above 99.1% and flexural strength of 920 ± 90 MPa had been prepared by this method sintered at 1450 °C for 3 h. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48889. [ABSTRACT FROM AUTHOR]

Ceramic foams with significant porosity and robust mechanical properties have received extensive attentions. However, it is still difficult to achieve excellent compressive strength at high porosity levels. In this work, a gelation of foamed boehmite sol method is proposed to settle this issue. The technological parameters during preparation process are systematically investigated. As‐prepared alumina ceramic foams possess unprecedentedly high compressive strength of 34.1‐89.1 MPa at high porosity levels of 66.0%‐87.2%, which is attributed to the present of hierarchical pore structure, small grain size and pore size. This work demonstrates a facile and novel method for the fabrication of high‐performance alumina ceramic foams toward practical applications. [ABSTRACT FROM AUTHOR]

In this work, gangue/palygorskite composite microspheres were fabricated through spray drying process and activated by calcination treatment. Its microstructure and adsorption capacity for the removal of dye (MB) were also studied, systematically. Results showed that kaolinite, α‐quartz and palygorskite were the major phases in microspheres after proper calcination (lower than 900°C). BET‐specific surface area of the microspheres reached the maximum value of 62.23 m2/g at 700°C, and then decreased with further increasing the heating temperature. In general, composite microspheres showed the largest adsorption capacity of MB after heat‐treated at 700°C. The qmax of MB onto microspheres was 29.9‐51.9 mg/g. The adsorption process of MB onto microspheres was well described by both the pseudo‐second‐order kinetic and Langmuir isotherm model. The composite microspheres also had extraordinary recyclability. This novel microsphere could be employed as a candidate for novel absorbent and filter medium in the practical application for dye treatment in industrial applications. [ABSTRACT FROM AUTHOR]

Ultralight ceramic foam materials with high porosity play an important role in increasingly hi‐tech areas due to the combinative merit of ceramic material and highly porous structure. So far, it remains challenging to fabricate alumina ceramic foams with extremely high porosity and high specific surface area that are comparable to aerogel materials by employing a low cost, eco‐friendly and convenient approach. For the first time, we propose the preparation of aerogel‐like ceramic foams with nanoscale cell wall and unprecedentedly high porosity using boehmite sol as both ceramic source and bubble interface stabilizer, based on sol nanoparticles stabilized foams using sodium lauryl sulfate (SDS) as modifier. The obtained ultra‐stable sol foams allow for the achievement of bulk foams with ultrathin cell wall with thickness in the range of 30‐90 nm, super‐high porosity up to 99%, and large specific surface area of 280 m2/g, which is attributed to the well‐organized assembly of nanoparticles at the liquid/air interfaces. This novel foam material demonstrates excellent adsorption ability for polar volatile organic gases (VOCs) due to its extremely high porosity and large specific surface area. Ultralgiht cellular ceramic foams composed of uniformly assembled nanoparticles with nanoscale cell wall. [ABSTRACT FROM AUTHOR]

Three‐dimensional ceramic nanofiber‐assembled materials with large specific surface area and excellent thermal insulation properties are attracting increasing interests for their unique structure and promising applications. In this paper, we propose a facile methodology to fabricate three‐dimensional silicon nitride nanofiber‐knitted ceramic foams via in situ reactive synthesis from silicon foams. Silicon particle‐stabilized foams are fabricated for the first time using long‐chain surfactant cetyltrimethyl ammonium bromide as a hydrophobic modifier. First, the fabrication and stability of silicon foams are investigated. Based on the stable silicon foams, silicon nitride‐based nanofiber‐knitted ceramic foams are synthesized via in situ reactive sintering in nitrogen atmosphere. The novel ceramic foam materials consist of three‐dimensional nanofiber‐assembled strut wall and nanofiber‐spheres in the pores. The diameter of obtained silicon nitride nanofibers ranges from 15 to 100 nm. The unique nanofiber‐knitted foams may have potential applications in specific fields, including catalysis, adsorption, separation, and thermal insulation. [ABSTRACT FROM AUTHOR]

Hierarchical structured porous ceramics have attracted tremendous research interests because of their numerous excellent properties including robust mechanical strength and large surface area. In this work, silicon carbide (SiC)‐based porous ceramics with three levels of pore hierarchy are fabricated from silicon particle‐stabilized foams and a subsequent one‐step calcination after they were embedded with coke. Three‐dimensional (3D) flexible nanofibrous network is adhered and wrapped on cell walls of porous ceramics, which is readily fine‐tuned and tailored by the temperature to provide optimized pore structure. The resultant SiC‐based porous ceramics present a density of 1.03 g/cm3 at a porosity of 72% with a large quantity of hierarchical micro‐ and macropores. This hierarchical structure leads to robust compressive strength (23.52 MPa) and large surface area (64.32 m2/g). The fabrication method is straightforward and sought‐after, providing a facile technical route for advanced hierarchical porous ceramics used in filtration and catalysis fields. [ABSTRACT FROM AUTHOR]

A novel kind of nanowire sponges, namely Si3N4 nanowire‐weaving microspheres, synthesized from a simple, convenient, high‐efficient approach are proposed here. As the reverse template, three‐dimensional foam skeleton structure with uniform pores and ultrathin pore walls is constructed via the effective particle‐stabilized foam method, where the silica sol and carbon black are chosen as the raw materials, providing the sufficient space for the growth of nanowires during the carbothermal reduction reaction process. The formation mechanism of this novel sponge is studied via multiple characterization methods. Si3N4 nanowires formed microspheres possess uniform and curving morphology due to the stable environment for growing via vapor–solid mechanism, leading to the relatively high specific surface area of 86.77 m2/g. Owing to in‐situ oxidation process, micro‐spherical SiO2 nanowire sponges with similar morphology are synthesized, which present diameter in range of 20‐40 nm and specific surface area of 50.47 m2/g. This work provides insights for the design of high‐performance nanowire sponges with promising applications in the filtration, thermal insulators, and catalyst supports fields. [ABSTRACT FROM AUTHOR]

Abstract: In order to investigate the relationship between pore structure and thermal conductivity as well as mechanical strength, porous alumina ceramics (PAC) with various pore structures were fabricated, using starch as the pore‐forming agent. Fractal theory was employed to characterize the pore size distribution more accurately than ever used parameters. The results show that the increase in starch content in PAC leads to an enhanced porosity, a higher mean pore size, and reduced fracture dimension, thermal conductivity and strength. The fractal analysis indicated that the fractal dimension decreases gradually and reaches its minimum value with increasing the starch content up to 25 wt%, but the further incorporation results in an opposite trend. It is suggested from micro‐pore fractographic analysis that the optimization of both thermal insulation performance and mechanical strength are positively correlated with the increase in the mean pore size and proportion of 2‐14 μm pores but negatively corrected with the porosity. These results provide a new perspective and a deeper understanding for fabrication of PAC with both excellent thermal insulation and mechanical performance. [ABSTRACT FROM AUTHOR]

Abstract: A novel method for fabrication of highly porous barium strontium titanate (BST) ceramic foams based on particle‐stabilized foaming method was developed for the first time, in which propyl gallate (PG) was employed as BST particle modifier. The results showed that the stability of wet BST foams closely depends on the pH value and PG concentration, which could be explained by the adsorption behavior of PG on BST particle surface. BST ceramic foams with dense, uniform, and closed pore and defect‐free wall were obtained. The pore size and porosity can be well controlled by adjusting solid loading and sintering temperature. It was revealed that not only sintering temperature but also solid loading significantly influenced the growth of BST grain. The BST ceramic foams exhibited high porosity in the range of 81%‐95%, low dielectric constant in the range of 47‐150, and low dielectric loss below 0.0025. The BST ceramic foams with higher porosity presented a tendency of lower dielectric constant and the fitting results indicated that the natural logarithm of dielectric constant was linear correlated with porosity. [ABSTRACT FROM AUTHOR]

The weak compressive strength of dried ceramic foams is a disadvantage of fabricating ultralight ceramic foams, especially for the ceramic foams with porosity exceeding 95%. In this study, dried alumina foams were enhanced by agar and PVA-freezing-thawing using sodium dodecyl sulfate as surfactant. It is found that the two additives have no negative influence on adsorption of sodium dodecyl sulfate on alumina particles as well as the hydrophobic character of alumina particles. Stable alumina particle-stabilized foams were prepared with less than 0.5 wt% agar and 1.0 wt% PVA. High additive concentration above the critical values weakens stability of wet foams, which is probably due to the aggregate of alumina particles caused by long-chain molecules connecting. The compressive strength of dried alumina foams has a significant improvement with the employment of agar and PVA-freezing-thawing. The dried foams prepared with 1wt% PVA assisted by freezing-thawing has porosity of 97.1% and compressive strength of 0.16 MPa, which could maintain integrity of dried foams without destruction in the fabricating process. [ABSTRACT FROM AUTHOR]

In order to realize the toughening effect of Si3N4 hollow microsphere, direct coagulation casting method via dispersant reaction is utilized to form porous green bodies of Si3N4 ceramics for the first time. It is found that the combination state between Si3N4 hollow microsphere and ceramic matrix is enhanced due to its superiority on the coagulation mechanism. This novel colloidal forming method efficiently contributes to the close contact between hollow microspheres and ceramic particles, leading to the improvement of interface strength between the pore‐former and ceramic matrix. More importantly, it is proved that ceramic hollow microspheres could well perform as both pore‐former and toughening phase. The porosity regulation of porous ceramics is realized by tailoring ludox and carbon amount through carbothermal reduction method. This method turns out to regulate the performance of porous ceramics better especially through the sintering parameters. Porous Si3N4 ceramics prepared with 5 wt% ludox addition which are treated in argon at 1400 °C possesses the optimal performance. They possess the fracture toughness of 2.45 MPa · m1/2, dielectric constant of 3.49, and thermal conductivity of 2.57 W/(m · K), which have promising applications in radome materials. In this research, direct coagulation method via dispersant reaction is employed to achieve porous Si3N4 ceramics with excellent mechanical performance. Benefited from the coagulation mechanism, better interface strength between Si3N4 hollow microsphere and ceramic matrix is obtained. As a result, Si3N4 hollow microspheres act as the toughening phase beyond the pore‐forming agent. [ABSTRACT FROM AUTHOR]