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Microwave and terahertz communications are increasingly significant, however, the lack of material information in terahertz band limits their development. Moreover, few lightweight materials with a high relative dielectric constant (εr) are found suited for satellite communication and wearable devices. In this study, we developed lightweight porous Ba4[(Sm0.1Nd0.9)0.9Bi0.1]28/3Ti18O54 (BSNBT) ceramics exhibiting a total porosity ranging from 6.3% to 26.5% (bulk density ranging from 5.47 to 4.29 g/cm3) and relatively high εr ranging from 85.6 to 56.8, which were obtained by sacrificial template method using polymethyl methacrylate spheres (PMMAs) of varying average particle sizes, from 9 to 34 μm, as sacrificial materials. A high refractive index ranging between 7.5 and 8.9 and a low absorption coefficient of approximately 17 cm−1 at 0.3 THz were obtained for the porous ceramics with different total porosities derived from PMMAs with average particle sizes of 9 and 19 μm. Furthermore, effective medium and Mie scattering theories were applied to understand the effects of porous structure on the dielectric properties in microwave and terahertz frequency ranges, respectively, owing to the different wavelengths in the BSNBT matrix. The results of this study suggest that introducing a porous structure can effectively exploit lightweight microwave dielectric ceramic materials and provide valuable information on their terahertz response mechanism. [ABSTRACT FROM AUTHOR]

Ceramic foams with extensive interconnected pores have great application potential in high‐temperature particulate matter (PM) capture. Considering that there are still challenges to synthesize ceramic foams with efficient filtration, a novel hierarchical‐structured alumina foam with three‐dimensional (3D) reticular architecture has been fabricated via combining chemical grafting pore‐forming agent and polyurethane (PU) foaming technology. Carbon black is grafted with carbamate functional groups in order to enable a better dispersion in highly viscous PU. Submicrometer and micrometer‐sized pores on the cell walls are observed in hierarchical‐structured ceramic foams. The resulting alumina foam exhibits 95.2% removal efficiency for PM particles and low pressure drop of only 50 Pa when grafted carbon black content is 3 wt%. This filtration performance is much higher than that of existing ceramic materials. These features, combined with our experimental design strategy, provide a new insight to design high‐temperature PM filtration materials with durable high performance. [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]

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]

Compressive strength is one of the most important mechanical properties for ceramic foams but the dependence of compressive strength of highly porous ceramic foams on porosity remains unclear up to now, especially for the ceramic foams with porosity above 94%. In this paper, the relationship between compressive strength and porosity of ceramic foams with high porosity in the range of 79–98% was studied for the first time. The alumina ceramic foams and zirconia foams were prepared by particle-stabilized foaming method using sodium dodecyl sulfonate (SDS) as foaming agent. It was found that the function relation between compressive strength and porosity depended on porosity level. Specifically, compressive strength of ceramic foams fitted well with Rice Model when the porosity ranged from 79% to 94%. When the porosity increased above 95%, compressive strength of ceramic foams showed linear relation to porosity, which was probably due to the characteristic of highly porous ceramic foams with thin and lamellate cell wall. [ABSTRACT FROM AUTHOR]

Abstract In the present work, Al 2 O 3 -Si 3 N 4 porous ceramics with a cactus-like architecture were fabricated by calcining Al 2 O 3 -Si binary particle-stabilized foams in the nitrogen atmosphere. A large number of acicular Si 3 N 4 nanobelts were constructed on the surface of cell walls as a consequence of CVD process to achieve an interlaced network. Such structure was beneficial to realize a high capture efficiency of particulate matters (PM) during filtration. Resultant products having a bulk density of 0.38 g/cm3 at an apparent porosity of 86% can potentially be applied as the air filters in environment field. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Aqueous ceramic particle-stabilized foams with UV light response are prepared. • Photocurable particle-stabilized emulsions with controllable structure are achieved. • The colloid foams/emulsions demonstrate excellent stability and photocuring ability. • Rapid and scalable synthesis of ceramic capsules is developed based on the emulsions. Abstract We herein report the design and preparation of ceramic particle-stabilized emulsions/foams with distinct ultraviolet light (UV) response, which can be used for the rapid fabrication of ceramic foams with complex shape, for synthesis of ceramic hollow spheres, and can potentially be used for 3D printing lightweight and hierarchical ceramics with porous skeleton. Photocurable foams/emulsions stabilized by ceramic particles are achieved for the first time using photosensitive oligomer as oil phase and/or using photosensitive aqueous solution containing acrylamide monomer as water phase. Four kinds of photocurable emulsions are demonstrated by adjusting emulsion structure and photosensitive phase. We further synthesize internal multiple-pore structured capsules and lightweight nanoparticle-assembled capsules in micron-scale based on the photocurable particle-stabilized, by separating emulsion into small droplets via diluting and stirring, followed by rapid curing under UV. This new strategy may potentially open opportunities for the rapid and cost-effective synthesis of high-output ceramic capsule materials. The synthesized thin-shell alumina capsules exhibit large specific area surface of 323.18 m2/g as well as uniform mesoporous structure in shell with average pore diameter of 3.4 nm, which has potential application in the fields of adsorption, load and release of materials and thermal insulation. [ABSTRACT FROM AUTHOR]

In order to reduce thermal conductivity but to exhibit better mechanical properties of porous alumina ceramics (PACs), a novel approach, based on the modification of pore structures (i.e. mean pore size, micro-pore proportions and pore shape factor) by impregnation of alumina sol, is reported in the present work. The properties of as-impregnated samples were compared with commercial alumina hollowsphere bricks. Results show that impregnation of alumina sol in PACs has a positive influence on pore structures, leading to a superior strength and a lower thermal conductivity. In particular, when 8 wt% alumina sol solid content is impregnated, the crushing strength (35.3 MPa) and thermal conductivity (0.15 W/m K at 200 °C) of sample are much better than that of the commercial alumina hollowsphere bricks. This novel method for excellent PACs provides promising applications as insulating lining materials in the fields of industrial furnace. [ABSTRACT FROM AUTHOR]