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Seven microporous MgO–Al2O3 ceramics with an Al2O3 content of 15–90 wt% were prepared using Al(OH)3 and calcined magnesite as raw materials. A wet mixing process was employed during sample preparation to transform the calcined magnesite with a larger particle size to smaller Mg(OH)2 particles. The in situ decomposition synthesis method and the Kirkendall effect were utilized to produce and control the pore structure of the microporous MgO–Al2O3 ceramics. There were two kinds of pores in the microporous MgO–Al2O3 ceramics. The first one resulted from the in situ decomposition of Al(OH)3 and Mg(OH)2 particles, which were small and equally distributed. Another one originated from the position of the Mg(OH)2 particles due to the Kirkendall effect caused by MgO diffusion. They were similar in size to the Mg(OH)2 pseudomorph particles. Simultaneously, the Al2O3 content affected the packing behavior and the spinel formation, which changed the characteristics of the pores and necks among the particles. These mechanisms also affected the strengths of the microporous MgO–Al2O3 ceramics. Thus, when the Al2O3 content was 45–90 wt%, the microporous MgO–Al2O3 ceramics had a high compressive strength (10.0–18.3 MPa) and apparent porosity (52.2%–58.4%). [ABSTRACT FROM AUTHOR]

β‐Sialon(z = 2, Si4Al2O2N6)/ZrN composite powders have been synthesized from coal ash, zircon, and active carbon at 1550°C for 6 hours, and β‐Sialon(z = 2)/ZrN/ZrON‐based composite ceramics (SZZCCS) have been prepared from as‐synthesized β‐Sialon/ZrN composite powders via pressureless sintering process. The effects of sintering temperatures (1450, 1500, 1550°C) on the phase compositions, microstructures, linear shrinkage ratio, bulk density, and oxidation characteristics of the SZZCCS were investigated in detail, and the oxidation process was also analyzed. It was found that the dense SZZCCS could be prepared at 1550°C for 1 hour, and they mainly consisted of β‐Sialon(z = 2), ZrN, and ZrON. The ZrN and ZrON particles were uniformly distributed on the β‐Sialon matrix. The sintering properties of the SZZCCS were greatly improved with increasing the sintering temperature. The SZZCCS sintered at 1550°C for 1 hour possessed excellent oxidation resistance at 900°C for 6 hours due to their dense microstructures. [ABSTRACT FROM AUTHOR]

In this work, the novel Al 2 O 3 -based ceramic filter prepared by replacing dense Al 2 O 3 raw material with microporous corundum-spinel raw material is proposed and enhanced. The effects of nano-Al 2 O 3 powder content (0, 2.5, 5 and 7.5 wt%) on the rheological properties of the slurries, microstructures, pore characteristics and mechanical properties of the filters were investigated. When the nano-Al 2 O 3 powder content increased from 0 to 5 wt%, the rheological properties of the slurries were optimized, resulting in a larger thickness diameter and uniform distribution of the filter skeleton. The nano-Al 2 O 3 powder with a high reactivity accelerated the diffusion mass transfer rate of ions and increased the sintering driving force, thus promoting the development and growth of the spinel grains. It also led to the formation of more spinel neck connections between the microporous corundum-spinel particles, which enhanced the cold compressive strength and thermal shock resistance of the filters, while the pore size slightly increased due to the spinel volume expansion between the particles. When the nano-Al 2 O 3 powder content further reached 7.5 wt%, the yield stress of the slurry increased markedly due to the agglomeration phenomenon, leading to an uneven distribution of the filter skeleton and a lower cold compressive strength of the filter. Overall, the mechanical properties of the novel Al 2 O 3 -based ceramic filters were greatly enhanced by the addition of 5 wt% nano-Al 2 O 3 powder. The filter skeleton had a bulk density of 2.19 g/cm3 and an apparent porosity of 41.8%. The novel Al 2 O 3 -based ceramic filter also exhibited a high cold compressive strength of 2.37 MPa and an excellent thermal shock resistance. It contained a rougher surface structure compared to existing filters and has the potential for better purification efficiency on molten metal in the future. [ABSTRACT FROM AUTHOR]

Abstract BiCuSeO is a kind of promising oxide-based thermoelectric material with special natural superlattice structure. Herein, the effects of Er doping and modulation doping on the thermoelectric properties of BiCuSeO have been investigated. The results indicate that Er doping can tune the Fermi level, widen the band gap, reduce the energy offset between the heavy band and the light band, and then greatly improve the electrical conductivity, power factor and ZT. Modulation doping based on Er doping can increase carrier concentration and power factor significantly while maintaining high carrier mobility. Meanwhile, due to the special heterostructure of the modulation doping sample, the phonon scattering is greatly enhanced, and the corresponding lattice thermal conductivity is significantly reduced. Finally, the maximum ZT value reaches 0.99 for the modulation doped Bi 0.92 Er 0.08 CuSeO bulk at 873 K, which was ~1.8 times as that of the pristine BiCuSeO sample. [ABSTRACT FROM AUTHOR]

Abstract Bi 1- x Pb x Cu 1- x Ni x SeO (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) BiCuSeO based ceramics have been prepared by mechanical alloying (MA) and resistance pressing sintering (RPS) process. The effects of Pb/Ni doping and 3D modulation doping on the thermoelectric properties have been investigated systematically. For Pb doping, it can tune the Fermi level and promote the band convergence, decreasing the band gap and significantly enhancing the carrier concentration. Besides, it contributes to higher effective mass and Seebeck coefficient due to the delocalized 6s orbitals from the lone pair electrons. For Ni doping, Ni ions could enhance Seebeck coefficient. The results indicates that the substitution of Pb at Bi site and Ni at Cu site resulted in the significantly increase of electrical conductivity and power factor. Based on this, 3D modulation doping led to the simultaneous increase of the electrical conductivity and power factor. The maximum power factor of the modulation doped sample (Bi 0.90 Pb 0.10 Cu 0.90 Ni 0.10 SeO) reached 0.64 mW m−1 K−2, and the maximum ZT value reached 1.08, which is 1.3 and 1.0 times higher than those of the undoped sample, respectively. Graphical abstract Pb/Ni doping combined with modulation doping led to the great increase of BiCuSeO based ceramics(Bi 1- x Pb x Cu 1- x Ni x SeO, x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) fx1 Highlights • Pb/Ni doping led to the great increase of carrier concentration and electrical conductivity. • Modulation doping based on Pb/Ni doping increases the electrical conductivity further. • The highest ZT is 1.08 for the modulation doped sample at 873 K. [ABSTRACT FROM AUTHOR]

Here, Bi 1- x Ba x CuSe 1- x Te x O ( x  = 0, 0.02, 0.04, 0.06, 0.08, 0.10) ceramics have been prepared by mechanical alloying (MA) and resistance pressing sintering (RPS) process. The effects of Ba/Te doping on the thermoelectric properties have been investigated systematically. For Ba doping, it can tune the Fermi level and promote the band convergence, decreasing the band gap and significantly enhancing the carrier concentration; for the Te doping based on Ba doping, it can profoundly reduce the difference of electronegativity in (Cu 2 Se 2 ) 2- layer, increase bond covalency, and then increase the electrical conductivity. The results indicate that the substitution of Ba/Te resulted in significant increases of electrical conductivity and power factor. Based on this, modulation doping leads to the simultaneous increase of the electrical conductivity and Seebeck coefficient. Finally, the maximum power factor of 0.98 mW m −1 K −2 and ZT value of 1.17 were obtained for the modulation doped Bi 0.90 Ba 0.10 CuSe 0.90 Te 0.10 O bulk, which were ~ 3.5 and ~ 2.2 times respectively as those of the pristine BiCuSeO ceramic. [ABSTRACT FROM AUTHOR]

Abstract The layered oxyselenide BiCuSeO thermoelectric ceramics are attracting much scientific attention for its excellent thermoelectric properties. Herein, Bi 1- x Sb x CuSe 1- x Te x O ( x = 0, 0.01, 0.02, 0.04, 0.06, 0.08) ceramics have been prepared by ball milling (BM) and resistance pressing sintering (RPS) process. The effects of Sb/Te doping and grain size on the thermoelectric/mechanical properties are investigated systematically. For the former, it can tune the Fermi level and promote the band convergence, decreasing the band gap and concurrently enhancing the carrier concentration; for the latter, it can profoundly modify microstructure into an all-scale hierarchical architecture to scatter phonons with broad range of mean free paths, effectively reducing the lattice thermal conductivity. The results indicates that the substitution of Sb/Te resulted in the significantly increase of electrical conductivity and power factor, and BM effectively reduces the grain size to ~ 387 nm in the sample after sintering, which leads to a decrease in the thermal conductivity and an increase in the electrical conductivity. The maximum power factor of 0.72 m Wm−1 K−2 and ZT value of 1.19 were obtained for Bi 0.92 Sb 0.08 CuSe 0.92 Te 0.08 O with BM time = 16 h at 873 K, which was ~ 2.7 and ~ 2.2 times as that of the pristine BiCuSeO ceramic. Graphical abstract Sb/Te doping combined with grain refining led to the great increase of BiCuSeO based ceramics(sample 0–3 stand for ball milling time=5 h, 8 h, 12 h 16 h, respectively) fx1 [ABSTRACT FROM AUTHOR]

Facile, eco-friendly and effective separation of oil-in-water emulsion under various conditions is urgently desired. In this work, novel 3D superhydrophilic/air-superoleophobic diatomite porous ceramics (3DSSPC) with superior separation performance for surfactant-stabilized oil-in-water emulsions were successfully fabricated via a foam gelcasting-freeze drying and subsequent surface modification approach. SiO 2 whiskers in-situ generated on the surface of disc-like diatomite particles increased the roughness of the porous ceramics, which, along with the organic film formed on their surface, conferred excellent superhydrophilic and air-superoleophobic properties. The continuous separation efficiency of the 3DSSPC for the surfactant-stabilized edible oil-in-water emulsion (oil concentration of 5 wt%) was higher than 99%, with a flux of 5.06 kg·m−2·s−1 (18,200 L·m−2·h−1), more importantly, the separation flux for an industrial oil-in-water emulsion containing suspended particles was as high as 5.69 kg·m−2·s−1 (20,500 L·m−2·h−1). In addition, the microstructure, superoleophobicity and separation efficiency of the 3DSSPC changed little even after 20 separation cycles. The good mechanical strength and outstanding chemical stability in strong acidic, alkaline, concentrated salty solutions and at high/low-temperature make the 3DSSPC a promising candidate for future treatments of industrial wastewater containing emulsified oil-in-water liquids. • A robust 3D architecture was designed and successfully fabricated for the first time for high-efficiency oil-in-water emulsions separation. • It demonstrates a separation efficiency higher than 99% with a flux of 18,200 L·m−2·h−1. • It has a continuous separation flux of 20,500 L·m−2·h−1 for industrial oil-in-water emulsion containing suspended particles. • It has robust mechanical and outstanding chemical stability under salt/acid/alkaline corrosion and high/low-temperature conditions. [ABSTRACT FROM AUTHOR]

In this study, five sets of MgO-based ceramic filters were prepared using porous MgO powder and α-Al 2 O 3 micro-powder as raw materials. The effect of α-Al 2 O 3 content on the microstructures, mechanical properties and purification efficiency of MgO-based filters were investigated via SEM, EDS, and immersion test in molten steel, etc. The results indicate that the reactive sintering between α-Al 2 O 3 and MgO promoted the formation and growth of neck connections of magnesium aluminate spinel between grains, increased the density of the filter skeleton, and decreased the pore size inside the skeleton. The higher density and smaller pore size of the skeleton, as well as the neck connection of spinel and crack deflection effect caused by magnesium aluminate spinel, comprehensively improved the strength and thermal shock resistance of MgO-based ceramic filters. Furthermore, the results from the immersion test in molten steel revealed that an appropriate amount of high-temperature liquid phase, smaller pore size, and in-situ generated spinel were beneficial for the filters to adsorb dissolved aluminum, dissolved oxygen, alumina inclusions, and secondary spinel inclusions in the steel. The filter with 20 wt% α-Al 2 O 3 had the best overall performance with a compressive strength of 2.35 MPa, a compressive strength after thermal shock test of 1.91 MPa and an efficiency of 77.3% in reducing the total oxygen content of the steel. • In this work, MgO-based ceramic filters with excellent overall performance were successfully prepared and tested by steel immersion. • The mechanical properties and purification efficiency of MgO-based filters were improved via the introduction of α-Al 2 O 3. • The effects of α-Al 2 O 3 content on the microstructures and properties of MgO-based filters were investigated. [ABSTRACT FROM AUTHOR]

Microporous aggregates are the key to the lightweight design and preparation of refractories for the working linings of the high temperature furnaces. In this work, the lightweight MgO-MgAl 2 O 4 refractory aggregates with core-shell structures were prepared by in-situ decomposition synthesis technology using Mg(OH) 2 and nano-size Al 2 O 3 as raw materials. The influence of the nano-size Al 2 O 3 content on the microstructures and properties was thoroughly studied. The results demonstrated that the microporous MgO core structures were formed after the decomposition of Mg(OH) 2 , and the MgAl 2 O 4 bonds between the microporous MgO core structures were formed through the reaction between the nano-size Al 2 O 3 and MgO. When the nano-size Al 2 O 3 contents were less than 9 wt%, the MgAl 2 O 4 bonds were discontinuous. With the increase of the nano-size Al 2 O 3 contents to 9–15 wt%, more continuous MgAl 2 O 4 bonds (i.e. MgAl 2 O 4 shell structures) were formed at the surface of the microporous MgO core structures. Overall, the optimized specimens were lightweight MgO-MgAl 2 O 4 refractory aggregates with the addition of 9 wt% nano-size Al 2 O 3 , which exhibited the microporous MgO@MgAl 2 O 4 core-shell structures, a median pore size of 268 nm, a high compressive strength of 105 MPa, and a low thermal conductivity of 4.1 W/(m·K) at 800 ℃. [ABSTRACT FROM AUTHOR]

In this study, two kinds of MgO ceramic filters were prepared by using porous magnesia powder and fused magnesia powder as raw material, respectively. The microstructures, mechanical properties and purification efficiency on the molten steel of two MgO ceramic filters were investigated by mercury porosimetry measurement, SEM, EDS and immersion test with molten steel, etc. The results demonstrate that compared with the filter FM prepared from the fused magnesia powder, the rheological property of the slurry of the filter PM was improved via the finer and uniformly distributed nano-sized Mg(OH) 2 particles generated by the hydration of the porous magnesia powder, which not only optimized the macropore structure but also promoted the growth of the sintering neck between the microparticles of the skeleton. Therefore, the MgO filter skeleton with a microporous structure was obtained, which elevated the strength and thermal shock resistance of the filter PM. According to the immersion tests with the molten steel, both filters significantly reduced the number of inclusions with size < 5 µm2 in the molten steel as well as their total oxygen contents, and the filter PM had better purification efficiency than the filter FM. The reason for the better purification efficiency of the filter PM was related to its smaller micro-sized pores, larger surface roughness, and certain high-temperature liquid phase in their skeletons. In general, the porous magnesia powder resulted in higher compressive strength, better thermal shock resistance and superior purification efficiency on the molten steel of the filter compared with the fused magnesia powder. [ABSTRACT FROM AUTHOR]

Recently, high-performance ceramic aerogels (CAs) have become a research hotspot because of their multi-functional properties. Compared to their oxide counterparts, non-oxide CAs show better thermal shock resistance and other high-temperature properties, making them suitable for applications in harsh environments. In this work, Si 3 N 4 -BC x N-TiN ceramic aerogels (SBCNT CAs) with molar ratios of B/C/Si/Ti = 2:1:5:5 were synthesized at 1623 K for 3 h via foam-gelcasting, from Si, Ti, melamine and boron acid raw materials. The prepared SBCNT CAs containing 91.0% porosity exhibited the highest compressive strength up to 1.0 MPa, and thermal conductivity of 0.144 W/(m·K) at 298 K. They also exhibited excellent service performance at 1473 K in Ar, demonstrating their great potential for high-temperature applications. [Display omitted] [ABSTRACT FROM AUTHOR]

High strength SiC reinforced Si 3 N 4 ceramics aerogels (SCSNCAs) were fabricated via foam-gelcasting and subsequent catalytic reaction, utilizing industrial Si and melamine as raw materials, a small amount of incidental Fe impurities in Si powder as the catalyst and cetyltrimethylammonium bromide (CTAB, the amount of 0.075 wt%) as foaming agent. The effects of solid loading level and reaction temperature on phase composition, microstructure and mechanical properties of the as-prepared SCSNCAs were examined. The aerogels prepared at 1423 K using a slurry of solid loading level of 30 wt% (Si:melamine = 3:1, mass ratio) had porosity of 91.9%, having compressive and specific strength of 0.8 MPa and 3.8 MPa·cm3·g−1 exhibited the lowest thermal conductivity of 0.066 W/(m·K) at 473 K. Compared with the control sample (without melamine, i.e., Si 3 N 4 aerogels without the formation of SiC), the specific strength of the SCSNCAs increased by about 10%, which was attributed to the additional reinforcement from SiC whiskers formed in the Si 3 N 4 matrix of the aerogels. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nano-whiskers based 3D Si 3 N 4 porous ceramics (3D-NWSNPC) were prepared via a facile one-pot foam-gelcasting/nitridation route at 1423–1523 K. • 3D-NWSNPC showed excellent thermal conductivity, and a certain degree of recoverability under cyclic compressive loading. • The sample with solid loading of 12.5 wt% exhibited the highest compressive strength of 1.9 MPa, even though its porosity was high up to about 91 %. Nano-whiskers based 3D Si 3 N 4 porous ceramics (3D-NWSNPC) with high-porosity (about 91–93 %), low density (0.17–0.25 g/cm3), low thermal conductivity, and a certain degree of recoverability under cyclic compressive loading and reasonably strengths were prepared at 1423–1523 K via a one-pot foam-gelcasting/nitridation route using inexpensive commercial Si powders as starting materials and hexadecyl trimethyl ammonium bromide as foaming agent. After nitridation at 1523 K, the sample with an original solid loading of 12.5 wt% exhibited the highest compressive strength of 1.9 MPa, even though its density was lowered to 0.25 g/cm3. The sample nitrided at 1473 K had a relative density of 7.3 %. Its compressive and specific strength were respectively 1.1 MPa and 5.5 MPa·cm3 g−1, and its thermal conductivity was as low as 0.074 W/(m K) (measured at 323 K). These outstanding properties would make the as-prepared 3D-NWSNPC a promising candidate for applications in catalysis, filtration, thermal insulation and many other important areas. [ABSTRACT FROM AUTHOR]

This paper presents a new technique for synthesizing porous silicon carbide (SiC) ceramics with a biomorphic microstructure through the molten salt reaction of a carbon template/silicon composite under a static argon atmosphere. The effects of varying the sintering temperature (1200 to 1400 °C) and corresponding holding time on the pore size distribution of the obtained ceramics is investigated, and the biomorphic cellular morphology of the residual carbon template in the porous β-SiC ceramic is analysed for the presence of α-SiC. The results reveal that the formation of SiC starts at about 1250 °C, at which point SiC exists as nanowires in the cellular pores of the carbon template. This unique hierarchical morphology is determined to be influenced by the molten salt media. [ABSTRACT FROM AUTHOR]