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Abstract A double-layer γ-Y 2 Si 2 O 7 /Y 2 O 3 -Al 2 O 3 -SiO 2 glass coating on porous Si 3 N 4 ceramic was fabricated by melt-infiltration/sintering (MIS) method, and its thermal shock behavior was investigated by rapid quenching thermal shock tests and transient finite element simulation method. Coupling effects of coating microstructure and mechanical properties on the thermal shock behavior were discussed. Results show that thickness of the bonding layer and Young's modulus of the surface layer play a decisive role in thermal stress during the thermal shock process. The coating with lower Young's modulus and thicker bonding layer shows better comprehensive performance. Highlights • Thermal shock resistance of double-layer γ-Y2Si2O7 /Y-Al-Si-O glass coatings were investigated. • Coupling effects of coating microstructure and mechanical properties on the thermal shock behavior were discussed. • High thermal shock resistance requires the coating has lower Young's modulus and thicker bonding layer. [ABSTRACT FROM AUTHOR]

Here we prepared porous silicon oxynitride (Si2N2O) ceramics by reaction sintering of SiO2 and Si3N4 using five different rare‐earth oxides (RE2O3, RE = Lu, Yb, Y, Sm, and La) as sintering aids. The influences of RE2O3 on the formation, densification, microstructure, and mechanical properties of Si2N2O ceramics have been investigated in detail. The results have indicated that with the increase in RE ionic radius, the formation temperature of Si2N2O decreases, and the densification process could be promoted by RE2O3 with larger RE3+ ionic radius. In addition, microstructures and mechanical properties are highly dependent on the RE2O3 additives. With the increase in RE3+ ionic radius, Si2N2O changes from platelike crystals to elongated crystals. The samples doped with La2O3 and Sm2O3 with elongated crystals exhibit higher flexural strength and higher Vickers hardness. [ABSTRACT FROM AUTHOR]

Porous hollow structures have attracted tremendous interests due to their geometrical beauty, unique structural features and fascinating physicochemical properties. In the present work, we developed a general procedure for the synthesis of hollow nanostructured carbon-wrapped cerium oxide (CeO 2 /C) via a microwave hydrothermal process without any surfactants or hard templates. The electrochemical performances of CeO 2 /C specimen were tested as anode materials in lithium ion batteries. The results showed that CeO 2 /C hollow spheres exhibited an exceptional cyclic stability with a high reversible capacity of 313 mA h g −1 after 500 cycles at a high current density of 1000 mA g −1 without signs of further degradation and also presented an excellent rate performance from 1000 to 10000 mA g −1 . The improved performances were attributed to the homogeneous carbon with 3D network structure in hollow spheres and the Ce 3+ in the oxygen-deficient fluorite-like CeO 2-x on the surface of ceria nanoparticles, which enhanced the conductivity of CeO 2 hollow spheres, suppressed the aggregation of active particles and reduced the apparent activation energy to facilitate the kinetics of Li + insertion-extraction. The unique hollow structure of CeO 2 wrapped by conductive carbon have made CeO 2 a promising candidate for future applications in various metal oxide electrodes to mitigate the mechanical degradation and capacity fading, critical for developing advanced electrochemical energy storage systems with long-cycle life and high-rate performance. [ABSTRACT FROM AUTHOR]

A dense β-Si 3 N 4 -based waterproof environmental barrier coating was fabricated using the liquid infiltration and filling method on porous Si 3 N 4 ceramic. Microstructure and thermal shock resistance of the coating were investigated. The results showed that the coating consisted of β-Si 3 N 4 , Y 10 Al 2 Si 3 O 18 N 4 and Y-Si-Al-O glass. As-prepared coating exhibited excellent thermal shock resistance. During thermal shock at ∆T=1200 °C, cracks were formed within the coating, but they did not penetrate through the whole coating due to the toughening mechanisms of the coating, including β-Si 3 N 4 particle bridging and crack branching. In addition, the coating had a good crack self-sealing ability during thermal cycling, which is mainly attributed to glass flow and oxidation of β-Si 3 N 4 particles within the crack. After thermal cycling for 25 times, the coating still had a good waterproof ability, and the water absorption of the coated porous Si 3 N 4 sample increased slightly from 4.5% to 9.3%. [ABSTRACT FROM AUTHOR]

The mechanism of interaction between crack-tips and pores in the porous ceramics was investigated in this paper. By using the J -integral numerical method, the effect of the pores on the stress-intensity factors of the crack tips is analyzed quantitatively. The presence of the pores may enhance or weaken the stress-intensity factors. The simulation results show that the pores in front of the crack will enhance the stress-intensity factors of the crack tip and promote the crack propagation and the pores at the side of the crack will weaken the stress-intensity factors of the crack tip and prevent the crack propagation. At the same time, the effects of different pores on the stress distribution around the crack-tip, with different pore-crack tip distance or positions, are presented. [ABSTRACT FROM AUTHOR]

This work presents computational solutions and experimental results on the most important parameters influencing thermal shock behavior. In this paper, the mesoscopic cracks were observed on the surface of the specimen which experimentally confirmed the decay in flexural strength after thermal shock. It has been shown that the crack width decreases with increasing porosity. For higher porosity, it is evident that the crack extended with obvious deflection and bifurcates. The numerical simulations within the framework of damage mechanics considering the coupling between the thermo and mechanical behavior of porous Si 3 N 4 on the mesoscopic level of observation can conveniently reproduce the evolution of thermal shock cracks, which is difficult to observe experimentally. The present theoretical-numerical-experimental study has led to an improved under -standing of the formation and evolution of thermal shock crack in porous ceramics. [ABSTRACT FROM AUTHOR]

• The carbon nanofibers with interconnected and porous structures are fabricated using a facile and novel strategy. • The formation of interconnected structures between fibers mainly stems from the aldolization of glutaraldehyde and starch. • The all-solid-state supercapacitors made from IPCNF electrodes have excellent electrochemical performances. In this study, a facile strategy is introduced to fabricate interconnected and porous carbon nanofibers for electrode materials to improve the electrochemical performances of supercapacitors. The well-developed all-solid-state supercapacitor shows specific capacitances of 71 and 57 F g−1 at current densities of 0.25 and 5 A g−1, as high as ∼ 80% retention rate. The energy density calculated based on supercapacitor device is as high as 9.8 Wh kg−1 at a power density of 125 W kg−1 and the maximum power density is 64.1 kW kg−1. Almost 100% capacity has been maintained after 10,000 charge and discharge cycles. [ABSTRACT FROM AUTHOR]

β-Si 3 N 4 -based coating was prepared on the porous Si 3 N 4 ceramic using the liquid infiltration and filling method. The effect of sintering temperature on microstructures, water absorption, mechanical properties and erosion resistance of the coatings were investigated. The results show that phase components of all the coatings consisted of β-Si 3 N 4 , Y 10 Al 2 Si 3 O 18 N 4 and Y–Si–Al–O glass. The coatings prepared at 1700 and 1800 °C had a good water resistance, which can be attributed to the high density of the coatings. The defects, including large pores and micropores, were produced within the coating when the sintering temperature was up to 1900 °C, thus leading to the reduction of the water resistance. Hardness and elastic modulus of the coating increased gradually as the sintering temperature increased from 1700 to 1800 °C, but it began to decrease when the sintering temperature was 1900 °C. The coating prepared at 1800 °C displayed a good erosion resistance. [ABSTRACT FROM AUTHOR]

Porous β- Si3 N4 ceramics are sintered at 1600°C in N2 and postheat treated at 1500°C under vacuum using Li2 O and Y2 O3 as the sintering additives. The partial sintering and phase transformation are promoted at low temperature by the addition of Li2 O. The addition of Y2 O3 is advantageous for the formation of high aspect ratio β- Si3 N4 grains. After postheat treatment, a large amount of intergranular glassy phase is removed, and the Li content in the samples is decreased. By this method, the β- Si3 N4 porous ceramic with a porosity of 54.1% and high flexural strength of 110 ± 8.1 MPa can be prepared with a small amount of sintering additives, 0.66 wt% Li2 O and 0.33 wt% Y2 O3, and it is suitable for high-temperature applications. [ABSTRACT FROM AUTHOR]

Abstract: Based on orthogonal experimental results of porous Si3N4 ceramics by gel casting preparation, a three-layer back propagation artificial neural network (BP ANN) was developed for predicting the performances of porous Si3N4 ceramics. The results indicated that BP ANN was a very useful and accurate tool for the prediction and optimization of porous Si3N4 ceramics performances. By using the developed ANN model, the influences of the compositions on performances of porous Si3N4 ceramics were investigated, and some important conclusions were drawn as follows: for the flexural strength of Si3N4 ceramics, solid loading has an optimum value where can achieve a maximum value, and the optimum solid loading decreases with the increase of monomer content; the porosity of sintering body monotonically decreases with the increase of solid loading, and it increases with monomer content; the porosity of sintering body monotonically increases with the increase of the ratio of crosslinking agent to monomer. [Copyright &y& Elsevier]

Porous β- Si3 N4 ceramics are sintered at 1600°C in N2 and postheat treated at 1500°C under vacuum using Li2 O and Y2 O3 as the sintering additives. The partial sintering and phase transformation are promoted at low temperature by the addition of Li2 O. The addition of Y2 O3 is advantageous for the formation of high aspect ratio β- Si3 N4 grains. After postheat treatment, a large amount of intergranular glassy phase is removed, and the Li content in the samples is decreased. By this method, the β- Si3 N4 porous ceramic with a porosity of 54.1% and high flexural strength of 110 ± 8.1 MPa can be prepared with a small amount of sintering additives, 0.66 wt% Li2 O and 0.33 wt% Y2 O3, and it is suitable for high-temperature applications. [ABSTRACT FROM AUTHOR]

Abstract: Al2O3 coatings were prepared using supersonic plasma spraying on the porous Si3N4 substrate at the spraying power of 52, 54, 58 and 60kW, respectively. The effect of spraying power on the microstructures and properties of Al2O3 coating was investigated. The feedstock particles were sufficiently melted and Al2O3 coatings become more and more compact with the increasing spraying power. However, the defects, including the surface cracks, interlamellar cracks and needle-like particles, were produced within the coating when the spraying power was 60kW due to the excessive power. As-received Al2O3 coatings sealed the surface pores of porous Si3N4, and decreased the water absorption obviously, but only with a slight decrease of the total porosity. Vickers hardness and flexural strength of porous Si3N4 with Al2O3 coating increased gradually as the spraying power increased from 52 to 58kW, but it began to decrease when the spraying power was up to 60kW due to the appearance of defects within the coating. [Copyright &y& Elsevier]

Abstract: A hierarchical macroporous carbon derived from phenol–formaldehyde (PF) resin was processed using ethylene glycol (EG) and starch as double porogens. The influences of carbonization temperature on morphological properties and pore microstructure of the porous carbon were investigated, and the formations of hierarchical macropores were analyzed. Obtained results demonstrated that both the carbonization temperature and the composition of the resin and the two porogens played key roles in determining the pore morphology and properties. Under certain conditions, a series of hierarchical macroporous carbons having relatively big macropores of diameter 10–40μm and relatively small macropores of diameter 0.5–2μm can be obtained. The formations of the big and small macropores can be attributed to the pyrolysis of starch and the phase separation of resin-rich and glycol-rich phases, respectively. [ABSTRACT FROM AUTHOR]