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Abstract: Highly porous Si3N4 with macroscopically aligned pores were prepared by the unidirectional freeze casting process using liquid N2 as refrigerant. The increased sintering temperature had no obvious influence on the porosity, but significantly promoted α→β-Si3N4 phase transformation and the growth of fibrous β-Si3N4 grains, and changed the pore structure. The flexural strength and fracture toughness of the sample sintered at 1900°C could reach 73MPa and 1.1MPam1/2, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Porous barium aluminosilicate (BAS)/Si3N4 composites were prepared by freeze casting process using liquid N2 as refrigerant. The pore morphologies, α → β-Si3N4 phase transformation, and mechanical properties of the resultant porous ceramics were strongly affected by the addition of polyacrylamide (PAM) into the slurries. The incorporation of 2wt.%PAM changed the ice crystals structure from lamellar with dendrites into featureless columnar ones, the feature of which was duplicated by the pores in the sintered ceramics. The lamellar pores with dendrites could favor the α → β-Si3N4 phase transformation, but were detrimental to the mechanical properties. The sample with 1wt.%PAM exhibited the highest strength and toughness in the resultant porous composites due to its columnar pore structure with less dendritic pores and higher aspect ratio of β-Si3N4 grains. A relative dense layer was formed at the bottom of the samples with PAM and its thickness increased with increasing PAM content. [ABSTRACT FROM AUTHOR]

Abstract: cBN/β-SiAlON composites with different cBN contents were fabricated by spark plasma sintering (SPS) process. The densification, thermal stability of cBN, microstructure and mechanical properties of the resultant composites were investigated. The addition of cBN particles to β-SiAlON could increase the Vickers hardness, flexural strength and fracture toughness of β-SiAlON. It is attributed to the high density, no obvious cBN to hBN transformation and good interface bonding between cBN grains and β-SiAlON matrix. [Copyright &y& Elsevier]

Abstract: The thermal shock behavior of 30wt%BAS/Si3N4 composite was evaluated by the water-quenching technique. The results show that the investigated composite possesses excellent thermal shock resistance. The critical temperature difference (ΔT c) of the composite is over 1100°C and the retained strength at a quenching-temperature difference of 1100°C is hardly affected by the quenching cycles. It is attributed to its high strength and low Young''s modulus. The in situ growth of elongated β-Si3N4 grains are also beneficial to the improvement of thermal shock resistance due to the increased crack propagation resistance by crack deflection and grain pull-out mechanisms. In addition, the formation of an oxide layer on the sample surface before quenching may act as an additional thermal barrier and leads to a reduction in the intensity of thermal shock. [Copyright &y& Elsevier]

Abstract: Y-α-SiAlON (Y1/3Si10Al2ON15) ceramics with 5wt.%BaAl2Si2O8 (BAS) as an additive were synthesized by spark plasma sintering (SPS). The kinetic of densification, phase transformation sequences and grain growth during sintering process were investigated. Full densification could be achieved by 1600°C without holding and using a heating rate of 100°Cmin−1, but the transformation from α-Si3N4 to α-SiAlON is not completed simultaneously with the densification process. The equilibrium phase assemblage could be reached after SPS at 1800°C for 5min and the resultant material possesses self-reinforced microstructure with high hardness of 19.2GPa and fracture toughness of 6.8MPam1/2. The complete crystallization of BAS is beneficial to the high temperature mechanical properties. The obtained could maintain the room strength up to 1300°C. [Copyright &y& Elsevier]

Yb-, Y- and Dy-doped mixed α/β-SiAlON ceramics were fabricated by hot-pressing using 10wt.% BaAl2Si2O8 (BAS) glass ceramic as an additive. The results showed that BAS could effectively facilitate the anisotropic growth of both α- and β-SiAlON grains. The α-SiAlON grains as well as the β-SiAlON grains were highly elongated. The obtained mixed α/β-SiAlONs possess much better mechanical properties than those of conventional mixed α/β-SiAlONs containing equiaxed α-SiAlON grains in their microstructure. [Copyright &y& Elsevier]

Abstract: Refractory Y-α-SiAlONs with elongated microstructure were obtained by hot pressing and post-heat treatment using BaAl2Si2O8 (BAS) as an additive. The results showed that BAS not only served as a liquid phase sintering aid to promote densification, but also facilitated the development of elongated α-sialon grains, resulting in excellent room and high-temperature mechanical properties. Increasing the amount of BAS addition and post-heat treatment could further effectively promote the anisotropic growth of α-SiAlON grains, the room-temperature flexural strength and fracture toughness of 10wt% BAS/Y-α-SiAlON could reach 634MPa and 7.2MPam1/2, respectively. The resultant materials could maintain the room strength up to 1400°C due to the extensive crystallization of BAS. [Copyright &y& Elsevier]

In this study, amorphous nano-sized Si 3 N 4 powders were surface modified by BN. Then a stable and dense Si 2 N 2 O ceramic was fabricated using the BN surface modified powders, rather than Si 2 N 2 O-Si 3 N 4 composites usually prepared from nano-sized Si 3 N 4 powders without surface modification. The effect of BN surface modification on phase transformation, microstructure and mechanical properties were also investigated. Si 2 N 2 O ceramics obtained by means of the present method have no residual Si, crystal SiO 2 and other oxide additives, which are usually produced by other methods and may seriously influence high-temperature structural and functional applications of Si 2 N 2 O ceramics. [ABSTRACT FROM AUTHOR]

Abstract: In this study, Si3N4 bonded porous SiC ceramics with high strength had been net-shapely fabricated by a new approach. In this approach, we proposed a two-step processing route composed of freeze casting and carbothermal reduction reactions in which carbon aerogels, derived from sol infiltration and pyrolysis, involved. The phase components, microstructures and properties of the prepared ceramics were investigated. The results showed that carbon aerogels with high apparent surface area had been completely reacted and new SiC and Si3N4 grains had been produced. The porous ceramics with flexural strength of 164.3MPa at 33% porosity and 80.5MPa at 46% porosity were obtained, whose linear shrinkages were only 1.06% and 1.94% during the whole processing respectively. [Copyright &y& Elsevier]

Abstract: The thermal shock properties of 5wt% BAS/α-SiAlON ceramics fabricated by spark plasma sintering (SPS) technique have been valuated with an indentation-quench method based on Vickers cracks. The obtained materials possessed excellent thermal shock resistance due to the formation of self-reinforced microstructure. The co-doped α-SiAlONs exhibited better thermal shock resistance, undergoing a more stable crack growth than the single-doped ones. It is attributed to the higher fracture toughness. [ABSTRACT FROM AUTHOR]

Abstract: Dense short silicon carbide (SiCsf) and carbon fibers (Csf) reinforced BaAl2Si2O8 (BAS) glass-ceramic composites with silicon nitride were fabricated by hot-pressing technique. The phase characterization, microstructure, mechanical properties and fracture behavior of the composites were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and three-point bending tests. The results showed that short silicon carbide and carbon fibers disperse homogeneously in BAS matrix, and had good chemical compatibility with the glass-ceramic matrix. The addition of Si3N4 could successfully eliminate the microcracks in the BAS matrix induced by the thermal mismatch between the fiber and matrix. Both the added short fibers could effectively reinforce the BAS glass-ceramic by the associated toughening mechanisms such as crack deflection, fiber bridging and pullout effects. [Copyright &y& Elsevier]

• The optimum preparation process of grouting materials was determined. • The grouting simulation experiment of micro cracks was designed independently. • The workability and environmental adaptability of DDMS modified epoxy grouting material were clarified. • DEP-Ⅱ grouting material was recommended for repairing micro cracks. Microcracks are common in the cast-in-situ concrete pavement of the bridge deck, DDMS was selected as modifier, AD- I, AD- II and AD- III active diluents were used as viscosity reducers to effectively repair the cracks. And the preparation process of low-viscosity epoxy grouting materials modified by silicone was optimized. Then the working properties (viscosity, gelation time and groutability) and mechanical properties of silicone modified low-viscosity epoxy grouting materials were clarified. Finally, the evolution law of mechanical properties of low-viscosity epoxy grouting material modified by silicone under high temperature impact, temperature change cycle and freeze–thaw cycle was revealed. The results show that the physical and mechanical properties of grouting material prepared under the conditions of reaction temperature 100 °C, reaction time 3 h and DDMS content 11% were the best. The repair depth of low-viscosity epoxy grouting material modified with silicone in 0.5 mm wide crack exceeded 10 cm within 5 min at 25 °C. But its gel time was longer, up to 24 ~ 28 h. After curing for 3 days, the shear strength and bond strength of the silicone modified low-viscosity epoxy grouting material under room temperature reached more than 90%, and its high-temperature shear strength and bond strength reached 70%~90%. Compared with EP grouting material, the low-temperature and normal-temperature impact toughness of the grouting material after adding diluent and DDMS increased by 57%~71% and 31%~48%, respectively. After high-temperature impact, temperature change cycle and freeze–thaw cycle, the mechanical properties of silicone modified low-viscosity epoxy grouting material decreased slightly, but it was still stronger than EP grouting material. Its tensile strength was still higher than 30 MPa, elongation at break was higher than 5.0%, and bond strength was higher than 3.0 MPa. [ABSTRACT FROM AUTHOR]

Abstract: Dense silicon carbide (SiC)-based ceramics were obtained by hot-pressing using BaAl2Si2O8 (BAS) as an additive. The results showed that BAS could serve as an effective liquid sintering aid to promote densification and facilitate the growth of SiC grains. The relative densities, flexural strength and fracture toughness of the composites increase with increasing the BAS content. The flexural strength and fracture toughness of 40wt%BAS/SiC composite could reach 510MPa and 7.0MPam1/2, respectively, The main toughening mechanisms are crack deflection, crack bridging and SiC grain pullout. The complete crystallization of BAS is beneficial to the high temperature mechanical properties and the obtained 40wt%BAS/SiC composite could maintain the room strength up to 1200°C. [Copyright &y& Elsevier]