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This paper revisits the vector of locally aggregated descriptors (VLAD), which aggregates the residuals of local descriptors to their cluster centers. Since VLAD usually adopts a small-size codebook, the clusters are coarse and residuals not discriminative. To address this problem, this paper proposes to generate a number of residual codebooks descended from the original clusters. After quantizing local descriptors with these codebooks, we pool the resulting secondary residuals as well as the primary ones to obtain the fine residuals. We show that, with two-step aggregation, the fine-residual VLAD has the same dimension as the original. Experiments on two image search benchmarks confirm the improved discriminative power of our method: we observe consistent superiority to the baseline and competitive performance to the state-of-the-arts. [ABSTRACT FROM AUTHOR]

Statistical-learning-based object detection is an important topic in computer vision. It learns visual representation from annotated exemplars to identify semantic defined objects in images. High-performance object detection is usually carried out in feature space and effective feature representation can improve the performance significantly. Feature representation is the encoding process which maps raw image pixels inside local regions into discriminant feature space. The motivation of this paper is to present a review on feature representation in recent object detection methods. Visual features applied in object detection are categorized according to the differences in computation and visual properties. The most valued features are introduced and discussed in detail. Representative extensions are introduced briefly for comparison. Descriptive power, robustness, compactness as well as computational efficiency are viewed as important properties. According to these properties, discussions are presented on the advantages and drawbacks of features. Besides, generic techniques such as dimension reduction and combination are introduced. Through this review, we would like to draw the feature sketch and provide new insights for feature utilization, in order to tackle future challenges of object detection. [ABSTRACT FROM AUTHOR]

Highlights: [•] Porous BN/Si3N4 with spherical-shaped pore structure was prepared by gel casting. [•] Micro spherical pores and irregular sub-micro pores composed the pore structure. [•] Increasing pore size has an increased inhibition on α- to β-Si3N4 transformation. [•] Mechanical and dielectric properties depending on the pore size were revealed. [ABSTRACT FROM AUTHOR]

Abstract: Porous BN/Si3N4 composite ceramics with different BN contents have been fabricated by gel casting. The rheological behaviors of the suspensions, microstructure, mechanical properties, dielectric properties and critical temperature difference of thermal shock (ΔT C ) of porous BN/Si3N4 composite ceramics with different BN contents were investigated. With BN contents increasing, the mechanical properties of the porous BN/Si3N4 composite ceramics were partially declined, but the dielectric properties and thermal shock resistances were enhanced at the same time. For the porous Si3N4 ceramic without BN addition, the porosity, flexural strength, dielectric constant and critical temperature difference were 48.1%, 128MPa, 4.1 and 395°C, while for the 10vol% BN/Si3N4 porous composite ceramics, they were 49.4%, 106.6MPa, 3.8, and 445°C, respectively. The overall performance of the obtained porous BN/Si3N4 composite ceramics indicated that it could be one of the ideal candidates for high-temperature wave-transparent applications. [Copyright &y& Elsevier]

Abstract: This paper presents a new dynamic generating graphical model for point-sets matching. The existing algorithms on graphical models are quite robust to noise but are susceptible to the effects of outliers. We investigated the influences of separators on point-sets matching in inference of graphical models theoretically and found that the separators that consist of outliers will interfere with message-passing, which will directly lead to failure of the existing methods. Because of this, in order to minimize the outliers in the separators, we propose a new algorithm for generating a graphical model and a corresponding Junction Tree for point-sets matching. A bi-mapping algorithm is also introduced to solve the problem of multi-mapping caused by outliers. Experiments were carried out on both synthetical data and real-world data with point-sets extracted by the Harris corner detector. The results show that the proposed algorithm is significantly more stable and possesses higher accuracy of point-sets matching, which can overcome the limitation of the sensitivity of outliers in the existing graphical models. [Copyright &y& Elsevier]

Abstract: In this paper, leucite ceramics with different shapes and fine integrity were directly developed from geopolymer precursors by the optimized heat treatment procedures. Phase compositions and microstructure, coupled with the mechanical properties, were systematically investigated. The effect of heating rates on the integrity of ceramics was also discussed. After high-temperature treatment at 800°C for 120min, the geopolymer was converted into a leucite ceramic. The relative density of the sample treated at 1000°C for 120min was 93% and the size of leucite grain was approximately 1–4μm. TEM results showed that the leucite grain was composed of lamellar and needle-shaped twins, which resulted from the displacive phase transformation as it went from cubic to tetragonal symmetry when it was cooled down. Samples with plate and bullet shapes maintained their fine integrity by the optimization of the heating procedures. Meanwhile, the flexural strength, Young''s modulus, fracture toughness and Vickers hardness of the leucite ceramic that resulted was 70.0MPa, 65.0GPa, 1.3MPam1/2 and 7.39GPa, respectively. [Copyright &y& Elsevier]

The processing of 3D carbon fiber reinforced SiCN ceramic matrix composites prepared by polymer impregnation and pyrolysis (PIP) route was improved, and factors that determined the mechanical performance of the resulting composites were discussed. 3D C f /SiCN composites with a relative density of ∼81% and uniform microstructure were obtained after 6 PIP cycles. The optimum bending strength, Young's modulus and fracture toughness of the composites were 75.2 MPa, 66.3 GPa and 1.65 MPa m1/2, respectively. The residual strength retention rate of the as-pyrolyzed composites was 93.3% after thermal shock test at Δ T = 780 °C. It further degraded to 14.6% when the thermal shock temperature difference reached to 1180 °C. The bending strength of the composites was 35.6 MPa after annealing at 1000 °C in static air. The deterioration of the bending strength should be attributed to the strength degradation of carbon fibers and decomposition of interfacial structure. [ABSTRACT FROM AUTHOR]

• Amorphous boron-rich Si 2 B 1 - 4 C 2 N monoliths were consolidated by high-pressure low-temperature sintering technique. • Amorphous boron-rich Si 2 B 1-4 C 2 N monoliths oxidize according to a classical parabolic rate law. • The increase in boron content weakens the oxidation resistance of amorphous boron-rich Si 2 B 1-4 C 2 N monoliths. • The formation of a dense and passivating oxide scale is primarily responsible for the high-temperature oxidation resistance. High-temperature oxidation behavior of dense amorphous boron-rich Si 2 B 1-4 C 2 N monoliths in flowing air was studied in detail. The oxidation products are those of amorphous silica and cristobalite that control the diffusion of oxygen inward. Oxygen diffusion leads to a dense and passivating scale, which acts as a barrier to oxygen. Amorphous boron-rich monoliths oxidize through a classical parabolic manner. The amorphous nature, three-layers structure of oxide scale and varying chemical bonds are primarily responsible for the oxidation resistance with respect to the nano monoliths. The increase in boron content is revealed to weaken the oxidation resistance of the amorphous Si 2 B 1-4 C 2 N monoliths. [ABSTRACT FROM AUTHOR]

Abstract BAS-BN ceramic composites were synthesized by hot-press sintering at 1500 °C with various BN doping contents of 10–50 wt%. The influences of BN on the phase composition, microstructure and mechanical properties of the composite ceramics were studied. Results showed that the addition of BN significantly affected the hexagonal → monoclinic phase transformation of BAS. Single celsian was noted at BN content of 10 wt%, while a mixture of hexacelsian, celsian and some amorphous phase was obtained as BN additions beyond 20 wt%. With the increase in BN contents, nearly a fully dense composite was obtained when the BN content was lower than 30 wt%. And the mechanical performance of the composites was significantly improved. For ceramics with an addition of 30 wt% BN, the flexural strength and fracture toughness reached the maximum values, which was 193.5 MPa and 2.57 MPa m1/2, respectively. And the bending strength is more than twice higher than that of pure BAS ceramic. [ABSTRACT FROM AUTHOR]

In this study, amorphous SiBCN powders were mechanical milled and consolidated by low-temperature sintering at different pressure to provide an insight into the densification and mechanical behavior of dense amorphous SiBCN monoliths. Results show that the mechanical properties undergo a gradual variation closely related to the microstructural evolution. The increased degree of densification with few defects and free volume results in significantly improving Young’s modulus and nano hardness in case of high pressure application. The consolidation at relatively low pressure (3 GPa) occurs by heavy deformation with the support of limited short-range diffusion, whereas the densification at higher pressure (5 GPa) is mostly diffusion controlled showing a classic sintering mechanism. At 1000 °C, higher pressure (5 GPa) suppresses crystallization leading to an effective solid-state reaction, while SiBCN monoliths consolidated by lower pressure (3–4 GPa) show a hybrid structure of dominant amorphous phases and few nanocrystals. [ABSTRACT FROM AUTHOR]

In this paper, a high temperature treatment procedure was designed to evaluate the effect of holding temperature on thermal evolution process of Li + substituted Cs-based geopolymer (Cs 0.7 Li 0.3 GP), including the thermal analysis, phase composition and microstructure evolution. With rising of holding temperature, amorphous unheated Cs 0.7 Li 0.3 GP gradually transformed into a multiphase system during the high temperature treatment process, which consisted of pollucite (CsAlSi 2 O 6 ), spodumene (LiAlSi 2 O 6 ) and amorphous glass phase. In the multiphase system, Cs + ions were in the form of pollucite grains, while Li + ions were in the form of spodumene nanocrystallines distributed in amorphous matrix. The pollucite grains gradually coarsened with rise in holding temperature, and the densification of the resulting products were also improved synchronously, which were related to the presence of amorphous glass phases. The amorphous glass phase would be in a molten state when holding temperature over 800 °C. And the presence of molten amorphous phase would make the mass transfer process easier, which could contribute to the growth of the crystal grains and the elimination of the pores. [ABSTRACT FROM AUTHOR]

In the present study, ablation behavior and properties of BN-MAS (magnesium aluminum silicate) composites impinged with an oxyacetylene flame at temperatures up to 3100 °C were investigated. As ablation time ranged from 5 to 30 s, the mass and linear ablation rates increased from 0.0027 g/s and 0.001 mm/s to 0.0254 g/s and 0.087 mm/s, respectively. A SiO 2 -rich protective oxide layer formed during the ablation process, which contributed to the oxidation resistance of the composites. Ablation products mainly consisted of magnesium-aluminum borosilicate glass, mullite, spinel and indialite. The thermal oxidation of h -BN during flame ablation and scouring of MAS by high-speed gas flow were the main ablation mechanisms. [ABSTRACT FROM AUTHOR]

The high-temperature oxidation behavior of various boron addition SiBCN monoliths has been explored. Boron addition promotes the formation of new B x C phase and growth of SiC gains. At the initial stage of oxidation, surface B x C and BN(C) are prior to SiC generating B 2 O 3 . As time progresses, SiC oxidizes to SiO 2 further reacted with B 2 O 3 forming stable SiO 2 -B 2 O 3 binary melt or borosilicate. Boron-enhanced SiC oxidation occurs immediately with the rapid consumption of BN(C), B x C and loss of B 2 O 3 from borosilicate decomposition, thereby promoting oxidation rate. Substantial SiC and BN(C) in amorphous SiO 2 for transition layer is the main structure feature. [ABSTRACT FROM AUTHOR]

The high temperature oxidation behavior of three SiBCN monoliths: carbon-lean SiBCN with substantial Si metal, carbon-moderate SiBCN and carbon-rich SiBCN with excessive carbon, was investigated at 1500 °C for times up to15 h. Scale growth for carbon-lean and −moderate monoliths at 1500 °C cannot be described by a linear or parabolic rate law, while the carbon-rich monoliths oxidize according to a approximately linear weight loss equation. The microstructures of the oxide scale compose of three distinct layers. The passivating layer of carbon and boron containing amorphous SiO 2 and increased oxidation resistance of BN(C) both benefit the oxidation resistance. [ABSTRACT FROM AUTHOR]

Porous boron nitride/silicon oxynitride (BN/Si 2 N 2 O) composites were fabricated by pressureless sintering at 1650 °C with Li 2 O as sintering aid. The influence of Li 2 O and hexagonal boron nitride (h-BN) contents on phase, microstructure, mechanical, dielectric and thermal properties of the resulting porous BN/Si 2 N 2 O composites was investigated. Increasing Li 2 O content facilitated densification and decomposition of Si 2 N 2 O into Si 3 N 4 . The apparent porosity of the composites increases with the h-BN content increases and Si 2 N 2 O grain growth was restrained by the dispersed h-BN particles. The dielectric properties and thermal conductivities (TC) were affected mainly by porosity. Porous BN/Si 2 N 2 O ceramic composites with 4 mol% Li 2 O and 25 mol% BN exhibit both low dielectric constant (3.83) and dielectric loss tangent (0.008) with good mechanical and thermal performance, suggesting possible use as high-temperature structural/functional materials. [ABSTRACT FROM AUTHOR]

A serial of multi-walled carbon nanotubes (MWCNTs) reinforced geopolymer composites were prepared, and then heated at elevated temperature to fabricate MWCNTs/leucite composites by in situ transformation. Effects of high-temperature treatment on the microstructure evolution and mechanical performance of the composites were investigated. The results indicated that the introduction of MWCNTs could improve the mechanical properties of geopolymer, and the optimum content was 3 wt%. The mechanical performance declined instead with the further increase in MWCNTs content up to 5 wt%, which could be attributed to the agglomeration of MWCNTs. Significant improvements in mechanical properties were achieved after the composites were treated in a temperature range from 950 °C to 1200 °C relative to their original state before heat treatment. The significant improvements could be described to the matrix densification, and leucite formation as well as the proper interface bonding state between carbon nanotube and leucite matrix. [ABSTRACT FROM AUTHOR]

Hybrid C f and SiC f reinforced geopolymer composites with Al 2 O 3 particles were successfully fabricated, and the effects of high-temperature treatment on the microstructure evolution and mechanical properties of C f -SiC f -(Al 2 O 3p )/KGP composites were investigated. Results showed that the amorphous matrix of C f -SiC f -(Al 2 O 3p )/KGP composites transformed into kalsilite and leucite phase after treated at 1000 and 1200 °C, respectively, due to the addition of fibers hindering crystallization of the geopolymer matrix. The addition of Al 2 O 3p was helpful to increase the thermal stability of composites after high-temperature treatment. Flexural strength and Young's modulus of the composites decreased after high temperature treatment and showed the maximum values at 1000 °C. All the composites showed a non-catastrophic fracture behavior after heat treated, which was attributed to fiber pulling-out and debonding. [ABSTRACT FROM AUTHOR]

The effects of in situ amorphous graphite coating on ablation behavior of SiC fiber reinforced SiBCN ceramics in an oxyacetylene flame are explored. The ablation products for both the monoliths and composites are similar, comprising amorphous SiO 2 and cristobalite. The ablation resistance stems from formation of dense, passivating oxide scale of B 2 O 3 containing amorphous SiO 2 . In different ablation stages, the ablation rates are synergistically controlled by various mechanisms. Interfacial structure and degradation of SiC fibers both deteriorate ablation resistance. The crystallization of SiC fibers leading to strength reduction is the main reason for poorer performance vs monoliths. [ABSTRACT FROM AUTHOR]

Homogeneously dispersed reduced-graphene-oxide (rGO) reinforced geopolymer composites were successfully prepared through in-situ reduction of graphene oxide (GO) under alkaline geopolymeric condition. The effects of treatment temperatures on the reduction of GO under the alkaline solution during the rGO/geopolymer preparation process were characterized systematically. The results showed that GO could be in situ reduced under alkaline geopolymer solution at various temperatures (25–80 °C) for 3 h. The reduction degree of rGO was improved with increasing the reaction temperature. The rGO was well dispersed, and the rGO/geopolymer composites showed amorphous structure. [ABSTRACT FROM AUTHOR]

In this study, the effect of curing temperature and SiO 2 /K 2 O molar ratio on the mechanical properties of metakaolin-based geopolymers were investigated. Different curing temperatures (from 50° to 90 °C) were used for curing process. A series of geopolymers with different SiO 2 /K 2 O molar ratio ( N ) were prepared, with N =2.4, 2.0, 1.6 and 1.2, respectively. The phase composition, microstructure and mechanical properties of the resulting geopolymers were studied. The results indicate that curing temperature and SiO 2 /K 2 O molar ratio impacts final microstructures and mechanical properties of the resulting geopolymers. Microstructures become denser with increases in curing temperature, which was beneficial to the improvement of geopolymer's mechanical properties. The optimum curing temperature was ≈ 80 °C giving the best mechanical properties with the compressive strength of 106.2 MPa and elastic modulus of 8.3 GPa, respectively. With increasing SiO 2 /K 2 O molar ratios, the microstructure was quite porous and contained unreacted metakaolin particles, and the corresponding mechanical properties declined sharply, attributed to low degrees of geopolymerization caused by high alkali content. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide/leucite nanocomposites (rGO/leucite) were prepared from reduced graphene oxide/geopolymer composites (rGO/geopolymer) followed by post high-temperature treatment process. The crystallization kinetics and effects of isothermal soaking times on microstructure evolution and mechanical properties of the final rGO/leucite composites were investigated systematically. The results show that the activation energy value for rGO/leucite crystallization was slightly lower than that of pure geopolymer which controlled by a three-dimensional growth mechanism. The scrolled and fold degree of rGO sheets in the rGO/leucite composites increased with the isothermal soaking times. The flexural strength and fracture toughness of the rGO/leucite after treated at 950 °C for 0.5 h reached their maximum values 75.4 ± 5.6 MPa and 1.40 ± 0.03 MPa m 1/2 , decreased with the isothermal soaking times, respectively. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide/cubic-leucite (rGO/cubic-leucite) composites were prepared from reduced graphene oxide/geopolymer (rGO/CsKGP) composites by simultaneous in situ crystallization process and thermal reduction of GO. The effects of both rGO addition and treatment temperature on the microstructure and mechanical properties of the rGO/CsKGP composites were investigated systematically. The results showed that rGO sheets in the rGO/CsKGP composites could be further in-situ reduced through high temperature treatment. The rGO/CsKGP composites fully transform to rGO/cubic-leucite composites after treating above 1000 °C for 30 min. Compared with the pure cubic-leucite matrix, the flexural strength and fracture toughness of rGO/cubic-leucite composites were 65.0 MPa and 0.64 MPa m 1/2 , increased by ~ 37% and ~ 14% respectively. These improvements are attributed to a combination of rGO reinforcement and grain refinement. [ABSTRACT FROM AUTHOR]

Carbon fiber felt reinforced geopolymer composites were easily and simply prepared by infiltrating geopolymer slurry into carbon fiber felt. The effects of fiber contents on the microstructure, mechanical properties and toughening mechanisms of the final composites were investigated systematically. Results showed that the mechanical properties of the composites improved remarkably due to the addition of carbon fiber felt. The flexural strength, work of fracture and fracture toughness of the composites reached the maximum values of 51.5±0.6 MPa, 1817.8±133.9 J m −2 and 1.27±0.12 MPa m 1/2 with increasing fiber contents of 5 vol%, respectively. The composites showed a typical pseudoplasticity behavior of fracture. The improvements of the work of fracture and fracture toughness for composites are attributed to the cracks deflection and carbon fiber pulling-outs. [ABSTRACT FROM AUTHOR]

In this paper, short SiC fiber (SiC sf ) reinforced geopolymer composites (SiC sf /geopolymer) were prepared and effects of fiber contents and lengths on the microstructure and mechanical properties of the composites were investigated. In-situ crack growth was carried out to study the fracture behavior and toughening mechanism of the composites. The results showed that SiC sf /geopolymer composite developed weak interfacial bonding state through mechanical interlocking rather than chemical interfacial reaction. The presence of SiC sf not only enhanced both flexural strength and work of fracture, but also prevented the catastrophic failure as seen in neat geopolymer. When fiber content was 2.0 vol% with length of 5 mm, the composite obtained the highest flexural strength and work of fracture, which were 5.6 and 63 times as high as those of neat geopolymer, respectively. In-situ crack growth together with fractographs showed that toughening mechanisms of the composite included formation and propagation of microcracks, crack deflection, fiber debonding and significant pulling-out. [ABSTRACT FROM AUTHOR]

SiBCN ceramics were prepared using various volumes of graphene platelets (GPLs) as nanofiller. The effects of the nanofiller on microstructure, and oxidation and thermal shock resistance of as-sintered ceramics were investigated. The phase composition and microstructures were very similar for all investigated ceramics consisting primarily of β-SiC, BNC and small amounts of α-SiC with relatively homogeneously distributed 5–10 nm thick GPLs in the matrix. For SiBCN ceramics incorporating graphene as nanofiller, a porous oxide layer forms at 1500 °C and the oxidation behavior shows a linear kinetics by thickness measurement method. Gas evolution during heating lead to a passive oxidation behavior and weight loss. Graphene reinforced SiBCN ceramics exhibit thermal shock resistance superior to monoliths of the same material. The graphene distributed in SiBCN matrix can dissipate the energy of crack growth and acts as a stopper to cracks. The toughening mechanisms offered by graphene, including pull-out and bridging appear to aid in ameliorating thermal shock effects. Furthermore, the existence of a dense oxide surface layer retards oxygen diffusion into the inner matrix and heals surface pores and cracks, which also contributes to thermal shock resistance. [ABSTRACT FROM AUTHOR]

MAS-BN composites were prepared by hot pressed sintering. The phase transformation of magnesium aluminum silicate ceramic (MAS) was investigated with special attention to the inhibiting crystallization mechanism of h -BN. The resulting data suggest particular pathways for the inhibiting effect of h -BN on the crystallization of MAS. The nucleophilic attack of N on M (M = Mg 2+ , Al 3+ and Si 4+ ) and electrophilic attack of B on O are the crucial factors for the formation of amorphous MAS phase. In addition, a chemical bonding formed between h -BN and MAS and the atoms of the matrix diffuse into the h -BN layer, leading to a strong bonding interface. [ABSTRACT FROM AUTHOR]

Geopolymer nanocomposites with different rGO contents were synthesized by in situ reduction of graphene oxide under alkaline solutions. The effects of rGO contents on the microstructure and the mechanical properties of the rGO/geopolymer composites were characterized systematically. Results showed that GO could be partially reduced in alkaline geopolymeric solutions using relatively short synthesis periods of 15 min at loadings of 0–0.5 wt% at room temperature. The resulting rGO was evenly dispersed in the final amorphous composite structures. Measured fracture toughness values increased 61.5% with increasing rGO contents to 0.5 wt%, reaching 0.21 MPa m 1/2 . The flexural strength of the rGO/GP reached a maximum value of 17.9 MPa with increasing rGO contents to 0.3 wt%. Strong interface bonding, crack deflection and propagation, rGO pull-out, wrapping and anchoring around geopolymer particles contributed to the improved fracture toughness and flexural strength. [ABSTRACT FROM AUTHOR]

Pure SiC ceramic monoliths were sintered at 1100–1200 °C and 5 GPa coupled with mechanically alloying. The mechanically alloyed SiC powders are nearly completely amorphous containing a small quantity of 2 nm-sized crystallites. The resulting monoliths consist of amorphous and 3C–SiC nanocrystallites (<5 nm), and offer relative densities ≥93.0%, nanohardnesses ≥34.0 GPa and elastic moduli ≥378 GPa. In the flowing air at 1500 °C, they undergo minimal mass change indicative of excellent oxidation resistance. [ABSTRACT FROM AUTHOR]

Homogeneously dispersed graphene reinforced geopolymer composites were easily and simply prepared through in-situ reduction of graphene oxide (GO) in alkaline geopolymeric solutions. The in-situ GO reduction degree, microstructure and mechanical properties of reduced graphene oxide (rGO)/geopolymer composites were investigated systematically. The results revealed that the rGO C/O ratio increased dramatically after in situ reaction at 60 °C for 72 h in geopolymeric solutions. The reduction is mainly attributed to conversion of C=O to C–O bonds and then elimination of residual oxygen-function groups under the alkaline conditions. The as-obtained rGO was uniformly dispersed and exhibited good long-term stability in the geopolymeric solutions. The final amorphous geopolymer matrix structure was unaffected by the homogeneously dispersed rGO yet strong interfacial bonding was observed. As a result, the fracture toughness of the composite with 1 wt% rGO was improved by ~17% compared with the pristine geopolymer. [ABSTRACT FROM AUTHOR]

C f /cubic-leucite composite was prepared through heat-treating carbon fiber reinforced 20 at.% cesium substituted geopolymer precursor composite (C f /CsKGP) at high temperatures. The thermal evolution, microstructure, mechanical and thermal expansion properties of the obtained composite were investigated, together with its non-isothermal oxidation behavior and high-temperature mechanical property. Post treatment at 1200 °C for 30 min in argon atmosphere, C f /CsKGP was completely transformed into C f /cubic-leucite composite, showing a better carbon fiber–matrix interfacial bonding and greatly improved mechanical properties as compared to C f /tetragonal-leucite composite. Sol-SiO 2 repeated impregnation process proved to be an efficient method to seal the cracks in C f /cubic-leucite formed during the heat treatment, and the impregnated composite showed good oxidation resistance and excellent mechanical properties at elevated temperature range from 700 °C to 1200 °C in the air. It was therefore concluded that the cesium-substituted potassium-based geopolymer precursor technique and the sol-SiO 2 impregnation process provide an alternative route for the preparation of ceramic composites for potential high-temperature applications. [ABSTRACT FROM AUTHOR]

Textured hexagonal boron nitride (BN) composite ceramics with mullite as sintered additive were fabricated by hot-press sintering under different pressures. The degrees of texture and the microstructures of these materials were evaluated using X-ray diffraction, pole figures and scanning electron microscopy. The results showed that the hexagonal BN composite ceramics have obvious directional orientation. The preferred orientation of the c-axis of hexagonal BN grains was along the direction of pressure, and the sintering pressure influences texture formation. [ABSTRACT FROM AUTHOR]