SiC composite ceramics for solar absorber and storage integration are new concentrating solar power materials.SiC composite ceramics for solar absorber and storage integration were fabricated using SiC,black corundum ...SiC composite ceramics for solar absorber and storage integration are new concentrating solar power materials.SiC composite ceramics for solar absorber and storage integration were fabricated using SiC,black corundum and kaolin as the raw materials,Co_(2)O_(3)as the additive via pressureless graphite-buried sintering method in this study.Influences of Co_(2)O_(3)on the microstructure and properties of SiC composite ceramics for solar absorber and storage integration were studied.The results indicate that sample D2(5wt%Co_(2)O_(3))sintered at 1480℃exhibits optimal performances for 119.91 MPa bending strength,93%solar absorption,981.5 kJ/kg(25-800℃)thermal storage density.The weight gain ratio is 12.58 mg/cm2after 100 h oxidation at 1000℃.The Co_(2)O_(3)can decrease the liquid phase formation temperature and reduce the viscosity of liquid phase during sintering.The liquid with low viscosity not only promotes the elimination of pores to achieve densification,but also increases bending strength,solar absorption,thermal storage density and oxidation resistance.A dense SiO_(2) layer was formed on the surface of SiC after 100 h oxidation at 1000℃,which protects the sample from further oxidation.However,excessive Co_(2)O_(3)will make the microstructure loose,which is disadvantageous to the performances of samples.展开更多
In recent decades, many additives with different characteristics have been applied to strengthen and toughen Al2O3-based ceramic cutting tool materials. Among them, SiC whiskers and SiC nanoparticles showed excellent ...In recent decades, many additives with different characteristics have been applied to strengthen and toughen Al2O3-based ceramic cutting tool materials. Among them, SiC whiskers and SiC nanoparticles showed excellent performance in improving the material properties. While no attempts have been made to add SiC whiskers and SiC nanoparticles together into the ceramic matrix and the synergistically toughening effects of them have not been studied. An Al2O3-SiCw-SiC np advanced ceramic cutting tool material is fabricated by adding both one-dimensional SiC whiskers and zero-dimensional SiC nanoparticles into the Al2O3 matrix with an effective dispersing and mixing process. The composites with 25 vol% SiC whiskers and 25 vol% SiC nanoparticles alone are also investegated for comparison purposes. Results show that the Al2O3-SiCw-SiCnp composite with both 20 vo1% SiC whiskers and 5 vol% SiC nanoparticles additives have much improved mechanical properties. The flexural strength of Al2O3-SiCw-SiCnp is 730＋ 95 MPa and fracture toughness is 5.6 ± 0.6 MPa.m1/2. The toughening and strengthening mechanisms of SiC whiskers and nanoparticles are studied when they are added either individually or in combination. It is indicated that when SiC whiskers and nanoparticles are added together, the grains are further refined and homogenized, so that the microstructure and fracture mode ratio is modified. The SiC nanoparticles are found helpful to enhance the toughening effects of the SiC whiskers. The proposed research helps to enrich the types of ceramic cutting tool and is benefit to expand the application range of ceramic cutting tool.展开更多
Silicon carbide (SiC) ceramics have excellent properties and widely used for high temperature applications. So far, joining techniques have been applied to fabricate large SiC ceramics with complicated shapes. In this...Silicon carbide (SiC) ceramics have excellent properties and widely used for high temperature applications. So far, joining techniques have been applied to fabricate large SiC ceramics with complicated shapes. In this work, the additive manufacturing (AM) technique was examined to fabricated SiC ceramics with complicated hollow structures using the Fused Deposition Modeling (FDM) type 3D-printer. To mold the hollow structure for the applications such as heat exchangers, the “support-less” condition must be achieved. Thus, extruded SiC-phenol resin compounds must be cured immediately after molding to keep the molded shapes. To increase the thermal conductivity of the SiC compounds, the combinations of commercial SiC powders with different average diameters were examined for increasing the volume fraction of SiC particles to the phenol resin. SiC compounds with optimized rheological properties for the modified FDM-type 3D-printer were successfully obtained.展开更多
A novel temperature fluctuation synthesis/simultaneous densification process was developed for the preparation of Ti3SiC2 bulk ceramics. In this process. Si is used as an in-situ liquid forming phase and it is favorab...A novel temperature fluctuation synthesis/simultaneous densification process was developed for the preparation of Ti3SiC2 bulk ceramics. In this process. Si is used as an in-situ liquid forming phase and it is favorable for both the solid-liquid synthesis and the densification of Ti3SiC2 rainies. The present work demonstrated that the temperature fluctuation synthesis/simultaneous densification process is one of the most effective and simple methods for the preparation of Ti3SiC2 bulk materials providing relatively low synthesis temperature. short reaction time; and simultaneous synthesis and densification. This work also showed the capability to control the microstructure, e.g., the preferred orientation, of the bulk Ti3SiC2 materials simply by applying the hot pressing pressure at different Stages of the temperature fluctuation process. And textured Ti3SiC2 bulk materials with {002} faces of laminated Ti3SiC2 grains normal to the hot pressing axis were prepared.展开更多
The microstructures and crack propagating characteristic of Si 3N 4 (μ)/SiC (n, w) composite ceramic were studied with AEM. The Si 3N 4 (μ)/SiC (n, w) composite ceramic consists of β Si 3N 4, β SiC, a smal...The microstructures and crack propagating characteristic of Si 3N 4 (μ)/SiC (n, w) composite ceramic were studied with AEM. The Si 3N 4 (μ)/SiC (n, w) composite ceramic consists of β Si 3N 4, β SiC, a small amount of α Si 3N 4 and α SiC, and amorphous phase. Most of Si 3N 4 grains were equiaxed crystal and also there were some bulky columnar ones. Most of SiC particles and SiC whiskers distributed at the Si 3N 4 grain boundaries and a few of smaller SiC particles in the Si 3N 4 grains. Most of amorphous structure was in the junction of several Si 3N 4 grains and thin amorphous layer was observed only at a few of Si 3N 4 boundaries. Failured cracks propagated mainly along the boundaries of the Si 3N 4 grains and partially passed through Si 3N 4 grains. The path of crack propagating might change, branching and twisting of the cracks might occur when the expanding crack meet the SiC particle and/or SiC whisker. Effect of the microstructure on strength and toughness of the composite ceramic was briefly discussed.展开更多
Al_(2)O_(3)/SiC composite ceramics were prepared fromα-Al_(2)O_(3) and SiC by a pressureless sinter method in this study.The effect of SiC contents on the mechanic properties,phase compositions and microstructure is ...Al_(2)O_(3)/SiC composite ceramics were prepared fromα-Al_(2)O_(3) and SiC by a pressureless sinter method in this study.The effect of SiC contents on the mechanic properties,phase compositions and microstructure is studied.Experimental results show that the vickers hardness,wear resistance and thermal conductivity of the samples increase with the increase in the SiC content,and the hardness of the sample reaches 16.22 GPa,and thermal conductivity of the sample reaches 25.41 W/(m.K)at room temperature when the SiC content is 20 wt%(B5)and the sintering temperature is at 1640℃.Higher hardness means higher scour resistance,and it indicates that the B5 material is expected to be used for the solar heat absorber of third generation solar thermal generation.The results indicate the mechanism of improving mechanical properties of Al_(2)O_(3)/SiC composite ceramics:SiC plays a role in grain refinement that the grain of SiC inhibits the grain growth of Al_(2)O_(3),while the addition of SiC changes the fracture mode from the intergranular to the intergranular-transgranular.展开更多
A polycrystalline dense Ti3SiC2 based ceramic material has been produced by several techniques. The effect of addition of TiC and SiC is also studied. The Ti3SiC2 material shows extraordinary electrical, thermal and m...A polycrystalline dense Ti3SiC2 based ceramic material has been produced by several techniques. The effect of addition of TiC and SiC is also studied. The Ti3SiC2 material shows extraordinary electrical, thermal and mechanical properties. Furthermore, it shows a damage tolerance capability and oxidation resistance. In this work, we have synthesized Ti3SiC2 by electro-thermal explosion chemical reaction (ETE) with high current density (900 Amperes/a.u) followed by uniaxial pressure. The structural properties of the as-prepared materials are studied by x-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDX) techniques. The chemical cartography, imaging and electronic properties are investigated using Ultra-STEM and electron high energy loss resolution spectroscopy (EELS) techniques, respectively. The surface of Ti3SiC2 is characterized by means of X-ray photoelectron spectroscopy (XPS). High resolution C 1s, Si 2p, Ti 2p, Ti 3s core level spectra are explained in terms of crystallographic and electronic structure. Valence band spectrum is performed to confirm the validity of the theoretical calculations.展开更多
By using self-made metal-alkoxide yttrium isopropoxide as a sintering additive and disperser of whisker, the SiC whisker reinforced AIN ceramics was prepared. Its apparent density is 99.5 percent of the theoretical de...By using self-made metal-alkoxide yttrium isopropoxide as a sintering additive and disperser of whisker, the SiC whisker reinforced AIN ceramics was prepared. Its apparent density is 99.5 percent of the theoretical density; its flexural strength and fracture toughness are 681 MPa and 5.21 MPa·m1/2 respectively. Comparing the result with that by applying Y2O3 powder as a sintering additive, the flexural strength is increased by 25% and the fracture toughness is increased by 33% . The dispersity of whisker by increased yttrium isopropoxide is significantly better than that by Triton X-100.展开更多
This article provides a review of current research activities that concentrate on Ti3SiC2. We begin with an overview of the crystal and electronic structures, which are the basis to understand this material. Following...This article provides a review of current research activities that concentrate on Ti3SiC2. We begin with an overview of the crystal and electronic structures, which are the basis to understand this material. Followings are the synthetic strategies that have been exploited to achieve, and the formation mechanism of Ti3SiC2. Then we devote much attentions to the mechanical properties and oxidation/hot corrosion behaviors of Ti3SiC2 as well as some advances achieved recently. At the end of this paper, we elaborate on some new discoveries in the Ti3SiC2 system, and also give a brief discussion focused on the ＂microstructure -property＂ relationship.展开更多
Bulk Si_2 BC_3 N ceramics were reinforced with SiC coated multi-walled carbon nanotubes(MWCNTs). The phase compositions, mechanical properties, and thermal shock resistance, as well as the oxidation resistance of the ...Bulk Si_2 BC_3 N ceramics were reinforced with SiC coated multi-walled carbon nanotubes(MWCNTs). The phase compositions, mechanical properties, and thermal shock resistance, as well as the oxidation resistance of the designed Si_2 BC_3 N ceramics were comparatively investigated. The results show that nano SiC coating can be formed on MWCNTs through pyrolyzing polysilazane, which improves the oxidation resistance of MWCNTs. A stronger chemical bonding is formed between the SiC coated MWCNTs and SiC particles, contributing to improved flexural strength(532.1 MPa) and fracture toughness(6.66 MPa m1/2). Besides, the 2 vol% SiC coated MWCNTs reinforced Si_2 BC_3 N ceramics maintains much higher residual strength(193.0 MPa) after thermal shock test at 1000 ℃.The enhanced properties should be attributed to:(1) the breaking of MWCNTs and the debonding between MWCNTs and SiC interfaces, which leads to more energy dissipation;(2) the rough surfaces of SiC coated MWCNTs increase the adhesion strength during the "pull out" of MWCNTs.展开更多
The MAX phase Ti3SiC2 has broad application prospects in the field of rail transit,nuclear protective materials and electrode materials due to its excellent electrical conductivity,selflubricating properties and wear ...The MAX phase Ti3SiC2 has broad application prospects in the field of rail transit,nuclear protective materials and electrode materials due to its excellent electrical conductivity,selflubricating properties and wear resistance.Cu–Ti3SiC2 co-continuous composites have superior performance due to the continuous distribution of 3 D network structures.In this paper,the Cu/Ti3SiC2(Ti C/Si C)co-continuous composites are formed via vacuum infiltration process from Cu and Ti3SiC2 porous ceramics.The co-continuous composites have significantly improved the flexural strength and conductivity of Ti3SiC2 due to the addition of Cu,with the conductivity up to 5.73×10^5 S/m,twice as high as the Ti3SiC2 porous ceramics and five times higher than graphite.The reaction between ingredients leads to an increase in the friction coefficient,while the hard reaction products(Ti Cx,Si C)lower the overall wear rate(1×10^–3 mm^3/(N·m)).Excellent electrical conductivity and wear resistance make co-continuous composites more advantageous in areas such as rail transit.展开更多
基金Funded by the National Key R&D Program of China(No.2018YFB1501002)。
文摘SiC composite ceramics for solar absorber and storage integration are new concentrating solar power materials.SiC composite ceramics for solar absorber and storage integration were fabricated using SiC,black corundum and kaolin as the raw materials,Co_(2)O_(3)as the additive via pressureless graphite-buried sintering method in this study.Influences of Co_(2)O_(3)on the microstructure and properties of SiC composite ceramics for solar absorber and storage integration were studied.The results indicate that sample D2(5wt%Co_(2)O_(3))sintered at 1480℃exhibits optimal performances for 119.91 MPa bending strength,93%solar absorption,981.5 kJ/kg(25-800℃)thermal storage density.The weight gain ratio is 12.58 mg/cm2after 100 h oxidation at 1000℃.The Co_(2)O_(3)can decrease the liquid phase formation temperature and reduce the viscosity of liquid phase during sintering.The liquid with low viscosity not only promotes the elimination of pores to achieve densification,but also increases bending strength,solar absorption,thermal storage density and oxidation resistance.A dense SiO_(2) layer was formed on the surface of SiC after 100 h oxidation at 1000℃,which protects the sample from further oxidation.However,excessive Co_(2)O_(3)will make the microstructure loose,which is disadvantageous to the performances of samples.
基金Supported by National Natural Science Foundation of China(Grant No.51175305)
文摘In recent decades, many additives with different characteristics have been applied to strengthen and toughen Al2O3-based ceramic cutting tool materials. Among them, SiC whiskers and SiC nanoparticles showed excellent performance in improving the material properties. While no attempts have been made to add SiC whiskers and SiC nanoparticles together into the ceramic matrix and the synergistically toughening effects of them have not been studied. An Al2O3-SiCw-SiC np advanced ceramic cutting tool material is fabricated by adding both one-dimensional SiC whiskers and zero-dimensional SiC nanoparticles into the Al2O3 matrix with an effective dispersing and mixing process. The composites with 25 vol% SiC whiskers and 25 vol% SiC nanoparticles alone are also investegated for comparison purposes. Results show that the Al2O3-SiCw-SiCnp composite with both 20 vo1% SiC whiskers and 5 vol% SiC nanoparticles additives have much improved mechanical properties. The flexural strength of Al2O3-SiCw-SiCnp is 730＋ 95 MPa and fracture toughness is 5.6 ± 0.6 MPa.m1/2. The toughening and strengthening mechanisms of SiC whiskers and nanoparticles are studied when they are added either individually or in combination. It is indicated that when SiC whiskers and nanoparticles are added together, the grains are further refined and homogenized, so that the microstructure and fracture mode ratio is modified. The SiC nanoparticles are found helpful to enhance the toughening effects of the SiC whiskers. The proposed research helps to enrich the types of ceramic cutting tool and is benefit to expand the application range of ceramic cutting tool.
文摘Silicon carbide (SiC) ceramics have excellent properties and widely used for high temperature applications. So far, joining techniques have been applied to fabricate large SiC ceramics with complicated shapes. In this work, the additive manufacturing (AM) technique was examined to fabricated SiC ceramics with complicated hollow structures using the Fused Deposition Modeling (FDM) type 3D-printer. To mold the hollow structure for the applications such as heat exchangers, the “support-less” condition must be achieved. Thus, extruded SiC-phenol resin compounds must be cured immediately after molding to keep the molded shapes. To increase the thermal conductivity of the SiC compounds, the combinations of commercial SiC powders with different average diameters were examined for increasing the volume fraction of SiC particles to the phenol resin. SiC compounds with optimized rheological properties for the modified FDM-type 3D-printer were successfully obtained.
基金the National Outstanding YOung Scientist Foundation Under Grant !No.59925208 the National Natural Science Foundation of China
文摘A novel temperature fluctuation synthesis/simultaneous densification process was developed for the preparation of Ti3SiC2 bulk ceramics. In this process. Si is used as an in-situ liquid forming phase and it is favorable for both the solid-liquid synthesis and the densification of Ti3SiC2 rainies. The present work demonstrated that the temperature fluctuation synthesis/simultaneous densification process is one of the most effective and simple methods for the preparation of Ti3SiC2 bulk materials providing relatively low synthesis temperature. short reaction time; and simultaneous synthesis and densification. This work also showed the capability to control the microstructure, e.g., the preferred orientation, of the bulk Ti3SiC2 materials simply by applying the hot pressing pressure at different Stages of the temperature fluctuation process. And textured Ti3SiC2 bulk materials with {002} faces of laminated Ti3SiC2 grains normal to the hot pressing axis were prepared.
文摘The microstructures and crack propagating characteristic of Si 3N 4 (μ)/SiC (n, w) composite ceramic were studied with AEM. The Si 3N 4 (μ)/SiC (n, w) composite ceramic consists of β Si 3N 4, β SiC, a small amount of α Si 3N 4 and α SiC, and amorphous phase. Most of Si 3N 4 grains were equiaxed crystal and also there were some bulky columnar ones. Most of SiC particles and SiC whiskers distributed at the Si 3N 4 grain boundaries and a few of smaller SiC particles in the Si 3N 4 grains. Most of amorphous structure was in the junction of several Si 3N 4 grains and thin amorphous layer was observed only at a few of Si 3N 4 boundaries. Failured cracks propagated mainly along the boundaries of the Si 3N 4 grains and partially passed through Si 3N 4 grains. The path of crack propagating might change, branching and twisting of the cracks might occur when the expanding crack meet the SiC particle and/or SiC whisker. Effect of the microstructure on strength and toughness of the composite ceramic was briefly discussed.
基金Funded by the National Key Technology Research and Development Program of the Ministry of Science and Technology of China(No.2018YFB1501002)。
文摘Al_(2)O_(3)/SiC composite ceramics were prepared fromα-Al_(2)O_(3) and SiC by a pressureless sinter method in this study.The effect of SiC contents on the mechanic properties,phase compositions and microstructure is studied.Experimental results show that the vickers hardness,wear resistance and thermal conductivity of the samples increase with the increase in the SiC content,and the hardness of the sample reaches 16.22 GPa,and thermal conductivity of the sample reaches 25.41 W/(m.K)at room temperature when the SiC content is 20 wt%(B5)and the sintering temperature is at 1640℃.Higher hardness means higher scour resistance,and it indicates that the B5 material is expected to be used for the solar heat absorber of third generation solar thermal generation.The results indicate the mechanism of improving mechanical properties of Al_(2)O_(3)/SiC composite ceramics:SiC plays a role in grain refinement that the grain of SiC inhibits the grain growth of Al_(2)O_(3),while the addition of SiC changes the fracture mode from the intergranular to the intergranular-transgranular.
文摘A polycrystalline dense Ti3SiC2 based ceramic material has been produced by several techniques. The effect of addition of TiC and SiC is also studied. The Ti3SiC2 material shows extraordinary electrical, thermal and mechanical properties. Furthermore, it shows a damage tolerance capability and oxidation resistance. In this work, we have synthesized Ti3SiC2 by electro-thermal explosion chemical reaction (ETE) with high current density (900 Amperes/a.u) followed by uniaxial pressure. The structural properties of the as-prepared materials are studied by x-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDX) techniques. The chemical cartography, imaging and electronic properties are investigated using Ultra-STEM and electron high energy loss resolution spectroscopy (EELS) techniques, respectively. The surface of Ti3SiC2 is characterized by means of X-ray photoelectron spectroscopy (XPS). High resolution C 1s, Si 2p, Ti 2p, Ti 3s core level spectra are explained in terms of crystallographic and electronic structure. Valence band spectrum is performed to confirm the validity of the theoretical calculations.
文摘By using self-made metal-alkoxide yttrium isopropoxide as a sintering additive and disperser of whisker, the SiC whisker reinforced AIN ceramics was prepared. Its apparent density is 99.5 percent of the theoretical density; its flexural strength and fracture toughness are 681 MPa and 5.21 MPa·m1/2 respectively. Comparing the result with that by applying Y2O3 powder as a sintering additive, the flexural strength is increased by 25% and the fracture toughness is increased by 33% . The dispersity of whisker by increased yttrium isopropoxide is significantly better than that by Triton X-100.
基金supported by the National Outstanding Young Scientist Foundation for Y.C. Zhou under Grant No. 59925208the National Natural Science Foundation of China under Grants No. 50232040, No. 50302011 and No. 90403027"863" Project,and High-Tech Bureau of the Chinese Academy of Sciences
文摘This article provides a review of current research activities that concentrate on Ti3SiC2. We begin with an overview of the crystal and electronic structures, which are the basis to understand this material. Followings are the synthetic strategies that have been exploited to achieve, and the formation mechanism of Ti3SiC2. Then we devote much attentions to the mechanical properties and oxidation/hot corrosion behaviors of Ti3SiC2 as well as some advances achieved recently. At the end of this paper, we elaborate on some new discoveries in the Ti3SiC2 system, and also give a brief discussion focused on the ＂microstructure -property＂ relationship.
基金supported financially by National Natural Science Foundation of China (NSFC, Grant Nos. 51702065 and 51621091)China Postdoctoral Science Foundation (Grant No. 2018M631924)
文摘Bulk Si_2 BC_3 N ceramics were reinforced with SiC coated multi-walled carbon nanotubes(MWCNTs). The phase compositions, mechanical properties, and thermal shock resistance, as well as the oxidation resistance of the designed Si_2 BC_3 N ceramics were comparatively investigated. The results show that nano SiC coating can be formed on MWCNTs through pyrolyzing polysilazane, which improves the oxidation resistance of MWCNTs. A stronger chemical bonding is formed between the SiC coated MWCNTs and SiC particles, contributing to improved flexural strength(532.1 MPa) and fracture toughness(6.66 MPa m1/2). Besides, the 2 vol% SiC coated MWCNTs reinforced Si_2 BC_3 N ceramics maintains much higher residual strength(193.0 MPa) after thermal shock test at 1000 ℃.The enhanced properties should be attributed to:(1) the breaking of MWCNTs and the debonding between MWCNTs and SiC interfaces, which leads to more energy dissipation;(2) the rough surfaces of SiC coated MWCNTs increase the adhesion strength during the "pull out" of MWCNTs.
文摘The MAX phase Ti3SiC2 has broad application prospects in the field of rail transit,nuclear protective materials and electrode materials due to its excellent electrical conductivity,selflubricating properties and wear resistance.Cu–Ti3SiC2 co-continuous composites have superior performance due to the continuous distribution of 3 D network structures.In this paper,the Cu/Ti3SiC2(Ti C/Si C)co-continuous composites are formed via vacuum infiltration process from Cu and Ti3SiC2 porous ceramics.The co-continuous composites have significantly improved the flexural strength and conductivity of Ti3SiC2 due to the addition of Cu,with the conductivity up to 5.73×10^5 S/m,twice as high as the Ti3SiC2 porous ceramics and five times higher than graphite.The reaction between ingredients leads to an increase in the friction coefficient,while the hard reaction products(Ti Cx,Si C)lower the overall wear rate(1×10^–3 mm^3/(N·m)).Excellent electrical conductivity and wear resistance make co-continuous composites more advantageous in areas such as rail transit.
