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Microstructure and EMW absorption properties of CVI Si3N4–SiCN ceramics with BN interface annealed in N2 atmosphere 下载免费PDF全文
Jimei Xue Xiaowei Yin Fang Ye Litong Zhang Laifei Cheng 《Journal of the American Ceramic Society》2018,101(3):1201-1210
A kind of chemical vapor infiltration (CVI) Si3N4–BN–SiCN composite ceramic with excellent electromagnetic wave (EMW) absorbing properties is obtained by CVI BN interface and SiCN matrix on porous Si3N4 ceramics, and then annealed at high temperatures (1200°C‐1500°C) in N2 atmosphere. The crystallization behavior, EMW absorbing mechanism and mechanical properties of the composite ceramics have been investigated. Results showed CVI SiCN ceramics with BN interface were crystallized in the form of nanograins, and the crystallization temperature was lower. Moreover, both EMW absorbing properties and mechanical properties of CVI Si3N4–BN–SiCN composite ceramics firstly increased and then decreased with the increase in annealing temperature due to the influence of BN interface on the microstructure and phase composition of the composite ceramics. The minimum reflection coefficient (RC) and maximum effective absorption bandwidth (EAB) of the composite ceramics annealed at 1300°C were ?47.05 dB at the thickness of 4.05 mm and 3.70 GHz at the thickness of 3.65 mm, respectively. The flexural strength and fracture toughness of the composite ceramics annealed at 1300°C were 94 MPa and 1.78 MPa/m1/2, respectively. 相似文献
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Jimei Xue Xiaowei Yin Fang Ye Litong Zhang Laifei Cheng 《Journal of the American Ceramic Society》2013,96(3):979-986
A thermodynamic calculation on the chemical vapor deposition of the SiCl4–NH3–CH4–H2–Ar system was performed using the FactSage thermochemical software databases. Predominant condensed phases at equilibrium were SiC, Si3N4, graphite, and Si. The equilibrium conditions for the deposition of condensed phases in this system were determined as a function of the deposition temperature, dilution ratio (δ), and reactant ratios of CH4/SiCl4 and NH3/SiCl4. The CVD phase diagrams were used to understand the reactions occurring during the formation of Si–C–N from the gas species and determine the area of SiC–Si3N4. The concentration of condensed‐phase products was used to determine the deposition conditions of CVD SiC–Si3N4. The present work was helpful for further experimental investigation on CVD Si–C–N. 相似文献
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Wei‐Ming Guo Shang‐Xian Gu Yang You Qiang‐Guo Jiang Shang‐Hua Wu Hua‐Tay Lin 《Journal of the American Ceramic Society》2015,98(12):3651-3654
Densification and thermal stability of hot‐pressed Si3N4–ZrB2 ceramics with and without additives were investigated in N2 atmosphere. The addition of MgO–Yb2O3, MgO–Y2O3, and Al2O3–Yb2O3 resulted in significant increase in relative density of the ceramics hot‐pressed at 1500°C from 48.5% to 98.0%, 97.3%, and 95.6%, respectively. There was weak reaction of ZrB2 with N2 to form ZrN in hot‐pressed ceramics. Then heat treatment at 1550°C resulted in the further reactions to produce ZrN, ZrSi2, and BN. The Si3N4–ZrB2 ceramics with MgO–Yb2O3 showed much better thermal stability as compared to the ceramics with Al2O3–Yb2O3. The small difference in density led to the obvious difference in thermal stability. Therefore, Si3N4–ZrB2 ceramics should be densified to full density, to obtain high thermal stability. 相似文献
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为了增韧Si3N4基陶瓷材料,以钨(W)作为第二相材料,Y2O3-Al2O3作为烧结助剂,采用气压烧结法制备了W/Si3N4复合陶瓷材料。研究了W含量对W/Si3N4复合陶瓷材料致密性、力学性能以及结构的影响。结果表明:在W含量小于5%(质量分数)时,样品致密度均达97%以上;在W含量为5%(质量分数)时,获得的W/Si3N4复合陶瓷材料综合性能最佳,弯曲强度、硬度和断裂韧性分别为(670.28±40.00) MPa、(16.42±0.22) GPa和(8.04±0.16) MPa·m1/2,相比于未添加金属W的Si3N4陶瓷材料分别提高了38.08%、13.08%和44.34%;通过分析W/Si3N4复合陶瓷材料样品抛光面和压痕裂纹的微观结构,发现W的引入能促使裂纹在扩展路径上更易发生偏转、分叉等增韧机制,消耗裂纹扩展能量,从而改善Si3N4陶瓷的断裂韧性。 相似文献
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Zhaoyun Xu Bo Wang Jianfeng Yang Zhongjian Zhao 《Journal of the American Ceramic Society》2014,97(11):3392-3395
Porous silicon nitride ceramics with various porosities were fabricated by liquid phase sintering of mixtures containing fibrous and equiaxed α‐Si3N4 powder with a various content ratios. The effects of the contents of the fibrous α‐Si3N4 powder (0%–100%) on the microstructure and mechanical properties of porous Si3N4 ceramics were studied. As the increase of the fibrous α‐Si3N4 powder content, both the density of green bodies and the linear shrinkage decreased, resulting in increased porosity due to the inhibited densification by the fibrous Si3N4 particle. XRD analysis proved the complete formation of single β‐Si3N4 phase. SEM analysis revealed that the microstructure of the low content of fibrous α‐Si3N4 porous ceramics was almost composed of fine elongated β‐Si3N4 grains with high aspect ratio while numerous coarse elongated β‐Si3N4 grains with low aspect ratio surrounding fine grains were formed as the content of the fibrous α‐Si3N4 powder increased. With the increase in content of the fibrous α‐Si3N4 powder from 0% to 100%, the porosity changed from 47.8% to 56.6%, and the flexural strength decreased from 146 to 62 MPa correspondingly, indicating a flexural adjustment of the porosity and mechanical properties. 相似文献
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Silicon nitridation mechanism in reaction‐bonded Si3N4–SiC and Si3N4‐bonded ferrosilicon nitride 下载免费PDF全文
Menglong Long Yong Li Xiuming Jin Guisheng Yao Jialin Sun Ramachandran V. Kumar 《Journal of the American Ceramic Society》2018,101(9):4350-4356
Reaction‐bonded Si3N4–SiC and Si3N4‐bonded ferrosilicon nitride, with Si powder, SiC particles and Fe3Si–Si3N4 particles as raw materials, respectively, are prepared in flame‐isolation nitridation shuttle kiln with flowing N2 at 1723K. There is columnar β‐Si3N4 in both Si3N4–SiC and Si3N4‐bonded ferrosilicon nitride. However, fibrous α‐Si3N4 is only observed in Si3N4–SiC and Si3N4‐bonded ferrosilicon nitride contains much more Si2N2O than Si3N4–SiC. By analyzing the oxidation thermodynamics of Si and Si3N4, it is known that in the process of producing Si3N4–SiC, Si is oxidized first to gaseous SiO and fibrous α‐Si3N4 is generated with SiO and N2. The existence of SiO is the reason of low silicon nitridation rate. But in the process of producing Si3N4‐bonded ferrosilicon nitride, Si3N4 is easier to be oxidized than Si and Si2N2O is generated on the surface of Si3N4 hexagonal prisms in ferrosilicon nitride particles. Meanwhile, Si in raw materials forms new ferrosilicon alloys with Fe3Si, which decreases the temperature of liquid appearance and blocks some open pores in the samples, which stops the matter loss of nitridation. Liquid ferrosilicon alloys favors β‐Si3N4 generation from Si direct nitridation and fibrous α‐Si3N4 transformation, which used to exist in ferrosilicon nitride raw materials. 相似文献
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Si3N4ceramics were prepared by pressureless sintering at 1 650 ℃ in nitrogen atmosphere using Si3N4powder as main starting material and adding nanoAl2O3powder( 3%,6%,9%,12%,and 15% in mass,the same hereinafter). The bending strength and fracture toughness( KIC) of the specimens were detected.The microstructure and phase compositions of the specimens were analyzed. The results show that Si3N4ceramics can be prepared by pressureless sintering when adding9%- 12% nano-Al2O3as active reactant,which dissolves in Si3N4,in-situ forming non-oxide SiAlON. The obtained Si3N4ceramics have the maximum bending strength of 710. 86 MPa and KICof 8. 61 MPa·m1 /2.The excellent properties come from many interwoven structures distributed uniformly in the ceramics matrix,which is composed of big and firm plate-like β-Si3N4,hexagonal SiAlON and sheet Si2N2O. 相似文献
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Preparation and Performance Study of Sialon‐Si3N4‐SiC Composite Ceramics for Concentrated Solar Power 下载免费PDF全文
Xiaohong Xu Xinbin Lao Jianfeng Wu Zhenggang Rao Yang Zhou Dezhi He Yi Liu 《International Journal of Applied Ceramic Technology》2015,12(5):949-956
For lowering the sintering temperature of silicon carbide ceramics used for solar thermal energy storage technology, O'‐Sialon and silicon nitride were employed as composite phases to construct Sialon‐Si3N4‐SiC composite ceramics. The composite ceramics were synthesized using SiC, Si3N4, quartz, and different alumina sources as starting materials with noncontact graphite‐buried sintering method. Influences of alumina sources on the physical properties and thermal shock resistance of the composites were studied. The results revealed that the employment of O'‐Sialon and silicon nitride could decrease the sintering temperature greatly to 1540°C. The optimum formula G2 prepared from mullite as alumina source achieved the best performances: 66.7 MPa of bending strength, 10.0 W/(m·K) of thermal conductivity. The composition parameter x = 0.4 of O'‐Sialon decreased to 0.04 after 30 cycles thermal shock, and the bending strength increased with a rate of 11.0% due to the increase of O'‐Sialon grain size, and the optimization of microstructure caused by the transformation of O'‐Sialon grains and densification within the samples. The good thermal shock resistance makes the composites suitable for the use as thermal storage materials of concentrated solar power generation. 相似文献
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Lei Fan Meng Zhou Zhongqi Shi Xuefeng Lu Chao Wang 《Journal of the American Ceramic Society》2014,97(5):1371-1374
Porous β‐Si3N4 ceramics are sintered at 1600°C in N2 and postheat treated at 1500°C under vacuum using Li2O and Y2O3 as the sintering additives. The partial sintering and phase transformation are promoted at low temperature by the addition of Li2O. The addition of Y2O3 is advantageous for the formation of high aspect ratio β‐Si3N4 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‐Si3N4 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% Li2O and 0.33 wt% Y2O3, and it is suitable for high‐temperature applications. 相似文献
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反应烧结氮化硅-碳化硅复合材料的氮化机理 总被引:1,自引:0,他引:1
为分析反应烧结氮化硅结合碳化硅(Si3N4-SiC)材料中微观结构和氮化硅分布不均匀的原因,对在隔焰燃气氮化梭式窑中应用反应烧结氮化方法制备的氮化硅结合碳化硅复合材料进行结构研究和热力学分析。结果表明:材料中的氮化硅以纤维状和柱状两种形状存在。Si的氮化机理为:Si首先被氧化成气态SiO,降低了体系的氧分压,当氧分压足够低时,Si与N2直接反应形成柱状Si3N4,气态SiO亦可与N2反应生成氮化硅,这是一个气-气反应,故生成的Si3N4为纤维状。氮化反应前SiO主要分布于材料孔隙和表面,因而生成的氮化硅分布不均匀,导致了反应烧结Si3N4-SiC材料结构的不均匀。 相似文献
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Fabrication and Microwave Dielectric Properties of Mg2SiO4‐LiMgPO4‐TiO2 Composite Ceramics 下载免费PDF全文
ZiFan Cheng Xing Hu Yi Li ZhiYuan Ling 《Journal of the American Ceramic Society》2016,99(8):2688-2692
Complete solid solutions between Mg2SiO4 and LiMgPO4 are confirmed by the XRD results. The phase constitution of 0.5Mg2SiO4‐0.5LiMgPO4 is found to be dependent on firing temperature. The chemical compatibility between Mg2SiO4 and rutile phase at sintering temperature is modified by incorporating LiMgPO4. The microwave dielectric properties of (1?y)(0.5Mg2SiO4‐0.5LiMgPO4)‐yTiO2 (y = 0–0.3) composite ceramics have been investigated. The optimized microwave dielectric properties for 0.35Mg2SiO4‐0.35LiMgPO4‐0.3TiO2 ceramics sintered at 1050°C show low dielectric constant (11.4), high‐quality factor (31 800 GHz), and low‐temperature coefficient of resonant frequency (?4 ppm/°C). 相似文献
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以氧含量相对较高的“平价”Si3N4粉体(氧含量1.85%(质量分数))为原料,Y2O3-MgO作为烧结助剂,制备低成本高热导率Si3N4陶瓷,研究Y2O3含量对Si3N4陶瓷致密化、显微结构、力学性能及热导率的影响。结果表明,适当增加Y2O3的加入量不仅可以促进Si3N4陶瓷的致密化和显微结构的细化,还有助于晶格氧含量的降低和热导率的提升。Y2O3含量为7%(质量分数)的样品在1 900 ℃烧结后的综合性能最佳,其相对密度、抗弯强度、断裂韧性和热导率分别为99.5%、(726±46) MPa、(6.9±0.2) MPa·m1/2和95 W·m-1·K-1。 相似文献
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Equiaxed β–Si3N4 ceramics prepared by rapid reaction‐bonding and post‐sintering using TiO2–Y2O3–Al2O3 additives 下载免费PDF全文
Li‐Xiang Wu Wei‐Ming Guo Ling‐Yong Zeng Hua‐Tay Lin 《Journal of the American Ceramic Society》2017,100(12):5353-5357
Sintered reaction‐bonded Si3N4 ceramics with equiaxed microstructure were prepared with TiO2–Y2O3–Al2O3 additions by rapid nitridation at 1400°C for 2 hours and subsequent post‐sintering at 1850°C for 2 hours under N2 pressure of 3 MPa. It was found that α–Si3N4, β–Si3N4, Si2N2O, and TiN phases were formed by rapid nitridation of Si powders with single TiO2 additives. However, the combination of TiO2 and Y2O3–Al2O3 additives led to the formation of 100% β–Si3N4 phase from the nitridation of Si powders at such low temperature (1400°C), and the removal of Si2N2O phase. As a result, dense β–Si3N4 ceramics with equiaxed microstructure were obtained after post‐sintering at high temperature. 相似文献
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Gaoming Zhu Xiaohong Wang Peizhong Feng Zhangsheng Liu Jinan Niu Farid Akhtar 《Journal of the American Ceramic Society》2016,99(4):1147-1150
MoB and SiC particulate reinforced MoSi2 matrix composites were synthesized in situ from Mo, Si, and B4C powder mixtures by self‐propagating high‐temperature synthesis (SHS). The SHS MoSi2–MoB–SiC products were vacuum hot‐pressed (HPed) at 1400°C for 90 min to fabricate high‐density (> 97.5% relative density) bulk composites. Microstructure refinement and improvements in the Vickers hardness and fracture toughness of the HPed composites were observed with increasing B4C content in the reaction mixture. The HPed composite of composition MoSi2–0.4MoB–0.1SiC exhibited grain size of 1–5 μm, Vickers hardness of 12.5 GPa, bending strength of 537 MPa, and fracture toughness of 3.8 MPa.m1/2. These excellent mechanical properties indicate that MoB and SiC particulate reinforced MoSi2 composites could be promising candidates for structural applications. 相似文献