共查询到19条相似文献,搜索用时 46 毫秒
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泡沫陶瓷由于具有一系列优异的性能,使得其应用范围越来越广泛,其制备方法也在不断地发展.先驱体转化法制备泡沫陶瓷是20世纪末才出现的一种新型工艺.它具有制备温度低、陶瓷组成和结构町设计、容易成型复杂构件等优点,成为目前泡沫陶瓷制备方法中的一个研究热点.根据泡沫陶瓷制备过程中成孔原理的不同,先驱体转化法制备泡沫陶瓷大致町以分为三类:(1)直接发泡法;(2)有机泡沫浸渍法;(3)添加造孔剂法.本文详细地介绍了由这三类先驱体转化法制备泡沫陶瓷的研究现状,并分析了其优缺点以及亟待解决的问题. 相似文献
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先驱体转化法制备含锆SiC纤维及其组成 总被引:1,自引:1,他引:1
以聚硅碳硅烷(polysilacarbosilane,PSCS)与乙酰丙酮锆为原料,用常压高温裂解法制备了Si-Zr-C-O纤维先驱体聚锆碳硅烷(polyzirconocar-bosilane,PZCS),经过熔融纺丝、空气预氧化、惰性气氛烧成等工艺,制得Si-Zr-C-O纤维.通过元素分析、Auger电子能谱、X射线衍射、核磁共振和扫描电子显微镜等一系列分析测试手段研究了Si-Zr-C-O纤维的组成结构与性能.结果表明:Si-Zr-C-O纤维的元素组成为SiC1.24HxO0.56Zr0.0129(摩尔比),平均强度为2.5GPa,平均直径为11 μm,纤维表面光滑平坦,没出现孔洞、裂纹、沟槽等缺陷,直径均匀.Si-Zr-C-O纤维表层和内部元素组成不同.Si-Zr-C-O纤维为非晶SiC纤维,纤维中包含较多的不定形游离C和O,以不定形SiCxOy复合相的形式存在,Zr则与复合相中的O相结合. 相似文献
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用杉木木粉浸渍高分子先驱体有机硅树脂,改变烧结温度和保温时间制备 SiOC 多孔木质陶瓷。用 X 射线衍射、扫描电子显微镜、红外光谱及热分析对样品的物相及微观结构进行了表征,并用四探针法测试样品的电学性能。结果表明:样品由 SiOC 玻璃相、α-石英和自由碳组成,化学结构主要含有 Si—O,Si—O—R,Si—C,C=C 和 C—H2。α-石英颗粒呈球状分布在样品的孔洞表面。样品在 Ar 中具有较好的热稳定性。但由于 SiOC 玻璃相和自由碳的氧化反应,样品在 O2中的质量损失较大。当烧结温度达 1200 ℃,保温 1h 时,样品具有较低的体积电阻率(0.03 ·cm)。 相似文献
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先驱体转化含铝碳化硅陶瓷纤维具有高强度、高模量、耐高温、抗氧化等特性,是高温陶瓷基复合材料理想的增强体之一。基于含铝Si C陶瓷纤维的制备工艺路线,从聚铝碳硅烷(PACS)的合成方法及其机理、PACS纤维不熔化处理方法和控制Si(Al)C陶瓷纤维缺陷的研究现状方面综述了先驱体转化含铝Si C陶瓷纤维制备的最新研究进展。讨论了现有PACS合成路线和不熔化处理工艺的优缺点。此外,围绕含铝Si C陶瓷纤维的制备路线,认为后续可持续关注的主要有探索新的PACS合成路线、高效不熔化处理方法和提高Si(Al)C陶瓷纤维力学性能的方法等方面。 相似文献
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Fabrication of dense polymer‐derived silicon carbonitride ceramic bulks by precursor infiltration and pyrolysis processes without losing piezoresistivity 下载免费PDF全文
Dense polymer‐derived silicon carbonitride (SiCN) ceramic bulks were fabricated by powder consolidation following precursor infiltration and pyrolysis (PIP) densification. The density and open porosity of the ceramics varied from 1.42 g/cm3 and 32.75% before the PIP to 2.29 g/cm3 and 3.64% after the PIP, respectively. The electrical conductivity of the ceramics sharply increased from 6.26 × 10?10 S/cm before the PIP process to 3.20 × 10?7 S/cm after the 1st cycle of PIP and then gradually increased to 6.89 × 10?6 S/cm after four cycles of PIP. However, the piezoresistive coefficient did not change with the PIP. The Raman and electron paramagnetic resonance results show that the graphitization level of free carbon in ceramics derived from PIP was higher than the ceramics derived from powder consolidation. The high graphitization level of free carbon leads to a high conductivity, and thus the conductivity of ceramics increased significantly after the PIP process. The carbon cluster size, which is related to the gauge factor of piezoresistivity, did not change significantly after the PIP process; thus, the gauge factor did not change significantly. Dense, large‐scale polymer‐derived ceramics were fabricated by combined conventional powder consolidation and PIP without the loss of piezoresistivity. These ceramics have potential application as both structural and functional components that can bear loads as well as monitor variations in external stress. 相似文献
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《Journal of the European Ceramic Society》2014,34(15):3559-3570
An analysis about the effect of carbon enrichment of allylhydridopolycarbosilane SMP10® with divinylbenzene (DVB) as a promising material for electrical conductive micro-electrical mechanical systems (MEMS) is presented. The liquid precursors can be micropipetted and cured in polytetrafluoroethylene (PTFE) molds to produce 14 mm diameter disc shaped samples. The effect of pyrolysis temperature and carbon content on the electrical conductivity is discussed. The addition of 28.7 wt.% of DVB was found to be the optimum amount. Carbon was preserved in the microstructure during pyrolysis and the ceramic yield increased from 77.5 to 80.5 wt.%. The electrical conductivity increased from 10−6 to 1 S/cm depending on the annealing temperature. Furthermore, the ceramic samples obtained with this composition were found to be in many cases crack free or with minimal cracks in contrast with the behavior of pure SMP10. Using the same process we demonstrate that also microsized ceramic samples can be produced. 相似文献
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《Journal of the European Ceramic Society》2005,25(2-3):193-197
Polymer derived ceramic parts of complex shape were fabricated by selective laser curing (SLC). The ceramic parts were built similar to the selective laser sintering process by sequentially irradiating layers consisting of SiC loaded polysiloxane powder with a CO2-laser beam (λ = 10.6 μm), which locally induces curing reaction of the polymer phase at moderate temperatures around 400 °C. The laser-cured bodies were converted to SiOC/SiC ceramic parts in a subsequent pyrolysis treatment at 1200 °C in argon atmosphere. The scanning speed and the power of the CO2-laser beam were varied, leading to pronounced differences in material properties. Laser irradiating a powder mixture containing 50 vol.% polymer/50 vol.% SiC resulted in relative green densities between 38 and 60%. Relative densities decreased to 32–50% after pyrolysis due to the polymer shrinkage. A post-infiltration with liquid silicon was carried out in order to produce dense parts. While before infiltration the bending strength only attained 17 MPa as a result of both microcracks in the SiOC matrix and a pronounced porosity, an average value of 220 MPa was achieved after post-infiltrating with Si. In the case of 50 vol.% SiC content the linear shrinkage after pyrolysis was only 3%. Thus, the SLC approach can be considered as a near-net-shape forming process of ceramic components with complex geometries. 相似文献
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《Ceramics International》2020,46(2):1362-1373
Cerium oxide and silicon oxycarbide (Ce/SiOC) porous nanocomposites have been synthesized through the polymer derived ceramic route. In the synthesis of the preceramic precursors, the addition of urea facilitates the deposition of Cerium atoms on the surface of SiO2 nanoparticles since it prevents the SiO2 from agglomeration. Both Ce and urea affects the structural and textural parameters of the obtained ceramics. Less crosslinked structures are formed when the urea concentration increases and it also provokes a reduction of the carbon crystallite size. Cerium, on the other hand, induces an increase of the carbon size as well as the number of SiOC units. Pore anisotropy and smoothness of the surface are also dependent on the composition of the material. As expected, the better thermocatalytic behavior against CO2 decomposition is found at the largest Ce amounts but also, smooth surfaces and low pore anisotropies favor the accessibility of the gases to the thermocatalytic centers. 相似文献
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Yujun Jia Tosin D. Ajayi Justin Morales Md Atiqur Rahman Chowdhury Godfrey Sauti Sang-Hyon Chu Cheol Park Chengying Xu 《Journal of the American Ceramic Society》2019,102(12):7584-7593
We report the thermal properties of boron nitride nanotube (BNNT) reinforced ceramic composites using the polymer derived ceramic (PDC) processing route. The nano-composites had a BNNT loading of up to 35.4 vol.%. TGA results showed that nano-composites have good thermal stability up to 900°C in air. BNNTs in nano-composites survived in an oxidizing environment up to 900°C, revealing that nano-composites can be used for high temperature applications. Thermal conductivity of PDC reinforced with 35.4 vol.% BNNT was measured as 4.123 W/(m·K) at room temperature, which is a 2100 % increase compared to that of pristine PDC. The thermal conductivity value increases with the increase of BNNT content. A thermal conductivity percolation phenomenon appeared when the BNNT content increased to 36 ± 5 vol.%. The results of this study showed that BNNTs could effectively improve the thermal conductivity of PDC materials. BNNT reinforced PDC could be used as thermal structural materials in a harsh environment at temperatures up to 900°C. 相似文献
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《Journal of the European Ceramic Society》2014,34(15):3597-3606
Corrosion resistant coatings are a promising solution to protect structural metals in harsh environments. Ceramic composite coatings made from polymer-derived ceramics are highly attractive due to the ease of their processing and the ability to work in various environments. This paper is focused on the performance of a TiSi2-filled SiOC ceramic composite coating system on 316 stainless steel (SS) substrates as a corrosion resistant coating. The best-performing quadruple-dip coatings were shown to be able to reduce the weight loss due to hot sulfuric acid (95+%, 104–107 °C) corrosion by 85% over a 30-day period. Coatings from the same system were also examined under 800 °C static (100 h) and cyclic (10 cycles) oxidation. Our results indicate that the coatings perform well under both conditions of prolonged high temperature oxidation and thermal cycling, suggesting the strong potential of this system as an environmental barrier coating (EBC). 相似文献
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《Ceramics International》2022,48(13):18392-18400
High melting point and hardness of boron carbide make it extremely difficult to be directly prepared as hollow microsphere. However, precursor derived method is an effective approach to prepare ceramic materials with complex shape. Therefore, in this work a novel boron carbide precursor, poly[1,7-bis(4-chlorophenyl)-m-carborane] (P4CB), was synthesized. The ceramic yield of the precursor P4CB reached as high as 90.25% at 900 °C in nitrogen. Oxidation of P4CB in air was barely observed below 500 °C, and a passive oxidation was exhibited beyond 700 °C. The P4CB/PAN slurry was prepared and coated on a polyoxymethylene (POM) ball substrate. After air crosslinking, substrate decomposition and heat-treatment at 1100 °C in Ar atmosphere, boron carbide hollow microsphere with diameter of approximate 1.34 mm and average shell thickness of 30 μm was finally obtained. The novel precursor could be also utilized to fabricate boron carbide ceramics with different shapes due to its high ceramic yield. 相似文献
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Peter E. Froehling 《Journal of Inorganic and Organometallic Polymers》1993,3(3):251-258
Polymerization of Cl2Si(CH3)CH2Cl with Mg in THF, followed by reduction with LiAlH4, gave a polycarbosilane with Si-H groups and branches at the Si atoms. The polymer could be cross-linked thermally at 150°C. Pyrolysis of the cross-linked material gave SiC with a yield of 70%.Presented at the XXVIth Silicon-Symposium, Indiana University-Purdue University at Indianapolis, March 26–27, 1993. 相似文献