小米基生物形态多孔SiC材料

本文介绍了以小米为原材料,利用生物模板技术法制备小米基生物形态SiC材料.通过热重技术分析了小米向碳模板的转化过程.以SEM、压汞技术和颗粒强度测定仪分析了碳模板与SiC的形貌结构和机械强度.结果表明:以液相渗硅法制备的生物形态SiC能很好的保持碳模板的形貌结构,颗粒破碎强度为10.6 N.溶胶凝胶-碳热还原法制备的SiC能较好保持碳模板的形貌结构,而气相渗硅法制备的SiC与碳模板在微观结构上有很大不同.后两种方法制备的SiC机械强度很差.     

硅液相浸渍反应制备TiC/SiC和TiN/SiC复相陶瓷

以滤纸、酚醛树脂和氧化钛为原料,经过模压成型、固化、碳化及不同条件下渗硅制备了TiC/SiC和TiN/SiC复相陶瓷。通过X射线衍射和扫描电子显微镜研究了TiC/SiC和TiN/SiC复相陶瓷的微观结构和物相组成,测量了复相陶瓷的弯曲强度和断裂韧性。结果表明:真空条件下液态渗硅获得的TiC/SiC复相陶瓷具有多孔的微观结构,其弯曲强度和断裂韧性较小。氮气气氛下液态渗硅制备的TiN/SiC复相陶瓷结构致密,有较高的弯曲强度和断裂韧性。不同反应生成的TiC,TiN陶瓷颗粒对液态硅的润湿性不同,使得生成的复相陶瓷具有不同的微观结构。TiN/SiC复相陶瓷中TiN颗粒的引入,在基体与第二相颗粒间的界面上产生拉应力和压应力,使达到这一区域的裂纹偏转,从而获得增韧效果。     

溶胶—凝胶法制备超滤Al2O3膜的研究—非担载超滤Al2O3膜的制备

以异丙醇铝为原料通过溶胶-凝胶法制备了非担载超滤Al     

掺铁氧体和SiC纤维水泥基复合材料的吸波性能

用溶胶凝胶法制备了W型Ba(Zn1-χCoχ)2Fe16O27六方铁氧体,并以铁氧体和短切SiC纤维与水泥复合,制备了水泥基复合材料.测量了该材料的电磁参数,并计算了该材料对电磁波的反射率.结果表明:χ为0.8时,W型Ba(Zn1-χCoχ)2Fe16O27六方铁氧体的吸波性能最好,该铁氧体的掺量(质量分数)为35%和短切SiC纤维掺量(质量分数)为0.2%时,水泥基复合材料在12～18GHz范围内具有最大反射率-13.5dB,有效带宽达到4.7GHz.     

磁性生物活性陶瓷的制备

采用溶胶-凝胶法制备前驱体,经高温烧结制备出磁性生物活性陶瓷。利用体外实验方法,结合X射线衍射、扫描电子显微镜和红外光谱分析了材料结构、晶相和生物活性。结果显示,溶胶-凝胶法可制备出微细的非晶态前驱体粉末,经1 050℃烧结的玻璃陶瓷主晶相为β-硅灰石和铁酸钴、磷硅灰石。陶瓷粉末平均粒径为300 nm。烧结的材料在模拟人体血浆浓度的模拟体液中浸泡7 d,在材料表面可生成大量磷灰石,显示出较好的生物活性。     

溶胶-凝胶法制备铁氧体材料及应用于建筑吸波领域的研究

信息化的发展和电子设备的使用使人类对吸波材料的需求越来越大,铁氧体作为一种良好的吸波材料运用于建筑等领域具有良好的实用价值,利用具有成本低、纯度高等优点的溶胶-凝胶法制备吸波性能更好的铁氧体材料的研究在不断完善。综述了溶胶-凝胶法制备铁氧体材料的3个研制阶段及其与无机材料复合的应用进展,并研究概述了建筑用铁氧体水泥基复合吸波材料的发展现状,指出其未来发展趋势。     

溶胶-凝胶法制备铁氧体材料及应用于建筑吸波领域的研究

信息化的发展和电子设备的使用使人类对吸波材料的需求越来越大,铁氧体作为一种良好的吸波材料运用于建筑等领域具有良好的实用价值,利用具有成本低、纯度高等优点的溶胶-凝胶法制备吸波性能更好的铁氧体材料的研究在不断完善。综述了溶胶-凝胶法制备铁氧体材料的3个研制阶段及其与无机材料复合的应用进展,并研究概述了建筑用铁氧体水泥基复合吸波材料的发展现状,指出其未来发展趋势。     

非水溶胶-凝胶法制备氧化锆陶瓷膜的技术研究

以无水四氯化锆为前驱体,无水乙醇为氧供体,金属钇粉为晶型稳定剂,采用非水溶胶-凝胶法制备氧化锆溶胶;并且通过浸渍提拉法在经过预处理的氧化铝基陶瓷基片上制备氧化锆陶瓷薄膜。通过X-射线衍射(XRD)、差热分析TG-DSC、扫描电镜(SEM)以及傅立叶变换红外光谱仪(FT-IR)等测试手段对实验的反应机制进行了结构和机理表征。研究结果表明:通过非水溶胶-凝胶法使得无水四氯化锆和无水乙醇反应生成锆醇盐,随着反应进行生成=Y-O-Zr≡键合并形成凝胶,然后通过低温合成四方晶型氧化锆。通过800℃,保温30 min制备出陶瓷膜孔径分布窄,孔径为50 nm左右,膜厚度为20μm,晶体发育完整,氧化锆晶体尺寸为80~120 nm左右,膜孔隙率达到25%左右。     

C_f/ZrB_2–ZrC–SiC超高温陶瓷基复合材料的设计、制备及性能

提出了溶胶–凝胶孔道构建–反应熔渗制备新方法,首先通过溶胶凝胶方法在纤维预制体中引入B_4C–C多孔体,获得C_f/B_4C–C多孔预成型体结构;在此基础上,结合反应熔渗Si–Zr合金,获得C_f/ZrB_2–ZrC–SiC超高温陶瓷基复合材料。研究了C_f/B_4C–C多孔预成型体结构对RMI过程和材料性能的影响,并揭示了孔隙结构对基体分布和界面损伤及复合材料性能的影响规律。结果表明:通过灵活调控C_f/B_4C–C孔隙结构可实现复合材料中ZrB_2–ZrC–SiC基体分布改善和(PyC–SiC)_2界面损伤缓解,大幅提升材料性能。当预成型体孔隙结构为25.9%和58.0μm时,制备的C_f/ZrB_2–ZrC–SiC复合材料基体可均匀分布于纤维束间和束内,同时纤维能得到良好的保护,材料表现出最优的力学性能(抗弯强度231 MPa)。     

利用溶胶-凝胶法制备连续莫来石纤维

利用溶胶-凝胶法以氢氧化铝、羧酸、硅溶胶为原料、结合干法纺丝制备了连续莫来石陶瓷纤维。通过TEM、TG-DSC、FT-IR、XRD、SEM等方法对纺丝溶胶的微观结构、纤维晶型以及纤维表面和内部结构进行了研究,利用流变仪对溶胶的流变性能进行了研究。结果表明：通过溶胶-凝胶法制备的前驱体溶胶可纺性优异,性能稳定;采用干法纺丝得到的连续莫来石凝胶纤维表面光滑、直径均匀;经陶瓷化处理后获得连续莫来石纤维,纤维直径11～13μm,单丝拉伸强度可达1.9GPa,1200℃煅烧后主晶相为莫来石相。     

气相硅反应性渗入法制备橡木结构SiC陶瓷

橡木经1200℃高温真空碳化转化为碳模板,再用反应性渗入方法在1500～1600℃、Ar气氛下气相渗硅0．5～8h,制成一种具有橡木显微结构的多孔SiC陶瓷。采用XRD和SEM对其物相变化和显微结构进行了表征。结果表明：随反应时间的延长,木炭的转化率增大,弯曲强度显著提高,而气孔率变化不大。在1600℃下反应8h时,木炭几乎完全转变成具有橡木显微结构的β-SiC陶瓷,其弯曲强度和气孔率分别为42．1MPa和46．4％。此外,还对气相Si在木炭中的渗入-反应机理进行了简单介绍。     

Effect of technological parameters on densification of reaction bonded Si/SiC ceramics

Si/SiC composite ceramics was produced by reaction sintering method in process of molten silicon infiltration into porous C/SiC preform fabricated by powder injection molding followed by impregnation with phenolic resin and carbonization. To optimize the ceramics densification process, effect of slurry composition, debinding conditions and the key parameters of all technological stages on the Si/SiC composite characteristics was studied. At the stage of molding the value of solid loading 87.5% was achieved using bimodal SiC powder and paraffin-based binder. It was found that the optimal conditions of fast thermal debinding correspond to the heating rate of 10?°C/min in air. The porous C/SiC ceramic preform carbonized at 1200?°C contained 4% of pyrolytic carbon and ～25% of open pores. The bulk density of Si/SiC ceramics reached 3.04?g/cm³, silicon carbide content was 83–85?wt.% and residual porosity did not exceed 2%.     

Thermal conductivity studies on Si/SiC ceramic composites

Ceramic heat exchangers are increasingly used in many nuclear power plants. Silicon carbide has been treated as a promising material for heat exchanger application since it has good thermal conductivity and corrosion resistance. In this work, four different types of Si/SiC ceramic composites were prepared by liquid silicon infiltration technique. Thermal conductivities of these ceramic composites at different temperatures are measured by the laser flash thermal conductivity method. Results show that the presence of free carbon and voids are notably affecting the thermal conductivity of these materials.     

Porous eco-ceramics of low thermal conductivity and high EMI shielding effectiveness from sawdust and sucrose by paste molding

A facile method for making porous SiC ceramics from sawdust avoiding high-temperature liquid or vapor phase silicon infiltration has been outlined. Cylindrical bodies prepared by hand pressing of aqueous pastes produced from sawdust, silicon powder, sucrose, and sintering additives are subjected to freeze-drying followed by carbonization and ceramization heat-treatments to produce porous SiC. The carbon-silicon reaction is completed at a minimum temperature of 1550 °C as verified from TGA and XRD analysis. The SiC produced from sawdust particles is firmly held together by the sucrose-derived SiC. The pore channels inherited in the sawdust particle remain in the SiC ceramics. A large population of nanowires is observed throughout the sucrose-derived SiC as well as on the pore channel surfaces of SiC formed from sawdust particles. The porosity decreases from ~88 to 75 vol%, the compressive strength rises from 0.5 to 12.5 MPa, and thermal conductivity rises from 0.23 to 0.98 W/mK when the sucrose to sawdust weight ratio rises from 0.5 to 2.5. The reflection contribution (1.9–3 dB) to the total EMI shielding effectiveness (16 To 31 dB) of the porous SiC ceramics is very low compared to the absorption contribution (15–28 dB). The carbonized bodies are amenable to machinating enabling the production of near-net-shape before ceramization. The presence of large excess of silicon observed in biomorphic SiC made by molten liquid infiltration is avoided in this method.     

聚碳硅烷粘结法低温制备碳化硅多孔陶瓷

分别以平均粒径为10μm和20μm的两种规格碳化硅(SiC)粉末为原料、聚碳硅烷(PCS)为粘结剂,通过包混、过筛、模压成型、1000℃热解等工序制备了SiC多孔陶瓷,研究了PCS含量对SiC多孔陶瓷微观形貌、线收缩率、孔隙率与抗弯强度的影响,并对两种规格粉末制备的SiC多孔陶瓷性能进行了对比。结果表明:随着PCS含量的增加,两种规格粉末制备的SiC多孔陶瓷微观形貌都逐渐变得致密,当PCS含量为13%时,两种规格粉末制备的多孔陶瓷都出现了微观裂纹。随着PCS含量的增加,两种规格粉末制备的SiC多孔陶瓷孔隙率都逐渐降低,线收缩率都逐渐增大,抗弯强度先增大后降低,在PCS含量为10%时,平均粒径为10μm与20μm的SiC粉末制备的多孔陶瓷抗弯强度取得最大值,分别为31.6MPa与29.0MPa。     

Reaction forming of silicon carbide ceramic using phenolic resin derived porous carbon preform

SiC ceramics were prepared with porous carbon preforms derived from phenolic resin by a reaction-forming method. The effects of the structure of the preform pores and the infiltration process on the properties of SiC ceramics were investigated, and components with complex shapes were fabricated by combining this process with stereolithography (SLA). Dense SiC ceramics were obtained from carbon preforms with high apparent porosities, but SiC ceramics with many macrodefects resulted from a carbon preform with an apparent porosity of 39%. The infiltration of molten silicon into the preform pore channel was accelerated under vacuum pressure, resulting in an increase in the depth of the Si infiltration. The growth of SiC was predominantly controlled by carbon diffusion at the last stage of the reaction. The extended grain growth caused the SiC grains to coalesce and some free Si was enveloped in the SiC grains. SiC components with complex geometries were fabricated by combining reaction forming with SLA. The geometry was controlled by SLA.     

Synthesis, characterization, and wear and friction properties of variably structured SiC/Si elements made from wood by molten Si impregnation

We have synthesized pre-shaped SiC/Si ceramic material elements from charcoal (obtained from wood) by impregnation with molten silicon, which takes place in a two-stage process. In the first process, a porous structure of connected micro-crystals of β-SiC is formed, while, in the second process, molten Si totally or partly infiltrates the remaining open regions. This process forms a dense material with cubic (β-)SiC crystallites, of which the majority is imbedded in amorphous Si. The synthesis of preshaped “sprocket” elements demonstrates that desired shapes of such a dense SiC/Si composite ceramic material can be achieved, thus suggesting new industrial applications.The structure and composition of numerous as-synthesized samples were characterized in detail by using a wide range of techniques. Wear and friction properties were also investigated, with polished samples. The properties found for the present samples are very promising for abrasive applications and for new generation brake systems.     

Facile preparation of morph-genetic SiC/C porous ceramic at low temperature by processed bio-template

A porous morph-genetic SiC/C ceramic material was fabricated using biomass-derived C template, Si powder, and Fe(NO₃)₃·9H₂O as the starting materials. The effects of heating temperature, and catalyst/Si mole ratio on the formation of SiC/C ceramic were investigated. In addition, the pore size distribution was obtained through pore size analysis, and the determination of oxidation resistance of SiC/C ceramics and C template was carried out by thermogravimetric analysis. The results show that copious amounts of SiC nanowires, which were distributed on the surfaces and interiors of the C template holes, were formed at 1300 °C with 4 wt% Fe as catalyst. The SiC nanowires significantly affected the oxidation resistance and microporous structures of the prepared materials. Moreover, a possible formation mechanism for the porous SiC/C ceramic was determined.     

Fabrication of Porous SiC Ceramics with Special Morphologies by Sacrificing Template Method

Sacrificial template technique is widely used in producing porous materials with controlled morphologies and tailored properties. In this paper, unique templates such as filters, carbon nanotube, carbon fiber and silica were used to make porous SiC ceramic with special morphologies. Template derived porous ceramic plates, SiC nano-net, fiber-inverse and bead-inverse porous SiC ceramic were successfully prepared from the preceramic precursor, polymethylsilane (PMS). The synthesis procedures were involved with the infiltration of the templates with appropriate concentration of the preceramic polymer, their curing, pyrolysis and subsequent template removal. The synthesized porous SiC was characterized by SEM, TEM, XRD and BET methods.