碳化硅晶须

1.SiC 晶须发展概况晶须是一种单晶纤维,是高度的结晶体,其化学完整性提供了一种与原子间结合力相等的强度,达数了百万英磅/英寸~2,第一批工业生产的晶须是 ThcrmokineticFiber 公司(TKF)在1962年生产的。从1962～1968年,TKF 生产并销售了多种晶须产品,包括针状品须,兰宝石棉和     

催化剂对合成碳化硅晶须的影响

以炭黑和SiO2微粉为原料,用双重加热技术合成了碳化硅晶须,考查了催化剂的种类、用量和加入方式对合成碳化硅晶须的影响。研究表明:以Fe2O3为催化剂,用量为原料SiO2总量的2%,在1250℃下、1.5h内可以获得平均直径为0.6μm、平均长度为30μm、生成率达80%的碳化硅晶须。     

碳化硅晶须对氧化锆陶瓷材料结构的影响

本文研究了不同晶须含量对可相变增韧的ZrO_2(2mol%Y_2O_3)陶瓷及完全稳定的ZrO_2(6mol%Y_2O_3)陶瓷结构的影响。结果表明:晶须的加入使ZrO_2材料的晶料明显细化,但对该类热压复合材料的致密度影响不大;纯ZrO_2(6mol％Y_2O_3)为单一的C相结构,加入晶须后有少量的t相出现;纯ZrO_2(2mol%Y_2O_3)热压材料由t m两相组成,晶须的加入降低了基体中m相的相对含量,但对断裂过程中t→m相交量影响不大。     

碳化硅晶须增强氧化锆复相陶瓷材料的组织观察

本文用ＴＥＭ,ＳＥＭ等手段研究了ＳｉＣｗ增强２Ｙ－ＺｒＯ２复相陶瓷材料的组织,结果表明,ＳｉＣｗ的加入可以显著细化２Ｙ－ＺｒＯ２材料的粒子,并使基本的断裂方式由以沿晶为主的混合型变为以穿晶为主的混合方式,晶须周围的ｍ－ＺｒＯ２可显著缓解该复合材料中的热应力。     

碳多孔体中碳化硅晶须原位生长条件的实验与模型研究

根据碳化硅晶须生长的特定驱动力要求，通过实验和建立气相传输模型研究了碳多孔体中碳化硅晶须原位生长的条件。模型和实验研究均表明：温度和多孔体表面气相组成对多孔体内的晶须原位生长起决定作用；体内附加反应可以改变晶须生长所要求的温度和表面气相条件。     

碳化硅晶须补强莫来石复合材料的SPS烧结致密化研究

采用SPS工艺制备了SiC晶须增强莫来石基复合材料。SEM分析结果表明,SiC晶须在莫来石基体中分布均匀,看不到晶须团聚,晶粒中可看到由于快速烧结而导致的微气孔残留;晶须的拔出、解离非常明显,是主要的晶须增韧机制。SiC晶须的取向,在热压烧结条件下呈各向异性。在不同方向的裂纹扩展、亦即材料的断裂韧性,也表现出明显的各向异性。采用30vol％SiC晶须增强莫来石,SPS烧结条件下材料强度比热压高10％左右,为570MPa,KIC为4．5MPa．m^1/2,比纯莫来石提高100％以上。同HP法烧结相比,SPS烧结明显有利于材料致密化。     

氮化硅低温转化合成碳化硅晶须研究

对氮化硅转化法制备碳化硅晶须的反应过程进行了热力学分析;采用氮化硅为硅源,石墨、活性炭和炭黑为碳源,氧化硼作为催化剂,利用氮化硅转化法分别在1500 ℃、1550 ℃、1600 ℃合成碳化硅晶须,通过X射线衍射和扫描电子显微镜分析合成晶须的特征.结果表明:合成反应在1450℃以上可以发生,且随着温度的升高,平衡常数急剧增加,SiC晶须直径变大;以活性炭和炭黑等较高活性的碳源代替石墨可以提高晶须的质量和生成量,通过对晶须合成过程的分析,推测晶须的生长属于螺旋位错生长机理.     

碳多孔体中碳化硅晶须的原位生长

根据碳化硅晶须生长的特定驱动力要求，运用多孔体中气相传输模型预测了碳化硅晶须厚位生长的条件。预测结果与实验结果一致。     

碳化硅纳米晶须的制备

以SiO2纳米粉和自制的树脂热解碳作原料,用一种新的加热设备－双重加热炉合成了直径在5－30nm范围内,长径比在50－300之间的碳化硅纳米晶须。用化学分析方法,X射线衍射仪、透射电子显微镜等手段对碳化硅纳米晶须进行了表征。研究结果表明：用双重加热炉合成碳化硅纳米晶须的最佳湿度范围为1250－1300℃,恒温时间为60－75min,碳化硅纳米晶须的产率最高可达82％（质量分数）。     

竹节状碳化硅晶须吸波性能研究

采用电磁波吸收材料来降低电磁波对设备的干扰及对人体的伤害,是目前常用的电磁波防护手段之一。特定结构碳化硅晶须作为一种一维介电材料,其优于普通的晶须、块状和颗粒状的吸波性能引起了研究人员的关注。本研究以生竹粉、硅粉和二氧化硅为原料,通过碳热还原法在不同温度下制备了竹节状碳化硅晶须,并对其结构和吸波性能进行了检测分析。结果表明：以1400℃烧结的竹节状晶须制备的试样在厚度为3 mm,频率为9.1 GHz时,最小反射损耗达到-14.4 dB,有效吸收带宽为1.8 GHz,吸波性能最好,具有进一步研究价值。     

Improvement of toughness of reaction bonded silicon carbide composites reinforced by surface-modified SiC whiskers

To improve the reliability, especially the toughness, of the reaction bonded silicon carbide (RBSC) ceramics, silicon carbide whiskers coated with pyrolytic carbon layer (PyC-SiC_w) by chemical vapor deposition (CVD) were introduced into the RBSC ceramics to fabricate the SiC_w/RBSC composites in this study. The microstructures and properties of the PyC-SiC_w/RBSC composites under different mass fraction of nano carbon black and PyC-SiC_w were investigated methodically. As a result, a bending strength of 550 MPa was achieved for the composites with 25 wt% nano carbon black, and the residual silicon decreased to 11.01 vol% from 26.58 vol% compared with the composite of 15 vol% nano carbon black. The fracture toughness of the composites reinforced with 10 wt% PyC-SiC_w, reached a high value of 5.28 MPa m^1/2, which increased by 39% compared to the RBSC composites with 10 wt% SiC_w. The residual Si in the composites deceased below to 7 vol%, resulting from the combined actively reaction of nano carbon black and PyC with more Si. SEM and TEM results illustrated that the SiC_w were protected by PyC coating. A thin SiC layer formed of outer surface of whiskers can provide a suitable whisker-matrix interface, which is in favor of crack deflection, SiC_w bridging and pullout to improve the bending strength and toughness of the SiC_w/RBSC composites.     

碳化硅晶片的制备技术

碳化硅晶须和晶片都是陶瓷基、金属基、树脂基复合材料的理想增强体，与碳化硅晶须相比，有关碳化硅晶片制备与应用的报道相对较少。论述了碳化硅晶片在复合材料中的应用，比较了国内外碳化硅晶片的各种制备技术。阐明了加热方式对碳化硅晶片制备的影响。指出低成本、新型热源的开发与推广应用有利于实现碳化硅晶片的规模化生产。     

Microstructure evolutions of SiC whiskers at high temperature and its effects on silicon carbide ceramics

SiC whisker with a single-crystal structure is promising in enhancing the strength and toughness of advanced structural ceramics, owing to its excellent properties. However, studies on its microstructure evolution at high temperature (>2000 °C) are scarce. Herein, SiC whiskers were calcined at 2100 °C, and XRD, SEM, and TEM were employed to analyze microstructure evolutions. Compared with raw whiskers, XRD results indicated serious annihilation of stacking faults after calcination. The annihilation led to the fracture of whiskers and the formation of β-SiC grains, and then partial grains underwent the phase transformation to form hexagonal prism and triangular prism α-SiC grains with diameters of about 10 μm, according to SEM and TEM results. Furthermore, SiC ceramics containing different whisker contents were innovatively fabricated by pressureless solid-state sintering. The flexural strength and fracture toughness of SiC ceramic containing 10 vol% whiskers were 540 MPa and 5.1 MPa m^0.5, resulting in 38% and 11% higher values than those without whiskers, respectively.     

燃烧合成氮化硅陶瓷晶须研究进展

燃烧合成法是一种高效能、低消耗的陶瓷材料合成方法。简要介绍了燃烧合成方法特点,评述了近年来燃烧合成氮化硅陶瓷晶须的研究进展,详细总结了原料选择、多种添加剂（如铁、稀土氧化物、铵盐等）对氮化硅晶须最终形貌和性能的影响, 总结了工艺参数,尤其是氮气压力和堆积密度对晶须生长的影响,并详细讨论了在燃烧合成过程中晶须的生长机理。     

Tribo-mechanical properties of composites based on polyoxymethylene reinforced with basalt fiber and silicon carbide whiskers

This paper presents an analysis of the hybrid reinforcement of polyoxymethylene composites. Basalt fibers and monocrystalline silicon carbide fibers were used as reinforcement. Basic tests of mechanical properties were carried out, such as the static tensile and flexural test. The tests were repeated under external factors, such as the influence of water aging and a wide range of exploitation temperatures. The materials were also subjected to tribological tests, that is, determination of the friction coefficient and the specific wear rate. Strength tests revealed an increase in the stiffness of the material as well as a reduction the friction coefficient and abrasive wear. The addition of monocrystalline fibers significantly limited water absorption, stabilized the strength properties in the water environment as well as provided better material's resistance to dynamic impact.     

Effects of aggregate/matrix-phase ratio on the in-situ synthesis of SiC whiskers and properties of reaction-bonded SiC

Reaction-bonded silicon carbide (RBSC) materials were synthesized by a carbon-buried firing method, using α-SiC powders with different sizes as aggregates, while silicon and graphite powders as matrix-phase materials for in-situ synthesis of β-SiC. The effect of the mass ratio of α-SiC aggregate to β-SiC matrix-phase on the in-situ synthesis of β-SiC whiskers was investigated and the optimum mass ratio was determined according to the properties of RBSC materials. The phase compositions, microstructure, and properties of the RBSC materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM), respectively. The results showed that the decreasing aggregate/matrix-phase ratio could increase the yield and aspect ratio of β-SiC whiskers by improving the amount of pores and SiO₂ content. The β-SiC whiskers with stacking faults grew along [111] direction. The in-situ formed β-SiC whiskers and SiO₂ in the matrix-phase enhanced the hot modulus of rupture (HMOR) of the RBSC materials, and the sample with the aggregate/matrix-phase ratio of 70:30 showed the highest cold modulus of rupture (CMOR) of 53.3 MPa, high HMOR of 43.3 MPa, and medium water absorption of 13.8%.     

亚微米碳化硅超细粉加工方法研究

介绍了一种亚微米硅超细粉的加工方法，对磨机转速，磨介配比，分散剂，纯化处理以及粉体性能等进行了研究，用该工艺方法加工亚微米碳化硅粉体，不需再次分级，粉体分布窄，一致性好，性能达到国外同类产品水平。     

碳化硅冶炼炉逸出气体的组成及理化性质研究

利用自行发明的多热源碳化硅冶炼炉，以煤（或焦炭）和石英砂为原料合成SiC，同时伴生大量副产品可燃性气体，研究了煤种和冶炼工艺对燃气的组成及酸碱性的影响，并对经济效益进行分析。结果表明，燃气中以CO气体为主，平均含量可达70％，CO＋H2平均含量达85％，CO＋H2＋CH4平均含量达90％，使用无烟煤、烟煤焦炭或焙烧料法可提高合成气中CO含量，若燃气用于火力发电可节约25．8％的电费成本。     

Experimental and numerical thermal analysis for direct microwave heating of silicon carbide

A comparison between experiment and numerical simulation of microwave heating of a parallelepipedic silicon carbide (SiC) sample is presented. Using a-2.45 GHz single-mode cavity, the evolution of the surface temperature is first experimentally studied for different orientations of the sample. A finite element analysis of this electromagnetic-thermal coupled problem is then conducted with the COMSOL Multiphysics^® software. Despite the different approximations of our model, a good agreement between experimental and numerical results is found, confirming that the heating of SiC depends only on the electric field. The effect of sample orientations and the cavity length on heating is also highlighted and analyzed.