碳化硅纳米晶须生长和显微结构

采用两步生长生在碳化硅纳米晶须，首先是二氧化硅与硅反应生成一氧化硅，再与碳纳米管先驱体反应生成β－ＳｉＣ纳米晶须，其直径为３～３５ｎｍ，长度为２～２０μｍ，用高分辨透射电镜研究晶须形貌，显微结构，讨论了碳化硅纳米晶须生长机制。     

采用碳纳米管制备的碳化硅纳米晶须研究

本文报道了采用两步生长法生成碳化硅（SiC）纳米晶须.首先通过二氧化硅与硅反应生成一氧化硅,然后生成的SiO与碳纳米管先驱体反应生成立方结构的β-SiC纳米晶须．其直径为3～40nm,长度为2～20μm．通过XRD、HREM、Raman、PL等检测手段,对生成的碳化硅纳米晶须的形貌、结构等进行了分析研究．其直径为3～40nm,长度为2～20μm．并具有峰值位于430nm的蓝光发射带,本文中还对碳化硅纳米晶须生长机制进行了讨论．     

热蒸发法碳化硅纳米晶须阵列的合成与表征

在1600℃不同真空度下, 采用热蒸发硅的方法, 在石墨基板和聚丙烯腈(PAN)炭纤维两种碳源基体原位生长具有一定取向的碳化硅纳米晶须——垂直于石墨片表面森林状和试管刷状碳化硅纳米晶须阵列。通过X射线衍射及场发射扫描电镜, 发现晶须为3C-SiC, 直径约100nm, 长度约50μm。炭纤维表面的产物顶端多为针尖状, 而石墨片表面的产物多为六方棱柱状。因其纳米尺寸效应, 在380nm波长的光激发下, 所制晶须在波长为468nm 附近出现光致发光峰。透射电镜、 多点衍射电子衍射图表明, 所制得的3C-SiC晶须为单晶, 其生长方向为3C-SiC的[111]方向。基于反应过程中硅熔体与碳源分离的事实, 讨论了3C-SiC晶须阵列生长的气固反应机理。      

南极磷虾甲壳素纳米晶须的制备与应用

利用南极磷虾壳制备甲壳素，然后采用TEMPO氧化法将其制备成甲壳素纳米晶须，将不同添加量的甲壳素纳米晶须加入壳聚糖/鱼胶基体中，制备壳聚糖/鱼胶/甲壳素纳米晶须复合膜材料。通过扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)和傅里叶红外光谱(FTIR)对甲壳素纳米晶须进行分析；通过SEM、光透射率、 XRD、热重分析(TG)对复合膜材料进行检测；通过小鼠皮下埋植实验对复合膜材料的降解性进行测试。研究结果表明，利用南极磷虾壳所制备的甲壳素纳米晶须呈针状或纤维状，平均直径为17 nm;甲壳素纳米晶须能够均匀分散在复合膜材料中，当甲壳素纳米晶须的添加量为7%时，复合膜的拉伸强度达到最大为18.37 MPa,相比于壳聚糖/鱼胶膜提高了160%,这说明纳米晶须添加到复合膜中能显著提高其机械强度。小鼠皮下降解实验表明，添加纳米晶须的复合膜降解速度变慢，第九周时，添加7%纳米晶须的膜材料降解率为66.2%。     

泡沫碳化硅陶瓷表面原位生长碳化硅晶须

采用固相和液相反应法在泡沫碳化硅陶瓷骨架表面原位生长碳化硅晶须,研究了催化剂和反应温度的影响．结果表明,催化剂氯化镍的作用使硅与碳直接反应生长出细长的碳化硅晶须．在适当的反应温度下生长的碳化硅晶须的表面光滑,线径比较大,有少量的呈弯曲状或竹节状;反应温度过高使得硅晶须的缺陷较多．在泡沫碳化硅陶瓷骨架的表面原位生长出碳化硅晶须属于LS生长机理．具有表面晶须的碳化硅陶瓷以深床体积过滤的方式用于过滤柴油机汽车尾气中的碳颗粒,表面晶须既能提高泡沫陶瓷过滤器的过滤能力,又有利于过滤器的再生．     

纳米 KTi6O13w合成中的形态演化和生长机理

以纳米TiO2为原料，通过煅烧反应制备了纳米K2Ti6O13晶须，对晶须合成中温度和时间诱导的相变、形态演化和生长机理等进行了原位研究．结果表明;纳米TiO2作原料可显著降低晶须合成温度，适宜的煅烧温度为900-1100℃．形态演化观察和高温XRD分析表明；K2Ti6O13晶须的相变及生长对温度极为敏感，形态演化是基于初期爆发式的相变和随后串并联式的长大．K2Ti6O13晶须的生长遵守本研究提出的串并联机制，晶须轴向的生长台阶是串并联生长的直接结果．     

原位合成莫来石晶须增强碳化硅泡沫陶瓷

以碳化硅粉、氧化铝、高岭土为主要原料,采用有机泡沫浸渍法制备出碳化硅泡沫陶瓷坯体,经原位合成反应法在碳化硅泡沫陶瓷内生成莫来石晶须,研究反应温度对莫来石晶须合成的影响,以及莫来石的理论设计含量对泡沫陶瓷的抗压强度和抗热震性能的影响。结果表明:在1 450℃下形成的莫来石晶须直径约为0.5~1.8μm,长径比约为8~30。当莫来石理论设计质量分数为25%时,泡沫陶瓷的抗压强度为1.76MPa,抗热震性能为15次。     

SiC陶瓷增韧的研究进展

碳化硅陶瓷以其优异的性能被广泛利用于各种领域，但其脆性限制了其性能的发挥，因此其增韧技术得到广泛研究并取得良好效果。综合评述了碳化硅陶瓷增韧机理和增韧方法的研究进展，包括晶须或纤维增韧、颗粒弥散增韧、表面改性技术增韧、自增韧、层状结构复合增韧的增韧机理和方法进。     

钛酸纳米晶须的制备及其对Th(Ⅳ)的吸附性能研究

以纳米金红石型TiO2为钛源,采用水热法制备钛酸纳米晶须,用XRD、FT-IR、SEM及TEM对钛酸纳米晶须的形貌及结构进行表征。结果表明在180℃水热条件下成功合成出钛酸纳米晶须。采用静态批式法研究了接触时间、pH值、离子强度、Th(Ⅳ)初始浓度、温度对Th(Ⅳ)在钛酸纳米晶须上的吸附影响。结果表明,pH值对Th(Ⅳ)在钛酸纳米晶须上的吸附有显著影响,而离子强度对吸附的影响相对较弱;吸附过程符合准二级动力学方程;吸附等温线符合Langmuir和Freundlich等温模型;通过热力学数据ΔG0、ΔH0 和ΔS0 分析发现,Th(Ⅳ)在钛酸纳米晶须上的吸附是一个吸热且自发的过程,升高温度有利于Th(Ⅳ)在钛酸纳米晶须上的吸附。Th(Ⅳ)在钛酸纳米晶须上的吸附主要以化学吸附或表面络合为主。     

磷酸三丁酯修饰Ti纳米晶须应用于吸附铀酰离子

采用纳米金红石型TiO₂为Ti源, 水热法合成了Ti纳米晶须, 将其表面负载磷酸三丁酯(TBP)制备出修饰Ti纳米晶须。用SEM、 TEM及傅里叶红外光谱仪对Ti纳米晶须及修饰Ti纳米晶须的形貌和结构进行表征, 分别研究了两种材料对铀离子的吸附性能, 考察了修饰Ti纳米晶须吸附铀的动力学及等温吸附模型。电镜表征结果表明, 水热温度为160 ℃成功合成出Ti纳米晶须, 其粒径范围为80~100 nm。吸附铀研究结果表明, 在3 mol/L NO-₃介质中修饰Ti纳米晶须表现出较高的吸附性能, 修饰Ti纳米晶须对铀的吸附动力学模型符合准二级动力学, 吸附等温线符合Langmuir和Freundlich等温吸附模型。将修饰Ti纳米晶须用于自来水中低浓度铀的回收, 结果较好。      

碳化硅晶须发展及应用概况

综合论述了ＳｉＣ晶须的高强，高硬，高化学稳定性以及其耐磨耐腐蚀和良好的抗高温氧化性等特点；评述了ＳｉＣ晶须的各种合成方法和国内外发展应用状况。     

Chemical vapour deposition of zirconium carbide and silicon carbide hybrid whiskers

Zirconium carbide and silicon carbide hybrid whiskers were codeposited by chemical vapour deposition using methyl trichlorosilane, zirconium chloride, methane and hydrogen as the precursors. The zirconium carbide and silicon carbide whiskers were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. The results indicate that the codeposition process is more effective in the presence of methane than in the absence of methane. The codeposition process and the growth of zirconium carbide in the whiskers can be accelerated at high temperature in the presence of methane. A growth model was proposed based on the deposition model of carbon, zirconium carbide and silicon carbide.     

Preparation of aligned silicon carbide whiskers from porous carbon foam by silicon thermal evaporation

Aligned silicon carbide whiskers were prepared from porous carbon foams by thermal evaporation of silicon. High-density silicon carbide whiskers were vertically deposited on the surface of siliconizing carbon foam. The whiskers were straight and hexagon-shaped with diameter of 1-2 μm and length of about 40 μm. They consisted of a single-crystalline zinc blende structure crystal in the [111] growth direction. The pore structure of carbon foam played an important role in determining distribution of the whiskers on the surface of siliconizing carbon foam. When carbon foam with higher porosity and larger pore size was employed, distributions of the whiskers were more ordered and more intensive. The whiskers were grown by the vapor-solid (VS) mechanism.     

Improved electrical,thermal, and mechanical properties of silicone rubber-based composite dielectrics by introducing one-dimensional SiC fillers

Journal of Materials Science: Materials in Electronics - In this paper, two kinds of one-dimensional (1D) silicon carbide (SiC) fillers, including silicon carbide whiskers (SiCw) and silicon...     

Threshold creep behaviour of discontinuous aluminium and aluminium alloy matrix composites: An overview

Several sets of creep data for aluminium and aluminium alloy matrix composites reinforced by silicon carbide particulates, silicon carbide whiskers or alumina short fibres are analysed. It is shown that for this class of discontinuous composites the threshold creep behaviour is inherent. Applying the concept of threshold stress, the true stress exponent of minimum creep strain rate of approximately 5 follows from the analysis even when the matrix solid solution alloy exhibits Alloy Class creep behaviour, for which the value of 3 for the true stress exponent is typical. The creep strain rate in the discontinuous aluminium and aluminium alloy matrix composites is shown to be matrix lattice diffusion controlled. The usually observed high values of the apparent stress exponent of creep strain rate and the high values of the apparent activation energy of creep are then rationalized in terms of the threshold creep behaviour. However, the origin of the threshold stress decreasing with increasing temperature but not proportional to the shear modulus in creep of discontinuous aluminium and aluminium alloy matrix composites is still awaiting identification. The creep-strengthening effect of silicon carbide particulates, silicon carbide whiskers and alumina short fibres is shown to be significant, although the particulates, whiskers and short fibres do not represent effective obstacles to dislocation motion.     

Preparation of silicon carbide whiskers from silicon nitride

Silicon carbide whiskers have been prepared by sintering silicon nitride powder in a graphite reactor at 1800°C under a nitrogen atmosphere. The whiskers differ in morphology: tubular needles, hollow faceted fibers with a square cross section, and solid fibers with a triangular cross section. The average diameter of the needles is 0.5?5 μm, and that of the faceted fibers is up to 20 μm. The fibers range in length up to several millimeters. Such silicon carbide whiskers can be used as reinforcing agents for structural ceramics based on nonoxide materials.     

Phase stability and microstructure of some gel-derived anorthite-based hybrid materials

The technical feasibility for producing five different anorthite-based binary and ternary hybrid ceramics containing zirconia and/or silicon carbide whiskers and/or gel-derivedin situ formed mullite whiskers was examined. The crystallization behaviour of the anorthite and the mullite gels and the phase stability of the hybrid ceramics were studied by X-ray diffractometry. The densification behaviour of the gel-derived materials, including the binary and the ternary composition materials, was examined by measuring densities of the sintered specimens by the immersion method. The microstructures were studied by scanning electron microscopy, supplemented by energy dispersive X-ray spectrometry. The results show the technical feasibility for producing anorthite-based fully dense binary and ternary hybrid ceramics of stable compositions containing zirconia and/or silicon carbide whiskers. However, the compositions containing mullite as a constituent produced hybrid ceramics within situ formed rod-like corundum crystals as the dispersed phase. Discrete monoclinic zirconia was present in all compositions containing this material.     

R-curve measurement of silicon nitride ceramics using single-edge notched beam specimens

R-curve behaviour of three kinds of silicon nitride-based ceramics has been studied using the single-edge notched beam (SENB) technique. If the notch is deep enough, the specimen shows stable fracture during the bending test, even when the sample is a brittle material. The conditions required to obtain stable fracture in the bending test are clarified by the analysis. The crack length of the specimen was also calculated from the changing load during the fracture test. In this study, coarse-grained silicon nitride shows a large increase of theR-curve. On the other hand, silicon nitride with silicon carbide whiskers shows noR-curve increase. The rise of theR-curve should be related to the microstructure of the ceramics, and especially to the grain size of the specimen, because silicon carbide whiskers are not large compared to the silicon nitride grains, and silicon carbide can reduce the grain growth of silicon nitride during sintering.     

Thermogravimetric and binder removal analysis of injection moulded reinforced ceramic composite

The study of the binder removal processes for injection moulded ceramic composite compacts was studied with the aid of a thermogravimetric analyser. It has been observed that a number of factors, such as the heating rate, the heating environment and the heating profile have an effect on the rate of binder removal. The matrix of the composite was alumina and the reinforcement was silicon carbide whiskers. It was confirmed that the presence of silicon carbide whiskers in the injection moulded compacts provided additional oxygen diffusion paths to enhance oxidative degradation. It was also found that the heating profile used for binder removal had a strong influence on the formation of internal cracks in the moulded components.     

Effects of amorphous silica coatings on the sintering behaviours of SiC whisker-reinforced Al2O3 composites

In this study, pressureless sintering of silicon carbide whisker (SiC_w)-reinforced alumina composites was investigated. SiC whiskers or Al₂O₃ powders were coated with amorphous silica, and sintering behaviour was analysed according to the powder characteristics of the composite. It was found that amorphous silica coatings improved densification as compared with uncoated powders, because the viscous flow allows the release of any tensile stress due to differential shrinkage between the matrix and the silicon carbide whiskers. Mullite occurred when amorphous silica coatings reacted with alumina at 1500 °C, which resisted the viscous sintering of the amorphous silica coatings.