C/C复合材料表面无催化剂CVD制备SiC纳米线的结构表征（英文）

在无催化剂条件下,以CH3SiCl3为前驱体,采用化学气相沉积技术(CVD)在C/C复合材料表面制备SiC纳米线。SEM形貌表明:CVD产物有大量数十微米长的纳米线,部分纳米线团聚呈球状,同时也发现类似带刺板栗外壳的短纳米线聚集,且纳米颗粒在其表面沉积等现象。XRD、拉曼光谱和红外光谱分析结果表明,此产物为典型的β-SiC。TEM形貌表明,此类纳米线的直径分布范围为10~100 nm,一些较细的纳米线可通过无定形SiC与较粗的纳米线结合在一起。在一根较粗SiC纳米线的无定形区域长出一根与其直径相近的分支,二者之间的夹角为70°,其与β-SiC晶体中[111]轴堆垛夹角一致。SAED和FFT结果表明,纳米线的生长轴线较多,在纳米线的竹节状区域存在大量堆垛层错和孪晶。边缘弯曲的SiC纳米线晶格面表明,螺旋位错生长为其主要的生长机制。     

热蒸发法制备金属碲纳米线

在真空管式炉内，以Bi2Te3为蒸发源，在蒸发温度560 ℃，保温时间2h条件下，采用热蒸发法在涂有Au溶胶的石英基片上制备出了大量碲纳米线。通过XRD、SEM、HRTEM等仪器对碲纳米线的组织结构和微观形貌进行了表征与分析。结果表明，制备出的碲纳米线为沿（101）方向取向生长的三方单晶碲纳米线，直径范围在40~100nm之间，生长机制符合VLS生长机制。蒸发源材料和Au溶胶是热蒸发法制备碲纳米线的关键因素。     

聚合物先驱体热解制备超长SiC纳米线

采用聚合物先驱体热解技术,以聚合物先驱体-聚碳硅烷(Polycarbosilane,PCS)为原料,在催化剂辅助作用下,于1200℃热解制备出超长碳化硅(SiC)纳米线.采用电子能量散射(EDS)、扫描电镜(SEM)、透射电镜(TEM)和x射线衍射(XRD)等分析手段对SiC纳米线进行了表征.结果表明,所制备的纳米线为高结晶性β-SiC,纳米线直径约为30 nm～300 nm,长度可达数毫米.利用.气-固"生长机制对SiC纳米线的生长过程进行了分析.     

烧结条件对碳热还原生成SiC纳米材料的影响

用SiO2干凝胶包覆滤纸经过碳热还原反应来制备SiC纳米线和纳米颗粒,通过XRD、IR、SEM、TEM等表征手段对反应前后的物相及其微观形貌进行了研究,并结合热力学对反应的机理进行了探讨.烧结的温度和压力对于各步反应有不同的影响,碳热还原生成SiC纳米线主要是由SiO和CO之间的气-气反应产生,通过优化反应条件,获得了粒径更小的SiC纳米颗粒和直径更小的SiC纳米线.     

从SiBONC陶瓷粉体中生长β-SiC纳米线

通过有机聚合物先驱体法使用四氯化硅(SiCl4)、苯甲醛(PhCHO)、烷基胺(RNH2)、三氯化硼(BCl3)为原料,通过有机-无机裂解转化制备了SiBONC陶瓷的纳米粉体.在对SiBONC陶瓷粉末坯体进行高温气压处理时,发现在坯体表面生长出大量β-SiC纳米线.通过XRD、FT-IR、SEM、TEM等分析测试手段分析了该纳米线的微观结构和物相组成,并初步推断了其生长机制.结果表明:该纳米线为结晶良好的β-SiC,其主要组成元素为Si、C及少量的O;其直径在20～200 nm之间,其平均长度在1 mm左右.     

原位自生SiC纳米线掺杂SiOC陶瓷粉体的制备与介电性能（英文）

以二茂铁为催化剂,催化裂解陶瓷聚合物先驱体制备了原位自生SiC纳米线掺杂的SiOC陶瓷粉体。SiC纳米线为堆垛方向为111的β相单晶体,直径为10～100 nm,长度可达数微米,均匀分布在SiOC粉体中。基于SiC纳米线微观结构分析,探讨了纳米线的生长机制。研究了复合陶瓷粉体的介电性能。结果发现,SiC纳米线含量可调控复合粉体的电性能,较高含量纳米线可赋予复合粉体较高的介电实部与虚部。     

铝液原位反应生成TiAl3晶须的条件和机制分析

分析了液相原位反应生成TiB2颗粒过程中，TiAl3晶须的生成条件和生长机理。结果表明，预制块中Ti与B的摩尔比显著影响TiAl3晶须的生成，TiAl3晶须的生长机理为VLS机制，由于晶须生长过程中触媒液滴中的Ti参加反应，使它与一般晶须生长的VLS机制有所不同。     

原位自生SiC纳米线掺杂SiOC陶瓷粉体的制备与介电性能

以二茂铁为催化剂,催化裂解陶瓷聚合物先驱体制备了原位自生SiC纳米线掺杂的SiOC陶瓷粉体。SiC纳米线为堆垛方向为<111>的β相单晶体,直径为10-100nm,长度可达数微米,均匀分布在SiOC粉体中。基于SiC纳米线微观结构分析,探讨了纳米线的生长机制。研究了复合陶瓷粉体的介电性能,结果发现,SiC纳米线含量可调控复合粉体的电性能,较高含量纳米线可赋予复合粉体较高的介电实部与虚部。     

大面积SiC纳米线网的合成及形成机理

利用气相化学反应法,在相对低的温度下,于自制石墨反应室中合成出二维半导体β-SiC纳米线网.该方法使用球磨及研磨混合后的Si和SiO2混合粉体及C3H6气体为原材料,通过调整基片与原料混合粉在石墨反应室的摆放位置、C3H6通入流量和时间、保温时间及其它工艺参数,可获得二维半导体β-SiC纳米线网.场发射扫描电镜、能量损失谱、X-Ray衍射、高分辨透射电镜结果表明纳米线彼此相连形成二维纳米线网,并且纳米线的直径大约在20 nm～70nm左右.值得注意的是绝大多数纳米线网的连接点是由3根纳米线交汇而成.纳米线是具有立方结构的β-SiC,其生长方向是〈111〉,并且存在大量面缺陷.最后对这种新型二维SiC纳米线网的形成机理进行了探讨.     

Ar/CO气氛下无催化剂热蒸发法制备SiC/SiO2纳米链及其生长机理(英文)

在Ar/CO气氛中采用无催化剂热蒸发法在炭纤维基体表面制备SiC/SiO₂纳米链。XRD、FT-IR、SEM和TEM结果表明:所制备的SiC/SiO₂纳米链由单晶结构SiC纳米线和无定形结构SiO₂球组成。CO的引入能促进形成SiO₂,从而在冷却过程中形成SiC/SiO₂纳米链。此外,光致发光光谱分析结果表明,SiC/SiO₂纳米链在约350 nm处显示出一个较宽的发射峰,主要是由于SiO₂球中的氧偏差以及SiC/SiO₂的界面效应。本研究能为一维碳化硅基材料气相生长的研究提供指导。     

硅纳米线的制备技术

硅纳米线作为一种新型的一维纳米材料，在纳米电子器件、光电器件及集成电路方面具有很好的应用前景。介绍了硅纳米线在制备方面的国内外研究现状与进展，重点讨论了基于金属催化气-液-固（VLS）生长机理、氧化物辅助生长机理的硅纳米线制备及模板法等制备硅纳米线的研究成果、特点及生长机理。与金属催化VLS生长机理相比，氧化物辅助生长硅纳米线不需要金属催化剂，能避免金属污染，保证了硅纳米线的纯度，因而是今后深入研究的方向。     

Oxidation-protective and mechanical properties of SiC nanowire-toughened Si–Mo–Cr composite coating for C/C composites

Oxidation-protective SiC nanowire-toughened Si–Mo–Cr composite coating prepared on the carbon/carbon (C/C) composites by chemical vapor deposition and pack cementation was investigated in this study. After incorporating SiC nanowires, the hardness, elastic modulus and fracture toughness of the composite coating were increased by 6.12%, 20.89% and 35.78%, respectively, due to the toughening and strengthening mechanisms including nanowire pullout, nanowire bridging, microcrack deflection and good interaction between nanowire/matrix interface. Thermogravimetric analysis revealed that the maximum weight loss of the coated C/C samples was decreased from 5.87% to 3.93% by incorporating SiC nanowires from room temperature to 1500 °C.     

以CuSe纳米粒子为催化剂制备超长ZnSe纳米线

采用化学气相沉积的方法,以Zn粉末为原料,CuSe纳米粒子为催化剂,在Si衬底上成功制备了毫米级ZnSe纳米线。用X射线衍射、EDS和SEM对产物的结构、成分和形貌进行了测试与表征。结果表明：生长的ZnSe纳米线为立方闪锌矿结构,长度达0.35～0.7mm,Zn和Se的摩尔比为1？0.97,其室温光致发光谱显示在325nm波长激发下,ZnSe纳米线在439nm处呈现自由激子的强烈发射,表明生长的ZnSe纳米线具有高的结晶质量。纳米线生长符合氧化还原反应下的气液固生长机制,并证明Cu3Zn合金充当了实际的ZnSe纳米线生长催化剂。     

Facile route to straight ZnGa2O4 nanowires and their cathodoluminescence properties

Single-crystalline ZnGa₂O₄ nanowires with high purity were grown on the Au and amorphous carbon layers coated Si substrates by a facile carbothermal reduction process. These ZnGa₂O₄ nanowires were straight along their growth direction, and the length and diameter were around 10 μm and 150 nm, respectively. The growth mechanism follows an enhanced vapor–liquid–solid (VLS) process. The carbon layers predeposited on the substrates can strongly enhance the VLS growth process of ZnGa₂O₄ nanowires. The cathodoluminescence (CL) spectrum of an individual nanowire exhibits a broad emission band centered at 537 nm, which can be ascribed to a large quantity of ionized oxygen vacancies.     

Oxidation protection and behavior of C/C composites with an in situ SiC nanowire–SiC–Si/SiC–Si coating

An in situ SiC nanowire–SiC–Si/SiC–Si protective coating was prepared on C/C composites by pack cementation and heat treatment. SiC nanowires suppressed the cracking of the coating by nanowire pullout and bridging and microcrack deflection, avoiding the oxidation of C/C composites. Results showed that the oxidation of the samples was a continuous weight gain process. The oxidation behavior was fitted to the parabolic–linear model and the final weight gain was 1.8% during thermogravimetric analysis from 50 to 1600 °C. The oxidation behavior was fitted to the parabolic model and the final weight gain was 0.51% during isothermal oxidation at 800 °C.     

Effects of supply time of Ar gas current on structural properties of Au-catalyzed ZnO nanowires on silicon (1 0 0) grown by vapor–liquid–solid process

ZnO nanowires were grown on Au-coated Si (1 0 0) substrates by the method of vapor–liquid–solid (VLS) growth processing technique. The effects of supply time of Ar gas current on morphology and microstructure of Au-catalyzed ZnO nanowires were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. The results showed that the morphologies of ZnO nanostructures strongly depended on the time of flowing Ar gas. When the time of flowing Ar gas was 90 s, ZnO showed nanowires with hexagonal structure. Their diameters and lengths were 160 nm and 20 μm, respectively, on average, and the Raman scattering peak located at 438 cm⁻¹ reached maximum intensity. The results also showed that the ZnO growth could be patterned by controlling the initial position of Au-coated area on the Si substrates.     

Microstructure and mechanical properties of SiC-nanowire-augmented tungsten composites

The effect of an addition of SiC nanowire on the microstructure and mechanical properties of tungsten-based composites is investigated in this study. SiC-nanowire-augmented tungsten composites were prepared by a spray-drying process and an in situ spark plasma sintering process. Three distinctive reaction phases, tungsten, tungsten carbide (W₂C) and rod-type tungsten silicide (W₅Si₃) were formed during the sintering process. The flexural strength was significantly increased from 706 MPa to 924 MPa in tungsten composites augmented with SiC nanowires, as was the formation of W₂C and W₅Si₃ phases. The rod-type W₅Si₃ bears significant stress by both sharing a portion of the load and providing a bridging mechanism. Furthermore, a high ablation resistance at an elevated temperature was observed for tungsten composites augmented with SiC nanowires.     

Investigation of interfacial bonding between Na2O–B2O3–SiO2 solder and silicon carbide substrate

Abstract

The interfacial characteristics of the SiC/glass solder/SiC joining part were investigated by means of thermodynamic and wetting behaviour calculation, microstructure observation, chemical structure and element analysis. The results of wavelength dispersive spectroscopy linear scan across the joint showed a relatively low increase in sodium content at the interfaces, which indicated that the sodium silicates in glass could react with silicon carbide substrate at the joining temperature, but it is not the reason for the good bonding between SiC and the interlayer. The mechanism of the good interfacial bonding lies in the formation of oxycarbide phase at the interface.     

Oxidation protection of SiC-coated C/C composites by SiC nanowire-toughened CrSi2–SiC–Si coating

Oxidation protective SiC nanowire-toughened CrSi₂–SiC–Si coating was prepared on SiC-coated carbon/carbon composites by chemical vapor deposition and pack cementation. SiC nanowires in the coating suppressed the cracking of the coating via various toughening mechanisms including nanowire pullout, microcrack bridging by nanowire and microcrack deflection, resulting in a good oxidation inhibition for the coated samples. The results showed that the maximal weight loss of the coated samples was only 2.55% in thermogravimetric analysis from room temperature to 1500 °C, and the weight loss of the coated samples was only 1.24% after isothermal oxidation at 1500 °C for 316 h.