Effect of polyborazine additive on thermolysis of polyphenylsilane and polyvinylsilane

To improve the ceramic residue yields and processabilities of polyphenylsilane (PPS) and polyvinylsilane (PVS), polyborazine (PBN) was employed as an additive. The ceramic residue yield of PPS increased from an original 39wt% to 65wt%, and of PVS from an original 26wt% to 64wt% by simply heating with 1wt% PBN at 70 °C. Furthermore, low viscous PPS and PVS were transformed into highly viscous polymers, which were found to be suitable for hand drawing into green fibers. The enhanced properties were attributed to an increased molecular weight, as analyzed by GPC. ¹H-NMR and ²⁹Si-NMR spectra suggested that dehydrocoupling of SiH₃ in PVS and SiH in PPS by PBN was responsible for the improved ceramic yields.     

Design of oxidation-resistant coatings for high-temperature composites

Fabrication of oxidation-resistant carbon fiber reinforced carbon composites requires use of high-temperature CVD deposition of coatings such as SiC. In this paper the use of low-temperature chemical approaches for depositing oxidation-resistant coatings was explored. Coatings of SiO₂, B₂O₃, and SiC were examined, with the intent of distinguishing possible failure mechanisms. Factors contributing to poor oxidation resistance of these coatings include presence of microcracks in the original preparation of the coating and diffusion of oxygen through the coating at high temperatures.     

Crystal and molecular structure of polyunsaturated macrobicyclic carbosilane C24H38Si6

The crystal and molecular structure of the polyunsaturated macrocyclic carbosilane 1,4,4,7,7,10,13, 13,16,16-decamethyl-1,4,7,10,13,16-hexasilabicyclo-[8.8.2]-eucosa-5,14-diene-2,8,11,17-tetrain containing SiC(sp), SiC(sp ²), and SiC(sp ₃) endocyclic bonds was studied by XRD. The two strained 12-membered rings of this molecule have different (trans-zigzag and staggered) conformations. The lengths of the endocyclic bonds SiC(sp) are 1.821–1.852 Å, SiC(sp ²) 1.855–1.874 Å, and SiC(sp ³) 1.847–1.853 Å. The structure of the rings was solved by direct methods and refined by the full-matrix least-squares method. Calculations were carried out with SHELXTL PLUS 5.1 software.     

Determination of the thickness and density of the ion bombardment induced altered layer in SiC by means of reflection electron energy loss study

The steady state surfaces of ion bombarded 3C-, 4H- and 6H-SiC samples were studied by means of reflected electron energy loss spectroscopy (REELS). The REELS exhibit a well-defined loss peak in the region of about 20 eV. The position of the maximum of the loss peak depends on the bombarding ion energy (decreasing with increasing ion energy), and on the primary electron beam energy (increasing with increasing primary energy). This behavior can be explained if we suppose that the plasmon energy in the altered layer (produced by ion bombardment) is different from that of the unaltered bulk. In this case the measured loss peak is the sum of two overlapping plasmon peaks. With modeling the system as a homogeneous altered layer and a homogeneous unaltered substrate the plasmon energy in the altered layer was derived to be 19.8 eV. The large change of the plasmon energy with respect to the bulk value of 23 eV is explained by a thin low density overlayer on the surface of the sample produced by the ion bombardment.     

Micromechanics of Damage Accumulation in a 2.5D Woven C-Fiber/SiC Ceramic Composite

The morphology of a C/PyC/SiC ceramic composite is studied and its microdamage mechanisms are revealed. Some models based on the micromechanical fracture mechanics are proposed to describe the possible damage processes. The influence of the observed microdamage on the stiffness reduction is studied. It is shown that the delamination between the layers and the cracks in the coating alone cannot explain the stiffness reduction observed in tests. Debonding between the SiC coating and pyrocarbon is suggested as another mechanism of the stiffness reduction.     

The application of PCMMcs and SiC by commercially direct dual-complex coating on textile polymer

To enhance the thermal insulation effect, waterproof/breathable fabrics were directly top dual-coated by the dry coating method with ceramic materials (silicon carbide, SiC). The fabric was base coated by the wet coating method with 5 wt% phase-change material microcapsules (PCMMcs) and tested for the emission of far-infrared (FIR) radiation. With increasing SiC content, the fabric altered some of the physical properties by increasing the FIR emissivity, emission power, water vapor transmission rate (WVTR) and heat release capacity. Scanning electron microscopy (SEM) analysis revealed the presence of the PCMMcs and SiC particles at the cross-section and surface of the coating, respectively, which exhibited a rugged and blocky shape. The results indicated that SiC addition did not affect the water entry pressure (WEP) in the fabric structure, but did alter the following physical properties: WVTR, interactions between the macromolecule chains and the susceptibility to humidity.     

Ultra fast synthesis of zinc oxide nanostructures by microwaves

We describe a novel route for the synthesis of nanostructured zinc oxide powder using a modified kitchen microwave. A SiC-based composite showing a very strong absorption of microwaves was used as a microwave heater. Tests showed that high temperatures exceeding 1700 C can be reached in less than hundred second exposure of the composite material of microwaves. Zinc oxide nanopowder was obtained by evaporation and oxidation of metallic zinc in the ambient atmosphere of the microwave oven. Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) techniques revealed the prepared powder includes a wide variety of nanostructures including nanoparticles, nanosheets and tetrapods.     

氢氟酸刻蚀对Ni/6H-SiC接触性质的作用

采用浓度为10%的氢氟酸（HF）刻蚀6H-SiC单晶片,研究了HF刻蚀时间对Ni/6H-SiC接触性质的影响．经24?h刻蚀的SiC基片在溅射Ni层后,其接触表现良好线性的电流-电压（I-V）曲线．低于这个腐蚀时间的接触具有明显的势垒,但在大于1000℃快速退火后,也得到了良好线性的I-V曲线．X射线衍射（XRD）和俄歇能谱（AES）深度元素分析表明Ni₂Si和C是快速退火后的主要产物．XRD和低能反射电子能量损失谱表明表层的C 关键词： 欧姆接触 SiC 富碳层 互扩散     

微波等离子体化学气相沉积方法在Si衬底上生长SiC纳米线

应用微波等离子体化学气相沉积方法,在单晶Si(100)衬底上生长出SiC纳米线.应用扫描电子显微镜、透射电子显微镜、能量损失谱(EDS)和选区电子衍射(SAD)等方法对纳米线化学组成和结构进行了分析和表征.给出该纳米线的生长机理 关键词： 微波等离子体化学气相沉积 SiC纳米线 生长机理