Pyrolytic conversion of an Al?Si?N?C precursor prepared via hydrosilylation between [Me(H)SiNH]4 and [HAlN(allyl)]m[HAlN(ethyl)]n

An iminoalane‐silazane polymer (ISP), an Al? Si? N? C precursor, has been synthesized via Pt‐catalyzed hydrosilylation between poly(allyl iminoalane‐co‐ethyl iminoalane) {[HAlN(allyl)]_m[HAlN (ethyl)]_n, AE‐alane} and 1,3,5,7‐tetrahydro‐1,3,5,7‐tetramethylcyclotetrasilazane {[Me(H)SiNH]₄, TCS}. The IR and ¹H NMR spectra of ISP indicate that the relative amounts of the allyl groups decrease slightly in comparison with those of AE‐alane, suggesting that hydrosilylation occurs partially. TG analysis up to 900 °C reveals that the ceramic yield of ISP is 83.1 mass%. It is suggested that the high ceramic yield can be ascribed to cross‐linking reactions occurring during pyrolysis. Possible reactions during pyrolysis are hydrosilylation, polymerization of the C?C bonds in the allyl groups and dehydrocoupling among the SiH groups, NH groups and AlH groups in ISP. The pyrolyzed residue at 1700 °C contains crystalline AlN, 2H‐SiC, β‐SiC and β‐Si₃N₄ and amorphous carbon, as revealed by solid‐state nuclear magnetic resonance (NMR) spectroscopy, Raman spectroscopy and X‐ray diffraction (XRD) analysis. Copyright © 2006 John Wiley & Sons, Ltd.     

Growth rate and morphology of silicon carbide whiskers from polycarbosilane

The growth rate of silicon carbide whiskers grown from polycarbosilane was measured and the growth morphology was investigated. The plot of whisker length vs. growth time was almost linear up to a certain growth time but tended to become time-saturated, independent of growth temperature. Cessation of whisker growth was caused by a change of the growth process from vapor–liquid–solid (VLS) to vapor–solid (VS). Decrease in whisker length with growth time was observed in the higher temperature range. Arrhenius plots of growth rate were almost linear in the lower temperature range, but deviated markedly from linearity in the higher temperature range. This deviation was caused by the coexistence of the VS process and the VLS process during whisker growth.     

Biomorphic SiC from lotus root

Biomorphic silicon carbide (bioSiC) with macro-channels and alveolate micropores was prepared by spon-taneous infiltration of melted silicon into a carbon template derived from lotus root at 1600 ℃. The carbon template and purified bioSiC samples were characterized by X-ray diffraction, scanning electron microscopy, camera and mercury intrusion. The results suggest that the bioSiC mainly consists of β-SiC and perfectly replicates the shape and microstructure of the carbon template. The bioSiC has a mean pore diameter of 91.1 μm and a porosity of 50.1%, both similar to those of the carbon template, 92.3 μm and 50.7%, respectively.     

Stability characteristics of single-layered silicon carbide nanosheets under uniaxial compression

The buckling behavior of single-layered silicon carbide nanosheets (SLSiCNSs) is investigated by employing an atomistic finite element model. Preserving the discrete nature of nanosheets, the beam elements are used to model the Si–C bounds. The effects of aspect ratio and boundary conditions on the stability of zigzag and armchair SLSiCNSs have been studied. Based on the results, it is observed that the buckling forces of small sheets are strongly size-dependent. However, the size-dependent behavior will diminish for larger sheets. Comparing the buckling force of armchair and zigzag nanosheets with same geometries and boundary conditions shows that the buckling force is independent of chirality.     

TiC Working Electrode. Voltammetric Characteristics and Application for Determination of Lead Traces by Stripping Voltammetry

The TiC working electrode was tested as a novel, potential electrode for anodic stripping voltammetric determination of lead(II) ions traces. To demonstrate the practical applicability of the TiC electrode, an underpotential deposition/dissolution (UPD) phenomena system in electrolyte without removal of oxygen was tested. The electrode was constructed be means of mounting a TiC disk (Ø=3.5 mm) in a resin body. Three compositions of TiC were tested differing in stoichiometry, namely TiC_0.6, TiC_0.8, and TiC_1.0. The key problem is the method of electrochemical activation of the TiC electrode. No or improperly activated electrode is not polarized and is unsuitable as a voltammetric sensor. The TiC electrode was used for the determination of Pb²⁺ in concentrations ranging from 1 to 100 nM. The instrumental parameters, composition of supporting electrolyte and procedures of the electrode activation were optimized. The repeatability of DP ASV runs in synthetic solutions covering the entire concentration range is better than 3%. The calibration curve is characterized by a correlation coefficient of at least 0.999. The detection limit was 2 nM for an electrodeposition time of 30 s. The method enables determination of Pb²⁺ in the presence of, among the others, high excesses of Cd, Cu, In, Sb, Se, and Tl ions as well as surfactants, Triton X‐100 and humic acids. The analysis of Pb²⁺ in synthetic solutions with and without surfactants, certified reference material and natural water samples have been performed. The voltammetric data were associated with the structural characterization of the electrode surface using scanning electron microscopy (SEM) and X‐ray fluorescence spectroscopy (XRF).     

High Temperature Thermal Insulation System for Millimeter Wave Sintering of B4C

Boron carbide (B₄C) is one of advanced materials and is being used in a wide rage of applications. The unique feature of this material is its large neutron-absorbing cross-section. Some of its most prominent applications are controlling rods in nuclear reactors and radiation protection. 24 GHz microwave processing for B₄C ceramics were performed under flowing argon gas using the sintering system. Sintering at the high temperature (up to 2200°C) was achieved using thermal insulation system consists of fiber-board, boron nitride powder, and boron nitride case. The sintered samples were achieved 90 % of theoretical.     

Uniform design and regression analysis of LPCVD boron carbide from BCl3-CH4-H2 system

Boron carbide was prepared by low pressure chemical vapor deposition (LPCVD) from BCl₃-CH₄-H₂ system. The deposition process conditions were optimized through using a uniform design method and regression analysis. The regression model of the deposition rate was established. The influences of deposition temperature (T), deposition time (t), inlet BCl₃/CH₄ gas ratio (δ), and inlet H₂/CH₄ gas ratio (θ) on deposition rate and microstructure of the coatings were investigated. The optimized deposition parameters were obtained theoretically. The morphologies, phases, microstructure and composition of deposits were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman micro-spectroscopy, transmission electron microscopy (TEM), energy dispersive spectra (EDS), and Auger electron spectra (AES), the results showed that different boron carbides were produced by three kinds of deposition mechanisms.     

Epitaxial SiC formation induced by medium energy ions on Si(1 1 1) at room temperature

In the search for silicon technology compatible substrate for III-nitride epitaxy, we present a proof-of-concept for forming epitaxial SiC layer on Si(1 1 1). A C/Si interface formed by ion sputtering is exposed to 100-1500 eV Ar⁺ ions, inducing a chemical reaction to form SiC, as observed by core-level X-ray photoelectron spectroscopy (XPS). Angle dependent XPS studies shows forward scattering feature that manifest the epitaxial SiC layer formation, while the valence band depicts the metal to insulator phase change.     

一种新型硅基3C-SiC的生长方法及光谱学表征

采用LPCVD技术, 以CH4和H2混合气体为反应源气, 在n-Si（111）衬底上生长3C-SiC晶体薄膜。H2在反应过程中作为稀释气体和运输气体, CH4作为碳源, 硅源有衬底硅来提供。利用X射线衍射分析仪、场发射扫描电子显微镜、激光拉曼光谱和傅里叶变换红外光谱分别研究3C-SiC薄膜的晶相结构、表面形貌及其光谱性质。结果表明此生长方法可以成功的成长出3C-SiC薄膜。