Micelle-mediated synthesis of single-crystalline β(3C)-SiC fibers via emulsion electrospinning

Submicroscale SiC fiber mats were prepared by the electrospinning of an oil-in-water(O/W) precursor emulsion, a subsequent thermal curing treatment, and calcination at 1600 °C. Low-molecular-weight PCS micelles entrapped within an aqueous PVP matrix played an important role in forming the continuous and dense core structure, resulting in pure SiC fibers. The manipulation of SiC fiber diameters could be obtained via control of the micellar PCS concentration (10-30 wt %), enabling the production of dense and highly crystallized SiC fiber architectures with diameters ranging from 200 to 350 nm.     

Processing and Properties of Al2O3-ZrO2(3Y)-SiC Nanocomposites

本文研究了非均相沉淀法制备 Al     

Self-diffusion of14C in polycrystalline β-SiC

The¹⁴C self-diffusion coefficients for both lattice (D _lc ^* ) and grain boundary (D _bc ^* ) transport in high purity CVDβ-SiC are reported for the range 2128 to 2374 K. The Suzuoka analysis technique revealed thatD _bc ^* is 10⁵ to 10⁶ faster thanD _bc ^* ; the respective equations are given by $$\begin{gathered} D_{I c}^* = (2.62 \pm 1.83) \times 10^8 exp\left\{ { - \frac{{(8.72 \pm 0.14)eV/atom}}{{kT}}} \right\}cm^2 sec^{ - 1} \hfill \\ D_{b c}^* = (4.44 \pm 2.03) \times 10^7 exp\left\{ { - \frac{{(5.84 \pm 0.09)eV/atom}}{{kT}}} \right\}cm^2 sec^{ - 1} \hfill \\ \end{gathered} $$ A vacancy mechanism is assumed to be operative for lattice transport. From the standpoint of crystallography and energetics, reasons are given in support of a path of transport which involves an initial jump to a vacant tetrahedral site succeeded by a jump to a normally occupied C vacancy.     

Microstructure and fracture toughness of liquid-phase-sintered β-SiC containing β-SiC whiskers as seeds

The effect of seeding on microstructural development and fracture toughness of -SiC with an oxynitride glass was investigated by the use of morphologically rodlike -SiC whiskers. A self reinforced microstructure consisting of rodlike -SiC grains and equiaxed -SiC matrix grains was obtained by seeding 1–10 wt% SiC whiskers, owing to the epitaxial growth of -SiC from the seed whiskers. Further addition of seeds (20 wt%) or further annealing at higher temperatures led to a unimodal microstructure, owing to the impingement of growing seed grains. By seeding -SiC whiskers, fracture toughness of fine-grained materials was improved from 2.8 to 3.9–6.7 MPa · m^1/2, depending on the seed content.     

About the iron carbonyl complex with C60 and C70 fullerene: [Fe(CO)4(η2C60)] and [Fe(CO)4(η2C70)]

The iron carbonyl complexes with C₆₀ and C₇₀ fullerenes were synthesized in high yield by photochemical irradiation of solutions of C₆₀ and C₇₀ in presence of Fe(CO)₅. The resulting complexes were studied by FT-IR, Raman and electronic absorption spectroscopy. All the data are consistent with the structures [Fe(CO)₄(η²C₆₀)] and [Fe(CO)₄(η²C₇₀)]. The thermal stability and decomposition reaction of the two complexes were studied by TGA-FTIR and Differential Scanning Calorimetry (DSC). Both complexes decompose at moderate temperatures releasing CO and Fe(CO)₅ in the vapor phase leaving a residue of metallic iron and free C₆₀ or C₇₀ fullerenes that can be recovered by solvent extraction of the decomposition residue.     

R-curve behaviour and microstructure of liquid-phase sintered α-SiC

R-curves for two liquid-phase sintered -SiC (SC-A and SC-B), of different microstructures, were characterized using indentation-strength method. Silicon carbide SC-B, with its coarser microstructure and 8 MPa · m^1/2 toughness, showed higher resistance to crack growth and more damage tolerance than silicon carbide SC-A, with its finer microstructure and 4.5 MPa · m^1/2 toughness. These results suggest that a coarse microstructure is beneficial to toughening and damage tolerance while a fine microstructure is beneficial to strengthening.     

Microstructural investigation and indentation response of pressureless-sintered α- and β-SiC

The microstructure and indentation response of pressureless-sintered - and -SiC were studied using a high-resolution electron microscope and analytical electron microscopy. The materials were manufactured with boron and carbon as sintering aids. It was found that the overall porosity of the materials was very low but a large number of carbon inclusions were present. X-ray diffraction revealed the fabricated -SiC material was of the same 3C polytype as the initial starting powder; however, electron microscope observations indicated that the material contained a high density of faulting of the -forms. High-resolution imaging of grain boundaries in these materials indicated that the boundaries were very clean, and when they contained an amorphous intergranular film it was at most 0.5 to 1 nm thick. The presence of boron was not detected. Deformation due to identation took several forms. Firstly, radial cracks extending from the corners of the indent suffered little hindrance from the matrix microstructure, such that transgranular fracture was the dominant mode. Secondly, the deformation zone beneath the indentations showed copious lattice microcracks with some preferred orientation during crack formation and propagation.     

Characterization of ultrafine γ-Fe(C), α-Fe(C) and Fe3C particles synthesized by arc-discharge in methane

Ultrafine -Fe(C), -Fe(C) and Fe3C particles were prepared by arc-discharge synthesis in a methane atmosphere. The phases, morphology, structure and surface layer of the particles were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) techniques and X-ray photoelectron spectroscopy (XPS). It was found that the mean particle size ranged from 9.8 to 12.8 nm. The surface of particles mostly consisted of a carbon layer and a little oxide. Phase transformation from -Fe(C) to -Fe(C) was studied by annealing in vacuum and by differential thermal analysis and thermogravimetry (DTA–TGA) measurement. The abundance of -Fe(C) was determined by a magnetization measurement to be approximately 30%. Phase transformation occurred between 300 and 500 °C in a flowing argon atmosphere. The Fe3C particles oxidized to -Fe2O3 and carbon dioxide at 610 °C or so. © 1998 Chapman & Hall     

Crystal and Molecular Structure of a New Complex of [60]Fullerene, 2(C60)·2(TMTSF)·(C6H6)

Abstract

A new molecular complex of [60]fullerene with composition 2(C₆₀)·2(TMTSF)·(C₆H₆) was synthesized. The structure and composition of the complex were found by an x-ray study. Crystal data: 2(C₆₀)2(C₁₀H₁₂Se₄)(C₆H₆), M = 2415.4, monoclinic, a = 19.388(4), b = 13.410(2), c = 32.467(6) A, β = 92.71(2)°, V = 8432(3) [Adot]³, space group P2₁/n, Z = 4, d_calc = 1.903 g/cm³, R = 0.0606. The crystal structure was shown to be layered with the alternating layers of three types. Two of them have the same composition (C₆₀, TMTSF) but different interorientation of molecules in a layer and different number of shortened contacts C…C and C…Se. The third layer consists of benzene molecules. The energy of intermolecular interactions C₆₀…. TMTSF was estimated by ab initio calculations. The TMTSF molecule has a “boat” conformation.     

Volume and dislocation diffusion of iron,chromium and cobalt in CVD β-SiC

Impurity tracer diffusion of ⁵⁹Fe, ⁵¹Cr and ⁵⁷Co in CVD β-SiC has been studied in the temperature range between 973 and 1873 K. The temperature dependence of the volume diffusion coefficients of iron and chromium can be expressed by linear Arrhenius equations. The preexponential factor and the activation energy are estimated to be 8.7×10⁻¹⁵ m² s⁻¹ and 111 kJ mol⁻¹ for iron, respectively, and 9.5×10⁻¹⁵ m² s⁻¹ and 81 kJ mol⁻¹ for chromium, respectively. The diffusion coefficients of iron and chromium are much higher than those of the self-diffusion in β-SiC. Furthermore, the activation energies for the diffusion of iron and chromium are about one-tenth of those for carbon and silicon in β-SiC. Therefore, it seems that an interstitial mechanism is predominant for the diffusion of iron and chromium in β-SiC. On the other hand, the diffusion coefficient of cobalt above 1673 K is higher than that of iron, while at lower temperatures it is much lower than that of iron. The difference in the diffusion coefficients at 1173 K is more than three orders of magnitude. Thus, the temperature dependence of the diffusion coefficients of cobalt shows a strongly curved Arrhenius relation. This suggests that cobalt atoms diffuse by an interstitial mechanism at higher temperatures and by a substitutional mechanism at lower temperatures. From the deeper regions of the penetration profiles of iron, chromium and cobalt the dislocation diffusion coefficients of them have been estimated.     

The formation ofβ-SiC fibres with SiO2-C-NaF(AlF3) components

The formation of-SiC fibres with SiO₂-C-NaF(AIF₃) components was investigated. It was found that the formation of a longer-SiC fibre was governed by the mole ratio of C/SiO₂ or C/NaF. Using a mole ratio for C/SiO₂ or C/NaF of 3 or more,-SiC fibres of length 3 mm were prepared in a closed system. On the other hand, short-SiC fibres were obtained in an open system.-SiC fibres prepared under the various experimental conditions were stable when heated in a high-concentration acidic solution such as HCl or H₂SO₄, and in an alkaline solution such as NaOH.     

Synthesis and phases evolution of Si–C–Ti from polycarbosilane (PCS) and metal Ti

Si–C–Ti ceramics were synthesized by reactive pyrolysis of polycarbosilane (PCS) precursor filled with metal Ti powder. Pyrolysis of mixture with atomic ratio of Ti:Si through 3:1–3:2 was carried out in argon atmosphere at given temperature up to 1500 °C. The metal–precursor reactions, and phase evolution were studied using X-ray diffraction and scanning electron microscopy with EDX. The Ti₃SiC₂ phase was obtained firstly from reaction of PCS and Ti. Ti₃SiC₂ formation starts at 1300 °C and its amount increases significantly in a narrow temperature range between 1400 °C and 1500 °C. In addition, addition of CaF₂ can promote the formation of Ti₃SiC₂ phase.     

HPLC Diode‐Array Analysis of C60 and C70 Polymeric Fullerene Oxides (Fullerene Polymeric Ozonides)

Abstract

It is shown by HPLC diode‐array analysis that the C₆₀ and C₇₀ polymeric fullerene oxides ([C₆₀]‐PFOs and [C₇₀]‐PFOs) which are polymeric ozonides, are composed by nine different components. The ozonide derivatives of C₆₀ and C₇₀ have been proved to be practically analogous in chemical structure and composition. The most important component of both [C₆₀]‐PFOs and [C₇₀]‐PFOs accounts for about 3/4 of each sample. The overozonation of [C₆₀]‐PFOs in methanol has been studied and shown to not produce any significant changes.     

AVLIGHT(爱浪)C360新感受

在2004年期间,音响行业里面最为炙手可热的名词应该是“宽频”二字了,不少音响产品都以标榜“宽频”作为卖点。不过可惜的是市面上的所谓宽频音响产品的质素良莠不齐,一般消费者一不小心就会被一大堆陌生的名词术语弄得晕头转向。而且,对于一般用户来说,要为这些有着“高新技术”的产品弄个完美的搭配也是不容易之事,往往会花费太多的金钱,走太多的冤枉路,而最终却享受不到高新技术应该带给我们的享受,那确实是不值得。在此笔者愿借《音响世界》的一纸篇幅,与大家分享一则真实的故事,是一段典型的非音响发烧友玩音响的苦乐历程,希望读者朋友能从中得到一点启发。     

P型Si_(80)Ge_(20)B_(0.6)-SiC纳米复合材料的微观结构与热电性能研究（英文）

采用感应熔炼、球磨与放电等离子烧结的方法制备了SiC第二相均匀分布的Si_(80)Ge_(20)B_(0.6)-SiC纳米复合热电材料。系统研究了细化Si_(80)Ge_(20)B_(0.6)晶粒尺寸与复合SiC纳米颗粒对材料热电性能的影响。球磨导致的Si_(80)Ge_(20)B_(0.6)晶粒尺寸的降低显著增加了材料的晶界数量,进而增强了晶界对中长波声子的散射,能够有效降低材料的晶格热导。Si_(80)Ge_(20)B_(0.6)基体中均匀分布的纳米SiC颗粒提供了额外的散射中心和界面,可进一步增强声子散射,降低材料的晶格热导。在纳米结构化与SiC纳米复合的共同作用下,材料在1000 K时热电优值ZT达到了0.62,较基体提高了17%。证明纳米结构化与纳米复合方法能够共同作用于硅锗合金,提高其热电性能。     

威廉·弗拉姆(William C.Pflaum)的报告(摘要)

世界包装组织秘书长、美国专业包装协会执行总裁     

测试(measurement and test)

具有试验性质的测量。一般认为，计量器具示值的检定或校准，有规范化的技术文件可依，可以通称为测量或计量，而除此以外的测量，尤其是对不属于计量器具的设备、零部件、元器件的参数或特性值的确定，其方法具有试验性质，一般就称为测试。测试(measurement and test)     

Poly(acrylonitrile-co-itaconic acid)–poly(3,4-ethylenedioxythiophene) and poly(3-methoxythiophene) nanoparticles and nanofibres

This work aimed to produce poly(acrylonitrile-co-itaconic acid) (P(AN-co-IA)) nanocomposites with poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3-methoxythiophene) (PMOT). An anionic surfactant sodium dodecyl benzene sulphonate was used in emulsion polymerization for nanocomposite production. Incorporations of PEDOT and PMOT on the nanoparticles were characterized by scanning electron microscopy (SEM), atomic force microscopy, Fourier transform infrared-attenuated total reflectance spectroscopy and ultra-violet spectroscopy. These nanoparticles were blended with PAN and the blends were electrospun to produce P(AN-co-IA)–polythiophene-derivative-based nanofibres, and the obtained nanofibres were characterized by SEM and energy dispersive spectroscopy. In addition, electrochemical impedance studies conducted on nanofibres showed that PEDOT and PMOT in matrix polymer P(AN-co-IA) exhibited capacitive behaviour comparable to that of ITO–PET. Their capacitive behaviour changed with the amount of electroactive polymer.