The absence of nitrone form in re-determined crystal structure of 2-hydroxyimino-3-methyl-4-nitro-2,5-dihydrothiophene 1,1-dioxide

Crystal and molecular structures of 2-hydroxyimino-3-methyl-4-nitro-2,5-dihydrothiophene-1,1-dioxide C₅H₆N₂O₅S (I) have been re-determined by single crystal X-ray diffraction analysis. The structure of I (space group P2₁2₁2₁, a = 6.124(1) Å, b = 9.205(2) Å, c = 14.884(3) Å, Z = 4) was solved by the direct method and refined anisotropically in the full-matrix approximation to R = 0.064 using all 1756 measured independent reflections (automated diffractometer CAD-4, λCuK_α, anomalous scattering taken into account). This study proves that the compound I contains a disordered group H-O-N=C, but not the isomeric nitrone group O←N(H)=C, as it has been concluded by the workers who pioneered single crystal X-ray diffraction study of I and erroneously took the second low-occupied oxygen position of the disordered hydroxyimine group for H at N atom.     

Calculation of the proton affinities of polyfluorobenzenes and the activation energies for 1,2-hydrogen shifts in their carbocations

Isolated polyfluorobenzene (PFB) molecules and their protonated forms are investigated by the AM1 method with full geometry optimization. The proton affinities of PFB are estimated for different protonated positions. The proton affinity of PFB averaged over all isomers is shown to decrease monotonically as the number of fluorine atoms in the molecule increases. The relative populations of different isomers of arenonium ions (AI) formed by PFB protonation are determined. From the calculated data, the value of ⁺ for the F atom in theipso-position is estimated as 1.00. The activation energies of the 1,2-hydrogen shifts in AI are calculated. The dependences of the proton affinity and the activation energies of 1,2-hydrogen shifts on the number of halogen atoms are found to have distinct characters for PFB and polychlorobenzenes. The physical reasons for these difference are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1878–1882, November, 1993.     

Effect of tetrahydrofuran on the conductance and ion-pairing of hydrogen chloride in wet and dry methanol mixtures

The molar conductance of dilute solutions of HCl in wet (68.5% methanol + 31.5% tetrahydrofurane mixtures at 25°C have been measured. The data were analyzed using the Fuoss-Hsia equation to calculate the infinite dilution molar conductances and association constants. The trend of the limiting conductances in these mixtures as a function of the water content shows, once more, the peculiar minimum due to the anomalous proton conductance mechanism. From these data the limiting molar conductance in the anhydrous binary solvent system was evaluated. The percentage excess proton mobility with respect to potassium ion has also been determined. All these data are compared to those found in a binary isodielectric methanol mixture containing as cosolvent 1,4-dioxane. This comparison shows that proton mobilities are very similar in both solvent mixtures. The dielectric constants, refractive indices, viscosities and densities of the methanol-tetrahydrofuran mixtures in the whole mole fraction range have been measured and are reported. An analysis of the excess molar volumes and viscosities shows a slight deviation of this system from ideality.     

Study of the first nucleation steps of thin films by XPS inelastic peak shape analysis

The initial steps in the formation of thin films have been investigated by analysis of the peak shape (both inelastic background and elastic contributions) of X‐ray photoelectron spectra. Surface coverage and averaged height of the deposited particles have been estimated for several overlayers (nanometre range) after successive deposition cycles. This study has permitted the assessment of the type of nucleation and growth mechanisms of the films. The experiments have been carried out in situ in the preparation chamber of an XPS spectrometer. To check the performance of the method, several materials (i.e. cerium oxide, vanadium oxide and cadmium sulfide) have been deposited on different substrates using a variety of preparation procedures (i.e. thermal evaporation, ion beam assisted deposition and plasma enhanced chemical vapour deposition). It is shown that the first deposited nuclei of the films are usually formed by three‐dimensional particles whose heights and degree of surface coverage depend on the chemical characteristics of the growing thin film and substrate materials, as well as the deposition procedure. It is concluded that XPS peak shape analysis can be satisfactorily used as a general method to characterize morphologically the first nanometric moieties that nucleate a thin film. Copyright © 2006 John Wiley & Sons, Ltd.     

LOW DENSITY POLYETHYLENE/CLAY NANOCOMPOSITES MODIFIED BY ETHYLENE COPOLYMERS： EFFECTS OF FUNCTIONALIZED SEGMENTS ON MORPHOLOGY

Melt extrusion was used to prepare binary nanocomposites of ethylene copolymers and organoclay and trinary nanocomposites of low-density polyethylene （LDPE）, ethylene copolymer and organoclay. X-ray diffraction （XRD） and transmission electron microscopy （TEM） were used to analyze the structure of the clay phase and the morphology of the nanocomposites. Influences of the comonomer in the copolymer and the content of the copolymer on the morphology of the resulting nanocomposites were discussed. The binary and the trinary composites may form intercalated or exfoliated structures depending on the interaction between the copolymer and the clay layers and the content of the copolymer.     

单壁碳纳米管的结构修饰

由于单壁碳纳米管具有独特的结构、电学及机械等性能，可望在许多新领域得 到应用，已引起广泛的关注。但由于单壁碳纳米管不溶于水和常见的有机溶剂，极 大地制约了其应用性能的研究。随着单壁碳纳米管制备技术的不断完善，其研究方 向已开始转向结构修饰及应用性能的研究。主要介绍近年来单壁碳纳米管结构修饰 方面的最新发展状况，重点讨论化学功能化及物理吸附。     

THE PREPARATION AND STUDY ON THE NANO-TiO2/SILK FIBROIN COMPOSITE FILMS BY THE SOL-GEL METHOD

Based on the sol-gel technique using butyl titanate as oxide precursor, the regenerated SF (silk fibroin)/nano-TiO2 composite films were synthesized. Different amounts of butyl titanate to SF were used to verify this effect on the characteristics of the formed materials. Samples were characterized by thermogravimetric analysis, X-ray diffractometry, UV, AFM and FT-IR spectroscopy.The experimental results reveal that, compared to the pure silk fibroin films, the mechanical strength of these regenerated SF/nano-TiO2 composite films were increased and the dissolubility in water of SF/nano-TiO2 composite films in aqueous solution were decreased. The diameter of nano-TiO2 particle films was about 80nm through UV and AFM. The nano-TiO2 particles were well dispersed in the regenerated silk fibroin. It was found that the crystal structures of the composite films were transited from typical Silk Ⅰ to typical Silk Ⅱ by the XRD and FTIR. Furthermore, the crystallinity of the composite films was obviously improved. Through the TGA, it was demonstrated that the heat transition temperature of composite films was also enhanced.     

纳米氮化镁的合成

在制备高硬度、高热导、耐磨、耐腐蚀、耐高温的新兴陶瓷材料氧化硼、氮化硅的固相反应中，氮化镁是不可缺少的烧结助剂［‘，’j．同时，氮化镁还可用于制备发泡合金和回收核废料等领域．目前氮化镁的制备方法有：镁粉直接与氮气反应法［‘，‘1、镁在氮等离子流中与氮反应法＊‘、在氮气气氛下镁线圈爆炸法‘’‘和低压化学气相沉积法［’j．在上述方法中，有些方法需要复杂和昂贵的设备．有些方法得到氮化镁的产率较低．镁粉直接与氮气反应是具有工业生产价值的方法一然而，这种方法需要SOO”C到gOO”C的高温．我们曾经报道过利用温和…     

Preparation of VPS and PVD coatings for metallographic and TEM investigations

The aim of the first part of the paper is to give some advice for the faultless metallographic preparation of vacuum plasma sprayed coatings. Several coating/substrate combinations using metals, alloys and ceramics were investigated to derive some general rules. The second part deals with a preparation technique for cross-sections- of physical vapour deposition coatings. This technique was optimized for TiN and Ti(C, N) coatings on hardmetals which were examined in an analytical transmission electron microscope.     

物理化学课程“热化学”主题学习历程研究——化学师范生知识建构的文本分析

为深入了解地方性师范院校化学师范生知识建构习惯和水平，探讨他们在大学专业基础课程中的学习历程，以物理化学课程中以“融合科学读写特色”的“热化学”学案作为研究载体，研究对象在学案引导下开展自学活动，并在阅读教材和文献基础上进行科学写作。采用量表工具针对大学生自学效果和反思活动进行评价，并采用SOLO分类评价科学写作作品，采用KWL工具评价学生的科学阅读收获。结果发现研究对象学习动机不强，不擅长在新的学科知识学习中联系已有专业课程知识，基于文本学习的建构活动水平极低，可能是因为他们在应试背景下的基础知识并未形成体系，先修课程中并未培养元认知学习策略。