纳微米PZT/水泥基压电复合材料的研究

采用溶胶-凝胶法合成了锆钛酸铅(PZT)纳微米粉体.XRD与SEM分析结果表明,经700 ℃煅烧的PZT粉体的平均晶粒尺寸约为26.4 nm,粉体团聚体的平均尺寸约为200 nm.采用干压成型-水化法制备了纳微米PZT/水泥基压电复合材料,研究了复合材料的压电及介电性能.SEM结果表明,PZT陶瓷相在基体中呈网状分布.PZT颗粒之间的良好连通性使复合材料具有优良的压电性能.     

A total X-ray scattering study of MnFe2O4 nanoparticles dispersed in a silica aerogel matrix

Structural information on a MnFe₂O₄-SiO₂ nanocomposite aerogel and on the pure silica aerogel matrix were obtained by total X-ray scattering experiments. The total pair distribution function of the silica aerogel is in agreement with literature data on melt-quenched silica. The total pair distribution function of the nanocomposite contains the contribution of all the pair correlations of the atomic species making the interpretation more difficult. The difference curve obtained by subtracting the total pair distribution function of the matrix from that of the nanocomposite, allows to selectively study the structural environment of the nanoparticles.     

One-dimensional SnF2 single crystals in the inner channels of single-wall carbon nanotubes: II. Structure and nanocomposite construction modeling

A structural model of the nanocomposite consisting of one-dimensional (1D) α-SnF₂ single crystals and single-wall carbon nanotubes (SWCNTs) is proposed. The main cationic motif is revealed in the structure of monoclinic modification: two-layer packing of tin cations along the [283] direction. Four theoretical structural projections of a 1D crystal on the plane parallel to the [283] direction are determined and described. A fragment of the α-SnF₂ structure in an SWCNT (with a channel diameter of 1.02 nm) is calculated. High-resolution electron microscopy (HREM) images are modeled. These images correspond to the actually observed HREM patterns.     

Electrical conductivity improvement of aeronautical carbon fiber reinforced polyepoxy composites by insertion of carbon nanotubes

An increase and homogenization of electrical conductivity is essential in epoxy carbon fiber laminar aeronautical composites. Dynamic conductivity measurements have shown a very poor transversal conductivity. Double wall carbon nanotubes have been introduced into the epoxy matrix to increase the electrical conductivity. The conductivity and the degree of dispersion of carbon nanotubes in epoxy matrix were evaluated. The epoxy matrix was filled with 0.4 wt.% of CNTs to establish the percolation threshold. A very low value of carbon nanotubes is crucial to maintain the mechanical properties and avoid an overload of the composite weight. The final carbon fiber aeronautical composite realized with the carbon nanotubes epoxy filled was studied. The conductivity measurements have shown a large increase of the transversal electrical conductivity. The percolative network has been established and scanning electron microscopy images confirm the presence of the carbon nanotube conductive pathway in the carbon fiber ply. The transversal bulk conductivity has been homogenized and improved to 10^? 1 S·m^? 1 for a carbon nanotubes loading near 0.12 wt.%.     

Linear and non-linear optical properties of 2,5-disubstituted pyrroles supported by a catalyst-free SiO2 sonogel network

The preparation and optical characterization of pyrrole based sol-gel hybrid materials generated by ultrasonic irradiation (Sonogel composites) are presented in this work. Pyrrole compounds were recently synthesized in our group by a modification of the Schulte-Reisch reaction; these molecular systems were dissolved at different concentrations in tetrahydrofuran (THF) and optimally embedded into a catalyst-free SiO₂ sonogel network. For this purpose, we exploited the novel catalyst-free (CF) sonolysis route to produce highly pure sol-gel glasses, generated via sonochemical reactions. This approach has been recently developed in our research group and has been successfully implemented to develop several hybrid composites for optical applications. By this method, homogeneous and stable solid-state hybrid samples suitable for optical characterization can be produced. The high porosity exhibited by the sonogel matrix allowed us to prepare several pyrrole doped composites with variable dopant concentration. The linear and nonlinear optical (NLO) properties of these amorphous hybrid structures were determined by absorption- and photoluminescent (PL)-spectroscopies, and by the optical third harmonic generation (THG) techniques, respectively. The implemented catalyst-free sonolysis route produced SiO₂-host networks of high chemical and optical purity, suitable for optical and photonic applications.     

Electron microscopy of carbon nanotubes

High-resolution electron microscopy was used to study multiwall carbon nanotubes obtained by the arc-discharge technique and double-and single-wall nanotubes produced by the arc-discharge catalytic synthesis. The structure of conical layer nanotubes obtained by the CVD technique is characterized in detail. It is established that heat treatment of nanotubes gives rise to their structural changes. The structure of nanotubes obtained by carbon evaporation in the N₂-Ar atmosphere under high pressure is determined. A new type of nano-and microtubes with surface-modulated walls is revealed. Possible applications of carbon nanotubes are reviewed.     

Poly(3,4-ethylenedioxythiophene)/carbon-based nanocomposite for gas sensing

Abstract

In this study, we have manufactured sensory films based on poly(3,4-ethylenedioxythiophene)/carbon nanotubes/reduced graphene oxide nanocomposite. The charge transport in obtained films was analyzed using impedance spectroscopy and temperature dependence of conductivity in the 90–325?K temperature range. The activation mechanism of charge transfer was established and the activation energy of conductivity was determined. The percolation effect in the nanocomposite was found with increasing the content of carbon nanoparticles. A decrease in resistance and an increase in the capacity of hybrid films due to the adsorption of water and ammonia molecules were revealed. Found features of the charge transport processes can expand the prospects of application of nanocomposite films for sensor electronics.     

Vertically aligned N-doped carbon nanotubes by spray pyrolysis of turpentine oil and pyridine derivative with dissolved ferrocene

Vertically aligned nitrogen-doped carbon nanotubes were synthesized from the pyrolysis of a mixture of turpentine oil, 4-tert-butylpyridine (C₉H₁₃N) and ferrocene on silicon and quartz substrate in nitrogen atmosphere at 700 °C by simple spray pyrolysis technique. SEM, TEM, TGA/DTA, Raman spectroscopy, XPS and electron probe micro analysis (EPMA) techniques were used to characterize the structural analysis and composition of the as-grown N-doped carbon nanotubes. Morphology of the films was greatly affected by the nature of the substrate. From the XPS and EPMA data, it was found that nitrogen content of the nanotubes were 1.6 at.% and 2 at.% on silicon and quartz substrate, respectively. Our studies show that two different types of N atoms can be present in these materials. These are ‘pyridinic’ and ‘graphitic’ nitrogen with binding energies of 398.2 eV and 400.4 eV, respectively. Raman spectroscopy reveals that graphitization of carbon nanotubes grown on silicon is better than nanotubes grown on quartz substrate. Thermogravimetric analysis showed that the thermal stability of as-prepared nanotubes grown on silicon substrate is higher than the nanotubes deposited on quartz substrate.     

制备工艺对羟基磷灰石包覆碳纳米管的影响

利用原位合成法获得羟基磷灰石包覆的碳纳米管复合粉体,对制备过程中可能影响羟基磷灰石包覆层效果的因素进行了探索.结果表明:羟基磷灰石可以在阴离子修饰后的多壁碳纳米管上形核结晶;在实验过程中,pH值影响最终产物的组成,而陈化温度和陈化时间对包覆层中羟基磷灰石晶粒的尺寸和厚度有明显影响.     

Synthesis and characterization of SiO2-PEG hybrid materials

Sol-gel is a promising technique for the synthesis of organic-inorganic hybrid materials both of class I and II. In materials of class I organic molecules are physically entrapped in an inorganic matrix, while in those of class II organic and inorganic parts are connected by covalent bonds. In this paper a sol-gel procedure to obtain SiO₂-PEG hybrids of class I, in which PEG is simply mixed at the sol stage, is compared to a sol-gel procedure to obtain SiO₂-PEG hybrid materials of class II, where a particular sol-gel Si-C precursor is synthesized. XPS analyses showed the different distribution of the organic phase in the SiO₂ matrix and the bond between PEG and SiO₂ for hybrids of class II. The PEG molecule in hybrid of class II showed an enhanced thermal stability up to 350 °C. Doping with a lithium salt was performed on hybrids of class II, and the ionic conductivity was measured.     

Magnetic and structural characterization of silver-iron oxide nanoparticles obtained by the microemulsion technique

In the present paper we report the magnetic characterization of silver-iron oxide nanocomposite obtained by the chemical microemulsion method. TEM images and X-ray diffractograms show that the nanocomposite consists of Ag nanoparticles of ～ 7 nm surrounded by a quasiamorphous matrix. The ZFC–FC curves and Mössbauer spectra obtained at different temperatures show a typical evolution of a system composed of weakly interacting nanoparticles with a blocking temperature (T_b) of ～50 K. The analysis of the magnetic data reveals that the matrix is formed by γ-Fe₂O₃ phase with a structural range order of ～2 nm.     

Al_2O_3包覆SrSO_4纳米复合粉体的制备与表征

采用直接沉淀-超临界流体干燥方法合成了纳米SrSO4粉体,以溶胶-凝胶法对其表面进行包覆Al(OH)3凝胶的处理,经煅烧后制备出Al2O3包覆SrSO4纳米复合粉体。通过XRD、TEM、SEM等对不同工艺条件下制备的纳米复合粉体的表面形貌和特性进行了研究。研究表明:当Al3+的浓度为0.1 mol/L、pH值为8时,可以获得好的氧化铝前驱体包覆SrSO4纳米复合粉体,经700℃煅烧3 h后获得了均匀、致密的Al2O3包覆SrSO4纳米复合粉体。     

Silica and silica-titania glasses prepared by the sol-gel process

Clear monolithic samples of silica and silica-titania glasses were prepared by the sol-gel process from alkoxides as starting materials. The effects of the composition of the initial alcoholic solutions on the gelation of the silica materials and the effects of using different titanium compounds on the formation of silica-titania gels and glasses were investigated. DTA and TGA revealed losses of water and organic volatiles during heat treatment of the gels at lower temperatures (up to 400°C) and the glass transformation and crystallization behaviour at higher temperatures (up to 1500°C). The effects of using atmospheres with varying oxygen contents on the DTA peaks caused by oxidation reactions were also studied.Structural changes occurring during heat treatment were monitored by infra-red spectroscopy which indicated that the water contents of the glasses after heat treatment to 900°C were about 1000 ppm. Transmission electron microscopy of ion beam thinned foils of a 80 SiO₂20TiO₂ composition showed a microstructure of extremely fine pores for heat treatments up to 1000°C. However, after extended heat treatments above 950–1000°C, the porosity appeared to decrease and a high concentration of fine crystallites of anatase (approximately 100 Å in diameter) embedded in a silica-rich glass matrix were obtained.     

Pt immobilization on TiO2‐embedded carbon nanofibers using photodeposition

Currently, the use of fuel cell electrodes containing Pt catalysts has been limited due to technological problems in this system, primarily the system's high cost. The improvement of Pt catalyst use has been achieved by changes in the Pt immobilization method. In this study, we have studied Pt immobilization on carbon nanofiber composites using the photodeposition method. First, we prepared the carbon nanofibers, which were homogeneously embedded TiO₂ using the electrospinning technology. These TiO₂‐embedded carbon nanofiber composites (TiO₂/CNFs) were then immersed in a Pt precursor solution and irradiated with UV light. The obtained Pt‐deposited TiO₂/CNFs contained Pt that was immobilized on the carbon nanofibers, and the Pt particle size was 2‐5 nm. The XPS spectra showed that the amount of Pt increased with an increasing UV irradiation time. The current densities and total charge also increased with an increase in the UV irradiation time, possibly due to an increase of active specific area by finely dispersed Pt nanoparticles. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fenton试剂对碳纳米管表面改性研究

利用Fenton试剂对碳纳米管进行表面改性,研究了Fenton, Fenton/超声波(US)以及Fenton/紫外线(UV)对碳纳米管表面的影响,并探讨了Fenton试剂与碳纳米管的作用机理.用热重分析(TGA)来观察纯化前后碳纳米管的纯度,用红外光谱(FTIR)分析碳纳米管表面官能团的变化,用透射电镜(TEM)对碳纳米管微观结构进行分析.结果表明:Fenton/UV反应能够在碳纳米管表面引入大量羟基以及少量的羧基,且不会较大程度地损坏碳纳米管的结构;机理分析表明, Fenton试剂主要是利用Fenton反应产生的羟基自由基(HO·)对碳纳米管的不饱和键进行羟基化加成.     

球磨法改善电学接触增强碳纳米管场发射性能

本文采用CNT与纳米银颗粒混合球磨的方法,改善了CNT与衬底电极的电学接触性能.并比较了球磨和电泳两种方法分别获得的CNT的场发射特性,结果表明:采用球磨法所获得的CNT场发射阴极的场发射性能远远优于电泳法.在球磨过程中,由于钢球、纳米银颗粒、CNT和衬底之间互相挤压,使CNT和银颗粒及衬底之间形成紧密牢固的接触,减少了界面的接触电阻,从而大大改善了界面的电学接触性能.而电泳沉积的CNT和衬底之间基本上是简单的物理附着力,接触电阻很大,而且由于这种作用力相对较弱,往往会导致发射体本身不稳定.球磨提供了一种改善电学接触的简单有效方法,并且适合于大规模生产CNT场发射冷阴极.     

Improved Photobleaching for (1,10-phenanthroline)tris[4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato]europium(III) Particle Embedded in Sol-Gel Derived Glass Film

In this research, we investigated improved photobleaching characteristics of (1,10-phenanthroline)tris[4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato]europium(III) by forming nano-particles embedded into a sol-gel derived silica glass film by a conventional sol-gel process. The relative photoluminescence intensities after the UV irradiation for 90 min were 88, 76, and 67% for nano-particles in the sol-gel derived glass film, powders in the sol-gel derived glass film, and raw powders, respectively. This result indicates that the phtobleaching of this Eu-complex can improved by forming nano-partcile structures by a reprecipitation method and embedding in the sol-gel derived silica glass.     

Nanocomposite SiO2(Si) films as a medium for non-volatile memory

Nanocomposite SiO₂(Si) films containing Si nanocrystals (NCs) in a SiO₂ dielectric matrix obtained through (i) plasma enhanced chemical vapor deposition (PE CVD) or (ii) pulse laser deposition (PLD) have been investigated as a medium for charge storage. The C–V method was used to characterize charging effects in the MIS structure (capacitor) with a nanocomposite SiO₂(Si) film as an insulator. The obtained results indicate (i) the capture of small negative charge at the positive gate voltage in the nanocomposite SiO₂(Si) film, (ii) significant capture of positive charge at the negative gate voltage, and that (iii) the difference between the positive and negative charge captured in both cases cannot be explained by dropping a part of the positive gate voltage in the semiconductor’s depletion region. A model of charge transport and capture in nanocrystals of nanocomposite SiO₂(Si) film is proposed to explain the experimental results.     

Energetics of CdSxSe1−x quantum dots in borosilicate glasses

The thermodynamics of CdSe quantum dots embedded in a glass matrix is of great interest because of the numerous applications as optical materials. In this study, the energetics and stability of CdSe quantum dots in a borosilicate glass matrix is investigated as a function of size using high-temperature oxide melt solution calorimetry. CdS_0.1Se_0.9 nanoparticles (1-40 nm) embedded in glass were analyzed by photoluminescence spectroscopy, electron microprobe, X-ray fluorescence, high-energy synchrotron X-ray diffraction, and (scanning) transmission electron microscopy using both electron energy loss and energy dispersive X-ray spectroscopy. As CdSe particles coarsen, their heat of formation becomes more exothermic. The interfacial energy of CdSe QDs embedded in a borosilicate glass, determined from the slope of enthalpy of drop solution versus calculated surface area, is 0.56 ± 0.01 J/m².     

Materials investigation of multi-walled carbon nanotubes doped silica gel glass composites

Multi-walled carbon nanotubes (MWNTs) doped silica gel glass matrix nano-composites were successfully prepared by sol–gel technique. Morphology of the composites was characterized by scanning electrical microscope and transmittance electrical microscope images. Pore structure of net MWNTs, silica gel glass matrix and resulted MWNTs doped composites were studied and compared. The results show that MWNTs are well dispersed in the gel glass matrix and sol–gel processing does not appear to affect the morphology of MWNTs. Pore structure of the silica matrix is changed by the introduction of MWNTs.