Advanced Materials Research Vols. 306-307

Abstract: Nano crystalline SnO₂ was prepared by sol-gel with PEG surfactant. CuO was doped in the SnO₂ by mechanical mixture and reaction congelation from CuCl. The samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen adsorption isotherms (BET). The results indicated that the average crystal size of SnO2 at sintering temperature of 550 °C was 10 nm, the conglomeration size of SnO₂ was about 100 nm. The specific surface area of pure SnO₂, mechanical doping SnO₂ and reaction doping SnO₂ were 110, 84, 72 m²/g, respectively. The thick film gas sensors made from these samples were examined. SnO₂ doped by different methods had different electrical and gas-sensing properties. The sensors based on CuO doped SnO₂ films exhibited less sensitive to ethanol gas but extremely higher sensitivity to H₂S gas than that of pure SnO₂.

Abstract: Conducting core–shell latex nanoparticles were synthesized by coating near–monodisperse, nanometer sized water–based polyurethane (PU) latex nanoparticles through in situ chemical polymerization of aniline. These latex nanoparticles showed nearly spherical shape and relatively narrow particle size distribution. It is found that good core–shell structure of latex nanoparticles could be well formed due to the interaction between the carboxyl groups of PU and imine groups of polyaniline (PANI), and the conductivity of the composite films can be controlled through adjusting the weight ratio of aniline monomer and PU latex.

Abstract: The nc-Ge/a-Si multilayer structures were fabricated by ion beam sputtering technique on silicon substrates at temperature of 400 °C. Raman scattering spectroscopy, atomic force microscopy (AFM) and room temperature photoluminescence were used to characterize the structure and optical property of the samples. It was found that the nc-Ge/a-Si multilayer sample can be obtained when the Ge sublayer is 3 nm. The room temperature photoluminescence was observed and the luminescent peak is located at 685 nm. Compared with the a-Ge/a-Si film, the intensity of PL of the nc-Ge/a-Si multilayer film becomes stronger due to the higher volume fraction of crystallized component.

Abstract: Oxide membranes are one kind of porous materials with many nano-sized pores. In our work, the two-step anodization method was used to fabricate Anodic aluminum oxide (AAO) membranes. The surface, cross-section micrographs and chemical composition were analyzed by field emission scanning electron microscopy (FESEM). From the FESEM micrographs, it can be easily seen that the self-ordered hexagonal pore channels were parallel and perpendicular to the surface of membrane when AAO membrane was prepared in oxalic acid at 0.2mol/L for 4h. In addition, the biggest pore diameter was 78nm, and the thickness ranged from a few microns to tens of microns in the suitable preparation parameters.

Abstract: The process of preparing magnesium hydroxide flame retardants with particular morphologies after hydrothermal treatment in the presence of organic modifier ethanediamine was mainly investigated. Influences of such factors as slurry concentration, modifier solution concentration and reaction temperature were studied. Meanwhile, the hydrothermally treated results were characterized by XRD, SEM, FTIR and TGA. The results indicate that when the reaction temperature was 180°C, and the reaction time ranges from 4 to 8 hours, the magnesium hydroxide and organic modifier solution concentration separately was 5% and 4 mol/L, a spherical crystalline magnesium hydroxide that has a symmetrical and regular crystal morphology was prepared. Such magnesium hydroxide materials were found to give an enhanced powder filtration.

Abstract: Considerable interest has recently been developed in processing bulk materials through the application of severe plastic deformation (SPD). High pressure torsion(HPT) is one of severe plastic deformation methods. By this method, the material grain size can be refined to 20~200nm, which are nanometer level, and the micro-hardness and mechanical properties of materials can be improved. So the nanometer material can be got through this method. In this paper, the results of the rigid-plastic finite element analysis of the plastic deformation behavior of bulk materials during the HPT processing are presented. The torque and strain patterns of the sample as well as the relationship between the slippage time and pressure are also investigated.

Abstract: The phase equilibrium of the LiCl-MgCl₂-Na₂­SiO₃-H₂O (LMNH) quaternary system at 150°C was studied and the phase diagram of the system was plotted, in order to synthesize hectorite with the nature brine, which was rich in lithium and magnesium. The solid phases were characterized by X-ray diffraction (XRD) and Energy Dispersive Spectrometer (EDS). It was found that hectorite, lithium silicate, karpinskite and brucite can be formed in this system.

Abstract: Carbon nanotubes, carbon spheres and slices of vertically aligned multiwalled carbon nanotubes (MWNTs) were synthesized simultaneously by chemical vapour deposition (CVD). Electron microscopy image showed carbon nanotubes were multiwalled carbon nanotubes, several micrometers in length. Carbon spheres were of uniform diameter (about 1 μm). Slices of vertically aligned multiwalled carbon nanotubes were about 5 mm in length, 3 mm in width and 8 μm in thickness. The interior of the slice was composed of densely packed, vertical aligned MWNTs, and faceted carbon beads. They were stable and easily separated from each other. The formation mechanism of slice was also discussed.

Abstract: A simple and novel method to synthesize metallic ion doped titania was investigated. In this work, undoped titania, stannum/titania, vanadium/titania and strontium/titania nanofibers have been fabricated by a sol-gel method with electrospinning techniques. The as-prepared composite nanofibers were incinerated at 500 °C respectively. The nanofibers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV-vis diffuse reflectance (DR) spectroscopy. The results suggest that crystal structures of stannum/titania, vanadium/titania and strontium/titania composite nanofibers were changed due to different material ion disturbing.

Abstract: We report the synthesis and characterization of a low-cost high-quality CdS quantum dots (QDs).The synthesis was performed in aqueous system. The aqueous CdS colloidal solution was prepared using thioglycollic acid as a capping agent. Zetasizer Nano ZS (Malvern, UK) was employed to characterize the partical size of CdS QDs. The UV-vis and photoluminescence (PL) spectra of samples were systematically characterized (the full width at half maximum was 38 nm). The maximum photoluminescence (PL) quantum yield (QY) was as high as 68.5 %. The fluorescence intensity was enhanced by copper (II). The relative fluorescence intensity was linear to copper (II) concentration over the range 4.0 ×10^-6 - 2.8×10^-5 g mL^-1. The regression equation was ΔI_F= 59.07+ 90.57c (c / μg mL^-1). The highly monodispersed CdS QDs could be used in many fields.