Advanced Materials Research Vols. 535-537

Abstract: Zinc substituted cobalt ferrite nanopowders with the general formula Co(1-x)ZnxFe2O4(with x = 0, 0.3, 0.5, 0.7, and 1) were prepared via the sol-gel route using citric acid as a chelating agent. The influence of zinc concentration on the microstructure, crystal structure and antibacterial property of zinc substituted cobalt ferrite nanopowders has been systematically investigated. The microstructure and elemental composition were characterized using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), respectively. Phase analysis of cobalt ferrite nanopowders was performed using X-ray diffractometry (XRD). The antibacterial properties of zinc substituted cobalt ferrite nanopowders were investigated. The results indicate that the substitution of zinc influences strongly the microstructure, crystal structure and antibacterial property of the cobalt ferrite nanopowders.

Abstract: Fragrance and flavor are valuable ingredients in toiletries, cosmetics and foods. They play a very important role in these products. However, fragrances and flavors are complex mixtures of comparatively volatile substances and labile components of which the sensory perception can be changed as a result of heating, oxidation, chemical interactions or volatilization. Microencapsulation technology is an effective method to minimize the harm of these problems. Encapsulation of fragrances or flavors has been attempted using various methods. In this paper, the chemical and engineering processes for encapsulation of fragrance and flavor are discussed. The different coating materials and their application are depicted.

Abstract: Different aspect ratio (length/width) gold nanorods were prepared in aqueous solution by seeding growth method. Aspect ratio of the nanorods was controlled accurately by changing the silver ions concentration. Ultraviolet-visible (UV-vis) spectra demonstrate the regularation that longitudinal plasmon resonance absorption wavelength of gold nanorods reveal red shift with the increase of aspect ratio. Gold nanorods were wrapped with Ag shells by chemical reduction silver ions on its surface. Different from gold nanorods, the transverse modes of the Au@Ag core-shell nanorods have two bands which contributed from the Ag and Au, respectively. On the other hand, centers of longitudinal surface plasmon of the core-shell nanorods exhibit blue shift with the Ag shell thickness increasing.

Abstract: Micro-components were electroplated using composite electroforming technology under magnetic field. The surface morphology of the micro components was examined using scanning electron microscope (SEM) and X-ray spectrometer was used to detect texture. The results show that: the texture and surface morphology of the micro components are influenced by the current density and the magnetic field intensity. With the increase of current density, the size of crystal grains decrease firstly but increase later .And as the increase of the magnetic field intensity, the size of crystal grains become smaller and more uniform. Besides, the current density and the magnetic field intensity have a great impact on the texture of castings. As the increase of the current density, the texture orientation changes from (111) to (200). At the same time, along with the increase of the magnetic field intensity, the diffraction peak (200) is suppressed while the diffraction peak (111) is enhanced obviously.

Abstract: A DNA/AuNP (gold nanoparticle) detecting nano-device has been constructed using DNA displacement (three-way branch migration).Here, DNA/AuNP conjugations and DNA circle are utilized as basic parts in nano-system, while sensitive fluorescent signals are applied as output results. Because of the accurate molecular recognition and effective strand displacements, this detecting system is able to yield correct results after receiving specific input DNA signals. In this work, the results are detected at three levels: PAGE gel bands, fluorescent signals and TEM images. Especially, in TEM images, positions of AuNPs are detected as an alternative approach to obtain output results. Combing these multiple detecting methods together, advantages of this DNA/AuNP system could be taken used entirely. It is believed that DNA/AuNPs conjugations nano-device will be applied widely in molecular detecting fields.

Abstract: Thermogravimetric curves of micro nanometer iron powder’s combustion were studied in different heating rates that were 10K/min, 20 K/min, 30 K/min and 40 K/min, and the particle sizes of iron were 100nm and 20μm. The iron’s kinetic parameters of combustion reaction were calculated by Coats-Redfern integral, differential and Kissinger methods, then the kinetic model was determined and the most probable mechanism function was verified by Popescu method. The results show that different heating rates, particle sizes and calculations can affect kinetic parameters and reaction mechanism. The activation energy of 100nm and 20μm iron powder’s combustion is 122.48 KJ/mol and 161.64 KJ/mol respectively. The combustion reaction of micro nanometer iron powder is controlled by random nucleation and subsequent growth model which is in agreement with Avrami-Erofeev equation. Rational control for the temperature and reaction time are conducive to optimize the combustion reaction of micro nanometer iron powder.

Abstract: The field emission properties of single-wall carbon nanotubes with purity higher than 70%,which were produced by dc arc discharge evaporation of a carbon electrode including 1% Fe catalyst in H2-Ar mixture gas was studied.The single-wall carbon nanotubes that were produced by this method possess high a ‘clean’ surface since the coexisting Fe catalyst nanoparticles can be completely eliminated by a two-step purification process.The field emission properties was verified by measuring the emission current density(J) versus the applied electric field(E), the corresponding Fowler-Nordheim(F-N) plot for the sample.Through looking at the emission photos, the uniformity of field emission is found to be excellent.

Abstract: BaMoO₄ nanocrystallites were synthesized successfully using Sol-gel process with (NH₄)₆Mo₇O₂₄•4H₂O, BaCl₂•2H₂O, citric acid and PEG400 as original materials. The result shows that well-crystallized BaMoO₄ nanoparticles were formed at 600°C with size of ca.50nm. The synthesized BaMoO₄ nanocrystallites were characterized by XRD and IR, and the optical property was studied as well.

Abstract: PVA nanofibers are generally required to be modified because of its poor stability in water. The water stability of PVA nanofibers was improved by heat treatment in this paper. The DSC test results showed that the crystallinity of heat-treated PVA nanofibers at 150°C for 10 min reached the maximum which increased by 12% compared with PVA nanofibers. From the SEM images it was observed that the heat-treated fibers didn’t dissolve in water but showed certain degree of agglutination and swelling. PVA nanofibers were taken as the inner layer of the sandwich structure purification material prepared with the hot pressing technology. The filtering experiments showed that the filtration properties were better when the area density of PVA nanofibers was 2.5 g/m2.

Abstract: β-SiC nanoparticles have been synthesized by electric pulses discharge (EPD) in Hexamethyl disilane. Dependence of photoluminescence (PL) from the samples with air-annealing are presented. Emission bands around 400 nm and 470 nm are observed at room temperature. The corresponding PL properties and possible mechanisms are discussed. The 400 nm peak may be result from the atom excess defect center at the surfaces of β-SiC nanocrystallites, while the 470 nm peak is believed to be related to the defects created in the interface boundary between β-SiC nanocrystallites and amorphous SiO₂.