Advanced Materials Research Vols. 284-286

Abstract: A carbonate precursor with high sintering activity was prepared by co-precipitation method under ultrasonic radiation. This precursor precipitant completely transformed to pure YAG phase after being calcined at 900 °C for 4 h. The properties of YAG nanopowders obtained under different synthetic process were studied by XRD, TG-DSC, FT-IR and SEM. The results show that the ultrasonic radiation can fine the precursor and reduce its agglomeration. YAG nanopowders with an average particle size of about 60 nm were obtained and particles were sphere-shaped with good dispersity.

Abstract: The natural carbon nanotubes(CNTs) have been found in the Sujiquan graphite ore deposit and the high resolution transmission electronic microscopy and the micro laser Raman Spectrum have been used to study their structure. The length of CNTs from n nm to 300nm and width vary between 0.n nm and 30 nm. The RBMs at 462cm^-1 in the first-order Raman spectrum of natural CNTs should originate from the inner diameters of 0.5nm. The obvious characteristic peak is at 1343.41 cm^-1and 1577.08 cm^-1 indicating high graphitization degree. The S1～S4 peaks also found in the second-order Raman spectra.

Abstract: The aim of the present paper is that, utilizing finite element method, considering the influence of different length of CNTs and different strength of interface to investigate the micro stress distribution of CNT reinforced magnesium matrix composite. When analyzing, the material character of magnesium is regarded as anisotropic. Utilizing the primary theory to calculate the anisotropic elasticity modulus; Define the reasonable length of CNTs; Considering the influence on the micro stress distribution of different interface strength.

Abstract: Dielectric constant is the most important material property which ground penetrating radar(GPR) data reflects. Based on experiment, through the determination of the compressive strength during concrete mixture ages and the real part and imaginary part of dielectric constant, the relationship between dielectric constant and the compressive strength of cement concrete material is studied. It is shown from the achievements that there has feasibility to non-destructively test the cement concrete material compressive strength by using GPR.

Abstract: One-dimensional Co_0.5Zn_0.5Fe₂O₄ nanostructures (nanofibers) with an average diameter of 154 nm were fabricated by electrospinning. These nanofibers were characterized by X–ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. Magnetic hysteresis loops were measured for randomly oriented and aligned Co_0.5Zn_0.5Fe₂O₄ nanofibers, in comparison with the corresponding powder sample synthesized using the conventional sol-gel process. The differences in magnetic properties are observed between the Co_0.5Zn_0.5Fe₂O₄ nanofibers and powders, and these differences mainly arise from the grain size and morphological variations between these two materials. In determining the magnetization ease axis for the aligned Co_0.5Zn_0.5Fe₂O₄ nanofibers the shape anisotropy is slightly dominant competing with the magnetocrystalline anisotropy.

Abstract: ZnO was prepared using zinc acetate dehydrate (Zn(CH₃COO)₂·2H₂O) and lithium hydroxide monohydrate (LiOH·H₂O) as raw material through a microwave-assisted sol-gel method. The prepared ZnO presents the wurtzite structure. The influence of different reaction temperature and heating time to the size of ZnO was researched. The photocatalytic activity of ZnO was evaluated by the degradation rate of C.I. Reactive Blue 4 in aqueous solution. The particle size of ZnO is about 4.33 nm at the reaction condition of 50°C for 10 min and the photocatalytic performance is the best. The degradation rate of C.I. Reactive Blue 4 could exceed 75% in 30 min at room temperature when the initial concentration of C.I. Reactive Blue 4 was 40 mg/L and the concentration of the quantum-sized ZnO was 0.1 g/L.

Abstract: A Monte Carlo method is employed to investigate the properties of electron transport with considerations of electron-phonon scattering including intervalley scattering and intravalley scattering. Under different electric fields, the coupling relations between electrons and phonons are studied, and the behaviors of absorbing and releasing phonons from electrons are also analyzed. The results show the scattering events of absorbing phonons from electrons decrease with the increasing simulation time. At the same temperature, the mean free path of electron increases initially and then decreases with the increasing electric field intensity, and finally approaches an asymptotic value.

Abstract: Ordered high surface area microporous carbon molecular sieves containing well-dispersed platinum nanoparticles have been prepared by chemical vapor deposition method. Acetonitrile was employed as carbon and nitrogen precursors to yield N-doped carbon molecular sieves. N-doped carbons have an average nitrogen content of ~ 4.1 wt%. Electrochemical tests showed that the rectangular-shaped CVs of N-doped carbons could be well retained over a wide range of scan rates (5~100 mV/s), and the CV curves presented a steep current change at the switching potentials. N-doped carbons exhibited excellent performance as an electrochemical supercapacitor with a calculated specific capacitance of 168 F/g. Meanwhile, it was noticed that a reasonable Pt loading would help to improve the capacitance. It was proposed that the polarizability or surface state modification by nitrogen doping and regular interconnected porous structure might contribute to the improvement of N-doped carbons’ electrochemical properties.

Abstract: Ultrafine ZnO powder was synthesized by precipitation method, using zinc sulfate and aqueous ammonium carbonate as raw material and precipitant, respectively. The influence of the concentration of aqueous ammonium carbonate on the precipitation rate of Zn²⁺ was discussed and their relationship was also illustrated. The precipitation rate of Zn²⁺ increased gradually with the mol ratio of CO₃^2-to Zn²⁺, which reached up to more than 96% when the mol ratio was 1.2. In addition, the crystal structure and morphology of the precursor and ZnO powder were also characterized using XRD and SEM. The results indicated that ZnO powder was hexagon wurtzite structure and spherical figure with high purity and regular crystal form.

Abstract: ZrAlN/Cu coating has been deposited onto Ti-6Al-4V substrates by reactive magnetron sputtering. The morphology of films was investigated by FESEM, the microstructure was studied by XRD, XPS and TEM. The plastic deformation characteristic of thin films were analysised from loading/unloading curves measured by nano-indentation method. Erosion tests were conducted to evaluate anti-erosion ability. Erosion rates were measured and characteristic damage features were identified on the surface of eroded specimens. The mechanisms of erosion are discussed in order to explain the promising performance of materials in erosive conditions. It was found that there is an significant increase of erosion resistance because of the increase of hardness and toughness.