Advanced Materials Research Vol. 499

Abstract: The authors report an approach to the fabrication of a periodic magnetic array using photosensitive polyimide-barium ferrite nanocomposite. These patterns are shaped by a some-like imprint technique, under the interactions between the magnetic nanoparticles and permanent magnetic mold. Scanning electron microscopy has been used to characterize the magnetic array and well-defined structures with magnetic arrays are obtained. The diameter of each dot is as small as 52um. The presented concept leads to a realization of a magnetic array, which offers advances in achieving micrometer-scale patterns with a very low cost and simple process.

Abstract: The temperature-induced liquid-liquid structural transition has been observed and testified in different kinds of alloys. The effect of liquid-liquid transition on the morphology of solid/liquid interface was investigated by means of the unsteady-state unidirectional solidification. The results showed that the interface instability of Sn-1wt.%Pb was developed after the liquid structural change, which suggested that the solute distribution coefficient decreased due to the structural change of liquid Sn-1wt.%Pb and the solute on the frontier of solid/liquid interface enriched.

Abstract: Using three natural graphites with different particle sizes, 80, 50 and 35 mesh, as raw material, expanded graphite was prepared by rapidly heating expandable graphite in a muffle and by irradiating it in a microwave oven, respectively. The resulting expanded graphites were used for adsorbing methyl blue in water. The results show that the removal rate of methyl blue is influenced by the treatment method of solution, the particle size of natural graphite and expansion method of expandable graphite. After selection of desired operation parameters, a higher removal rate is achieved.

Abstract: Using three natural graphites with different particle sizes, 80, 50 and 35 mesh, as raw material, three expanded graphites were prepared by irradiating expandable graphite in a microwave oven. Results show that the particle size of natural graphite influences strongly the expansion ratio of expanded graphite, and the larger the particle size, the larger the expansion ratio. In addition, the expansion mechanism of expandable graphite is discussed.

Abstract: This paper aims to simulate the failure behaviour of composite laminates subjected to uniaxial loading using commercial software (ANSYS) and FE programme (Fortran). For the first time, the built-in failure criteria functions provided by ANSYS were explored extensively and successfully exploited to predict the failure curves of composite laminates. Finite element (FE) models are developed to replicate physical testing. A FE programme is developed using Fortan-90 to determine the lamina stresses based on High Order Shear Deformation Theory (HSDT). These stresses are then used to determine the strength of the plates using the Maximum Stress Failure Criteria. Then FE models are developed using ANSYS to replicate the procedure. Standard ANSYS formulation is utilised and laminate failure was predicted based on Maximum Stress and Tsai-Wu Failure Criteria. The failure curves for both approaches were plotted and found very close to the experiment results. The results show that the FE programme and ANSYS simulations produce an average error of 8% and 15% respectively. Nevertheless, simulations using ANSYS allows easier modification and manipulation. Therefore, it can be concluded the current study is useful and significant and contributes significant knowledge to the failure behaviour of composite laminate. Moreover, the simulations performed could eventually replace tedious and expensive physical testing.

Abstract: It has come to light that the Mg₂Ni-type alloy with a nanocrystalline/amorphous structure possesses superior hydrogen storage kinetics. The Mg₂Ni-type Mg₂₀Ni_10-xM_x (M=Cu, Co; x=0, 4) hydrogen storage alloys were synthesized by a melt-spinning technique. The microstructures of the as-cast and spun alloys were characterized by XRD, SEM and HRTEM. The gaseous and electrochemical hydrogen storage kinetics of the alloys was measured. The results show that whatever spinning rate the as-spun (M=Cu) alloys hold an entire nanocrystalline structure. As spinning rate approaches to 20 m/s, the as-spun (M=Co) alloys display a nanocrystalline and amorphous structure, confirming that the substitution of Co for Ni facilitates the glass formation in the Mg₂Ni-type alloy. Furthermore, such substitution results in the formation of secondary phases Mg₂Cu and MgCo₂ instead of changing the major phase of Mg₂Ni. The melt spinning markedly improves the gaseous and electrochemical hydrogen storage kinetics of the alloys. The hydrogen absorption ratio (R₅^a ), hydrogen desorption ratio (R₂₀^d ) and the high rate discharge ability (HRD) notably mount up with the growing of the spinning rate.

Abstract: In this study, influence of Bi₂O₃ on the structure and magnetic properties of barium ferrites has been studied in samples performed by using the solid-state reaction method. Samples, prepared with different amount of sintering additive are sintered at temperatures from 850°C to 950°C. The scanning electron microscope micrographs shows that the samples with 3wt% additive, calcinated at 900°C, have a particle size smaller than 1μm. Annealing treatment in air at 950°C led to an order-of-magnitude increase of the saturation magnetization of 60.42emu/g and coercive force of 4150.5Oe, which are due to the liquid phase sintering mechanism and the increasing grain size.

Abstract: Multi-walled carbon nanotubes (CNTs)/Al in-situ composite powders over Al as catalyst carrier had been synthesized successfully using transition metal Ni by chemical vapor deposition. CNTs were mainly characterized by transmission electron microscopy. It was found that reaction temperature had great influences on the structures of carbon products obtained. Detailed discussions according to the structures of CNTs at different reaction temperatures were given. A deduced model for explaining the growth mechanism of CNTs governed by temperature was developed.

Abstract: Changes of mechanical properties and chemical structure of polyester (PET) fibers are studied through UV simulated accelerated ageing experiments with N₂, air and O₃ as the atmosphere. The structure, thermal stabilities and tensile strength are obtained by FTIR, DTA-TG, XRD, SEM and micro-mechanics test. The difference of degradation process in various atmospheres is discussed in this paper. The results show that the fracture tensile strength of PET multifilament decreases with the increase of UV irradiation time. And oxidation and then decarbonylation take place on the surface. Besides, Melting temperature (T_m), the temperature of quality loss by 10% (T₁₀) and the crystallization also decrease. However, in O₃ atmosphere the oxidation develops very quickly and fully, therefore, the carbonyl on the surface is eliminated and decreases significantly, and the tensile strength decreases much faster than those in N₂ and air. The skin layer of irradiated fibers appears serious damaged. The mechanism of chemical degradation for samples irradiated in N₂ environments is similar to those irradiated in air.