Advanced Materials Research Vols. 197-198

Abstract: Carbon foams were prepared by a polymer sponge replication process and their microwave absorbing properties were investigated. The electric conductivity of carbon foam has a direct effect on its microwave absorbing property, as the carbon foam with a medium electric conductivity of 0.46S/m has got a relatively excellent microwave absorbing property and demonstrated a characteristic of broadband absorption. Some structure modification has been made on carbon foams to fruther imrove their microwave absorbing performance. The result shows that making slots, especially gradient slots on the surface of carbon foams can greatly improve their microwave absorbing properties, while the reflection coefficients for a three-layered carbon foam structure exceeds -10dB with the combination effect of multilayer structure design and parameters gradient variatioin in the whole frequency range of 2.6-18GHz, which is usually to be considered as the practical application standard for microwave absorbing materials.

Abstract: Magnetorheological fluid (MRF) is a new kind of smart material, it is very necessary for us to study its tribological properties because it will be widely used in engineering application. In this paper, the tribological behavior of Carbonyl Iron-based magnetorheological fluid (MRF) was investigated on a four-ball tribological tester, the influence of lubricant on friction coefficient and wear scar diameter was discussed, the morphology of the wear steel surfaces lubricated with MRF were observed by a scanning electron microscope. The results show that the addition of MoS₂ can significantly improve the tribological properties of clay-based MRF. However, the friction and wear properties of silica-based MRF become bad after the addition of MoS₂. The morphology of worn surface lubricated with the MRF added MoS₂ is similar to that without additive, but the groove of wear marks lubricated with clay-based MRF is more shallower and the area of the worn surface is smaller in the condition of adding MoS₂.

Abstract: Studied the ABAC pattern quasiperiodic phononic crystal properties by transfer matrix method, The results show that the frequency of ABAC pattern quasiperiodic phononic crystal initial band gap is lower than AB and AC pattern and the band gap is wider, simultaneously produce strongly localized resonant modes in the first band gap, frequency and quantity of the localized resonant modes are different with different parameters of material C. These properties are useful to the fabrication of the acoustic or elastic wave filters.

Abstract: Ba₄Sm_9.33Ti₁₈O₅₄ (BST) ceramics were prepared by conventional solid-state reaction method. The effect of CuO-Bi₂O₃ co-doping on the sintering behavior and microwave dielectric properties of BST ceramics has been investigated. The results indicated that when the total addition of CuO-Bi₂O₃ doping agent was 1.0wt%, the sintering temperature of BST ceramics was reduced to 1240°C as a result of liquid-phase sintering effect derived from CuBi₂O₄. When the total addition of CuO-Bi₂O₃ was fixed at 1.0wt%, the microwave dielelctric properties of BST were improved by adjusting the mass percentage of Bi₂O₃. With the increase of Bi₂O₃ amount from 20wt% to 80wt%, the dielectric constant (ε_r) decreased, the quality factor (Q•f) increased and the temperature coefficient of resonant frequency (τ_f) shifted from negative value to positive value. The excellent microwave dielectric properties of ε_r=82.51, Q•f=7878GHz and τ_f=+6.02ppm/ were obtained for the sample with Bi₂O₃ amount of 80wt% when sintered at 1240°C for 3h.

Abstract: A more exact general analytical formula of preditcting the magnetostrictive coefficient is derived for any aspect ratio based the deflection difference between the x and y directions. The curvatures are found by minimizing the total energy of the system, which taking into account shear strain energy. The in-plane stress distribution including shear stress for short specimen is also given by the ANSYS® finite element package to illustrate the role of shear strain in the deformation of magnetostrictive film-substrate system.

Abstract: Up-conversion luminescent materials of Y₂O₂S: Yb, Tm with different doping concentrations of Tm³⁺ ion (0.5 mol%–4 mol %) and Yb³⁺ ion (4 mol%–16 mol %) were prepared by flux method. As Tm³⁺ doping concentration was 1 mol% and Yb³⁺ doping concentration was 8 mol%, the blue and red up-conversion luminescent intensity reached the maximum. The concentration quenching of Tm³⁺ was due to the reducing of the distance between Tm³⁺ ions and the cross-relaxation increasing. The concentration quenching of Yb³⁺ was attributed to increasing of nonradiative transition. The blue emission intensity of ¹G₄→³H₆ was always weaker than the red emission intensity of ³F₃→³H₆, and the blue emission intensity of ¹G₄→³H₆ is similar with the red emission intensity of ¹G₄→³F₄.

Abstract: Chitosan-g-MA was prepared with methyl acrylate using ceric ammonium nitrate (CAN) as an initiator under nitrogen atmosphere in aqueous solution and characterized by FTIR spectroscopy. The effects of concentration of CAN, the amount of MA, reaction temperature on graft copolymerization were studied by determining the grafting percentage and grafting efficiency. The maximum grafting percentage and grafting efficiency obtained under these conditions were 640 % and 68 %, respectively.

Abstract: We have performed ab-initio total energy calculations using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT) to study structural parameters, electronic structure, chemical bonding and optical properties of orthorhombic Li₂BeSiO₄. The calculated lattice parameters are in agreement with experimental data. The band structure shows a direct band gap. From the DOS analysis, charge densities and population analysis, electronic and chemical bonding properties have been studied. Furthermore, in order to understand the mechanism of optical transitions of orthorhombic Li₂BeSiO₄, the complex dielectric functions are calculated and analysed.

Abstract: CNTs was opened and surface modified by K₂Cr₂O₇ and HNO₃. The ratio of CNTs weight loss was used to show the effect of oxidation and the morphologies of CNTs was observed by TEM and IR. The results showed that the concentration of K₂Cr₂O₇, oxidation temperature and oxidation time all affected the oxidation results. Among these three factors, oxidation temperature produced the largest effect; As the CNTs was oxidized, the wall of CNTs was corroded firstly and made the wall of CNTs thinner, then the curved-site of CNTs was attacked by oxidant and made the CNTs break in several section. So the solution would enter into the cavity of CNTs. Hydrophilic groups would be introduced in the inner and outer surface of CNTs with the oxidation reaction continuing. It would be good to the compatibility of CNTs with other materials.

Abstract: Polypyrrole (Ppy)-coated viscose fibers have been prepared by vapor phase and liquid phase pyrrole deposition technique, respectively. Comparative morphological and electrical property analysis was carried out on the viscose fiber prepared with both vapor and liquid phase processes. The result showed the configuration of Ppy coatings and electrical property had a strong relation with the deposition technique. Ppy-coated viscose fiber prepared by vapor phase show a high uniform polypyrrole coatings, fine Ppy granular structure, lower electrical resistance, and good fastness performances to abrasion.