Advanced Materials Research Vol. 1035

Abstract: Due to many sensing properties, magnetic fluid is used in a novel application--sensor. The measuring circuit is an important part for a sensor. Designing and calculation of the measuring circuit for pressure difference sensor with magnetic fluid were done. The power frequency and the input voltage are the two important factors for the measuring circuit. By experiments and calculations, the power frequency range is 20-70kHz and the input voltage for the circuit is 8V. The measuring circuit for inductive sensors was selected and calculated by analyzing measuring circuit for sensor.

Abstract: In this paper, Pine needles (PNs) were used to synthesize porous activated carbon by the carbonization and activation processes. The material for PNs were carbonized at 600 °C and activated at 800 °C(denoted as AC-800) show typical amorphous character, and display porous structures with high specific surface areas 2729 m²/g via XRD and BET measurements. As the electro-active material, AC-800 electrode exhibit ideal capacitive behaviors in aqueous electrolytes, and the maximal specific capacitance is as high as 286 F/g at the current density of 1 A/g. Furthermore, AC-800 electrode shows excellent electrochemical cycle stability with ~94 % initial capacitance being retained after 2000 cycles. The desirable capacitive performances enable the PNs to act as a new biomass source of carbonaceous materials for high performance supercapacitors and low-cost electrical energy storage devices.

Abstract: This study utilizes accurate first principle method to conduct a comparative study on he electronic structure of multiple borides. State density of the borides is also summarized. It is found that lanthanum boride has special electronic structure characteristics. Therefore, it is presumed that there is high superconducting transition temperature (Tc) in lanthanum boride. This study is able to provide asignificant theoretical reference for further experimental research.

Abstract: Arcjet plasma enhanced CVD was used to grow diamond. Nucleation of diamond was studied at the early stage of growth cause. The micro-structural probes (transmission electron microscope (TEM), high resolution electronic microscope (HREM), selected area diffraction (SAD) and electron energy loss spectra (EELS) were used to characterize the nuclei. It was found that nuclei formed following the amorphous carbon formation. The critical nucleus size was deduced to be less than 20 nm. The growth of nucleus would form the network-like structure. The incubation period of nucleation was deduced as 6–8min under the condition of high concentration of CH₄ in H₂.

Abstract: A portable tester for accessing the electrical properties of human skin surface is reported. A pair of interdigital electrodes (IDE) that contact directly with the human skin, is used as the sensing element. The impedance of the sensing system is modeled as a resistance and a capacitance in series. A square wave signal is applied so that impedance of the IDE is measured in a charging/discharging way. The response voltages of the IDE at two excitation frequencies, 10 kHz and 600 Hz, are measured successively during one measurement cycle. Since the equivalent capacitance of skin performs different frequency-dependent property other than the resistance, their values can be resolved from the measured response voltages. A microprocessor-based system is implemented as a prototype battery-powered portable unit for household measurements. Good repeatability and satisfied accuracy have been obtained by experimental results.

Abstract: In order to investigate the electrical conductivity of carbon nanotubes (CNTs)/polyethylene (PE) composites, the relationship curves between the external electrical filed strength and the electrical conductivity of CNTs/PE composites with different microstructures were generated based on numerical simulation. The simulation models of CNTs/PE composites were designed through changing the content, aspect ratio and orientation degree of CNTs. After DC electrical field is applied between top and bottom surfaces of the composites, the distribution of electrical current density was calculated based on the finite element method by using the COMSOL simulating software, and then the electrical conductivity is obtained. Research results indicated the electrical conductivity of the composites increases significantly with the increase of aspect ratio of CNTs at the same CNT content and electrical field strength. As the orientation degree of CNTs along the applied electrical field increases, the electrical conductivity of the composites obviously increases. It can therefore be concluded that the changing of microstructures of CNTs/PE composites is effective to control the electrical conductivity of the composites.

Abstract: Current research efforts toward achieving ceramic/polymer composites which fulfill the balance between sufficiently high dielectric constant (ε) and low dielectric loss (tanδ) are presented. In this paper, ceramic/polymer composite films made of CaCu₃Ti₄O₁₂ (CCTO) powder as filler, which is modified by silane coupling agent vinyltrimethoxysilane (A-171), and polyvinylidene fluoride (PVDF) copolymer as matrix were prepared by solution casting method. The morphology and dielectric properties (DP) were studied by transmission electron microscopy (TEM) and impedance analyzer. The effect of pH and ethanol concentration on the dielectric properties of A-171@CCTO/PVDF were studied. The results show that constant could reach 54.17 and loss 0.05 when mass fraction of A-171 is 0.4% at 1 kHz. pH=4 and using anhydrous ethanol are the optimal conditions.

Abstract: nanoand micro size Cu were employed separately and investigated comparatively. Different volume fraction of Cu was added into PVDF film in order to investigate the content of filler effect on the dielectric properties of polymer composites. XRD and SEM were used to analyze the crystalline phase and microstructure of the films. The results show that two sizes of Cu have the same peak features, and with the continuous increase of the content of Cu, it disperse better in PVDF. The dielectric constant (ε) of the composite containing 16 vol% micro-CCTO filler is 16 at 100 Hz and room temperature, and its dielectric loss (tanδ) is only 0.15, which is substantially better than others. Besides, for 18 vol% nanoCu/PVDF composite tanδ is 0.25 and ε is 18 at 100 Hz. Moreover, ε and tanδ of nanoCu/PVDF composite are both higher than those of micro-Cu/PVDF. Analysis shows that the composites with nanoCu have higher dielectric constants, which is mainly from the interfacial polarization.

Abstract: The Bi_0.5(Na_1-xK_x)_0.5-yBaTiO₃ (BNK-BT) lead-free ceramics have been prepared by the solild reactive sintering method. XRD patterns show the BNK-BT ceramics had a perovskite structure. Piezoelectric and dielectric properties of the ceramics also have been studied. The results show that the samples had the best piezoelectric and dielectric properties when x=0.20, y=0.10. And the maximum of d₃₃ is 149 pC/N, while the relative dielectric constant is 1087.

Abstract: A femtosecond laser pulse duration is shorter than many physical/chemical characteristic times, which makes it possible to control electron dynamics such as ionizations and electron densities. This study expermetally investigtes the effects of laser fluence on sub-wavelength periodic surface structuring based on ultrafast laser electron dynamics control. A quantum model for the sub-wavelength periodic surface structuring is also proposed, which considers both the wave properties in the photon particle-properties based plasma model for photon-electron interactions and transient localized changes of material properties. It shows that the laser fluence strongly affects the ablation crater shapes. The prediction of ablation crater shape and periodicity is in agreement with experimental data.