Advanced Materials Research Vols. 941-944

Abstract: Multiscale simulations using the quasicontinuum (QC) method with the embedded-atom method (EAM) potential are performed to investigate the process of nanocontact including sliding and subsequent withdrawal between Ni tip and Au substrate. The multiscale model reveals that deformation twinning in Au substrate is induced not only by the sheer stress but also by the adhesive stress. Combining with the generalized planar fault energy (GPF) curve of Au, the underlying formation mechanism of deformation twinning is studied in detail. During the withdrawal process, the dislocation degeneration and the vacancy evolution are observed.

Abstract: Hollow nanofiber In₂O₃ is synthesized by electrospinning. The as-synthesized materials are characterized by scanning electron microscope (SEM) and X-ray power diffraction (XRD). The formaldehyde sensing properties of the devices using In₂O₃ films are investigated at different operating temperatures. The results reveal that the response of hollow nanofiber In₂O₃ sensor is about 2.5 to 1 ppm formaldehyde at the optimum operating temperature of 270°C. The response and recovery time is about 3 s and 19 s, respectively. Moreover, sensor possesses a good selectivity to some common gas.

Abstract: The polarization dependent nonlinear absorption was observed in ordered Au nanowire array. The linear and nonlinear polarized absorption at 780 nm is investigated by Z-scan. When the angle between the polarization direction of input laser and the long axis of Au nanowires is 90°(perpendicular), the linear absorption reaches the maximum and the nonlinear absorption reaches the minimum. The nonlinear absorption coefficient β decreases from positive to negative as the angle increase from 0° to 90°. There may be two nonlinear absorption mechanisms resulting in this phenomenon: two-photon absorption and saturable absorption in nanoscale.

Abstract: Different surfactants such as Triethanolamine, Sodium dodecyl sulfate (SDS), and Polyvinylpyrrolidone (PVP) are applied in surface modification of nanoTiO₂. The dispersion of nanopowder processed with different surfactants in water is evaluated using settlement method, in order to make more even composite films. The result shows that dispersion effect will be better when Triethanolamine is combined with the other two types of surfactants than only single type of surfactant is used. The best surfactant for dispersing nanoTiO₂ is the mixture of Triethanolamine and Sodium dodecyl sulfate with mass ratio of 2:1 and 30% of surfactant amount; the experiment condition is set as both stirring and ultrasound times are 15 minutes, the initial settlement time of nanoTiO₂ is set as 2.5 hours, and the total settlement time is set as more than 120 hours.

Abstract: The graphene/Polyacrylonitrile (PAN) composites have drawn increased attention due to their significant improvements in mechanical and physical properties. A post treatment, enhancing the mechanical properties of the electrospun graphene/PAN fibrous yarns, was investigated in this study. The yarns obtained by this post treatment showed increased average strength and decreased elongation, which demonstrated that the as-reported method was an effective way to prepare higher performance electrospun graphene/PAN yarns. The method has potential application in preparation of micro ropes and self-assembled 3D electrospun fibrous yarns. Moreover, it is an innovation to apply dyeing during the investigation of the electrospun fibers under tension condition to analyze the tensile mechanism of yarns. The annular cracks were observed, which was recognized as the immediate cause for the yarns lengthening. Furthermore, according to its growth and fracture, the tensile mechanism of electrospun fibrous yarns was revealed.

Abstract: Ordered magnetic Fe_xCo_1-x alloy nanowires were synthesized in a porous alumina template by electrodeposition. The structural and magnetic properties of the as-deposited nanowires were investigated by SEM, TEM, XRD, EDS and VSM, respectively. The influence of the complexing agent on the stoichiometric properties is discussed, and the results indicate that the modulation of buffer and complexing agent has great influence on the electrodeposition process.

Abstract: The sedimentation bulk density and rheology of tertiary-butyl alcohol (TBA)-based hydroxyapatite/calcium phosphate glass ceramic suspension system have been examined in terms of oxide solid loading (10, 15 vol.%), and types of additives (dispersant, dispersant/gelator, dispersant/gelator/surfactant), and calcium phosphate glass ceramic content. Sedimentation density of hydroxyapatite decreased by adding calcium phosphate glass ceramic mainly due to the coarse and hence low surface area of calcium phosphate glass ceramic powder; the decrease effect was nearly offset when the dispersant was added. The suspension viscosity generally behaved in an opposite manner to the sedimentation density. A shear thinning rheology was shown in applied shear rate, regardless of processing variables.

Abstract: Nd₂Ti₂SiO₉ ceramics with low-firing temperature by BaCu (B₂O₅) addition were prepared by the conventional solid-state reaction route and the sintering behavior, phase purity, microstructure and microwave dielectric properties were investigated. The XRD analysis results show a single phase Nd₂Ti₂SiO₉ is formed and no secondary phase is found. Addition of BaCu (B₂O₅) can effectively lower the firing temperature by about 150 °C. The Nd₂Ti₂SiO₉ ceramics with 4wt% BaCu (B₂O₅) sintered at 1150 °C exhibit good microwave dielectric properties with a permittivity of 28.8, a Q×f value of 16110 GHz, and a temperature coefficient of resonant frequency of-12.3 ppm /°C, which is suitable for microwave communication applications.

Abstract: The effects of Cr₂O₃ additions on the mechanical and electrical properties of alumina ceramics were investigated. The phase composition, organizational structure of ceramics were analyzed and observed using XRD and SEM. The results show that doping with small amount (<7wt.%) of Cr₂O₃ can improve the mechanical (15% for bending strength, 83% for Vickers hardness) and electrical properties (minimum resistivity 9.8 × 10¹²Ω·cm), but when doping amount above 7wt.% , these properties were decreased.

Abstract: CaCu_{(3+ x)}Ti₄O₁₂ (x = 0, 0.001, 0.002, 0.004 and 0.008) ceramics with variation in copper micro-scale excess were prepared via solid-state reaction, Aqueous technology of tape casting was applied to obtain thick films of, about 100 μm in thickness. Crystal phases of the samples were identified by XRD. SEM of samples revealed that copper micro-scale excess can accelerate some important solid phase reactions in the sintering process, most because of liquid phase sintering mechanism. EDX analysis indicated that copper micro-scale excess could compensate for a lack of copper in sintering process. The Cu_3.004 sample exhibited the best dielectric properties with a very low dielectric loss (0.029), while retaining a very high dielectric constant (91,536), and the Cu_3.002 and Cu_3.004 samples exhibited a well frequency and temperature stability which was of significant industrial relevance. In this work, it was concluded that a certain amount of Cu micro-scale excess could improve dielectric properties, frequency stability and temperature stability of CCTO ceramics.