Materials Science Forum Vols. 675-677

Abstract: This paper proposes a new smart sensor for the detection of damage in structures using mechanoluminescence (ML) material SrAl2O4:Eu (SAOE). SAOE is a kind of functional ceramics that can emit visual light when it is subjected to external mechanical action. The luminescence of SAOE is very high so that it enables us to view the visual light with naked eye. A smart film sensor is fabricated using SAOE powder and polymer. The effect of load frequency on the emitted visual light is investigated under cyclic loading conditions. Furthermore, detection of a crack and evaluation of the stress concentration and stress intensity factors are performed using SAOE film sensor. Experimental results demonstrate that the visual light emitted by SAOE film sensor has good correlation with the equivalent strain and stress.

Abstract: The band structures of flexural waves in a ternary locally resonant phononic crystal thin plate are studied using the improved plane wave expansion method. And the thin concrete plate composed of a square array of steel cylinders hemmed around by rubber is considered here. Absolute band gaps of flexural vibration with low frequency are shown. The calculation results show that the band gap width is strongly dependent on the filling fraction, the radius ratio, the mass density and the Young’s modulus contrasts between the core and the coating. So by changing these physical parameters, the required band gap could be obtained.

Abstract: A novel synthesis route for the production of Sr3MgSi2O8:Eu2+,Dy3+ sub-micron quasisphere phosphor powder is reported. Both the host and activator cations were co-precipitated in water-ethanol mixed solutions and precipitation was performed with analytical grade ammonium citratetribasic. As the dispersion media, optimum concentration for PEG in the precursor solution is determined to be 0.08 g/mL. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and fluorescence spectrophotometer were employed to characterize the phosphor. The effect of the calcining temperature on the crystalline particle and luminescence properties of Sr3MgSi2O8:Eu2+,Dy3+ is systematically discussed. Sr3MgSi2O8:Eu2+,Dy3+ single phased quasi-sphere phosphor was achieved by calcining the asprecipitated precursor at 1100°C. Sr2SiO4 was identified as the intermediate phase during the calcination process. Despite the small particle size, the emission intensities were higher by the present method. However, the afterglow characteristic was not better than that prepared by solidstate reaction in the comparable condition.

Abstract: The novelty of the current work lies in the simple synthesis of a new class of monodisperse, luminescent silica spheres produced upon calcination of hybrid amine-functionalized silica spheres which can known the role of ethylenediamine (en) on the morphology and luminescence properties of the resultant silica spheres.

Abstract: A novel spindle-like zinc oxide (ZnO) nanocrystalline thin film was successfully fabricated on Ni thin film layer by ultrahigh-vacuum dc magnetron sputtering. Then the as-grown films were annealed in air at various temperatures from 673 to 1073 K, the corresponding structural features and surface morphology were studied by X-ray diffraction (XRD) and field emission scanning electronic microscopy (FE-SEM). The results reveal that the dominant direction of grains movement changed from perpendicular to parallel to the film interfaces. A correlation of the band gap and photoluminescence (PL) properties of nanocrystalline ZnO films with particle size morphologies and strain was discussed. Especially, PL emission in UV range, which is due to near band edge emission is more intense in comparison with the green band emission (due to defect state) was observed in all samples, indicating a good optical quality of the deposited films.

Abstract: A series of La0.67Sr0.33MnO3/Ag composites were synthesized using a sol-gel method followed by a conventional solid-state reaction route. The temperature dependence of the magnetic properties and electrical resistivity has been investigated between 80 and 450 K. Except for the sample with x = 0.01, Ag addition has increased the conductivity of this system dramatically. Curie temperature (TC) is almost independent of Ag content and is 352 K for Ag-dopant samples, while the metal–insulator transition temperature TP increases with Ag addition, which is mainly due to the improvement of grain boundaries and opening a new metal conductivity channel caused by the segregation of Ag on the grain surfaces. At low temperature, the ρ - T curves are fitted well by the expression of ρ= ρ0 + ρ2T2 + ρ4.5T4.5 while all data for the above TC can be fitted by using the adiabatic small-polaron-hopping model ρ = ρ0T exp(E/kBT ).

Abstract: The magnetic and electrical properties of La0.67Sr0.33MnO3 ( LSMO ) are influenced very much by the Nb dopant. However, this doping effect is restricted by the limited Nb solution into LSMO due to the low calcined temperature. As a result, a second phase LaNbO4 appears in our samples. Enhancements of the low-field magnetoresistance (LFMR) were observed both at 77 K and room temperature in the manganite system prepared by doping Nb2O5 into LSMO powders. The doping amount x of Nb ions ranges from 0-10 % molar ratio. The MR ratios at 77 K with H = 1 T and H = 0.1 T are 33.8 % and 24 % for the x = 0.07 doped sample, respectively. A MR effect up to 9 % was also found for the sample with x = 0.05 at room temperature, which is 2.2 times as large as that for LSMO (4.1%). The spin dependent tunneling and scattering at the interfaces of the grain boundaries are responsible for the LFMR while the high field magnetoresistance (HFMR) originates from the spin dependent transport related to noncollinear spin structure at the interfaces.

Abstract: Microcapsules with triallylamine-containing core surrounded by polyelectrolyte shell of controlled thickness were prepared via layer-bylayer assembly technology. First, isocyanate end-capped polyurethane was synthesized through the reaction of isophorone diisocyanate and poly(1,4- butylene adipate). Then, polyurea microcapsules containing triallylamine were prepared by the interfacial polymerization with branched polyethylenimine (PEI) as the water-phase macro-monomer and the prepared isocyanate end-capped polyurethane as the oil-phase macromonomer. Finally, stable weak polyelectrolyte microcapsules were prepared by assembly of poly(acrylic acid)(PAA) and branehed PEI to build up polyelectrolyte multi-layers, and this was followed by glutaraldehyde mediated cross-linking to further increase the mechanical strength of the final capsules. Results showed that the obtained microcapsules were narrowly distributed in size and the mean diameter could be adjusted. This kind of capsule might be used to construct pressure-sensitive materials.

Abstract: Recently, there has been a growing importance of development of ‘athermal glass’ having no temperature dependence in its optical path length and is expected to be used in optical devices for the optical fibre transmission system. The athermal characteristic is usually evaluated by temperature dependence of optical path length, (1/l)･(dS/dT) ( l : geometrical length, S : optical path length, T : temperature), which is the summation of nα and dn/dT (n: refractive index, α: linear coefficient of thermal expansion). In the present work, the refractive index and liner coefficient of thermal expansion have been determined for silicate glasses containing titanium oxides in the temperature range from room temperature to about 673 K, using ellipsometry and utilizing the sessile drop method. The values of nα and temperature coefficient of n ranged from 1.289×10-5 K-1 to 3.345×10-5 K-1 and from 0.270×10-5 K-1 to 1.467×10-5 K-1, respectively, depending on the glass composition. Consequently, only 80SiO2-5TiO2-15Na2O glass has shown almost the same degree of athermal characteristic as SiO2 glass, having more advantages in practice due to its lower melting temperature than SiO2.

Abstract: To achieve a satisfied conductivity of nano-size silver printed circuit, post deal with nano-size silver conductive film was investigated. Based on the preparation of nano-size conductive ink and conductive circuit, the coated conductive film was treated by series concentrations of hydrochloride solutions, and then scanned by laser beam. The influence of resolutions concentration and dipping time were investigated separately. Atomic force microscopy (AFM), fourier transform infrared (FTIR) and four-probe tester, were applied to characterize the different tested samples. It was found that when the coated silver conductive ink samples were dipped in 20% hydrochloride for 60min, 15°C before laser scanning, the conductivity reaches 0.3Ω/□. It is therefore considered that the “dip in” method provide an efficient alternative to improve the conductivity which from nano-size silver ink.