Advanced Materials Research Vol. 979

Abstract: We presented the effect of annealing temperature on nanocrystallite growth toward zinc oxide (ZnO) nanorods based on the hydrothermal process. The hydrothermal growths of the ZnO nanorods were prepared with zinc nitrate hexahydrate and hexamethylenetetramine solution at 90°C for 6 hours. The structural, morphological, optical, and anti-bacterial properties of the ZnO nanorods, prepared at different annealing temperatures, were characterized by grazing-incidence X-ray diffraction (GIXRD), field-emission scanning electron microscopy (FE-SEM), and UV-Vis spectrophotometer. The GIXRD patterns of the ZnO nanorods corresponded to the wurtzite structure. The FE-SEM results showed that the prepared ZnO nanorods were in the form of the hexagonal shape. The anti-bacterial behaviors of suspension of ZnO nanorods against Escherichia coli (gram-negative) would be discussed in this paper.

Abstract: Magnetite (Fe₃O₄) nanoparticles were successfully synthesized by the sol-gel method from ferric nitrate-EG (EG=ethylene glycol) gel. The precursors were calcined in argon under an atmospheric pressure at the temperatures varied from 400°C to 500°C. The synthesized magnetic nanoparticles were characterized by X-ray diffractrometer (XRD), field emission scanning electron microscope (FE-SEM) and vibrating sample magnetometer (VSM). The XRD patterns of powder calcined temperature at 400^๐C showed clearer Fe₃O₄ phase than those calcined at other temperatures. The particle size and morphology of magnetic nanoparticles were studied using FE-SEM. The FE-SEM images showed that the particle sizes varied from 30-108 nm. The particle sizes increased with the increase of calcination temperature. VSM measurements indicated that the Fe₃O₄ nanoparticles were soft ferrite with the maximum magnetization (M_m) and coercivity (H_c) of 35 emu/g and 17 Oe, respectively.

Abstract: In the field of superconductivity the most interesting area is the studying of the mechanism of the high T_c superconductor (HTS). Understanding of this mechanism, we can raise the critical temperature (T_c). There are many proposals theoretical descriptions for HTS. We focus on the spin density wave (SDW) and charge density wave (CDW), the static wave of spin density and charge density arising from the nesting property of Fermi surface that were observed in the superconductor. The model Hamiltonian of superconductor having SDW and CDW coexistence was studied by Greens function method. The analytic expression of zero-temperature gap of superconductor with the coexistence of the SDW and CDW were derived. By varying the effective potential, the phase diagram of the SDW and CDW was constructed then the band structure and density of states (DOS) of coexistent phase were also studied.

Abstract: Silica with nanostructure are the high quality silica that are used in many industry areas. The applications of silica nanostructure frequently depend on physical properties such as morphology and size of structure. Rice husk ash is the waste from biomass power plants and is a high quality, raw material as a silica source. The conventional methods for synthesis of nanosilica from rice husk ash are energy consumption or time consumption. The objective of this work was to investigate the synthesized of nanosilica from rice husk ash via sodium silicate solution. nanosilica particles were obtained via alkaline extraction and a fast acid precipitation method at room temperature by adding inorganic salts and without surfactant or template. The flow synthesis was investigated at ambient temperature, varying the concentration of hydrochloric acid, sodium chloride, and flow-rate while fixing the concentration of sodium silicate. The samples were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results revealed that the sodium chloride is significantly inorganic salt for generated nanosilica, with uniform spherical morphology (80-150 nm), without curing or aging time. In the flow synthesis method, the silica nanoparticles, of diameter around 10 nm and aggregate particles of around 50 to 200 nm, were obtained. This method may be applicable to control different grade of silica and can easily scaling up of silica production for different industries.

Abstract: In this research, the Y123 (YBa₂Cu₃O_x) and Y134 (YBa₃Cu₄O_x) superconductors were synthesized by solid state reaction and melt process, respectively. The crystal structure of all the samples were then determined using the Rietveld full-profile analysis method to indicate orthorhombic structure. The resistivity measurements showing T_c onset of Y123 lower than Y134 for solid state reaction but higher than Y134 melt process. However, the critical temperature off-set of Y134 has lower than of Y123. The SEM and EDX show that all samples were inhomogeneous. The SEM micrograph for solid state reaction Y123 has many pores between the grain and the grain size clearly demonstrated and bigger than Y134. It was seen that these pores are party eliminated in melt process samples. FTIR spectra detected the trace of carbonate residue in all samples.

Abstract: In this research, we studied the surface critical magnetic field () of a layered magnetic superconductors by Ginzburg-Landau approach. After the 1^st Ginzburg-Landau equation was calculated, a surface critical field was solved by variational method analytically. Our formula obtained was depended on the magnetic property of superconductor. We found that H_c3 of antiferromagnetism and paramagnetism superconductors were shown the same behaviour as non-magnetic superconductors. For diamagnetism and ferromagnetism superconductors, the higher and the lower values of critical magnetic field were found, respectively. However, the H_c3 was strongly depended on the non-linear of magnetic field intend of all kind magnetism.

Abstract: In this research, we synthesized Y123 superconductor and Y235 superconductor doped with fluorine by solid sate reaction with Y₂O₃, BaCO₃, CuO and CuF₂ as precursor. The physical properties of Y235+F_x (Y₂Ba₃Cu₅O_y-xF_x) and Y123+F_x (YBa₂Cu₃O_y-xF_x) superconductors were studied at x = 0,0.1, 0.2. The calcinations process was done twice in air at 810 °C for 24 hr and was increased to 925 °C for one hour. The sintering process was done at 925 °C for 24 hr and reduced to 500 °C for 24 hr. Our samples obtained were characterization by the four point probe technique, SEM and EDX, respectively. The surface of all samples were inhomogeneous and no impurity. The critical temperature onset of Y123+F_x and Y235+F_x were equal to 92 K, 95 K, 93 K and 92 K, 93 K, 92 K with x= 0, 0.1, 0.2, respectively.

Abstract: In this research, the effects of ZnO nanoparticles additive on crystallization behavior, dielectric and ferroelectric properties of Bi_0.5(Na_0.81,K_0.19)_0.5TiO₃ ceramics were investigated. The samples were synthesized by solid state reaction technique, where powders were calcined at 850 °C for 4 h and ceramics were sintered at 1100-1150 °C for 4 h. Phase formation was determined by X-ray diffraction technique (XRD). The X-ray diffraction analysis of the ceramics suggests that all samples exhibited a perovskite structure. The dielectric properties under room temperature and various temperatures were also determined. Dielectric measurement data showed that the additive influenced dielectric constant and dielectric loss. Furthermore, the hysteresis loop behaviors slightly changed with increasing the nanoparticles contents.

Abstract: Glasses composition of xSrO:(70–x)B₂O₃:30SiO₂ when 25≤x≤50 mol% were prepared using the melt quenching technique and investigated the other properties of glasses. The density of the glasses was measured using Archimedes’ principle; the molar volume of the glasses has been derived from density measurements data. The hardness of glasses sample was measured by using the Vickers hardness. Mass attenuation coefficients have been determined experimentally for the glass system at photon energy 662 keV, the results compared with theoretical calculations from WinXCom computer software. The reported data should be useful for decision chosen of these glasses in radiation shielding.

Abstract: Tantalum oxide (Ta₂O₅) thin films were deposited as the protective layers for the metal surface finishing by the DC reactive magnetron sputtering system. The effect of the Ta₂O₅ film thickness, ranging from 25 nm to 200 nm, on the physical properties and the anti-corrosive performance were investigated. The grazing-incidence X-ray diffraction (GIXRD) and the atomic force microscopy (AFM) were used to examine the crystal structures and the surface topologies of the prepared films, respectively. The XRD results showed that the Ta₂O₅ thin films were all amorphous. The AFM micrographs demonstrated the film morphology with quite smooth surface features. The surface roughness tended to be rough when the film thickness was increased. To examine the protective performance of the films, the poteniostat and galvanometer was utilized to examine the electrochemical activities with the 1M NaCl as the corrosive electrolyte. The results from the I-V polarization curves (Tafel slope) indicated that, with the Ta₂O₅ thin film, the current density was significantly reduced by 3 orders of magnitude when compared with the blank sample. Such results were observed because of fully encapsulated surface of the samples were covered with the sputtered Ta₂O₅ thin films. The study also showed that the Ta₂O₅ thin film deposited at 50 nm yielded the most extreme protective performance. The Ta₂O₅ thin films therefore could be optimized for the smallest film thickness for highly potential role in the protective performance of the metal surface finishing products.