Applied Mechanics and Materials Vol. 804

Abstract: The gamma ray and X-ray shielding properties of PVA containing different proportions of BaSO₄ as an aggregate have been investigated. The photon linear attenuation coefficients were measured by using ²⁴¹Am radioactive source (59.54 keV). Gamma rays were counted by a NaI(Tl) detector. It was found that the shielding efficiency increased when increasing the amount of BaSO₄ and specimen thickness. The linear attenuation coefficients were 0.085, 0.125, 0.179, and 0.189 for 0.2, 0.4, 0.6, and 0.8%w/v of BaSO₄. The X-ray attenuation test was performed using the diagnostic X-ray machine for energy of 45 kVp. The optical density of X-ray films was investigated. The results showed that the optical density of X-ray film decreased when increasing the amounts of BaSO₄.

Abstract: In this research, zinc oxide (ZnO) films were prepared using a wet chemical reaction via a microwave technique. X-ray diffraction techniques (XRD) and energy dispersive x-ray spectroscopy (EDS) were used to study the phases, crystalline structures, chemical compositions and optical properties of the films, respectively. Optical transmittance was also measured through UV-VIS spectroscopy. Surface film morphologies were investigated by scanning electron microscopy (SEM). As a result, a ZnO phase with a hexagonal structure was detected. The EDS spectrum shows that elements of Zn and O were present. The average optical transmittance value for all films was 75% at a wavelength of 370-375 nm, a comparison among the films obtained at different times show a transmittance value slightly higher for films obtained at higher times. A calculation of the energy band gap of ZnO films was estimated to be in the range of 3.31 to 3.35 eV. Additional, the ZnO films showed a smooth surface.

Abstract: Silicon-based thermoelectric device fabricated using standard semiconductor manufacturing technique is a promising technology that could lead to a mass production of clean energy. The vertical wall fabrication on Si substrates is typically achieved by high cost plasma etching and involved hazardous gases. The proper wet etching condition offers an economically alternative method in obtaining vertical wall on the Si substrate. Experimental trials were conducted by design of experiments (DOE) technique to find an anisotropic wet etching condition that achieves vertical etched wall on (100) Si wafer. Three considered factors assigned to the DOE were NaOH concentration, solution temperature, and IPA addition. The response aimed for this study was not only targeting at 90° wall but also providing highest etch rate. The experimental results showed that in order to get the 90° wall, the best etching condition achieved was using 45% wt of NaOH concentration, 40°C solution temperature, and without IPA added. This condition gave an etch rate of 97.11 nm/min with surface roughness (R_a) of 10.58 nm.

Abstract: Dielectric properties of hydrothermally decomposed Y₂NiMnO₆ ceramics prepared under several sintering conditions were investigated at room temperature. As the results, dielectric constants at 200 Hz were found about 928 and 23x10³ for samples sintered at 1000 and 1400 oC, respectively. The dielectric permittivity for samples sintered at 1400 oC for different sintering times from 6 to 24 hours have yielded the best dielectric permittivity value of 10⁴. On the other hand, low sintering temperature had resulted in smaller dielectric loss in comparison to larger dielectric loss generally found in the ceramics with high sintering temperature.

Abstract: Barium titanate (BT) additive in lanthanum modified lead zirconate titanate (PLZT) was used to modify the microstructure and resultant properties of (1-x) PLZT– x BT where x= 0, 0.05, 0.10, 0.15, 0.20 and 0.25. Oxide powders were synthesized by mixed oxide synthetic route via a rapid vibro-milling technique. All of samples were sintered at 1275°C with the soaking time of 4 h. The ceramic samples were investigated for phase formation and evolution, dielectric behavior and ferroelectric properties. Introduction of BT in PLZT lattice resulted in ferroelectric tetragonal-rhombohedral structure, and further increase of BT content resulted in stabilizing the ferroelectric tetragonal perovskite phase. Dielectric behavior and ferroelectric properties were examined as a function of BT content.

Abstract: The sound absorbing efficiency of natural rubber (NR) foam is affected by the cell morphology of foam. Potassium oleate (K-oleate) and sodium bicarbonate (NaHCO₃) were used as blowing agents to create open-cell foam. Amounts of the blowing agent were varied from 0.5 to 8.0 part per hundred of rubber (phr) to evaluate cell size and number of foam cell as well as sound adsorption coefficient of NR foam. The NR foam specimens were prepared using mould and air-circulating oven for vulcanizing and foaming processes. The results indicated that K-oleate at 2.0 phr and NaHCO₃ at 0.5 phr led to form NR foam with the smallest cell size and the largest number of foam cell. At low frequencies, the optimum sound adsorption coefficient of NR foam was caused by filling K-oleate 2 phr. However, that of NR foam at high frequencies was provided by 0.5 phr-NaHCO₃ addition.

Abstract: Zinc oxide nanostructures were synthesized by an electrochemical dissolution and deposition process. The zinc plates were immerged in deionized water and used as two electrodes. The process was operated by applying the electric field of 10, 12.5, 25 and 50 V/cm, the constant voltage of 10 V and varied the temperatures from room temperature to 70 °C during 1 h. It was found that the electric field and temperature of electrolyte solution had affected to morphologies of ZnO NSs and were grown in forms of nanoflakes, nanoparticles and nanorods.

Abstract: This research was conducted to improve the ferroelectric properties of PZT based ceramics by studying the effect of sintering conditions in terms of temperature and soaking time (time of sintering) on the ferroelectric properties of ceramics in the 0.8Pb (Zr_1/2Ti_1/2)O₃-0.2Pb (Zn_1/3Nb_2/3)O₃ system prepared by vibro-milling mixed-oxide method. The XRD patterns of specimens showed perovskite structure for all compositions. The pyrochlore phase was not observed in this system. The sintering temperature and soaking time affects the ferroelectric properties of ceramics by the optimum sintering condition for 0.8PZT-0.2PZN ceramic is sintered at 1250°C for 2h.

Abstract: In present study, the Co_0.7Zn_0.3Fe₂O₄ ceramic was prepared using solid state reaction. The crystal structure of prepared ceramic indicated as solid solution. The SEM result indicated the dense structure of prepared ceramic as increased sintering temperature. For VSM result of Co_0.7Zn_0.3Fe₂O₄ ceramic indicated the super paramagnetic behavior with high magnetization. These results could lead us to the development of Co_0.7Zn_0.3Fe₂O₄ ceramic preparation optimized for specific applications.