Papers by Author: S. Maensiri

Abstract: A preparation of well-dispersed magnetite nanoparticles was demonstrated in this study. Magnetite nanoparticles (MNPs) were synthesized by a hydrothermal method using aloe vera extract and serial centrifugation was employed to separate the sizes of well-dispersed particles. Well-dispersed MNPs with average sizes of 241, 227, 195, 165, 141 and 93 nm were obtained. They were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and vibrating sample magnetometry (VSM). XRD results indicated the MNPs were Fe₃O₄. Magnetic hysteresis loop measurements of the samples showed superparamagnetic properties. Pulsed nuclear magnetic resonance (NMR) showed stable proton (¹H) spin-spin relaxation time (T2) values of water with suspended magnetite nanoparticles over a time course of 20 min, suggesting they were well-dispersed. The synthesized magnetite nanoparticles showed low cytotoxicity to NIH 3T3 cells at concentrations of 1-10%.

Abstract: Alumina nano-particles was grafted with poly(2-hydroxyethyl methacrylate) (PHEMA) utilizing the sequential method; that is, the alumina surface was first rendered with initiator, benzophenone, by UV-irradiation followed by the grafting polymerization of HEMA on the surface which was initiated thermally and propagated via the free-radical polymerization. FT-IR spectroscopy confirmed the successful grafting of PHEMA onto the alumina surface. Determined by thermalgravimetry (TG), the amount of benzophenone on the alumina surface was found to increase with the UV-irradiation time; however upon grafting of PHEMA, the amount of grafted-PHEMA was the same irrespective of the reaction time. The glass transition temperature (Tg) of grafted-PHEMA on alumina particles was approximately 93 °C that is higher than that of PHEMA which has Tg around 85 °C. This indicates the more restricted movement of grafted-PHEMA compared with the ungrafted-PHEMA.

Abstract: A perovskite-type phase of solid solution of BiFeO3-BaTiO3 powders were synthesized by a solid-state reaction via a rapid vibro-milling technique. The effect of calcination condition on the phase formation, and characterization of BiFeO3-BaTiO3 powders were investigated. The formation of the BiFeO3-BaTiO3 phase investigated as a function of calcination conditions by TG–DTA and XRD. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques and vibrating sample magnetometer (VSM) was used to characterize the structures and magnetic properties of prepared samples. The rapid vibro-milling is employed for the first time in this work as a significant time-saving method to obtain single-phase BiFeO3-BaTiO3 powders.

Abstract: A perovskite-type phase of Bismuth Ferrite, BiFeO3, powder was synthesized by a solid-state reaction via a rapid vibro-milling technique. The effect of calcination condition on the phase formation, and characterization of BiFeO3 powder was investigated. The formation of the BiFeO3 phase investigated as a function of calcination conditions by TG–DTA and XRD. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques and vibrating sample magnetometer (VSM) were used to characterize the structures and magnetic properties of prepared samples. The rapid vibro-milling is employed for the first time in this work as a significant time-saving method to obtain single-phase BiFeO3 powders.

Abstract: Nano-sized powders of CaCu3Ti4O12 (crystallite size of 44, 58 and 71 nm) have been synthesized by a polymerized complex method, followed by calcination the synthesized precursor at 600, 700 and 800°C in air for 8h. The CaCu3Ti4O12 powders were then characterized by XRD, FTIR and SEM. Sintering of the powders was conducted in air at 1100°C for 16h. The XRD results confirmed a typical perovskite CaCu3Ti4O12 structure in all the sintered ceramics, although the presence of a second phase of CaTiO3 was observed in the sample sintered using the powders calcined at 600°C. Microstructure of the sintered CaCu3Ti4O12 ceramics was observed by SEM and the grain size of the materials evaluated with polished using the line intercept method were found to be ~ 10-20 μm. A giant frequency-dependent dielectric constant samples (ε ~10000-60000) with weakly temperature dependence and was observed in the all the samples. The highest dielectric constant of the material was found to be ~60000 (at 140-160°C, 100 Hz) in the sample sintered using the powders calcined at 700°C. The origin of the high permittivity observed in these CaCu3Ti4O12 ceramics is attributed to the Maxwell-Wagner polarization mechanism.

Abstract: This paper reports on the fabrication of nanofibres of ceramic compounds using electrospinning technique. In a typical process, ceramic nanofibres are fabricated by electrospinning a precursor mixture of appropriated metal sources, polymer and solvent, followed by calcination treatment of the electrospun composite nanofibres. In this work, the electrospinning set up as well as experimental procedure are described in detail. The fabrication of thermoelectric oxide NaCo2O4, ferroelectric Ba1-xSrxTiO3 and semiconductor TiO2 nanofibres with diameter of ~20-200 nm are demonstrated. The characterization of the fabricated nanofibres using TG-DTA, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy is also investigated.

Abstract: Nanocrystalline cordierite powders were prepared by the polymerized complex method. The synthesized precursor was calcined in air at 600-1200 oC for 1h, and the calcined powders were fully characterized by TG/DTA, BET, XRD, SEM, and TEM. The XRD and selected-area electron diffraction (SAED) analysis confirmed the development of the phase composition of cordierite powders showing amorphous phase after calcination at temperature below 800oC, mixed phases of spinel and μ-cordierite phase after calcination at 800oC and 900oC, and mixed phases of spinel, μ- cordierite and α-cordierite phases after calcination at above 900oC. The BET specific surface areas of the calcined powders varied from 3 to 107 m2/g, depending on calcination temperature. The highest specific surface area of 107 m2/g was found in the powders calcined at 800oC. The average particle sizes evaluated by BET were less than 60 nm, depending on calcination temperature. The powders calcined at 800oC and 1000oC were uniaxially pressed and pressureless-sintered in air at 1250-1350oC for 2h. Densities of the sintered samples evaluated by Archimedes’s method were 87- 91 % of theoretical value. The crystal structure of all the sintered samples, determined by XRD, was mainly α-cordierite, having a small amount of spinel as second phase.