Siwaporn Meejoo

INCORPORATION OF IRON INTO NANO HYDROXYAPATITE PARTICLES SYNTHESIZED BY THE MICROWAVE PROCESS

This research focuses on understanding the nature of the Fe ions substituted in hydroxyapatite ((HAP) Ca10-xFex(PO4)6(OH)2-xyx: x = 0, 0.2 and 0.4) powder synthesized at temperatures between 500°C and 1000°C and their crystallization. The DSC scan indicates a solid state phase transition at about 757°C for the as-prepared powder HAP. The transformation of HAP to β-tricalcium phosphate (β-TCP, β-Ca3(PO4)2) is seen when the powder were heated to 750°C. The sizes of the crystallites were determined to be about 46–51 nm, 33–40 nm and 33–59 nm for Fe content of 0, 0.2 and 0.4 mol%, respectively. The ESR parameters for the Fe3+ ions, g = 4.23 and 8.93 indicated that the ions were subjected to a rhombic ion crystal field within the HAP structures. The g values of ~2.01 indicated that the particles were super-paramagnetic and ferromagnetic iron nanoparticles, having an average size about 0.2–0.5 μm in length.

Temperature Effect on Chicken Egg Shell Investigated by XRD, TGA and FTIR

The main purpose of this work is to study the structure of Anadara granosa shell sample and its structural transformation upon heat treatments. The sample was ground and characterized as powder throughout this work. Structural identifications of all samples were characterized, and determined qualitatively by using X-ray diffraction, IR spectroscopy and thermogravimetry measurement (TGA). It was found that the specimen is made of aragonite, a common phase of CaCO3 mineral. The powder sample was annealed at specific temperatures over the range of 200°C - 900°C and the effects of heat treatment on the structure of Anadara granosa shell samples were studied. The results show that aragonite transforms to calcite at the temperatures between 200°C and 400°C and completely becomes calcite between 400-500°C. Then, the calcite transforms to calcium oxide at the temperatures between 500°C - 900°C. The exact structures and quantities of phase at different annealing temperatures were studied by Rietveld refinement. In our study, we also used IR spectroscopy and TGA to study the effect of water absorption of the samples on the phase transformation.

SURFACE MORPHOLOGY OF SUBMICRON CRYSTALS IN ALUMINUM NITRIDE FILMS GROWN BY DC MAGNETRON SPUTTERING

Aluminium nitride (AlN) thin films were fabricated on a glass substrate by reactive magnetron sputtering. Raman microscopy was then employed to follow the characteristics of their optical and acoustic phonon modes. At the optimal sputtering time of 30 minutes, the defect-induced first and second order Raman spectra were observed in 400–800 cm-1 band which were mostly related to the coating compositions. However, at the 30-, 60- and 90-minute sputtering, crystals of submicron size order of AlN were achieved. This could be clearly identified by the presence of Raman peak at 658–662 cm-1. Powder X-ray diffraction (PXRD) patterns revealed the development of (002) and (101) planes of hexagonal wurtzite AlN phase. The optimal average grain size measured by atomic force microscopy (AFM) is at 330 nm. It was found that the hardness was strongly dependent on roughness of the film, the maximum of which was achieved at 20.00 GPa. The presence of F-type defects in AlN films was investigated by X-band (~9.44 GHz) ESR spectrometer at 295 K. The ESR experiments were carried out by applying magnetic field perpendicular to AlN film, which showed the ESR six-peak multiplet signal at ~290 mT arising from superhyperfine interactions between nuclear spin I = 5/2 of 27Al and electron spins trapped in nitrogen vacancies. The ESR signals are simulated and the ESR parameters are calculated. The vacancies are clearly randomly distributed as the ESR signals are independent of rotation angle (φ) about the normal of the film. All these results were analyzed and presented as a function of the deposition parameters and composition, and crystalline phases existed in the films.

Substitution of Iron in Preparation of Enhanced Thermal Property and Bioactivity of Hydroxyapatite

Incorporation of Iron into hydroxyapatite (HAp) has generated a novel material for which their properties differ from those of conventional HAp. Although XRD indicated that the as-prepared iron-substituted hydroxyapatite (HApFe) is of a single crystalline phase similar to that of HAp, we found that carbonate ions can incorporate in the HApFe structure 3 times better than in HAp. As results, HApFe possesses the Vickers microhardness about 1.5 times higher than that of HAp. Thermal behaviors and bioactivity of HApFe are discussed in comparison to those of HAp. Various experimental methods have been employed in this work including powder XRD, IR, SEM, DSC/TGA and Vickers Hardness testing.

EFFECTS OF HEAT TREATMENT ON BLUE SAPPHIRES AS MONITORED BY ESR SPECTROSCOPY

We report effects of heat treatments on physical properties and finding optimal heating condition to add value to Thai blue sapphires. The color of sapphire arises from the presence of trace 3d-transition ions in its crystal lattice. For blue sapphire, the color is due to a charge transfer mechanism between Fe2+ and Ti4+ ions. However, iron may adopt both Fe3+ and Fe2+ due to oxygen vacancies. Fe3+ and Fe2+ yield sapphire yellow and green colors, respectively. Therefore, we have to convert as many as possible of Fe3+ to Fe2+ by heating the blue sapphire in N2 atmosphere for 12 h. Experimental results reveal that the ratio of lattice parameter c/a increases with the heating temperature and reaches maximum at 1700°C, which can be caused by displacement of Fe3+ ions or more Fe3+ ions being converted to Fe2+. ESR signals show that the number of Fe3+ ions decreases roughly linearly with the heating temperature. The intense sky blue color was achieved after the 1500°C heat treatment, having the ratio ~0.78. The optimal heat treatment should therefore be at 1500°C in flowing N2 atmosphere for Thai blue sapphires which yield intense sky blue color and good crystal clarity. The blue sapphires exhibited good clarity but light sky blue due to the increase in lightness after the treatment at 1700°C. A monoclinic distortion of the corundum structure has been found to start at the 1600°C treatment by ESR spectrometer. This is also clearly evident from low angle shifts of XRD peaks after heating at 1700°C. We can therefore conclude that the color change of Thai blue sapphires arises from the conversion of Fe3+ to Fe2+ and thus the change in crystal field. The monoclinic distortion of the crystal structure may also play an important role in coloring the sapphires after the heat treatment at 1600–1700°C.

ESR Spectrometer as a Possible Tool for Rapid Analysis of Cane Sugar Purity

A method for quantitative/qualitative determination of cane sugar purity by ESR is devised. Refined sugar, plantation white sugar, soft brown sugar and raw sugar are used as samples in this work. The sucrose radical is produced by pulverization of sugar and it increases as the particle size decreases. Based on pulverization-induced sucrose radical, ESR study demonstrates the effects of sugar purity on characteristic of ESR spectrum. The relationship between the sucrose contents and peak area under the ESR spectrum is manifested. It is found that the peak area or sucrose radical concentration increases linearly with the increase of sucrose content. Using the linear regression method, the sucrose amount can be revealed. This approach is a promising fast and accurate method for sugar purity analysis.

Electron Spin Resonance Studies of Mn2+ in Freshwater Snail Shells: Pomacea Canaliculata Lamarck and Fossilized Snail Shell

We study paramagnetic Mn2+ ions present in the nowadays shells of univalve freshwater snails of Pomacea canaliculata lamarck (PCL) and the fossilized freshwater snail (FFS), Viviparus. All these shells are abundant in Thailand. The PCL shells were ground into fine powder. A set of seven samples were then separately annealed for 2 h in air atmosphere at different annealing temperatures while the FFS powder was characterized as-received. The PCL shells mainly consist of aragonite and a fraction of calcite. The heat treatments of the PCL powder samples at temperature higher than 450 degrees C resulted in an irreversible phase transformation from aragonite to calcite. However, it is found that the FFS shell is mainly made of calcite, with a minor fraction of aragonite. The crystal structure of the high-temperature-annealed PCL samples are quite similar to that of FFS, which indicates that the metamorphosis (aragonite → calcite) in the FFS shell had occurred but was not yet completed, although it had remained under the pressure and temperature of the Earths crusts over millions of years. Our detailed ESR spectral analyses of PCL and FFS show that Mn2+ ions enter the Ca2+ sites during a biomineralization process. Simulated ESR parameters of PCL-500 of Mn2+ at a uniaxial site of calcite are reported. It is surprising to find that the ratio of Mn2+ concentration present in FFS to those in PCL shells evaluated from ESR spectra is as much as 10:1.

THE SPIN HAMILTONIAN PARAMETERS CALCULATION OF 14N AND 15N IN NATURAL TYPE I DIAMOND

The main purpose of this work is to present the ESR spectra and calculate the spin Hamiltonian parameters of 14N and 15N impurities in natural diamond. The ESR spectra of diamond crystal were measured on ESR spectrometer operating at X-band microwave frequency. The results of ESR spectra show that the diamond has a P1 center. This center gives rise to three strong resonance absorption peaks at θ = 90°, φ = 0° due to hyperfine interaction between electron spin and nuclear spin of 14N. The ESR spectra of 15N impurity consist of two satellites at the same rotation angle (φ). The effects of isolated substitution nitrogen on carbon atom produced a symmetric distortion from Td to C3V symmetry. According to this symmetry, the resonance magnetic field positions of ESR spectra for the rotation angles of 0°, 90° and 180° are almost overlap. The g-factor values and spin Hamiltonian parameters of 14N and 15N are: g = 2.0019, A⊥ = 29.73, A‖ = 40.24 and g = 2.0019, A⊥ = −39.90, A‖ = −57.05, respectively.

Revelation of Causes of Colour Change in Beryllium-Treated Sapphires

Blue sapphires are treated with Be in oxidizing atmosphere to change the blue colour into yellow. Untreated and Be-treated samples are examined using laser ablation inductively coupled-plasma-mass spectrometry (LA-ICP-MS), electron spin resonance (ESR) and ultraviolet–visible (UV–vis) spectroscopy. The results show that the yellow colouration in Be-heated blue sapphires is not due to Be diffusion from the surface of sapphire. Be behaves as a sole catalyst in this process. We find that the charge transfer between the ferrous (Fe2+) and ferric (Fe3+) is the reason of the colour change. The above conclusions are confirmed by ESR measurements to determine the connections between the Fe3+ ions before and after Be-treated heat treatments.

Mechanochemical Treated Multi-Walled Carbon Nanotubes for Incorporation of Metal Ions

Ni catalyst was removed from as received multi-walled Carbon Nanotubes (MWNTs) by acid treatment. Then, the nanotubes were treated with 4M HCl during a ball milling processing yielding mechanochemical treated MWNTs (mech-MWNTs). TEM micrographs indicate that the mech-MWNTs were still of a tubular form but with much shorter length. The equilibrium adsorption of metal ions, e.g Cu2+ and Ni2+, on the mech-MWNTs was investigated at room temperature. The adsorption isotherms gave excellent consistence with the Langmuir theory and the best fit values of K-1 and Κmax can be evaluated using non-linear least-squares. As results, the maximum of Cu2+ and Ni2+ ions uptake on to the mech-MWNTs are 0.93 ± 0.004 mg/g and 2.11 ± 0.01 mg/g respectively. There is no evidence indicating that the pore structure and layer surfaces at both ends of the mech-MWNTs are appropriate sites for metal ions adsorption.