Oratai Jongprateep

Effect of Al and Mg Doping on Dielectric Properties of BaTiO3 Synthesized by Solution Combustion Technique

It has been accepted that doping and parameters related to synthesis and processing of ceramic samples could affect dielectric properties. This study aimed at synthesizing BaTiO3 BaAl0.1Ti0.9O3 and BaMg0.1Ti0.9O3 powders by the solution combustion technique and examining their dielectric constants and dielectric losses. Initial powder exhibited average particle size in sub-micrometer range. Grain sizes in micrometer range were observed in the pressed and sintered samples. Dielectric constants and dielectric losses of the samples ranged from 52.2 to 91.4 and 3.3 × 10−3 to 4.7 × 10−3 at 1 MHz, respectively. BaMg0.1Ti0.9O3 samples achieved the highest dielectric constant, while BaAl0.1Ti0.9O3 samples exhibited the lowest dielectric constant. Enhancement of the dielectric properties was attributed to smaller grain sizes, while lower density in the samples resulted in reduced dielectric constants.

Effect of Solids Loadings, Sintering Temperatures and Sintering Periods on Microstructure of Hydroxyapatite

Attributed to its biocompatibility and osteoconductivity, hydroxyapatite (HAp, Ca10(PO4)6(OH)2) has been extensively utilized as a bioactive material. As the implant material, HAp is required to be fabricated into a porous form. The present study was therefore aimed at synthesizing HAp powder by solution combustion technique and at fabricating porous HAp specimens. Calcium nitrate and ammonium dihydrogenphosphate (NH4H2PO4), with Ca/P ratio equal to 2.3, were used as initial reagents in the HAp synthesis process. X-ray diffraction analysis confirmed that HAp was present as the primary phase, while minor secondary phases, Tri-calcium phosphaste (TCP) and CaO, were also observed. To prepare porous specimens, HAp slip with solids loadings ranging from 15 to 25 vol% was cast into acrylic molds and sintered. The sintering temperatures were 1350°C and 1450°C, and sintering periods ranged from 2 to 4 hours. Results from microstructural analysis revealed that high solids loadings, sintering temperatures and sintering periods resulted in decreasing of porosity. Porosity in the range between 30 and 90%, which was in an acceptable range for orthopedic applications, was observed.

Effects of Ageing Periods on Compositions and Sizes of Titanium Dioxide Particles Synthesized by Sol-Gel Technique

Titanium dioxide has attracted worldwide attention due to its prominent photocatalytic activity. It is generally accepted that nanoparticulate titanium dioxide with pure anatase structure exhibits high reactivity. Sol-gel is a simple and cost-effective technique capable of synthesizing anatase-phase titanium dioxide with particle sizes in nanometer range. This research aimed at examining effects of ageing periods on compositions and sizes of titanium dioxide synthesized by sol-gel technique. Experimental results revealed that prolonged ageing period demoted formation of anatase phase. Pure anatase phase was observed at ageing period of 1 day, while both anatase and rutile phases were observed at ageing periods of 4 and 7 days. The results also indicated that particle sizes decreased as the ageing periods increased. Nanoparticulate titanium dioxides with average sizes of 71.5, 50.4, and 29.7 nanometer were observed at ageing periods of 1, 4, and 7 days, respectively.

Compositions and Particle Sizes of (RE)Ba2Cu3O7-X Superconductor Powders Synthesized by the Solution Combustion Technique

Superconducting compounds (RE) Ba2Cu3O7-x (RE = rare earth such as Y, Er, Sm and Nd) can be exploited in various industrial applications such as cables, electric motors and energy storage systems. The project aimed at synthesizing fine-particle YBa2Cu3O7-x, ErBa2Cu3O7-x, SmBa2Cu3O7-x and NdBa2Cu3O7-x, powders with compositions suitable for the applications. Solution combustion technique was employed in the synthesis, using urea as fuel. Compositional analysis obtained from x-ray diffraction indicated that the as-synthesized powders contained the desired (RE)Ba2Cu3O7-x (RE123) superconducting phase and impurities, including (RE)2BaCuO5 (RE211), BaCO3 and Ba(NO3)2. However, majority of the impurities were eliminated when the powders were calcined at 900°C. Only (RE)Ba2Cu3O7-x (RE123) and (RE)2BaCuO5 (RE211) phases remained after calcination. Results from scanning electron microscope showed that the as-synthesized powders obtained from the solution combustion technique had relatively small particles with average particle size of 0.67 micrometers, while the calcined powders exhibited coarsening effects with average particle size of 4.4 micrometers.

Effects of Sn Concentration on Chemical Composition, Microstructure and Photocatalytic Activity of Nanoparticulate Sn-Doped TiO2 Powders Synthesized by Solution Combustion Technique

Utilization of photocatalytic properties of materials can be perceived through a wide range of applications, such as anti-bacterial, water treatment, and self-cleaning materials. It has been established that doping can result in alteration of photocatalytic activities. This study aimed at studying effects of tin concentration on chemical composition, microstructure, band gap energy, and photocatalytic activities of tin-doped titanium dioxide powder synthesized by solution combustion technique. Experimental results revealed that concentration of tin significantly influenced chemical composition of the powders. A semi-quantitative analysis indicated that tin oxide secondary phase increased from 11 to 23 wt%, as the Sn increased from 2.5 to 10 mol%, respectively. Tin concentration, nevertheless, did not significantly influence microstructure of the powders. All powders had average particle size ranging from 13.1 to 13.4 nm, which agglomerated into clusters with average sizes ranging from 103 to 140 nm. A slight increase of band gap energy was observed at higher tin concentration. The most prominent photocatalytic activities, determined from decomposition of methylene blue, was found in the titanium dioxide powder with 2.5 mol% Sn.

Effects of Eu Doping and Calcination Temperatures on Chemical Compositions, Microstructure and Luminescent Intensity of BaAl2O4

Photoluminescent (PL) materials are commonly utilized in applications such as leakage test, crack monitoring, banknote forgery detection, and fingerprint detection. Doping, chemical compositions and microstructure, are generally accepted as factors that influence luminescent intensity of spinel-structure phosphors such as SrAl2O4, CaAl2O4, and BaAl2O4. This study aimed at synthesizing BaAl2O4 photoluminescent powders by solution combustion technique. Effects of Eu doping and calcination temperatures on chemical compositions, microstructure and luminescent intensity of the materials were also examined. Experimental results indicated that Eu concentrations did not exhibit a significant effect on chemical composition and particle morphology. Higher calcination temperatures, on the contrary, resulted in reduction of secondary phase formation, and in alteration of morphology of particles and pores. The greatest luminescent intensity was achieved in the BaAl2O4 sample with 3 mol% Eu subjected to calcination at 900°C. Enhancement of the luminescent intensity in this sample might be attributed to minimal secondary phase and pore content.

Microstructures and Dielectric Constants of Ba0.05SrxCa0.95-xTiO3 (x=0, 0.225, 0.475, 0.725 and 0.95) Synthesized by the Solution Combustion Technique

Barium strontium calcium titanate is a dielectric material exploited in fabrication of electronic devices such as capacitors, signal filters and satellite components. Dielectric properties can be enhanced through compositional and microstructural control. This study, therefore, aimed at synthesizing barium strontium calcium titanate (Ba0.05SrxCa0.95-xTiO3, where x = 0, 0.225, 0.475, 0.725 and 0.95) powders by a solution combustion technique. The powders were pressed, sintered at 1450°C and tested for their properties. Experimental results revealed that strontium content did not significantly influence chemical composition, particle sizes and density. All powders exhibited a single phase corresponding to Ba0.05SrxCa0.95-xTiO3 with fine particles with the average size smaller than 0.4 micrometer. All sintered samples had density higher than 95% of theoretical density. On the contrary, the results indicated that strontium content affected grain size, grain morphology and dielectric constant of the sintered samples. The highest dielectric constant of 531 (at 1 MHz) was achieved in the Ba0.05Sr0.225Ca0.725TiO3. Dielectric constant was discussed with respect to microstructure.

Effects of synthesis techniques on chemical composition, microstructure and dielectric properties of Mg-doped calcium titanate

Calcium titanate (CaTiO3) has been recognized as a material for fabrication of dielectric components, owing to its moderate dielectric constant and excellent microwave response. Enhancement of dielectric properties of the material can be achieved through doping, compositional and microstructural control. This study, therefore, aimed at investigating effects of powder synthesis techniques on compositions, microstructure, and dielectric properties of Mg-doped CaTiO3. Solution combustion and solid-state reaction were powder synthesis techniques employed in preparation of undoped CaTiO3 and CaTiO3 doped with 5-20 at% Mg. Compositional analysis revealed that powder synthesis techniques did not exhibit a significant effect on formation of secondary phases. When Mg concentration did not exceed 5 at%, the powders prepared by both techniques contained only a single phase. An increase of MgO secondary phase was observed as Mg concentrations increased from 10 to 20 at%. Experimental results, on the contrary, reveale...

Chemical Composition-Microstructure-Dielectric Constant Relations of Mg-Doped Calcium Titanate Synthesized by Solid State Reaction Technique

It has been generally accepted that doping of dielectric materials could significantly contribute to compositional and microstructural evolution, which consequently lead to alteration in dielectric properties. In this study, the effects of adding magnesium (Mg) at 5,10 and 20at% on the chemical composition, microstructure and dielectric constant of calcium titanate (CaTiO3) synthesized by solid state reaction was assessed. Chemical composition analysis using an X-ray diffraction technique CaTiO3 doped with 5 at% Mg has been found to contain a single phase whereas samples doped with 10 and 20 at% Mg both exhibited apparent secondary phase (MgO). Microstructural examination however, revealed that no significant variation in particle size, grain size and density were evident among the samples of different Mg contents. Average dielectric constants obtained from the entire samples ranged from 245.9 to 387.6 (at 1 MHz) and the sample with the highest dielectric constant was that doped with 5 at% Mg. Enhancement of dielectric constant in the samples with the lowest level of Mg doping has been attributed largely to the homogeneity of its chemical composition.

Effects of Aluminium Contents and Consolidation Techniques on Chemical Composition, Microstructure and Dielectric Properties of Strontium Titanate

It has been accepted that compositions and microstructures significantly affected dielectric properties of materials. In general, chemical compositions were influenced by additive contents, while consolidation techniques controlled microstructure of the materials to have appropriate grain sizes. This study, therefore, aimed at examining effects of aluminium contents and consolidation techniques on chemical compositions and microstructures of the strontium titanate. Experimental results revealed that at higher aluminium contents, only small quantities of TiO 2 secondary phase were present, while grain sizes generally decreased. The results also indicated that the cold isostatic pressing technique led to high sintered density. The greatest dielectric constant (281.5 at 1 MHz) obtained in this study was achieved in strontium titanate sample with 30 at% of Al addition, pressed by cold isostatic pressing. Enhancement of dielectric constant of the sample was attributed to low secondary phase, fine grain sizes and high sintered density.