Papers by Author: Gobwute Rujijanagul

Abstract: Geopolymers are aluminosilicate inorganic polymers. In this study, the effects of replacement metakaolin with diatomite in geopolymer materials were investigated. The geopolymer materials were prepared by leaching diatomite (from Lampang province) and metakaolin (from Ranong province) with alkaline activator solutions. The fresh slurry was cast into plastic molds with a cubic shape and then cured at room temperatures. Effects of ratios between diatomite and metakaolin were investigated. Furthermore, influences of curing time on the properties of the studied samples were also determined. Many techniques for material characterization such as XRF, XRD, and SEM were employed in this work. The mechanical property of geopolymer compressive strength was tested after curing. It was found that compressive strength of the samples increased with increased amounts of diatomite.

Abstract: Fuel cell is an electrochemical cell which converts chemical energy into electricity via electrochemical reaction of hydrogen and oxygen gases. It is also an alternative energy with environmental friendly. Generally, the fuel cell consists of many parts. Electrolyte is an important part for fuel cell because it has high ion conductivity which leads to increase electrical conductivity of the fuel cell. In case solid oxide fuel cell, barium cerate-based ceramics have been much attention due to their good properties for the fuel cell. In this work, the BaCe_1-xY_xO_3-δ (x = 0.20) ceramic was synthesized by a solid state reaction in order to study their mechanical and electrical properties. The ceramic was sintered at high temperature of 1500°C with various soaking times. The crystalline phase structure was investigated by X-ray diffraction (XRD). The surface morphologies was observed by a scanning electron microscope (SEM). The impedance properties was measured by LCR meter. The obtained results suggestes that the ceramic sinter at 1500°C with 15 h dewell time shows the best properties as compared to other ceramics.

Abstract: The present study focuses on the new application of geopolymer ceramic composites as substrate cultures, resulting from the geopolymer properties being similar to those of the substrate cultures such as water absorption, non-biodegradation, high porosity, and light weight. The geopolymers were synthesized from ceramic wastes and metakaolin using the geopolymerization method via a reaction with an alkaline solution. To compare usefulness for substrate culture applications, the porosity of different samples was varied. Moreover, the properties of all samples were investigated using an additional method of verification. The chemical characteristics were evaluated by FT-IR spectroscopy. The microstructures, pore sizes, pore distributions and surface areas of the pores were examined with image analysis using scanning electron microscopy (SEM). The densities were determined using the Archimedes’ method. The porosity and water absorption were also measured. The mechanical properties were investigated by using a compression testing machine.

Abstract: In this research, the effects of biochar additive on the properties of geopolymer materials were investigated. Normally, the geopolymer can be used for adsorption materials due to good ion exchange capacity. Biochar also has the application as an adsorption material for pollutant removal. Biochar particles were prepared from waste materials in pyrolysis condition. The geopolymer materials were prepared by mixing metakaolin and aluminium oxide in alkaline activator solutions of Na₂SiO₃ and NaOH. Biochar was mixed with geopolymer by 0, 10, 20, and 30 % weight of binder. A NaOH concentration of 15 M, and Na₂SiO₃/NaOH ratios of 1.5 by weight were used. The density, porosity, and water absorption were measured. The phase formation, microstructure, and bonds of the sample were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). The adsorption capacity of each sample was determined by methylene blue adsorption tests. The result of the removal efficiency of all samples shows high adsorption capacity (60-70 %). It should be interesting alternative materials used for remove of aqueous solution.

Abstract: The properties of metakaolin-based materials were investigated. The studied materials were prepared by mixing metakaolin and aluminum oxide in alkaline solution. The obtained samples were cast into plastic molds and then left at 27°C for 24 h. The properties of the materials were investigated using XRD, FTIR, and SEM. The obtained results suggested that reaction of the mixed materials occurred. The adsorption properties of the materials, including removal efficiency, distribution coefficient, and uptake capacity were determined. The obtained results revealed that the studied materials exhibited high adsorption capacity, which is good for the adsorbent applications.

Abstract: Bioactive glass ceramics from Na₂O-CaO-P₂O₅-TiO₂ system have been fabricated by conventional melt quenching method. In order to change the fabricated glass to glass ceramic samples, a heat treatment technique was employed using temperatures ranging between 700 and 900°C for 2 h. Glass transition and crystallization temperature were analyzed via differential thermal analyzer (DTA). In addition, phase formation and microstructure of the glass-ceramics were also investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). From the crystallization kinetics, the crystallization rate constant (n) of the glass was found to be close to the value of 3, indicating the two-dimensional growth of crystals occurred in the glass ceramics. From the XRD results, the major crystalline phases were sodium titanium phosphate and calcium sodium phosphate along with titanium dioxide as the minor crystalline phases presented in high heat treatment temperatures (750-900°C) of the glass ceramics. SEM of the crystallized base glass Na₂O-CaO-P₂O₅-TiO₂ system, showed that crystallization of dendritic-like growths in the glass ceramics.

Abstract: The work is focused on an attempt to develop a route for the fabrication of piezoceamic-polymer composites having (1-3) type connectivity. The process included the extrusion of rods of diameter approximately 200 mm. A commercial piezoelectric, PC-5 was modified by addition of a lithium/bismuth based glass former together with excess PbO to lower the sintering temperature to about 1000 °C. The fast firing sintering was employed. The rods were assembled and impregnated with an epoxy resin to form 1-3 composites containing approximately 50 and 20 vol% piezoceramic. The measurement values showed that, the piezoelectric constant, d₃₃ = 232 pCN^-1 and 215 pCN^-1, thickness electromechanical coupling coefficient, k_t = 0.51 and 0.5 and the mechanical quality factor, Q_m = 14 and 5 for the composites containg PZT rods at 50 vol% and 20 vol% respectively. Their acoustic impedances were 5.1 and 3.6 for the 50 vol% and 20 vol% of PZT rods respectively. The results show that with lower volume% of PZT could result in lower acoustic impedance which can be further improved for biomedical imaging and hydrophone applications.

Abstract: In this research, the Bi_0.5(Na_0.80K_0.20)_0.5Ti_0.99Ti_0.10O₃ were prepared via a conventional solid-state reaction method, and their properties were related with calcination temperature. The crystalline structure of BNKTZ ceramics was assessed by X-ray diffraction (XRD) method. Other physical properties, i.e. porosity, density, microstructure, and electrical properties were determined. XRD patterns for all samples showed a pure perovskite, where coexistence between rhombohedral and tetragonal phases was observed for some conditions. The optimum dielectric constant was obtained for the ceramic calcined at 800 °C. The ferroelectric and piezoelectric properties were improved and showed the highest values for the calcination temperature around 900-1000°C. The improvements of ferroelectric and piezoelectric properties were proposed to be due to the ceramics had compositions closed to MPB composition. Furthermore, density also had a contribution for the improvements.

Abstract: The properties of modified Bi_0.5Na_0.5TiO₃ (BNT) based lead-free ceramics were investigated. The BNT-based ceramics were prepared by a solid-state mixed oxide method Phase formation was determined by X-ray diffraction technique (XRD). The X-ray diffraction analysis of the ceramics suggested that all samples exhibited a perovskite structure without second phase. The value of dielectric constant increased with increasing in sintering temperature. Moreover, high sintering temperatures could improve ferroelectric properties of BNT base lead-free ceramics.

Abstract: In the present study, mullite powders were prepared from fired Ranong kaolin powder at high temperatures. Differential thermal analyses and X-ray diffraction (XRD) technique were used to understand kaolin–mullite reaction sequence and phase formation of the starting material after a heat treatment, respectively. It was found that phase of mullite started to occure at ∼1000 °C. Microstrural study by a scanning microscope, indicated that there was a change in microsture after the heat treatment, i.e. grain shape changed from equiaxed to needle grains shape . The AC conductivity decreased with decreasing the sintering temperature and 1500 °C ceramic presented a very high frequency stabilty of conductivity, suggesting that this martial can be used as an electrical insulator for wide frequency range.