Key Engineering Materials Vol. 659

Abstract: Porous geopolymer could be synthesized by using metakaolin and silica fume as foaming agent. The foam morphology was estimated in the function of water, silica fume content, and curing temperatures. Raw materials were mixed by Hobart mixer for 5 minutes and then poured in to cylinder mold after that cured at 70 degree celsius for 24 hours. During the synthesis process, the complex reaction would occur such as polycondensation and oxidation. These reactions affect to chemical and physical properties of porous sample. The parameters that mention above affect to density, physical, and chemical properties. The thermal conductivity of porous geopolymer that contained with 14 molal NaOH concentration yield the lowest values of 0.5101 W/mK and pore size distribution of 0.01-0.8 mm.Keywords: Porous geopolymer, thermal conductivity, metakaolin

Abstract: For ceramic industry, efflorescence is undesirable and cannot be completely eliminated from the finished products. The efflorescence is caused by soluble salts in the raw material and mostly appears as white deposit at the product’s surface. In this research, the removal of sulfate in the raw materials was studied. In addition, the sulfate ions were immobilized by forming a water-insoluble compound. The sulfate ions in the raw materials and fired products were extracted by distilled water, and the concentration was determined by using a UV-visible spectroscopy following the ASTM C1580-09 standard. Three sources of the raw materials from Tambon Suan Phung, Ratchaburi, Tambon Mae Win and Mae Ta, Chiang Mai, were analyzed for sulfate concentrations. The clay from Tambon Suan Phung, Ratchaburi which had the highest sulfate concentration was selected for further study on the effect of inhibitor and firing temperature on efflorescence inhibition. To reduce solubility of the sulfate, three kinds of inhibitor, i.e. barium chloride, barium carbonate and barium hydroxide, were added into the raw material at various concentrations, i.e. 0.5, 1.0, 1.5 and 2.0 wt% and homogeneously mixed by ball milling followed by the addition of distilled water to prepare the clay slip. The clay products were mold casted to 1 x 1 x 3 inch³ in size. Then, they were fired at 800, 900 and 1000 °C. It has been revealed that the addition of barium carbonate at 2 wt%, which is the highest amount employed in this study, and firing temperature of 900 °C resulted in least sulfate leaching due to the formation of water-insoluble barium sulfate. To perform a field test, the fired samples with and without the addition of barium carbonate were immersed in water for 4 months. The efflorescence was observed on the sample without barium carbonate within the 1^st month. In contrast, with the addition of barium carbonate, no efflorescence was observed after testing for 4 months.

Abstract: Zirconia toughened alumina (ZTA) ceramic has been fabricated by the powder injection moulding process. The ZTA ceramic, composed of 80 wt% alumina and 20 wt% zirconia, was mixed with a water-soluble, multi-component binder system. The binder ingredients were polyethylene glycol (PEG), polyvinyl butyral (PVB) and stearic acid (SA). Powder injection moulding was performed with powder loadings in the range of 48-52 vol%, using a laboratory-scale injection moulding machine. Water leaching was used for partial binder removal prior to thermal debinding and then sintering at 1650 °C for 2 hours. Microstructural examination of the ZTA ceramic revealed that zirconia inhibited alumina grain growth and, therefore, improved the mechanical and physical properties of the specimens. It was found that powder loading had an influence on density, hardness and strength of the specimens. A flexural strength of 334 MPa and hardness value of 2093 kg/mm² was obtained from specimens injection moulded with 52 vol% powder loading feedstock. The highest sintered density achieved was 97% of the theoretical value.

Abstract: Aluminium borate nanowhiskers with varying aspect ratio were synthesized via sol–gel synthesis. The morphology of aluminum borate (Al₄B₂O₉ and Al₁₈B₄O₃₃) nanowhiskers could be controlled by varying the aluminum to boron (Al:B) molar ratio in the sol–gel derived precursors. Sintering temperatures (850 and 1100°C) and sintering times (4 and 32 hours) also affected the phase composition and size of the nanowhiskers. Citric acid was also added in the sol–gel derived precursors as a surface stabilizer for obtaining uniform finely dispersed nanostructures. Fine nanowhiskers were obtained by the calcination at 850°C, whereas higher temperature of 1100°C led to thicker and longer nanowhiskers and became rod-like crystals. The morphology and phase composition were investigated by field emission scanning electron microscope and X-ray diffraction. Chemical bond vibrations in the synthesized nanowhiskers were investigated by Fourier-transform infrared spectroscopy.

Abstract: The scientific process was used to explain characterization and physical properties of the clay sample close to the ancient Nan kiln site. These samples were obtained from JQA, FQB, PQC and NQD. X-ray diffraction (XRD) and X-ray fluorescence (XRF) technique were used to determine the chemical composition and phase transformation before and after fired at 800-1250 °C. XRF result was confirmed that all clay samples mainly contained SiO₂ (>80 wt. %) XRD pattern indicated that quartz was the majority of phase in the all of them. High amount of Fe₂O₃ (>1.6 wt. %) was related to the red-brown tone color. The clay sample could be fired up to 1280 °C without wrapping behavior; it was found that FQB clay had the highest firing resistance due to the maximum quartz content.

Abstract: The PSZTM ceramics from Pb_0.94Sr_0.06(Zr_0.52Ti_0.48)O₃ doped with 0.1 mol% Mn were prepared by a solid state reaction and. Two different methods were used to calculate the amount of Mn-dopant into PSZT powder. One was calculated rely on B-site precursor represented by B method. The other was computed based on the amount of calcined PSZT called C method. This study was to investigate the effect of the two different calculating formulations of Mn doped PSZT ceramics by B and C methods on phase formation, microstructure, physical and electrical properties. The results were observed that phase identification showed the formation of perovskite structure in both cases. Besides, the mechanical quality factor (Q_m) of the PSZTM ceramics derived from B method was two times higher than those from C method. Nevertheless, the dielectric constant (K), piezoelectric coefficient (d₃₃) and planar coupling coefficient (k_p) of the PSZTM ceramics from B method were slightly lower than those of derived from C method. This could be drawn the conclusion that PSZTM with 0.1 mol% Mn prepared by B method can be used as hard-type piezoelectric material.

Abstract: This study examined the feasibility of utilizing lignite bottom ash as a partial substitute for ball clay in an insulating brick composition. Lignite bottom ash is a waste byproduct that is high in alumina and silicates and is therefore a candidate material for replacing aluminosilicate minerals such as clay. The lignite bottom ash powder was obtained from the Mae Moh power plant, Thailand. Small brick specimens were produced by die pressing a mixture of lignite bottom ash, ball clay and aluminum hydroxide. The composition of the mixture contained a fixed amount of aluminum hydroxide, while the lignite bottom ash replaced from 30 to 70% of the ball clay. The pressed samples were sintered at 1300 oC for 1 hour in air. The density, porosity, strength and thermal properties of the samples were measured. A microstructural analysis of the sintered brick was also performed. It was found that the porosity of the samples increased from 35 to 45% with increased lignite bottom ash content. The modulus of rupture and the thermal conductivity of the bricks were reduced with increased lignite bottom ash content, likely due to the increased amount of porosity. Dilatometric analysis found that the thermal expansion increased with increased amounts of lignite bottom ash, possibly as a result of an increased amount of glassy phase. Despite the high thermal expansion coefficient at high temperature, the feasibility of using lignite bottom ash in the insulating brick composition was demonstrated.

Abstract: In this study, the mechanical properties of steel fibre reinforced geopolymer (SFRG) are investigated. The geopolymer is consisted of fly ash, silica fume and activator solution, sodium silicate and sodium hydroxide. Five mix proportions of fly ash and silica fume are varied to study the effect of fly ash/silica fume ratios (FA/SF). This experimental series focus mainly on flexural strength and flexural toughness performance of SFRG. Hooked-ends steel fibers are used at 0.5% and 1% by volume fractions. The experiment is carried out based on ASTM C1609 (beam specimens) for flexural performance. The results showed that fibre can significantly enhance the both flexural strength and toughness of geopolymer. The enhancement also increases with the increasing fibre volume fraction.

Abstract: An alumina/glass composite was examined for use as a high-temperature ceramic adhesive for bonding of 96% alumina bodies. Four compositions of alumina and glass, 90:10, 80:20, 60:40, and 40:60 by wt.% were studied, referred to here as A, B, C, and D, respectively. Rectangular bend bars were produced from compositions A-D by die pressing. Two half-sized bend bars of 96% alumina were bonded together using pastes produced from compositions A-D. The sintering shrinkage, the phase analysis, the flexural strengths, and the fracture surfaces of the sintered bend bars were examined. The XRD analysis showed a decrease in the alumina and an increase in mullite as the glass content was increased. The dilatometric results found that the onset temperature for sintering shrinkage decreased as the glass content was increased. Composition C was found to have the highest flexural strength of 94 MPa, however the flexural strength of the adhesive joint sample, was only 36 MPa. Composition D had the lowest flexural strength of 43 MPa, but it had the highest flexural strength of the adhesive joint at 61 MPa. The increased adhesive strength of composition D could be due in part to penetration of the excess glass phase into the 96% alumina body. Therefore the flexural strength of the pure compositions alone could not be used to reliably predict the adhesive bond strength. The fracture surfaces of the adhesive joints showed increasing uniformity as the glass content increased, which indicated stronger adhesion.

Abstract: In this study, the effects of different solvents such as ethanol, ethylene glycol, glycerol on the preparation of BiVO₄ via solvothermal process, and the influent of calcination heat treatment were studied. The crystal structure, surface area, morphology and optical properties of the obtained BiVO₄ particles were investigated by means of X-ray Diffraction (XRD), Brunauer Emmett Teller method (BET), Scanning electron microscope (SEM) and UV-Vis reflectance spectroscopy (UV-Vis DRS), respectively. XRD patterns reveal that all of the obtained BiVO₄ samples prepared by solvothermal at 130°C for 4 h have monoclinic structure. The UV-Vis DRS demonstrates that the band gaps of prepared BiVO₄ are about 2.38-2.40 eV. The photocatalytic activity was evaluated by photo-degradation of rhodamine B (Rh B) solution under visible light irradiation (λ>420 nm). As the results, the BiVO₄ prepared by using ethanol having high crystallinity and surface area showed the highest visible light photocatalytic activity compared to using glycerol and ethylene glycerol, respectively. Furthermore, the photocatalytic activity of BiVO₄ prepared by using ethylene glycerol and glycerol could be enhanced by calcination heat treatment at 500°C for 2 h.