Papers by Author: Sitthisuntorn Supothina

Abstract: Thin films of vanadium oxide were synthesized by DC magnetron sputtering on a glass slide. Process parameters including temperature, argon and oxygen ratio (Ar:O₂) and base pressure were investigated. It was found that the control of sputtering base pressure is very important in realizing the pure VO₂ (M) thin films. These thin films have grown at low base pressure of 5x10^-6 mbar. The results of the valence electron analysis show the outstanding phase of VO₂ and a small amount of V₂O₅ and V₂O₃ phases. The hysteresis loop of electrical resistance property of the VO₂ thin films illustrated the quality of film, which is related to metal-insulator transition phase (MIT) at the transition temperature (T_c) of approximately 63°C. The sample was tested for its electrical properties by a four-probe setup with a temperature controller during heating and cooling cycles.

Abstract: The separation of oil from water is significance for environmental de-pollution application. To obtain selectivity of liquid, filter papers were coated to bear highly hydrophobic and oleophilic functionality that can allow only oils to pass through them. The coating solutions were prepared by mixing poly(methylhydro siloxane, PMHS) and fumed silica at various proportions. To determine an optimum coating condition, properties of the treated filter papers were investigated by measuring water contact angle and surface free energy, examining surface morphology and testing for selective removal of diesel oil from water. The optimum coating solution was at the PMHS:fumed silica weight ratio of 1.25:1.00. The treated filter paper exhibited high hydrophobicity with water contact angle of 142.80 ± 0.36 degrees and surface free energy of 0.78 mJ/m². In addition, it exhibited high selective removal of diesel oil from water with oil absorption capacity of 2.3 g/g.

Abstract: A latex cup is used to collect latex from a rubber tree which is an economic plant in Thailand. The fresh latex or crude rubber consists of organic compound and water which can wet and adhere to surface of the collecting cup. In this research, surface of the latex cup was treated with polymethylhydrogen siloxane-functionalized silica compound to improve hydrophobicity so that it could repel the dirt and latex, resulting in an anti-adhesion between the latex and the cup. Surface of the latex cup was etched with 10 % v/v hydrofluoric acid for 30 min before application of the siloxane coating which was performed by immersion in the solution, painting and spraying, respectively. The result revealed that the immersion method exhibited optimum property justified by high value of water contact angle, low surface free energy, surface roughness and the field test. At the optimum polymethylhydrogen siloxane : fumed silica ratio of 3 : 1 wt%, the treated sample had water contact angle of 139.24 ± 0.78 degrees and possessed surface energy of 1.07 mJ/m². The field test conducted in the rubber field in Trang province revealed good durability of the coating. The water contact angles were 132.15 ± 2.05 and 129.20 ± 2.34 degrees after 2 weeks and 1 month, respectively, of the field service.

Abstract: This paper reports studies to investigate the relationships between hydrophobicity of biochar surface and soil water retention. The studied biochars were produced from acacia wood, cashew wood and bamboo. The resulting materials were oxidized via liquid oxidation to generate hydrophilic biochars containing oxygenated functional groups on the surface. All biochars were characterized and their ability as soil additives to enhance water retention was assessed. Our results suggest that hydrophobicity/hydrophilicity of biochars is not the major factor governing water retention ability of this particular soil. However, hydrophilicity of biochar helps improve soil permeability by providing better wettability to the soil.

Abstract: Solar-reflective yellow pigment was synthesized by a solid-state reaction of the Sm₂O₃ and CeO₂ in the presence of the (NH₄)₆Mo₇O₂₄ employed for the Mo doping. The raw materials were wet milled in acetone for 6 h to acheive a homogeneous slurry followed by calcination at 1100, 1300 and 1500 °C for 6 h. The effect of the Mo doping was investigated by adding 10, 15, 20, 25 and 30 wt.% (NH₄)₆Mo₇O₂₄. XRD analysis of the undoped product revealed the formation of Sm₂Ce₂O₇ at 1300 °C along with the unreacted Sm₂O₃ and CeO₂, and revealed the completed reaction at 1500 °C. The addition of (NH₄)₆Mo₇O₂₄ resulted in the formation of Sm₂Ce_2-xMo_xO_7+δ, where x = 0.02, 0.03, 0.04 and 0.05 depending on the amount of the Mo dopant employed. The doping also significantly affected the product’s color; it turned from ivory white to yellow with the increase of dopant content up to 20 wt.% and became dark green afterward. Increasing firing temperature from 1100 to 1500 °C led to brighter yellow due to the substitution of Mo⁶⁺ for Ce⁴⁺. At the optimum synthesis condition, i.e. 20 wt.% doping and 1500 °C firing temperature, the product was most yellowish and had 69.2 % near-infrared reflectance.

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: Solar-reflective green pigment was synthesized from the starting powder consisting of chromium oxide (Cr₂O₃), aluminum oxide (Al₂O₃), titanium dioxide (TiO₂), and vanadium oxide (V₂O₅) by high-speed, wet milling at the speed of 300 rpm for 2 h followed by calcination at 1150 or 1200 °C for 0.5-5 h. X-ray diffraction analysis revealed the presence of reduced chromium oxide, Cr₂O_2.4, which is the major component, and rutile TiO₂ phase of which its XRD peak intensities were intensified upon calcination as a result of phase transformation from amorphous portion in the starting TiO₂. Microstructural analysis revealed significant particle growth after calcination at 1200 °C for 5 h due to Ostwald ripening. Highest near-infrared reflectance of 70.1% was obtained from the product calcined at 1150 °C for 0.5 h. Higher calcination temperature and/or extended period of calcination time led to a reduced reflection which is ascribed to an increased of particle size of the synthesized pigment.

Abstract: A mulberry paper has been used to produce many consumer products such as lantern, card, packaging and decorating articles. Similar to other cellulosic materials, the mulberry paper bears abundant hydroxyl groups on its surface. Besides easily ignited, it can absorb water or humidity. To improve its thermal stability and to reduce deterioration caused by moisture adsorption, the mulberry paper was coated with a flame-retardant substance which was monoammonium phosphate (MAP) and a hydrophobic substance which was poly (methylhydrogen siloxane) (PMHS). The coating was conducted by immersing the mulberry paper in coating solution for 2 min followed by drying at 50 °C for 30 min. By varying a weight ratio of the PMHS and MAP, the PMHS:MAP weight ratio of 10:10 was found to be the optimum coating solution. The coated mulberry paper had good thermal property according to the thermogravimetric analysis. The uncoated mulberry paper showed residue of about 21% while the coated mulberry paper showed the increased residue of more than 50%. The burning test revealed that the coated mulberry paper was self-extinguished after removal of the ignition source while complete burning was observed on the uncoated paper. Moreover, it was water repellent with a water contact angle of 101.48 ± 5.81 degrees.

Abstract: Two different viscous coating materials, which are Polydimethylsiloxane (PDMS) mixed with 10%wt of Dicumylperoxide (DCP), and Semifluorinate Silane (SFS), were applied to silicon micro-asperity. The cosine’s Young and viscosity of those coating materials are -0.3584,-0.3496 and 3.176x10-3, 1.339 x10-3 Pas, respectively. The rough surfaces with nine asperity shapes were studied. The results shown that, pillar shape has an effect on water contact angle (WCA): Stripe asperity cannot make the average WCA greater than 150. When consider the pillar asperity, the WCA falls between 152 and 157, which exhibits a superhydrophobic surface property. However, actual WCA of the micro-asperity coated with PDMS+10%wt of DCP is lower than that coated with SFS around 1 to 7. High viscous material makes the asperity size bigger than the design and decreases the WCA: the low viscous material is more suitable for coating on the asperities.

Abstract: In this paper, we report innovative gloves that are coated with hydrophobic film such that the outer surface of the gloves is hydrophobic. A coating precursor containing polymethyl hydrogensiloxane, silica nanoparticle, semifluorinated silane and Pt-catalyst was painted onto the gloves. The coated gloves were kept at room temperature for 12 h to make the film dry, and then tested for their chemical resistance with 10 M NaOH, conc. HCl, conc. H2SO4 and conc. HNO3 solutions, as well as the standard buffered solutions (pH = 1, 4, 10, and 12) at 25oC by dropping the chemicals onto the coated gloves. It was found that the nitrile gloves had similar contact angles to the latex gloves when tested with the standard buffered solutions while the nitrile gloves had higher contact angles compared to the latex gloves when tested with different aqueous-based hazardous chemicals. The nitrile gloves coated with the hydrophobic film showed high acid droplet contact angle, leaving behind much lesser damage from hazardous chemicals.