Papers by Author: Pisith Singjai

Abstract: Carbon nanotubes (CNTs) were deposited by electrophoretic deposition (EPD) on Bombyx mori (silk) and Cannabis sativa L. var. sativa (hemp) fibers to improve their mechanical properties. The CNTs were functionalized in mixed acids in order to introduce carboxylic acid groups on their surfaces. The tensile strength and strain at break point of both the modified fibers were approximately two times higher than those of the virgin natural fibers. The addition of small amounts of Mg(NO₃)₂.6H₂O, (CH₃COO)₂Ni.4H₂O significantly improved the deposition of the functionalized CNTs on the hemp fibers.

Abstract: Stainless steel/carbon nanotubes (CNTs) nanocomposite powders were synthesized by chemical vapor deposition (CVD) method with ethanol as a carbon source. The effects of synthesis temperature and time on microstructure and chemical composition of the powders were investigated. The as-received stainless steel powders were synthesized at temperature in between 550-800°C for 30-180 min at a pressure of 10 Torr. The optimum synthesis condition was found to be 800°C for 120 min. Average diameter of CNTs grown on stainless steel particles slightly increased with increasing growth temperature. The synthesis time, however, was found to have no effect on the size of CNTs.

Abstract: Carbon nanotubes (CNTs) and helical nanofibers (HNFs) were selectively grown on copper substrates by chemical vapor deposition using acetylene as a carbon source. The experiments were carried out by using Ni, Fe and Co as single and co-catalysts which were deposited onto the substrates by a sparking method. The catalyst-coated copper substrates were heated at 750°C in a mixed-gas-flowing tube furnace, at an argon flow rate of 100 ml/min and various acetylene flow rates of 3, 5 and 10 ml/min. The larger diameter of HNFs was grown only on Ni and Ni-Fe catalysts at the acetylene flow rates of 5 and 10 ml/min whereas the uniform smaller diameter of CNTs was preferentially grown on Fe-Co and Ni-Fe catalysts at the flow rate of 3 ml/min. We suggest that Co likely prevents the formation of HNFs whereas Ni promotes.

Abstract: This research studied microstructure and characterizations of Portland cement with carbon nanotubes (CNTs) which were used as an additive material at 0 %, 0.5 % and 1 % by weight of cement. The compressive and flexural strength tests of mixes were conducted using water/cement ratios (w/c) of 0.5. Samples of mixes were selected for SEM analysis and then ground for TGA analysis. The results show that the compressive strength and flexural strength at all aging time of Portland-CNTs cement composites was higher than that of control mix. Microstructure results show that CNTs was filled in pores between matrix phases to show denser phase and TGA graphs show similar phases to PC mix.

Abstract: 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.

Abstract: Iron oxide nanoparticles were prepared from an iron nitrate solution by a pyrosol technique. The precursor solution was atomized by a mist generator in order to form an aerosol which was brought into a tube furnace by a controlled flowing air stream. The pyrolysis of the aerosol was occurred to form the particles inside the furnace at 350 °C. Scanning electron microscopy images have shown that a mean diameter of the particles is in good agreement with the third root of the precursor concentration. X-ray diffraction patterns have revealed that the main peaks from the samples are corresponding to the α-Fe2O3 phase.

Abstract: Synthesis of silicon carbide nanowires (SiC NWs) from an alumina doped silica-graphite rod is reported. The rod was gradually heated up to a growth temperature by passing current through it under constant flowing argon at atmospheric pressure. The as-grown layers, deposited on the rod surface were separated from the inner core and characterized using scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, selected area electron diffraction, X-ray diffraction and Raman spectroscopy. A non-uniform layer thickness of alumina coating on SiC NWs was clearly observed when the doping was increased from 1 to 2 and 3 wt.%.

Abstract: Carbon nanotubes (CNTs)/epoxy resin composites were prepared by using a sonication technique. Microstructure, mechanical and physical properties such as hardness, wear resistance, tensile strength and density of the composite samples were examined. The tensile strength of the 0.6 vol.% CNTs/epoxy resin composites compared with the monolithic epoxy resin increased 183%. The hardness and wear resistance were maximum at 0.8 vol.% CNTs. Moreover, SEM image of the composites indicated that there is good adhesion between CNTs and the epoxy resin.

Abstract: Carbon nanotubes (CNTs) were grown on 304 stainless steel using iron as a catalyst. By using the applied voltages of 4-6 kV, iron wire with 0.5 mm in diameter was sparked for 1, 2, 10 and 100 times to form catalytic dots on the steel substrate. CNTs were subsequently grown in a gas mixture of 10 ml/s Ar and 0.1 ml/s C2H2 at a temperature range 700 - 900 K for 300 s (5 min). The dots and CNTs were characterised using AFM, SEM and TEM to determine their characteristics.