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Eswar Prasad K.,Indian Institute of Science | Chollacoop N.,National Metal and Materials Technology Center | Ramamurty U.,Indian Institute of Science
Acta Materialia | Year: 2011

The subsurface microhardness mapping technique of Chaudhri was utilized to determine the shape, size and distribution of plastic strain underneath conical indenters of varying semi-apex angles, α (55°, 65° and 75°). Results show that the elastic-plastic boundary under the indenters is elliptical in nature, contradicting the expanding cavity model, and the ellipticity increases with α. The maximum plastic strain immediately under the indenter was found to decrease with increasing α. Complementary finite-element analysis was conducted to examine the ability of simulations to capture the experimental observations. A comparison of computational and experimental results indicates that the plastic strain distributions as well as the maximum strains immediately beneath the indenter do not match, suggesting that simulation of sharp indentation requires further detailed studies for complete comprehension. Representative strains, εr, evaluated as the volume-average strains within the elastic-plastic boundary, decrease with increasing α and are in agreement with those estimated by using the dimensional analysis. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source

Yoosuk B.,National Metal and Materials Technology Center | Tumnantong D.,Chulalongkorn University | Prasassarakich P.,Chulalongkorn University
Fuel | Year: 2012

Unsupported sulfide catalysts are a potentially promising approach towards furthering the understanding and development of a better heterogeneous catalytic system capable of performing the hydrodeoxygenation (HDO) of bio-oil proficiently under mild and short reaction conditions and times, respectively. Amorphous unsupported Ni-Mo sulfide, prepared from ammonium tetrathiomolybdate (ATTM) by a one step hydrothermal method, is already sulfided and so does not need a sulfidation step. The addition of the Ni promoter prevents the growth of Mo sulfide particles and causes a reduction in the surface area and a change in the pore characteristics as the amount of added Ni was increased. Ni sulfide alone (no Mo) showed a completely different morphology and properties compared to those of the Mo-containing sulfides, with or without the copresence of Ni. The activity and selectivity of catalysts was investigated using phenol as a model substrate in the direct-deoxygenation (DDO) and hydrogenation (HYD) reactions in a HDO system. The Ni-Mo sulfide catalyst with optimal Ni amount had a significantly higher phenol conversion efficiency (96.2 mol%), and favored a HYD pathway, than that seen for the Mo sulfide one (71.0 mol%) that favored a DDO pathway. H2-temperature programmed desorption (TPD) suggested that this synergy was mainly derived from a change in the quality and not the number of the active sites. The synergetic effect was a function of the stoichiometric composition with the maximum synergetic effect being obtained at a Ni/(Mo + Ni) ratio of 0.3. This could result from the high dispersion of the active species and the generation of a more active Ni-Mo-S phase. © 2011 Elsevier Ltd. All rights reserved. Source

Tantirungrotechai J.,Center for Catalysis | Thepwatee S.,Center for Catalysis | Yoosuk B.,National Metal and Materials Technology Center
Fuel | Year: 2013

Sr/MgO catalysts for biodiesel production were synthesized by the wet impregnation method. The formation of basic sites on the catalysts was investigated by thermal analysis, XRD, and Hammett indicator method. The calcination temperature and Sr/MgO molar ratio affect the structure as well as the catalytic activities. Among the catalysts tested, the best performance catalyst was prepared with a 0.10 Sr/MgO molar ratio and a calcination temperature of 600 °C. This catalyst had a base strength in the range of 15.0-18.4 and was also active for biodiesel synthesis at room temperature. The catalytic activities under various reaction variables were also evaluated. The biodiesel yield of 93% was achieved within 30 min from the transesterification of soybean oil with methanol at 65 °C using 5 wt.% loading of the synthesized catalyst and methanol to oil molar ratio of 12:1. © 2013 Elsevier Ltd. All rights reserved. Source

Kaewpengkrow P.,Chulalongkorn University | Atong D.,National Metal and Materials Technology Center | Sricharoenchaikul V.,Chulalongkorn University
Bioresource Technology | Year: 2014

The objective of this study was to catalytically upgrade bio-oil from organic vapors of Jatropha wastes using Py-GC/MS. Catalytic testing included Al2O3, ZrO2, TiO2 (rutile, T1) and TiO2 (anatase, T2) supporter catalysts modified with transition metals (Pd, Ru or Ni) by impregnation method. In non-catalytic runs, the main vapor products were fatty acids (60.74%). With the presence of Al2O3 based catalysts, carboxylic acids were obviously reduced to 0.76-19.61% while hydrocarbons were the main products (42.00-64.06%). Comparing among four supporters, total hydrocarbon yields increased with presence of all catalysts. Higher yields were obtained by T2>Al2O3>CA>NiCA>RuCA catalysts. Al2O3 and T2 supports were the most effective for increased hydrocarbons while decreased oxygenated compounds (15%) which is one of the primary aims of this study. The result indicating that high surface area resulted in better catalytic activity but also adversely promoted N-compounds. Therefore these catalysts can be applied to improve properties of pyrolytic products. © 2014 Elsevier Ltd. Source

Yoriya S.,National Metal and Materials Technology Center
International Journal of Electrochemical Science | Year: 2012

This work presents the formation of TiO2 nanotube arrays fabricated by electrochemical anodization of titanium in the fluoride-based diethylene glycol (DEG) electrolyte, with an aim towards elucidating how variation of inter-electrode spacing affects changes in electrolyte properties and corresponding morphological features of TiO2 nanotube array films. Enlargement of nanotube morphologies of DEG fabricated nanotubes is attainable through a simplified synthesis technique and manipulation of electrolyte properties. Electrolyte conductivity and titanium concentration are found to drastically increase with decreasing anode-cathode separation. Resulting titania nanotube array morphologies also tends to increase significantly, particularly observed in intertubular spacing that increases by a factor of 15 as reducing the electrode spacing from 4.5 cm to 0.5 cm under a fixed electrolyte condition. Due to the combination effect of electrolyte properties and high field strength between the electrodes, the self-enlargement potential is believed to be a driving force for nanotube separation. The unique characteristic of discrete, well-separated nanotube structure is expected to extend and enhance the applications of anodic TiO2 nanotube array films. © 2012 by ESG. Source

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