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Masuzawa T.,International Christian University | Sato Y.,International Christian University | Kudo Y.,International Christian University | Saito I.,University of Cambridge | And 8 more authors.
Journal of Vacuum Science and Technology B:Nanotechnology and Microelectronics | Year: 2011

A recent study demonstrated that electron emission occurs from conduction bands of heavily nitrogen (N)-doped diamond, utilizing the benefit of negative electron affinity [H. Yamaguchi, Phys. Rev. B 80, 165321 (2009)]. In addition, doping N-doped diamond films with dimethylurea (DMU) allowed high reproducibility. In this article, field emission properties of N-doped diamond films were compared between samples doped with DMU and one doped with urea. Fowler-Nordheim analysis and voltage-distance plot analysis showed that the barrier height for the urea-doped film was smaller than for DMU-doped counterparts, while the barrier height showed only a slight decrease when the DMU concentration in the reactant solution was changed from 10 to 1000 ppm. Ultraviolet photoelectron spectroscopy indicated that this difference in barrier height did not originate from the electron affinity. Time of flight secondary ion mass spectroscopy (TOF SIMS) exhibited that the concentration of C-N bonds in the urea-doped sample was an order of magnitude higher than in the two DMU-doped samples. This result suggests that only nitrogen atoms incorporated as C-N enhance the field emission properties of N-doped diamond films. Further TOF SIMS analysis of N-doped diamonds with urea or DMU doping may clarify the C-N distribution in relation to the electron emission under low electric fields. © 2011 American Vacuum Society.

Morimoto M.,Energy Technology Research Institute | Sugimoto Y.,Energy Technology Research Institute | Sato S.,Energy Technology Research Institute | Takanohashi T.,Energy Technology Research Institute
Energy and Fuels | Year: 2014

This study compared various thermal cracking processes for Athabasca oil sand bitumen according to the relationship between vacuum residue (VR) conversion and the product yield for each process, using reported data. The conversion was defined as the fraction of VR that was converted to lighter products. The conventional processes examined were visbreaking, delayed coking, and fluid coking, and the developing processes were high conversion soaker cracking (HSC), heavy to light (HTL), IYQ, Eureka, and supercritical water cracking (SCWC). HSC and SCWC were higher severity visbreaking-type processes with conversions of 0.49 and 0.39-0.50, respectively. HTL and IYQ (recycle) were lower severity fluid coking-type processes with a conversion of 0.52. IYQ (once through) and Eureka showed the highest conversions (0.62-0.68). Supercritical water (SCW) upgrading was operated experimentally at higher severity, with a conversion of 0.64, and showed the highest yield of distillate product (DP) among all thermal cracking processes investigated. Analysis of the conversion-yield relationship revealed the thermal cracking behavior of Athabasca bitumen. The key for achieving higher conversions with lower coke yield was considered to be efficient mass transfer of the volatile fraction stripped away from the condensed phase, which is a liquid fraction at the experimental condition. The condensed-phase decomposition showed an upper limit of conversion of 0.55, and that with a high mass-transfer system exceeded 0.65. © 2014 American Chemical Society.

Sharma A.,Energy Technology Research Institute | Takanohashi T.,Energy Technology Research Institute
27th Annual International Pittsburgh Coal Conference 2010, PCC 2010 | Year: 2010

Catalytic gasification of coal is an efficient way to achieve high gasification rates at as low as 700 °C temperatures. The problem of deactivation of catalyst due to the interaction of catalyst with mineral matter in the coal was overcome by using HyprCoal, an ash less product of solvent extraction process as feed coal for catalytic process. Synthesis gas is the main desirable product and its composition H2/CO ratio is important for its use in the downstream FT process. However, in a catalytic gasification process it is difficult to control the gas composition because of the effect of catalyst on water-gas shift reaction. Effect of temperature and gasifying agent composition on gasification rate and synthesis gas composition were investigated. Experiments were carried out with pure steam, pure CO2 and mixture of steam and CO2 as gasifying agents in the 600∼700 °C temperature range to investigate the effects. Results showed that by adjusting the steam to CO2 ratio of the gasifying agent it is possible to control the synthesis gas composition. Effect of CO2 addition on reaction kinetics was discussed along with the calculated gas compositions. A new single step process to produce a desired synthesis gas from catalytic gasification has been proposed.

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