Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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Thermodynamic investigation of the effect of oxygen and hydrogen chloride potential upon generation and decomposition behavior of dioxins

Nagahiro Saito, Takahiro Ishizaki, Akio Fuwa

Toxicological and Environmental Chemistry Vol. 75 ( 3-4 ) page： 161 - 179 2000

Language：English Publishing type：Research paper (scientific journal)

The thermodynamic equilibrium of the C-H-O-Cl system has been calculated to elucidate the generation and decomposition behavior of dioxins, and is discussed from the viewpoint of the oxygen and hydrogen chloride potential. The dioxins behavior is greatly dependent on the oxygen potential, i.e. higher temperature and oxygen potential lead to the complete decomposition of dioxins, while low hydrogen chloride potential under insufficient oxygen condition leads to an increase of multi-chlorine displacement of dioxins.

DOI： 10.1080/02772240009358902

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Thermodynamic function derivation of dioxin substances using semi-empirical molecular orbital theory

Saito N., Fuwa A.

Proceedings of the TMS Fall Extraction and Processing Conference Vol. 3 page： 2009 - 2018 1999.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the TMS Fall Extraction and Processing Conference

In this investigation, respective thermodynamic parameters of heats of formation, standard entropy and specific heat capacity at constant pressure for PCDDs, PCDFs, Co-PCB and PCBs as well as polychlorinated-benzens and polychlorinated-phenols have been evaluated by quantum chemical calculation using a semi-empirical molecular orbital method with the PM3 Hamiltonian and statistical thermodynamic correlation. The values of heats of formation for the dioxin substances and their precursors are calculated in the range of ±200 kJ/mol. The tolerance analysis indicates that the maximum discrepancy with experimental values would be reasonably estimated to be ±28 kJ/mol. The values of standard entropy for these compounds would be in the range of + 270 to + 500 J/mol K, and the estimated discrepancy between the calculated experimental heats of formation would be in the range of + 1 to + 9 J/mol K.

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Prediction of Elementary Reaction Mechanism for the CVD Process in Si<inf>2</inf>Cl<inf>6</inf>-H<inf>2</inf> System using Semi-Empirical Molecular Orbital Method

Saito N., Fuwa A.

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals Vol. 63 ( 3 ) page： 319 - 325 1999

Language：English Publishing type：Research paper (scientific journal) Publisher：Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals

From our previous experimental study of the Si chemical vapor deposition in Si2Cl6-H2 system, the following elementary reaction mechanism was proposed: decomposition of Si2Cl6 to produce SiCl2, which becomes the adsorbent; Si2Cl6(g) → 2SiCl3(g) → SiCl4(g) + SiCl2(g) (→ SiCl2(a)), and hydrogen reduction reaction of the absorbed SiCl2 to produce Si(s). The preliminary quantum chemistry study for this reaction mechanism has shown that the reaction is so infeasible that the above-mentioned elementary reaction mechanism is unreasonable. The most feasible and appropriate reaction mechanism has been shown as follows: (Step 1) Si2Cl6(g) → SiCl4,(g) + SiCl2(g) (Step 2) SiCl2(g) +a → SiCl2(a) (Step 3) SiCl2(a) + H2(g) → SiCl(a) + 2HCl(g) (Step 3-1) SiCl2(a) + H2(g) → Si-2HCl(a) (Step 3-2) Si-2HCl(a) → Si(a) + 2HCl(g) where, a is the active site on silicon surface. On the assumption that step 3 is the rate-determining step, this elementary reaction mechanism can explain the experimental observation in the rate expression on the concentration dependence with respect to Si2Cl6 and H2.

DOI： 10.2320/jinstmet1952.63.3_319

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Prediction of pressure dependent rate constant for the reaction, SiH<inf>4</inf>(g)→SiH<inf>3</inf>(g)+H(g), using RRKM theory aided by ab-initio MO

Saito N., Hirota M., Ishizaki T., Fuwa A.

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals Vol. 63 ( 4 ) page： 520 - 526 1999

Language：English Publishing type：Research paper (scientific journal) Publisher：Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals

The pressure dependent rate constant for the reaction, SiH4(g)→SiH3(g)+H was predicted using the Rice-Ramspger-Kassel-Marcus theory aided by Ab-initio molecular orbital (MO). It was calculated under conditions in which the temperatures were from 600 to 1500 K intervals of 100 K. The Arrhenius type rate expression was shown.

DOI： 10.2320/jinstmet1952.63.4_520

Scopus

Effect of citric acid and EDTA addition on Cu-In alloy electrochemical deposition

Ishizaki T., Saito N., Fuwa A.

Materials Transactions, JIM Vol. 40 ( 9 ) page： 867 - 870 1999

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Transactions, JIM

The standard electrode potential for Cu is 0.34 V and that of In is -0.34 V, which means that their deposition potentials are far apart, making the co-deposition difficult from a simple solution containing Cu and In ions. In order to bring these deposition potentials closer, a complex forming reagent of citric or EDTA is added to the CuSO4-In2(SO4)3 solution. The effect of these reagents was examined by linear sweep voltammetric measurement. An electrochemical deposition experiment of Cu-In alloy was conducted where effect citric acid or EDTA addition, current density and Cu concentration were examined.

DOI： 10.2320/matertrans1989.40.867

Scopus

Theoretical analysis for thermal chemical vapor deposition from Tetraethoxysilane using a semi-empirical molecular orbital method

Hirota M., Saito N., Ishizaki T., Fuwa A.

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals Vol. 63 ( 7 ) page： 931 - 937 1999

Language：English Publishing type：Research paper (scientific journal) Publisher：Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals

In order to elucidate the reaction mechanism for the Tetraethoxysilane (TEOS) thermal decomposition at atmospheric pressure, its pertinent elemental reactions involving the SiO(OC2H5)2 reaction intermediate were first proposed. For respective species formed in these elemental reactions, the total energy and the electronic state were calculated using a semi-empirical molecular method. The adsorption process which involves adsorbent species formation and surface reaction mechanism were then analyzed from the standpoint of molecular orbital formation and charge transfer mechanism, and the results are summarized as follows: (1) A reaction intermediate, SiO(OC2H5)2(1A1), is probably formed through the following β-elimination reaction route: Si(OC2H5)4(1A1)→SiO(OC2H5) 2(1A1)+C2H4(1A1)+C2H5OH (1A1). (2) The adsorption of SiO(OC2H5)2(1A1) on SiO2 occurs with charge transfer from the dangling bond of silicon atom at an active site of the SiO2 surface to the π*-LUMO unoccupied orbital of SiO(OC2H5)2(1A1). (3) The sequence of surface reactions is considered as follows: (1) First, a dissociation reaction of C2H5(2A′) takes place, whereby producing a double bond between silicon atom and oxygen atom of the intermediate, since they possess unpaired electrons. (2) Si-O bond is successively formed following the mechanism similar to the one operating in the adsorption of SiO(OC2H5)2(1A1) on SiO2. (3) Electronic state of the reactant finally formed is in the 1A1 state, which has a σ-orbital to be fully occupied with electrons.

DOI： 10.2320/jinstmet1952.63.7_931

Scopus

Texture of thin silicon films deposited from Si<inf>2</inf>Cl<inf>6</inf>

Kato Y., Saito N., Fuwa A.

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals Vol. 60 ( 8 ) page： 744 - 750 1996.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals

Thin Silicon films were deposited on non-crystal quartz glass substrates by hydrogen reduction of Si2Cl6 at temperatures from 650 to 900 °C in a horizontal hot wall reactor. The microstructures of the thin silicon films deposited under various experimental conditions were analyzed. The thin silicon films deposited from 750 to 850 °C have the highest degree of preferred (220) plane orientation with the 〈111〉 direction along the plane, and the cross-sectional morphology exhibits a columnar structure. The experimental values of the lattice spacing approach a value cited in JCPDS for the films deposited in a higher temperature range. In the lower temperature range the morphology of surface is flat and smooth, and in the higher temperature range the surface becomes uneven remarkably.

DOI： 10.2320/jinstmet1952.60.8_744

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