Masao Taniguchi

A new method of sulfur vapor pressure control and its application to the V-S system

A new apparatus for obtaining partial pressure of sulfur was devised by using liquid sulfur and carrier gas of nitrogen. This successfully works in the range of ∼10−4 to ∼1 atm of Ps2 at any temperature higher than about 400°C up to about 1000°C. As an application of it, the equilibrium study of V-S system was done at 800°C. Two phases V3S4 and V5S8, each having homogeneity range, were found while no existence of the V2S3 phase could be detected thermodynamically and X-ray crystallogrpahically at this temperature. The standard free energy of following reaction, VS43 + 215S2 = VS85, was calculated by considering the transition-Ps2 and the activities aVS85 and aVS43 · ΔG° (1073K) = −1150 cal·mole−1was obtained with an estimated uncertainty of ± 100 cal to the above reaction.

Stable range of copper molybdenum sulfide CuxMo6S8−y and measurement of the superconducting critical temperature Tc

Abstract Copper molybdenum sulfides Cux Mo 6 S 8−y with rhomobhedral structure have been prepared by vacuum seal technique at 1000°C. The nonstoichiometric range of copper x varies between 2.0 and 4.0, and that of sulfur (8−y) varies between 7.75 and 8.00. The compositional dependence of the lattice parameters a R and α R , and that of the super-conducting critical temperature Tc have been examined. Both a R and α R remarkably increase with increment of copper content but they are almost independent of sulfur content. Tc is about 10K at both x = 2.0 and 2.5, and about 6K and 7K at x = 3.0 and 3.5, respectively but it varies only a little with variation of sulfur content. Copper content may affect Tc but the compositional change in sulfur has very little effect on Tc.

A rechargeable lithium battery employing iron Chevrel phase compound (Fe1.25Mo6S7.8 as the cathode

Abstract Powder of iron Chevrel phase compound (Fe 1.25 Mo 6 S 7.8 ) was used as the cathode for lithium secondary battery. 1 M LiClO 4 in PC was used as an electrolyte. The discharge and discharge—charge cycling properties were measured galvanostatically at a constant current density from 7.5 μA cm −2 to 0.7 mA cm −2 . A theoretical energy density of 217 W h kg −1 (only the weight of the cathode and incorporated lithium was considered for the estimation) was obtained at the first discharge when C.D. was fixed at 0.3 mA cm −2 (cut-off 1.0 V). A good rechargeability of more than 1100 times was observed in the case of relatively shallow discharge—charge experiment. Lattice expansion with intercalation of lithium ions in the iron Chevrel phase compound was less than that in copper Chevrel phase compounds which had been investigated previously.

Phase relationship on Mo-S system at high temperatures

Abstract Changing the partial pressure of sulfur Ps 2 at temperatures of 750° and 950°C, phase equilibria on the Mo-S system by solid-gas reaction were investigated. Hexagonal 2H-MoS 2 and monoclinic Mo 2 S 3 phases were identified from the x-ray powder diffraction pattern. The 2H-MoS 2 had a slight homogeneity range, i.e. MoS 1.978 to MoS 2.0 at 950°C, MoS 1.983 to MoS 2.0 at 750°C. No remarkable variation of lattice parameters for the MoS 2 was observed. The composition of the Mo 2 S 3 phase was not stoichiometric MoS 1.5 but MoS 1.457 at 950°C. At 750°C the composition of the Mo 2 S 3 phase could not be determined since it was quite difficult to establish the equilibrium state between the gas and the condensed phases. This finding agreed well with the result of Morimoto and Kullerud.

Nickel-Molybdenum Sulfide Ni[sub 2]Mo[sub 6]S[sub 7.9] as the Cathode of Lithium Secondary Batteries

Nickel-molybdenum sulfide Ni{sub 2}Mo{sub 6}S{sub 7.9} (nickel Chevrel phase, NiCP) was tested as the cathode of lithium secondary batteries. The Li/NiCP cell could be galvanostatically discharged up to {ital x} = 4 {approximately} 5(Li{sub {ital x}}Ni{sub 2}Mo{sub 6}S{sub 7.9}) when the current density was smaller than 0.5 mA/cm{sup 2}. No evidence of nickel deposition from the NiCP cathode was observed even after the cell was deeply discharged to {ital x} {approx equal} 4. This resulted in the small distortion of the NiCp crystal lattice upon lithium intercalation, which was clearly observed by the experimental result that the {alpha}{sub r} value of the rhombohedral lattice parameter hardly changed before and after lithium intercalation. As a result, the NiCP cathodes showed excellent discharge-charge cycling properties. In a deep cycling test carried out between 1.5--2.7 V, more than 50% of the initial discharge capacity was maintained even after 200 cycles. In shallow range cycling tests performed in the ranges of 0.5{lt}{ital x}{lt}1 and 1{lt}{ital x} , 2, the cells were cycled more than 5000 and 1700 times, respectively.

Synthesis of vanadium sulfides under high pressure

Vanadium sulfides were synthesized in a temperature range of 350–750°C and in a pressure range of 10–250 MPa (1 MPa = 9.87 atm), with an apparatus used for hydrothermal synthesis. The nonstoichiometric compositional range of the V1+x S2 phase, which cannot be prepared under atmospheric pressure, is VS1.661−VS1.732 (0.155 <x < 0.204). It was impossible to synthesize vanadium disulfide VS2 under the present experimental conditions. Equilibrium phase diagrams for the V5S8−S system under 100 and 200 MPa have been proposed on the basis of the present results. Also, the phase relationship between V5S8 and V1+x S2 has been established and a pressure-temperature phase diagram for the V−S system has been drawn.

Thermal analysis and kinetics of oxidation of molybdenum sulfides

AbstractThe thermal oxidation process of stoichiometric MoS2 and nonstoichiometric “Mo2S3”, together with the kinetics of oxidation of MoS2, were studied by using TG and DTA techniques in the Po2 range 1-0.0890 atm. MoS2 was oxidized completely to MoO3 in one step:n n

Thermodynamic studies of the V3S4−V5S8 system at temperatures from 650 to 800°C

MoS_2 + 7/2O_2 to MoO_3 + 2SO_2