Papers by Author: Atsunori Kamegawa

Abstract: Al–based hydrides have been extensively investigated in order to their application for hydrogen storage. To explore new hydrides, the samples in Al–X–H systems (X = Sr, V, Hf) were synthesized at 873–1173 K for 2–8 h under 5 GPa with internal hydrogen source. Unidentified phases in XRD analysis were observed in samples with nominal composition of Al–50mol%SrH₂, AlH₃–60mol%VH₂ and Al–50mol%HfH₂. Judging from SEM–EDX analysis, the chemical composition of these phases were Al/Sr=1/1, Al/V=2/3 and Al/Hf=1/2. In Al–Sr system, hydrogen content was determined to be about 2.78mass% by fusion analysis. Corresponding chemical formula of the new hydride was estimated to be AlSrH₃ with a perovskite–type crystal structure. Hydrogen desorption of 0.55 mass%H in the Al-60V sample was observed above about 400K by TG–TDS. The new compound, Al₂V₃H_1.8~2.2 had a tetragonal structure. In Al–Hf system, the new compound had almost no hydrogen. Then, the chemical fomula of newly founf compound was estimated to be AlHf₂ with a tetragonal structure.

Abstract: Effects of hydrogenation process of the microstructure, electrical conductivity and mechanical properties for the Cu-(1~3) mass%Ti alloys were investigated. During hydrogenation process at 350°C, 7.5 MPa for 48 h, the disproportionation reaction occurred with forming of Ti hydrides in the alloy. It is found that remarkable simultaneous improvements of mechanical strength of 1094 MPa and electrical properties of 21%IACS are obtained in the hydrogenated Cu-3mass%Ti alloy.

Abstract: Hydrogen storage materials are attracting much attention as media of storing hydrogen. High-pressure synthesis has been widely used for exploration of novel materials. We have reported that many new Mg-based hydrides or alloys have been synthesized by anvil-type apparatus under the pressure of GPa-order. In Mg - TM ( TM = Nb, Ta ) - H systems, it was reported that novel FCC-type hydride which is similar in crystal structure and composition to Mg7TiH13-16 was synthesized under 8 GPa. On the other hand, there is few reports of novel Ca-based hydrides to be synthesized under high pressure. However, the compressibility of calcium is higher than that of magnesium. Thus, there is a tendency for Ca compounds to be synthesized by lower pressure than Mg ones. This study describes the synthesis of new Ca-based hydrides by this high-pressure techniques. In Ca - TM ( TM = Ti, Hf, V, Nb and Ta ) systems, the influence of applied pressure on present phases were investigated. For the composition of CaH2 - 14.3 mol%ZrH2 in Ca - Zr - H system, novel hydride was synthesized at 1073 K for 2 h under 5 GPa. Crystal structure of the novel hydride was found to be FCC-type with a lattice parameter of a = 0.531 nm. In addition, the thermal stability and hydrogen contents of this novel hydride were investigated. In Ca - Hf - H system, the unknown phase was observed in the sample of CaH2 - 12.5 mol%HfH2 prepared 1073 K for 2 h under 5 GPa. This unknown phase is FCC structure with lattice parameter of a = 0.528(2) nm.

Abstract: The high-pressure synthesis of new hydrides of Mg-RE-H systems, where RE = La, Ce and Pr, were conducted by using a cubic-anvil-type apparatus, and their crystal structure, thermal stabilities and hydrogen contents were investigated. In MgH2-xmol%REH (REH = LaH3, CeH2.5 and PrH3), new hydrides with primitive tetragonal structure were synthesized around x = 25 - 33 under GPa-order high pressures. The lattice constants were a = 0.8193 nm, c = 0.5028 nm, a = 0.8118 nm, c = 0.4979 nm and a = 0.8058 nm, c= 0.4970 nm at x = 25 in Mg-La, Ce and Pr systems, respectively. The hydrogen contents of the novel compounds were 4.1 mass%, 3.7 mass% and 3.9 mass% in Mg-La, Ce and Pr systems, respectively, and the chemical formulas were found to correspond to Mg3LaH9, Mg3CeH8.1 and Mg3PrH9. The new hydrides decomposed into Mg and rare-earth hydride at about 600 K (Mg3LaH9: 614 K, Mg3CeH8.1: 609 K, Mg3PrH9: 630 K) with an endothermic reaction.