In order to elucidate the phase diagram of the zirconium-hydrogen system at high hydrogen contents, a pressure-composition-temperature study of this system in the temperature range 550 to 850℃ has been carried out from ZrH to ZrH2. From the isotherms obtained in this investigation, the position of the boundary between the two-phase (β +δ) region and the single phase δ region was more precisely defined (where β designates the hydrogen stabilized high tem¬perature zirconium phase, and 5 the cubic hydride phase). The isotherms also show no evidence of a two-phase hydride region (cubic + tetragonal hydrides co¬existing) in this temperature range, as has been observed at room temperature.
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