Measurements of vapor pressure of Y and activity of Y in Y–O alloy by multi-Knudsen cell mass spectrometry

The vapor pressure of Y at 1423–1573 K was measured by multi-Knudsen cell mass spectrometry using Cu or Ni as a reference substance, and it was expressed as follows:ln(PY (Pa))=25.08±0.27−47,100±400T.The activities of Y in Y–O alloys with oxygen concentration up to 27.3 at.%, which involve αY, αY + βY, βY, and βY + Y2O3 phases, were measured using elemental Y as the reference substance. The activities were calculated by using vapor pressure of Y and they were thermodynamically consistent with the phase diagrams.