Pressure-composition isotherms of TbNiAlHx

Accurate isotherms of TbNiAlHx were measured at 60, 150, 200, 250 °C with a Sieverts-type apparatus. The intermediate TbNiAlH0.33 and TbNiAlHx (0.4 < x < 0.6) hydrides were confirmed to be present at the higher temperatures. Orthorhombic TbNiAlHx (x > 0.9) was detected at all temperatures. The hydrogen content after desorption at 10 mbar and 60 °C is similar to prolonged storage at room temperature. The reaction between hexagonal TbNiAlH0.6 and orthorhombic TbNiAlH0.9 was found to have a desorption enthalpy of 50.7 kJ/(mol H2). Methodology and requirements for making accurate measurements of isotherms are discussed.