C 14 Type Ti(Zr)-Mn Hydrogen Storage Alloys for Heat Pumps

Abstract

The controllable ranges of hydrogen equilibrium pressure, pressure hysteresis and plateau characteristics of Ti(Zr)-Mn hydrogen storage alloys with C 14-type (MgZn₂ type) Laves phase were improved by optimizing the alloy composition and the fabrication process. It was found that the ratio of, Zr to Ti controls the equilibrium pressure in a wide range (e, g.10-10⁸ Pa at 20°C, corresponding to a temperature range -50+ 250°C at 1.013×10⁵ Pa). Modification of the alloy composition by partial substitution, for example Cr, Cu and Ni for Mn, and the alloy homogenization by annealing at a high temperature, 1000-1200°C, were effective for improving the hysteresis and plateau characteristics in all range of hydrogen equilibrium pressure.
Ti(Zr)-Mn alloys react with hydrogen more rapidly than La-Ni and Fe-Ti alloys, and exhibit no degradation in cycle life tests in a closed system.
Based on these results we chose three alloy system s with different equilibrium pressure, and applied them to a double effect heat pump system operated at a low pressure. The system achieved high coefficency of performance (COP), 0.65 in cooling and 1.78 in heating, and proved to be promising for effective use of high temperature waste heat.