Deuterium absorption and material phase characteristics of Zr₂Fe

Deuterium absorption and material phase characteristics of Zr₂Fe (SAES St 198) were studied. Scanning electron microscope images of polished surfaces, electron probe microanalysis and X-ray powder diffractometry indicated the presence of a continuous Zr₂Fe phase with secondary phases of ZrFe₂, Zr₅FeSn, α-Zr and Zr₆Fe₃O. A statistically-designed experiment to determine the effects of temperature, time and vacuum quality on activation of St 198 revealed that when activated at low temperature (350 °C) deuterium absorption rate at 350 °C was slower when the vacuum quality was poor (2.5 Pa vs. 3 × 10^-4 Pa). However, at higher activation temperature (500 °C), deuterium absorption rate at 350 °C was fast and was independent of vacuum quality. Deuterium pressure-composition-temperature (P-C-T) data are reported for St 198 in the temperature range 200-500 °C. The P-C-T data over the full range of deuterium loading and at temperatures of 350 °C and below are described by the following expression given in terms of the equilibrium D₂ absorption pressure, P_D2, and the getter loading, q: K_Oe^-( δH_a RT) = q² P_D2(q^*-q)² where ΔH_a and K₀ have values of 101.8 kJ mol^-1 and 3.24 × 10^-8 Pa^-1, respectively, and q^* is 15.998 kPa L^-1 g^-1. At higher temperatures, one or more secondary reactions in the solid phase occur that slowly consume D₂ from the gas phase. X-ray diffraction and other data suggest these reactions to be: 2Zr₂FeD_x→xZrD₂+ x 3ZrFe₂+2- 2 3xZr₂FeZr₂FeD_x+2- 1 22D₂→2ZrD₂+Fe where 0 < x < 3. Reaction between gas phase deuterium and Zr₂Fe formed in the first reaction accounts for the observed consumption of deuterium from the gas phase by this reaction.