Anelastic studies of hydrogen diffusion in niobium

Abstract

The diffusional behavior of hydrogen in niobium was investigated in the temperature range 300°–20°K using internal friction techniques. In the high temperature range pulse-echo high frequency measurements were used while flexural vibrations were used in the low temperature range. Using these techniques the frequency dependence, orientation dependence, and concentration dependence of the hydrogen relaxations were studied in high purity Nb and Nb-O(N) alloys. Relaxation due to two types of hydrogen complexes were observed: 1. (a) hydrogen pairs, and 2. (b) oxygen (or nitrogen)-hydrogen pairs. The hydrogen pair was shown to have an enthalpy of motion of 1265 cal/mole and an enthalpy of binding of 1490 cal/mole. The oxygen (or nitrogen)-hydrogen pair was shown to consist of a single hydrogen atom bound to the oxygen interstitial with an enthalpy of about 2000 cal/mole. The hydrogen motion enthalpy in the strain field of the oxygen atom was 3900 cal/mole. The relaxations were shown to obey a classical Arrhenius temperature dependence at high temperatures and to exhibit enhanced relaxation rates at low temperatures. The data was shown to be in agreement with the theory of Flynn and Stoneham for the diffusion of light interstitial solutes.