Hydride Formation during Cathodic Polarization of Zr and its Anodic Polarization Behavior

Abstract

In order to clarify the kinetics of hydrogen absorption in Zr during galvanostatic cathodic polarization in 4N H₂SO₄, 1N Na₂SO₄ and 1N NaOH, the hydrogen content was determined by solid state vacuum extraction at 900°C. In addition, the anodic polarization behavior of Zr hydride formed by the cathodic treatment was investigated by means of galvanostatic and potentiostatic methods.
The results obtained are as follows:
(1) The δ phase which had a fcc type structure (a=4.810±0.005 Å) and the ε phase which had a fct type structure (a⁄c=0.930±0.002) were formed during the cathodic polarization.
(2) The rate of hydrogen absorption increased abruptly at current density i_l, above which the rate was independent of c.d.
i_l=5×10⁻² A/cm² (in Na₂SO₄),
i_l=1×10⁻¹ A/cm² (in NaOH).
The rate was initially linear but then became palabolic, indicating that the hydrogen diffusion was rate controlling. A value of 3×10⁻¹¹ cm²/sec was obtained for the diffusion coefficient of hydrogen in Zr.
(3) In the anodic polarization curve, the peak of current was created by oxidation of Zr hydride.
The unitary formation rate R calculated from the gradient of the E-t curve was linearly related to logi, but R decreased with hydrogen content.