Kinetics of the reaction of hydrogen with zirconium was studied in the temperature range of 600 - 900 ℃ using weight gain method in the flow system of Ar atmosphere. The rate controlling step of the reaction is shown to be diffusion of hydrogen through the zirconium lattice. Diffusion of hydrogen in δ zirconium hydride was studied in the temperature range of 660 - 850 ℃. Hydrogen diffused from a surface of constant concentration into a homogeneous phase, developing a second phase on the surface. For the above conditions, the diffusion equation was solved using the method treated by Wagner for this case. By correction with the measurement of the displacement of moving boundary, average concentration at 750 ℃ is given by,
$\overline{C}={\frac{4.680D^{1/2}}{h}}ㆍ{t}^{1/2}$ where D is diffusivity, t is time and h is specimen thickness. Similar expressions can be obtained for the other temperatures. By plotting C vs. $t^{1/2}$, we can calculate diffusivity from the slope. The temperature dependence of diffusion coefficient is given by
$D^ δ = 6.20 × 10^{-3}\exp [-(15,800 ± 1,800)/RT] ㎠ /sec$
Diffusion of hydrogen in homogeneous β-zirconium was also studied in the temperature range of 753-900 ℃.
The temperature dependence of diffusion coefficient is,
$D^ β =2.40 × 10^{-4}exp [-(7,000 ± 1,800)/RT] ㎠ /sec$
Oxide film on the surface of zirconium reduced the rate of diffusion of hydrogen in zirconium.
