Nitrogen Diffusion in Zirconium Nitride

Abstract

<p>Diffusion of nitrogen in zirconium nitride was studied using the l5N gas-solid exchange technique.</p> <p>Two kinds of samples were used: ZrN 0.71-0.79 spheres, 60u and 90u diameter and ZrN 0.93 slabs 254u thick. The spheres were prepared by dropping 99% powdered zirconium nitride through an electric arc while the slabs were obtained by direct nitridation of 99.995% zirconium sheets at 1150°C in very pure nitrogen at 1 atm. These samples were carefully characterized by chemical analysis, density and lattice parameter measurements, electron microanalysis, X-ray diffraction and scanning electron microscopy techniques.</p> <p>The diffusion annealings were performed at a pressure of 200 Torr and in the temperature range 1000-1200°C. The rate of depletion of 15N in the isotopically enriched gas phase was measured by a mass spectrometer and used to calculate the self-diffusion coefficient.</p> <p>The diffusion coefficients for spheres and slabs could be respectively represented by</p> <p>Dspheres(cm^2/sec) = (2.97+18.76-2.56)x 10^-10 exp (-(23,000+/-5,400)/RT)</p> <p>and</p> <p>Dslabs(cm^2/sec) = (4.08+88.23-3.90) x 10^-6 exp(-(36,000+/-4,500)/RT)</p> <p>These results are in good agreement with the chemical diffusion coefficients available in the literature. It is shown that the rather low activation energies, in particular in the case of spheres, do not preclude a vacancy mechanism for nitrogen diffusion.</p>