Nitrogen Diffusion in Zirconium Nitride

ABSTRACT,Diffusion of nitrogen in ZnNo.93 plates obtained by direct nitr idation of 99.995 weight per cent zirconium sheets at 1150 ~ was studied using the ~SN gas-solid exchange technique. These specimens were characterized by chemi-cal analyses, density, lattice parameter, and structural measurements. The diffusion anneals were performed at a nitrogen pressure of 220 Torr and at temperatures in the range 1000~176 The tracer diffusion coefficient can be expressed as D * (cm2/sec)---- 4.08 • 10-6 exp--36,600/RT. These results when compared to determinations of the chemical diffusion coefficients ob-tained from Zr nitriding kinetics demonstrate that nitrogen transport in the polycrystalline solid at temperatures less than 1200 ~ is associated with a short-circuit diffusion mechanism. Diffusion studies on metal ni~rides have been a sub-ject of l imited interest. Indeed, diffusion coefficients have been reported for on ly a few transition metal ni-trides which are chemical coefficients for nitrogen dif-fusion except for uranium mononitride where tracer diffusion coefficients are available for both nitrogen and the metal species. The purpose of this investiga-tion, accordingly, was to determine the nitrogen tracer diffusion coefficient in zirconium mononitride and to compare this determination to diffusivities obtained from models for the nitr idation of zirconium (1-6) and the sintering of this nonstoichiometric compound (7). Experimenta