Diffusional Creep in Polycrystalline Sodium Chloride

Steady-state creep of polycrystalline sodium choride having grain size stabilized by the addition of an aluminum oxide dispersion and containing about 4% porosity was investigated at 740°C over a range of grain sizes from 65–130 μ and at stresses from 2.1–8.4 kg/cm2. Deformation was viscous (strain rate directly proportional to stress) at a rate in good agreement with the Nabarro—Herring equation, assuming the deformation rate to be limited by chlorine ion diffusion. Grain-size dependence and absolute creep rates were satisfactorily predicted with Laurent and Bénard's diffusion data, including the influence of grain size on diffusion coefficients.