A general theory of solid-state diffusion in strained systems is developed on a molecular-kinetic basis. The theory predicts that for simple strains the diffusion coefficient is an exponential function of the lattice parameter and that the rate of change of the diffusion coefficient with strain is linearly related to the interatomic forces. It has also been shown that for plastic flow the diffusion coefficient is a linear function of strain rate. All the conclusions are confirmed by the data available in the literature.

The thermodynamic and transport properties of high-temperature air are found in closed form starting from approximate partition functions for the major components in air and neglecting all minor components. The compressibility, enthalpy, entropy, the specific heats, the speed of sound, the coefficients of viscosity and of thermal conductivitiy, and the Prandtl numbers for air are tabulated from 500° to 15,000° K over a range of pressure from 0.0001 to 100 atmospheres. The energy of air and the mol fractions of the major components of air can be found from the tabulated values for compressibility and enthalpy. It is predicted that the Prandtl number for fully ionized air, which is in complete equilibrium, will become small compared to unity, the order of 0.01, and this implies that boundary layers in such flow will be very transparent to heat flux.