Critical behavior of binary gaseous mixtures

The behavior of the kinetic coefficients of binary gaseous mixtures has been studied in a vicinity of the gas-liquid critical line. It is shown experimentally by the diffusion equalization of concentration that the mutual diffusion coefficient D depends on the reduced temperature tau[tau = (T - T-c)/T-c, where T-c is the critical temperature] as a power function with exponent gamma similar to 1.2 up to tau similar to 10(-3)-10(-4) at the approach to the critical point. The dependence D similar to tau(0.6) predicted by the scaling theory should be observed in closest proximity of the critical point. It is shown that the diffusion equalization of the isotope concentration does not have any peculiarity near the critical point. Equations of state are proposed for both pure substance and binary mixtures, based on up-to-date theories. They may be used to calculate the required thermodynamic derivatives for describing the temperature dependences of kinetic coefficients. The crossover temperatures have been determined. The experiments performed are in good agreement with our theoretical calculations. [S1063-651X(99)13402-0].