Study of Equilibrium Critical Phenomena in Fluid Argon

Citation

Wu, Shyue Yuan (1972) Study of Equilibrium Critical Phenomena in Fluid Argon. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z20H-HM70. https://resolver.caltech.edu/CaltechTHESIS:11212017-114310188

Abstract

The refractive index of fluid argon was measured by using the method of angle of minimum deviation for λ_Na = 5893Å. The measurements were carried out along the coexistence curve and along fourteen single phase isotherms from 150.7° to 163°K at pressures from 40 to 90 atmospheres.

The Lorentz-Lorenz relation was used to relate the refractive index data to the densities and subsequently to find the isothermal compressibilities along the singla phase isotherms. Following the law of rectilinear diameter and the simple power laws for critical exponents, the values of the critical temperature and exponents for argon were found to be T_c = 150.725° ± 0.010°K, β = 0.3574 ± 0.0027, and γ = 1.170 ± 0.013. Also values of n_c = 1.08611 and P_c = 47.983 atm were determined. These values agree well with others reported for argon. Comparison of the values of β and γ with those predicted by the classical theory and the three-dimensional lattice gas model suggests that the latter gives a better description of the critical behavior of fluid argon.

Analysis of the reduced chemical potential differences, computed from the refractive index data along the singla phase isotherms, has been made by using the scaled equation of state first proposed by Widom. Reasonable values T_c and γ were obtained when the value of β determined above was used.

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