Coexistence curve of perfluoromethylcyclohexane+carbon tetrachloride near the critical point in composition-pressure and composition-temperature space

Abstract

Coexistence curves in volume fraction-temperature ( -T) space and in volume fraction-pressure ( -p) space have been measured for the binary system perfluoromethylcyclohexaneϩcarbon tetrachloride in the temperature range T c -TϽ0.8 K and in the pressure range p -p c Ͻ3.2 MPa near the critical point (T c , p c , c ). The observed coexistence curves were expressed by the simple scaling relationThe exponent was determined as ␤ T ϭ0.326Ϯ0.001 and ␤ p ϭ0.330Ϯ0.006, which agree with each other and with the theoretical value ␤ϭ0.327 for the Ising model. The observed coefficients give (B p /B T ) 1/␤ ϭ0.42Ϯ0.02 K/MPa, which may be compared with the slope (dT/dp) c ϭ0.38 K/MPa of the p -T critical line in light of a thermodynamic argument. This means that the pressure range is converted into the temperature range with the slope (dT/dp) c as a scale factor.

Dynamic scaling of the critical mixture perfluoromethylcyclohexane–carbon tetrachloride

“…The perfluoromethylcyclohexane (C 7 F 14 )-carbon tetrachloride (CCl 4 ) mixture of critical composition has been prepared according to Pelger et al who specified a critical volume fraction c V = 0.4470 of C 7 F 14 . This value is slightly smaller than the more recently reported c V = 0.454 [31] Figure 2. Ultrasonic attenuation coefficient per squared frequency, α/ν 2 , for the C 7 F 14 -CCl 4 mixture of critical composition at six measuring frequencies ν plotted versus temperature T (see figure 1 for the symbols).…”

“…but agrees well with the C 7 H 14 critical mole fractions X c = 0.285 = c V = 0.447 [32] and X c = 0.2858 [33] of previous studies. The critical temperature given by Pelger et al was T c = 301.622 K [30] which compares with T c = 301.776 K [31,32] and T c = 301.75 K [34]. Kruus reported a somewhat lower (T c = 301.20 K [35]) and Tveekrem et al a slightly higher (T c = 302.223 K [33]) critical temperature.…”

“…The pressure dependence of the critical temperature amounts to dT c /dp = 0.38 × 10 −6 K Pa −1 [31]. Using the density data from the literature [57] the thermal expansion coefficient of the C 7 F 14 -CCl 4 mixture of critical composition has been expressed as [25] α p = (2.683 −α0 + 9.795) × 10 −4 K −1 .…”