AUTHOR=Yurtseven Hamit , Yilmaz Aygül 

TITLE=Analysis of the Heat Capacity for Pure CH4 and CH4/CCl4 on Graphite Near the Melting Point and Calculation of the T–X Phase Diagram for (CH3)CCl3+CCl4

JOURNAL=Frontiers in Physics

VOLUME=4

YEAR=2016

URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2016.00024

DOI=10.3389/fphy.2016.00024

ISSN=2296-424X

ABSTRACT=<p>We study the temperature dependence of the heat capacity C<sub>p</sub> for the pure CH<sub>4</sub> and the coadsorbed CH<sub>4</sub>/CCl<sub>4</sub> on graphite near the melting point. The heat capacity peaks are analyzed using the experimental data from the literature by means of the power-law formula. The critical exponents for the heat capacity are deduced below and above the melting point for CH<sub>4</sub> (<italic>T</italic><sub><italic>m</italic></sub> = 104.8 K) and CH<sub>4</sub>/CCl<sub>4</sub> (<italic>T</italic><sub><italic>m</italic></sub> = 99.2 K). Our exponent values are larger as compared with the predicted values of some theoretical models exhibiting second order transition. Our analyses indicate that the pure methane shows a nearly second order (weak discontinuity in the heat capacity peak), whereas the transition in coadsorbed CH<sub>4</sub>/CCl<sub>4</sub> is of first order (apparent discontinuity in C<sub>p</sub>). We also study the T–X phase diagram of a two-component system of CH<sub>3</sub>CCl<sub>3</sub>+CCl<sub>4</sub> using the Landau phenomenological model. Phase lines of the R+L (rhombohedral + liquid) and FCC+L (face-centered cubic + liquid) are calculated using the observed T–X phase diagram of this binary mixture. Our results show that the Landau mean field theory describes the observed behavior of CH<sub>3</sub>CCl<sub>3</sub>+CCl<sub>4</sub> adequately. From the calculated T–X phase diagram, critical behavior of some thermodynamic quantities can be predicted at various temperatures and concentrations (CCl<sub>4</sub>) for a binary mixture of CH<sub>3</sub>CCl<sub>3</sub>+CCl<sub>4</sub>.</p>