Graphite tricritical point

III. N2 on Graphite Phase Diagram Submonolayers and Melting Tricritical Point... 

Figure 12. Proposed schematic low-coverage melting phase diagram of N2 on graphite according to the tricritical point model. Full lines correspond to the ideal thermodynamic system that is, AT = 0. Dashed curves were obtained with two different temperature smear-ings AT > 0. (Adapted from Fig. 3 of Ref. 276.)...

Figure 23. Detail of the phase diagram of Nj on graphite near the tricritical point obtained from vapor pressure scans at fixed temperature. (Adapted from Fig. 1 of Ref. 237.)...

The ac heat capacity and vapor pressure isotherm experiments of CO on exfoliated graphite foam [112] allowed the detailed investigation of the narrowing of the commensurate solid-fluid coexistence region as the tricritical point is approached see Fig. 51 for this part of the phase diagram and Fig. 52 for the calorimetric data corresponding to the paths I to VII marked in the phase diagram. The vapor pressure isotherms indicate that the transition... 

Figure 51. Experimental phase diagram of CO physisorbed on graphite with the phases fluid (F), commensurate (CD) and incommensurate (ID) orientationaliy disordered solids, reentrant fluid (RF), second-layer fluid (2F), vapor (2V), liquid (2L), and orientationaliy disordered solid (2SD) phases. Filled circles and triangles represent phase boundary locations from heat capacity and vapor pressure measurements, respectively. Solid and dashed lines indieate phase boundaries believed to be associated with first-order and continuous transitions, respectively dash-dotted lines correspond to speculated boundaries. The large filled triangle and the large filled circle mark the two-dimensional Potts tricritical and critical points, respectively the tricritical point marked with an open triangle is tentative. Lines I-VII with arrows are experimental paths of the heat capacity scans shown in Fig. 52. Coverage unity corresponds to a coverage of CO forming a complete (Vs x VS) monolayer. (Adapted from Fig. 1 of Ref. 112.)...

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