Graphitized Graphite Carbon Phases

The atomic partial charge of the model phase and hydrocarbon does not change significantly after optimization of the eomplex form, while the electron potential is slightly shifted toward the molecular interaction side. These results clearly indicate the existence of different retention mechanisms on graphitized carbon phases, a hydrophobic interaction and hydrogen bonding. 

Figure 5.3 Adsorption of 2,3,4,6-tetrachlorophenol on a model graphitized carbon phase. White, light-gray, dark-gray, and black balls represent hydrogen, carbon, chlorine, and ojg gen, respectively. The atomic size of 2,3,4,6-tetrachlorophenol is 2.5 times the size of the model phase. Reproduced hy permission of Springer, ref. 25.

The molecular interaction energy values of alkenes were smaller than for their related alkanes. This result supports the idea that the hydrophobic interaction due to the van der Waals energy is the predominant molecular interaction in reversed-phase liquid chromatography. No dipole-dipole or 71-71 interactions influenced the direct interaction. The lack of dipole-dipole or 71-71 interactions can be studied from chromatographic behavior on a graphitized carbon phase. 

Figure 6.7 Adsorption of decane and cis-l,3,5,7,9-pentadecene on a model graphitized carbon phase. Small and large balls represent hydrogen and carbon, respectively.

Adsorption of p-anisidine on a model graphitized carbon phase. White, light-gray, dark-gray, and black balls represent hydrogen, carbon, nitrogen, and o>ygen, respectively. 

Figure 6.10 Relationship between molecular interaction energy and log on a model graphitized carbon phase at (a) pH 10 and (b) pH 2.

The simplest model phase in reversed-phase liquid chromatography is a graphitized carbon phase that is a polycyclic aromatic hydrocarbon (PAH). 

The precision of the correlation between the log k and molecular interaction energy values vras high, as long as the analyte structure was simple and flat, as demonstrated in Section 6.9.2. Specifically, such analyses are most successful when studying retention mechanisms on graphitized carbon phases (Section 6.3). This is because the most effective system for such analyses is a homogeneous and flexible model phase where the docking process may not cause errors. 

It is noted in Sections XVII-10 and 11 that phase transformations may occur, especially in the case of simple gases on uniform surfaces. Such transformations show up in q plots, as illustrated in Fig. XVU-22 for Kr adsorbed on a graphitized carbon black. The two plots are obtained from data just below and just above the limit of stability of a solid phase that is in registry with the graphite lattice [131]. 

Fig. XVII-22. Isosteric heats of adsorption for Kr on graphitized carbon black. Solid line calculated from isotherms at 110.14, 114.14, and 117.14 K dashed line calculated from isotherms at 122.02, 125.05, and 129.00 K. Point A reflects the transition from a fluid to an in-registry solid phase points B and C relate to the transition from the in-registry to and out-of-registry solid phase. The normal monolayer point is about 124 mol/g. [Reprinted with permission from T. P. Vo and T. Fort, Jr., J. Phys. Chem., 91, 6638 (1987) (Ref. 131). Copyright 1987, American Chemical Society.]...

Fig. 1. Carbon-phase diagram where A, solvent-cataly2ed diamond growth B—G, diamond formation direcdy from graphite C, graphite formation from diamond, D, approximate region where formation of Lonsdaleite occurs from weU-ordered graphite crystals (7,8). To convert GPa to atm, multiply by...

Figure 6.3 The iron-carbon phase diagram showing the alternative production of iron and cementite from the liquid alloy, which occurs in practice, to the equilibrium production of graphite...

Cast irons, although common, are in fact quite complex alloys. The iron-carbon phase diagram exhibits a eutectic reaction at 1 420 K and 4-3 wt.<7oC see Fig. 20.44). One product of this eutectic reaction is always austenite however, depending on the cooling rate and the composition of the alloy, the other product may be cementite or graphite. The graphite may be in the form of flakes which are all interconnected (although they appear separate on a... 

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