Properties Of Liquid Carbon Research Articles

Characterization of three phases of liquid carbon by tight-binding molecular dynamics simulations.

We have performed systematic molecular dynamics simulations to study the structures of liquid carbon at 5000 K with the weight density ranging from 1.4 to 3.5 g cm-3, using a three-center tight-binding potential of carbon. The simulation results show that the bonding characteristics of the liquid changes predominately from twofold to threefold, and then to fourfold coordination as the density increases. Signals of two structural changes at the densities of about 1.9 and 3.0 g cm-3 respectively are revealed by the slope changes in the density dependence of structural, electronic and dynamical properties. Our simulation results suggest that there are three distinct liquid carbon phases in this density range. However, further thermodynamics calculations, e.g., free energy calculations, would be required to clarify the possible liquid-liquid transitions.

06/00578 Measurements of the melting point of graphite and the properties of liquid carbon (a review for 1963–2003): Sawatimskiy, A. I. Carbon, 2005, 43, (6), 1115–1142.

06/00578 Measurements of the melting point of graphite and the properties of liquid carbon (a review for 1963–2003): Sawatimskiy, A. I. Carbon, 2005, 43, (6), 1115–1142.

Graphite melting and properties of liquid carbon

The results of fast heating (by electrical pulse current) of highly oriented pyrolytic graphite specimens are presented. Experimental data are obtained for graphite melting: the enthalpy of solid and liquid phases under melting, the heat of melting, and the heat capacity of solid and liquid phases near melting. Liquid carbon resistivity is measured under fast heating of cylindrical graphite specimens in thick-walled sapphire capillary tubes. Preliminary data for the isobaric heat capacity Cp for liquid carbon up to 10,000 K and for the isochoric heat capacity Cv up to 8000 K are presented.

Pulsed Laser Melting of Graphite

ABSTRACTExperimental evidence for laser melting of graphite, by irradiation with 30ns pulses from a ruby laser, is presented. RBS-channeling analysis, Raman scattering and TEM measurements reveal that the surface of graphite melts at a threshold energy density of about 0.6 J/cm2. For laser pulse energy densities above 0.6 J/cm2, the melt front penetration depth increases nearly linearly with increasing energy density. An intense emission of carbon particles during and after irradiation is observed. The thickness of the carbon layer removed in this process also increases nearly linearly with increasing pulse fluence. A dramatic redistribution of ion implanted impurities is also observed. Furthermore, the crystalline structure of the resolidified material is shown to depend on the energy density of the laser pulse. In order to explain these phenomena, a model for laser melting of graphite at high temperatures to form liquid carbon has been developed in which a free electron gas approximation is used to describe the properties of liquid carbon. The model is solved numerically to give the time and depth dependences of the temperature as a function of the laser pulse energy density. Very good agreement is found between the observed melt depth dependence on laser pulse energy density, as determined by RBS-channeling, and the model calculations. The redistribution of ion implanted impurities and the modification of the crystalline structure, caused by the pulsed laser irradiation, are also consistent with the model and permit the determination, for the first time, of interfacial segregation coefficients for impurities in liquid carbon. The model also predicts that liquid carbon at low pressure (p < 1 kbar) has metallic properties.

Thermodynamic properties of carbon up to the critical point

Thermodynamic data on solid, liquid, and gaseous carbon have been carefully selected from the literature or estimated, and vapor pressure have been calculated up to the critical point. Using certain assumptions about the properties of liquid carbon and nonideal gas corrections for carbon vapor, our calculations show the triple point and critical point to be 4765 and 6810°K, respectively, with critical density 0·64 g/cm 3, and critical pressure 2200 atm. The dominant vapor species above ∼ 2000°K is C 3, while C 7 is also of importance from 4500 to 6810°K. Coexistence curves which summarize the densities and enthalpies of solid, liquid, and vapor carbon are plotted. The density of liquid carbon is assumed to be 20% less than that of graphite at the triple point. The enthalpy of fusion is given as 30 kcal/g-atom C. Sublimation enthalpies are found to be 50–66 kcal/g-atom C at 3000–4765°K, and vaporization enthalpies about 20 kcal/g-atom C at 4765–6000°K.