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The properties, interactions, and reactions of cyclic water clusters (H(2)O)(n=1-5) on model systems for a graphite surface have been studied using pure B3LYP, dispersion-augmented density functional tight binding (DFTB-D), and integrated ONIOM(B3LYP:DFTB-D) methods. Coronene C(24)H(12) as well as polycircumcoronenes C(96)H(24) and C(216)H(36) in monolayer, bilayer, and trilayer arrangements were used as model systems to simulate ABA bulk graphite. Structures, binding energies, and vibrational frequencies of water clusters on mono- and bilayer graphite models have been calculated, and structural changes and frequency shifts due to the water cluster-graphite interactions are discussed. ONIOM(B3LYP:DFTB-D) with coronene and water in the high level and C(96)H(24) in the low level mimics the effect of extended graphite pi-conjugation on the water-graphite interaction very reasonably and suggests that water clusters only weakly interact with graphite surfaces, as suggested by the fact that water is an excellent graphite lubricant. We use the ONIOM(B3LYP:DFTB-D) method to predict rate constants for model pathways of water dissociative adsorption on graphite. Quantum chemical molecular dynamics (QM/MD) simulations of water clusters and water addition products on the C(96)H(24) graphite model are presented using the DFTB-D method. A three-stage strategy is devised for a priori investigations of high temperature corrosion processes of graphite surfaces due to interaction with water molecules and fragments.

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To study the influences of coal ash fusion on pore structure and surface morphology, four typical Chinese coals with different AFT (ash fusion temperature) were pyrolyzed in the range 950-1400°C. The evolution of pore structure and surface morphology of chars prepared at different temperatures and heating rate were investigated by N 2 adsorption/desorption at 77 K. The results of N 2 gas adsorption/desorption isotherms indicate that different coals and chars showed different adsorption/desorption characteristics at relative pressures of 0-0.5 and 0.5-1. The pore shape inside coal and char particles was analyzed based on the N 2 adsorption/desorption isotherms. Two fractal dimensions D 1 and D 2 (at relative pressures of 0-0.5 and 0.5-1, respectively) were calculated using the fractal FHH (Frenkel-Halsey-Hill) method. Specific surface area and average pore size of samples were also obtained through the BET model. Results show that the melting ash very probably caused the changes of pore structure inside the char particles or even inhibited the formation of pores when coal pyrolyzed in slow heating rate at the range of AFT. Fractal dimension of chars not only relates to pyrolysis temperature and heating rate, but also connects to the original coal. Fractal theory is suitable to describe the pore structure and surface morphology. Relationships between fractal dimension and carbon content, as well as fractal dimension and ash content, were also determined by second polynomial fitting.