Physics of fracture and mechanics of self-affine cracks

CO chemisorption on Pt supported on fractal surfaces was simulated in order to compute chemisorption dimension and active sites fractal dimension. Pt deposition was simulated using different models on both fractal and planar surfaces. The potential energy surface with two adsorption positions model was used to compute Pt–CO interaction and a Lennard–Jones 6–12 potential was used to simulate CO–CO interaction. Two Pt phases on fractal surface, one at low concentration — the dispersed phase and the second at high concentration — the aggregated phase characterized by weak interactions with support are obtained. The results are in accord with experimental data of CO chemisorption on Pt supported on γ-alumina. Computed data obtained for planar support are compared with those obtained on fractal support. The effect of fractal support on chemisorption data is underlined.

SIMULATION OF CO CHEMISORPTION ON Pt SUPPORTED ON FRACTAL SURFACES

A computer program which is able to simulate adsorption on fractal surfaces was developed. The fractal surfaces are generated as Takagi surfaces. The computer program is based on a DLA-algorithm. Adsorption was simulated in different conditions: 1. equivalent active sites (homogeneous surfaces); 2. active sites with different adsorption probabilities; the probability associated with every active site is computed using a van der Waals potential. Our simulation allows us to explore the actual structure of the gas-solid interface and to study the sensitivity to energetic disorder. The fractal dimension of gas-solid interface vs. adsorption coverage curves are computed.

M. Vass

Papers

Computer simulations of fractal surfaces: application in adsorption