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We propose a kinetic model to describe the temperature dependence of the shape of islands formed during submonolayer epitaxy on anisotropic metal surfaces. Our model reveals that "anisotropic corner rounding" is the key atomic process responsible for a transition in island shape, from chain structures at lower temperatures, to compact islands at higher temperatures. Exploiting data for the temperature and flux scaling of the island density, we analyze such behavior observed experimentally in Cu/Pd(110) epitaxy, estimating activation barriers of 0.45 and 0.3 eV for anisotropic terrace diffusion, and 0.65 eV for the slow cornerrounding process. Disciplines Chemistry | Mathematics CommentsThis article is from Physical Review B 56 (1997) We propose a kinetic model to describe the temperature dependence of the shape of islands formed during submonolayer epitaxy on anisotropic metal surfaces. Our model reveals that ''anisotropic corner rounding'' is the key atomic process responsible for a transition in island shape, from chain structures at lower temperatures, to compact islands at higher temperatures. Exploiting data for the temperature and flux scaling of the island density, we analyze such behavior observed experimentally in Cu/Pd͑110͒ epitaxy, estimating activation barriers of 0.45 and 0.3 eV for anisotropic terrace diffusion, and 0.65 eV for the slow corner-rounding process.

The Ca-based sorbent looping cycle represents an innovative way of CO 2 capture for power plants. However, the CO 2 capture capacity of the Ca-based sorbent decays sharply with calcination/carbonation cycle number increasing. In order to improve the CO 2 capture capacity of the sorbent in the Ca looping cycle, limestone was modified with acetic acid solution. The cyclic carbonation behaviors of the modified and original limestones were investigated in a twin fixed-bed reactor system. The modified limestone possesses better cyclic carbonation kinetics than the original limestone at each cycle. The modified limestone carbonated at 640-660°C achieves the optimum carbonation conversion. The acetic acid modification improves the long-term performance of limestone, resulting in directly measured conversion as high as 0.4 after 100 cycles, while the original limestone remains at a conversion of less than 0.1 at the same reaction conditions. Both the pore volume and pore area distributions of the calcines derived from the modified limestone are better than those derived from the original limestone. The CO 2 partial pressure for carbonation has greater effect on conversion of the original limestone than on that of the modified sorbent because of the difference in their pore structure characteristics. The carbonation conversion of the original limestone decreases with the increase in particle size, while the change in particle size of the modified sorbent has no clear effect on cyclic carbonation behavior.