Adsorption energy of stoichiometric molecules and surface energy at morphologically important facets of a Ca(OH)2 crystal

Non-dispersive (polar) contribution to adsorption energy of stoichiometric molecules and surface energy of morphologically important {0 0 0 1} and {(1) over bar 0 1 0} type facets of a Ca(OH)(2) crystal are evaluated on the basis of calculation of the corresponding surface-associated Madelung constants. At the nano-size level, this contribution both of the adsorption and surface energies of indicated types of facets have been obtained to depend predominantly on the characteristic size r(1) of a {0 0 0 1} type facet due to much stronger bonding of ions within individual (0 0 0 1) basal planes in comparison with that between ions belonging to adjacent (0 0 0 1) planes. The non-dispersive component of the surface energy of Ca(OH)(2) crystal is highly anisotropic, with much higher value calculated for the {(1) over bar 0 1 0} type facets. Both for {0 0 0 1} and {(1) over bar 0 1 0} facets, the non-dispersive surface energy in the edge and near-edge area substantially exceeds that at center of the facet, regardless of the crystal sizes. In the size range of r(1) >= 40 nm, out of the marginal area the surface energy of a facet is not practically influenced by the size effect and may be characterized with a sufficient accuracy by corresponding value that is achieved in the limit of large sizes, r(1) --> infinity. At small sizes r(1) <= 4 nm, the distribution of the surface energy on each of {0 0 0 1} and {(1) over bar 0 1 0} type facets is strongly inhomogeneous and is very sensitive to variation of the characteristic size r(1). The non-dispersive adsorption energy of stoichiometric Ca(OH)(2) molecules on the {0 0 0 1} and {(1) over bar 0 1 0} facets with variation of the size r(1) follows the same trend as the corresponding non-dispersive surface energy. Analytical expressions are obtained for the total (sum of non-dispersive and dispersive components) surface and total adsorption energies that incorporate the size effect resulting predominantly from the non-dispersive component. The proposed theoretical approach may be applied to analysis of the same energy characteristics of the materials that are isostructural with the Ca(OH)(2): alkaline earth hydroxides - Mg(OH)(2), Sr(OH)(2), and Ba(OH)(2), as well as some other compounds with the brucite structure. (C) 2012 Elsevier B.V. All rights reserved.