| Abstract
| - Molecular dynamics simulation was applied to study the relative growth rates of seven crystal faces of α-Al2O3 in the presence of 1,4-butanediol. In particular, the adsorption energy of 1,4-butanediol on various crystal faces was computed using 200 solvent molecules. The following sequence was obtained: (Eads(012) > Eads(001) > Eads(102) > Eads(113) > Eads(110) > Eads(111) > Eads(010)). The above sequence is in the reverse order of the experimentally observed growth rates of the respective faces. The two faces that exhibit the lowest adsorption energy (i.e., (111) and (010) faces) are the ones that do not emerge in the final morphology of α-Al2O3 particles in practice. On examination of the data, it was found that 1,4-butanediol molecules preferentially adsorb onto the crystal faces that have larger numbers of octahedral faces per unit area (e.g., the (001) face). In other words, the binding of the growth units of α-Al2O3 onto such crystal faces is less favorable than the other crystal faces. In addition to the adsorption energy, our results show that the growth habits are also influenced by the mobility of 1,4-butanediol near the crystal growth faces. In fact, the computed diffusion coefficients of 1,4-butanediol near the (012) and (102) faces are the lowest compared to those of the (001), (110), and (113) faces. This may explain why (012) and (102) faces do not emerge unless moderate stirring is applied. Nevertheless, the above conclusions were draw based upon cleaved α-alumina surfaces without relaxation (i.e., surface energy effects of the solid substrate were not included).
|
