Investigation of the Effects of Sodium Dicarboxylates on the Crystal Habit of Calcium Sulfate α-Hemihydrate.

The effects of disodium malonate, disodium succinate, disodium glutarate, and disodium adipate on the crystal habit of calcium sulfate α-hemihydrate (CaSO4·0.5H2O, α-CSH) were studied using experimental studies and molecular dynamics simulations. The calculation and experimental results provided insight into the mechanism of the interaction between the additives mentioned above and the different faces of α-CSH that dominate the morphology of α-CSH. The calculation results indicated that the formation of high-aspect-ratio α-CSH, namely, calcium sulfate α-hemihydrate whiskers (α-CSH whiskers), in aqueous solution was due to the interaction between liquid water and side faces of the α-CSH crystal, which inhibits the growth of α-CSH along the radial direction. However, when a trace amount of crystal habit modifier, such as disodium succinate or disodium glutarate, was added to the aqueous solution, the growth rates along the directions normal to the {0 0 1} and {1 1 4} faces were considerably inhibited. Thus, α-CSH crystals with a low aspect ratio were synthesized using a hydrothermal method. In addition, the calculation methodology used in this work could provide a powerful tool for selecting suitable crystal habit modifiers for preparing α-CSH and other inorganic crystals.