Modeling Gypsum Crystallization on a Submicrometric Scale

Abstract

Gypsum needle crystallization from a suspension of calcium sulfate hemihydrate grains in an aqueous solution is studied on a mesoscopic scale. We build a simulation model, which assumes that gypsum formation is limited by heterogeneous nucleation and precipitation with an initial autocatalytic surface-controlled needle growth and a final diffusion-controlled growth. The model introduces a minimal number of parameters whose effect on growth dynamics and gypsum morphology is analyzed. We find that the increase of nucleus number per hemihydrate grain decreases induction time and needle length and increases needle entanglement, i.e., improves the mechanical properties of the material. The simulation results correctly reproduce experiments with and without treatment of the reactants. The simulation model can be used to predict the behavior of the reactive system in conditions that are not compatible with experimental observations.

Effect of Supersaturation on Competitive Nucleation of CaSO4 Phases in a Concentrated CaCl2 Solution

“…The diffusion coefficients of D DH and D HH can be assumed to be the same since DH and α-HH both have the same lattice ions, Ca 2+ , SO 4 2− , and H 2 O. On the basis of eq 16, the ratio of the pre-exponential factors of DH to α-HH is 0.83, which contributes little to the R HH .…”

“…1,2 Water-mediated transformation can take place among different phases based on a dissolution−crystallization mechanism. 3,4 In electrolyte solutions at elevated temperature, DH can transform into α-HH, 5,6 which is a kind of important cementitious material and has been widely applied in the molding, binding, and construction industry for its superior workability and high strength, 3 and as bone cements owing to its excellent biocompatibility and osteoconductivity. 7 In solutions that are supersaturated with respect to DH, α-HH, and AH, competitive nucleation is supposed to occur.…”

Microstructural formation of gypsum by setting in the presence of hydroxypropyl methylcellulose (HPMC)

“…Several explanations can be found in the literature [11][12][13][14][15][16][17][18][19][20][21][22] for the retardation in gypsum (or cement) hydration in the presence of organic compounds such as: nucleation control, disturbance in the crystal growth, decrease in ion mobility [4]. The water-soluble polymers such as cellulose ethers contain numerous hydroxyl groups which are able to form hydrogen bonds with oxygen ions on the surface of anhydrous materials (absorption).…”

Kinetics of plaster hydration and structure of gypsum: Experiments and kinetic Monte Carlo simulations with added gypsum seeds

“…To this end, an astonishing variety of additives have been tried in order to control the kinetics of the reaction while improving the mechanical properties of the resulting product [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]. Electrical conductivity [2,18,19], calorimetry [20,21], acoustic emission [13,22] and Raman spectroscopy [23] have been used to follow the dynamics of the reaction. The nanoscale structure of the material has been characterized [24,25], including by nuclear magnetic resonance (NMR) [26] and cryogenic transmission electron microscopy [27].…”

“…In order to bridge the gap between these two remote scales, we developed a model which simulates the growth of gypsum needles at the submicrometer scale. We use the tools of statistical physics to account for the interactions of many growing gypsum monocrystals [19,22,23,43,44]. When considered at a mesoscopic scale, reaction and diffusion are stochastic, Markovian processes [45,46].…”