Surface induced constant composition crystal growth kinetics studies. The brushite–gypsum system

• Published in: Journal of crystal growth Vol. 223; no. 1; pp. 213 - 224
• Main Authors: Hina, A., Nancollas, G.H., Grynpas, M.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.02.2001; Elsevier
• Subjects: A1. Growth models; A2. Growth from solutions; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Growth from solutions; Materials science; Methods of crystal growth; physics of crystal growth; Physics; A2. Growth from solutions; A1. Growth models; pH value; Inorganic compounds; Interface energy; Synthetic mineral; Calcium sulfates; Heterogeneous nucleation; Gypsum; Supersaturation; Experimental study; Aqueous solutions; Supersaturated solution; Crystal growth from solutions; Crystal nucleation; Kinetics; Calcium Acid phosphates; Hydrates
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/S0022-0248(00)01026-5

The possible oriented growth of one crystalline phase on the surface of another is especially important in systems containing both phosphate and sulfate salts of calcium. Whether the overgrowth results from a true epitaxial relationship is dependent on factors such as the thermodynamic driving forces and the free energies of the surfaces. Despite the fact that calcium sulfate dihydrate (CSD, gypsum) and calcium hydrogen phosphate dihydrate (DCPD, brushite) show many crystallographic and structural analogies, their surface reactions are quite different. The nucleation and growth of gypsum on brushite surfaces has been investigated in supersaturated solutions of calcium sulfate dihydrate at 25.0°C using the constant composition (CC) method. During the kinetics experiments, the harvested solid phases were examined by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDS). Induction periods, τ, preceding the initial formation of gypsum crystals at the brushite surfaces, varied markedly with relative supersaturation, σ. A thin layer wicking method was used to investigate the interfacial free energies of the growing phases, and these data were also calculated from the kinetics results. The interfacial free energy, γ, estimated from initial growth rates was 8.4 mJ m −2, while that calculated from the induction times was 8.9 mJ m −2. These values were in agreement with those determined directly using thin layer wicking.