engleski

Engineering crystal growth of calcium hydrogenphosphate dihydrate

The factors underlying calcium hydrogenphosphate dihydrate (DPCD) interactions with several structurally different additives: glutamic and aspartic acid, sodium citrate, hexaammonium tetrapolyphosphate, calcium phytate and polyaspartic acid were studied. DCPD crystals were prepared by fast mixing of equal volumes of the anionic and cationic reactant solutions. The initial conditions were c(CaCl2) = c(Na2HPO4) = 0.021 moldm-3, c(NaCl) = 0.3 moldm-3, pHi 5.5. The respective additive was added to the anionic component prior to pH adjustment. After mixing, crystals were grown without further stirring in the course of 24 hours at 37oC. The respective additives were added to the anionic component prior to pH adjustment. Crystals were characterised by X-ray diffraction, while their morphology was observed by optical and scanning electron microscopy (SEM). The Miller indices of the crystal faces were determined from SEM micrographs, after the orientation of the most prominent face was ascertained by the Weissenberg method. Mechanism of additive-DCPD crystals interactions depends on size and structure of additive molecule, structural fit between organic molecule and the ionic structure of particular crystal face. Small molecules (ions) specifically adsorb on lateral faces primarily by electrostatic interactions, while macromolecules and molecules with hindered structure specifically adsorb on the dominant (010) crystal face, for which a certain degree of structural fit is necessary.

additives, calcium hydrogenphosphate dihydrate, crystal morphology

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