Zdrojový dokument:Scientific papers of the University of Pardubice. Series A, Faculty of Chemical Technology. 17/2011
ISSN:1211-5541
Abstrakt:
The formation of amorphous calcium phosphate (ACP) was studied in the context
of urinary stones formation. Processes of ACP precipitation were observed in
simulated medium: in aqueous solutions of potassium chloride and artificial urine
(SRAU) at the ionic strength of 0.3 mol dm–3. Amorphous structure of calcium
phosphate was verified by X-ray diffraction analysis and Raman spectroscopy.
Thermochemical study of ACP precipitation was investigated by using the
isoperibolic reaction twin calorimeter. The experiments were carried out at the
initial concentrations of ACP in the range from 6 to 14 mmol dm–3 for KCl solution
and 6-16 mmol dm–3 for SRAU. The ACP precipitation was performed by reaction
of Ca2+ and ions with Ca:P molar ratio close to 1.5 at the temperatures of
298.15 K and 310.15 K. The molar enthalpy of ACP formation was calculated by
use of ACP solubility which was determined in this work. Molar enthalpies of ACP
formation, )Hm, are 29.8 ± 0.9 kJ mol–1 at 298.15 K and 36.3 ± 0.9 kJ mol–1 at 310.15 K in KCl solution, and )Hm
298.15 = 35.4 ± 1.3 kJ mol-1 and )Hm
310.15 = 41.6
± 1.5 kJ mol–1 in SRAU.