Synthesis of Calcium Orthophosphates by Chemical Precipitation in Aqueous Solutions: The Effect of the Acidity, Ca/P Molar Ratio, and Temperature on the Phase Composition and Solubility of Precipitates

Studies on chemical precipitation of the calcium orthophosphates have shown that their phase compositions do not vary depending on molar ratio Ca/P but are sensitive to solutions acidity and temperature. These are two key factors that determine the phase transformation progress of metastable phases...

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Bibliographic Details
Published in:Processes 2020-09, Vol.8 (9), p.1009
Main Authors: Nikolenko, Mykola V., Vasylenko, Kateryna V., Myrhorodska, Victoria D., Kostyniuk, Andrii, Likozar, Blaž
Format: Article
Language:English
Subjects:
Acidity
Aqueous solutions
Calcium
Calcium phosphates
Chemical precipitation
Chemical synthesis
Correlation
Electrolytes
Hydroxyapatite
Mathematical analysis
Metastable phases
Methods
Phase composition
Phase transitions
Phosphates
Precipitates
Research methodology
Solid phases
Solubility
Titration
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Summary:Studies on chemical precipitation of the calcium orthophosphates have shown that their phase compositions do not vary depending on molar ratio Ca/P but are sensitive to solutions acidity and temperature. These are two key factors that determine the phase transformation progress of metastable phases into less soluble precipitates of the phosphates. It was proposed to compare calcium orthophosphates solubility products with calcium cations quantities in their formulas. It was found that there was a linear correlation between calcium orthophosphates specific solubility products and their molar ratios Ca/P if hydroxyapatite and its Ca-deficient forms were excluded from consideration. It was concluded that the relatively large deviations of their solubility products from the found correlation should be thought of as erroneous data. That is why solubility products were changed in accordance with correlation dependence: pKS for hydroxyapatite was 155, pKS for Ca-deficient hydroxyapatites was 114–155. The solubility isotherms, which were calculated on the basis of the corrected pKS values, coincided with the experimental data on solid-phase titration by Pan and Darvell.
ISSN:2227-9717
2227-9717
DOI:10.3390/pr8091009