Effect of Mixing Ratio and pH on the Reaction Between Ca4(PO4) 2O and CaHPO4

Published

May 1, 2000

Author(s)

S Matsuya, Shozo Takagi, Laurence Chow

Abstract

The reaction of Ca₄(PO₄)₂O (TTCP) and CaHPO₄ (DCPA) in an aqueous solution has been shown to be responsible for the hardening of a calcium phosphate cement. This reaction was investigated by monitoring pH changes and composition of solid phases. In the first set of experiments (no attempt to control pH), 2.5 g of each of mixtures with TTCP/DCPA molar ratio from 0.25 to 2, was placed in 12.5 mL of 0.15 mol/L KCl solution, at initial pH about 7, and the pH was allowed to drift for 24 h. Results show that at any time up to 24 h, the pHs were higher for slurries with higher TTCP/DCPA molar ratios. For the slurries with TTCP/DCPA molar ratio of > 0.83, the 24 h pHs of the slurries were 9 to 11, whereas for those with TTCP/DCPA of < 0.67, the pHs were between 5.3 and 7. The slurries with TTCP/DCPA molar ratios between 0.5 and 1 (Ca/P molar ratio = 1.5 to 1.67) reacted completely within 24 h to form hydroxyapatites (0HAp). Ca₅(PO₄)₃OH. In the second set of experiments, 2g of an equimolar TTCP and DCPA mixture was placed in 20 mL of 0.15 mol/L KCl solution. The pH values were kept constant (6, 8 or 10) by using H₃PO₄ and Ca(OH)₂ or HCI and KOH as titrant solutions. At pH8, DCPA and TTCP dissolved at about the same rate, whereas at pH 10, DCPA was consumed more rapidly than TTCP. At both pHs, OHAp was the only product formed. However, at pH 6, the composition of reaction products depended on the types of the titrants used. Specifically when H₃PO₄ and Ca(OH)₂ were used, hydrolysis of TTCP was the predominant reaction and both octacalcium phosphate and OHAp were formed, But, when HCI and KOH were used, only OHAp was formed. In this case hydrolysis of TTCP and DCPA appeared to proceed independently with TTCP hydrolysis beginning immediately and progressing slowly through 48 h while the DCPA hydrolysis began several hours after the reaction started but was completed in 24 h.

Citation

Journal of Materials Science-Materials in Medicine

Volume

11

Issue

No. 5

Pub Type

Journals

Keywords

calcium phosphate cement, chemical reaction, dicalcium phosphate, hydroxyapatite, tetracalcium phosphate

Citation

Matsuya, S. , Takagi, S. and Chow, L. (2000), Effect of Mixing Ratio and pH on the Reaction Between Ca₄(PO₄) ₂O and CaHPO₄, Journal of Materials Science-Materials in Medicine (Accessed April 24, 2024)