Solubility of CaHPO4 2H2O in the quaternary system Ca(OH)2-H3PO4-NaCl-H2O at 25 C

Patel, Paras R.; Grégory, Thomas; Brown, W. E.

doi:10.6028/jres.078a.043

Cited by 30 publications

(13 citation statements)

References 8 publications

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“…The titration curve for DCPD was found to be significantly lower, at most around one fifth of the value in terms of Ca concentration, than the results reported for the conventional excess-solid approach in the range of pH 3.6-7.8 [Gregory et al, 1970;Holt et al, 1925;Kugelmass and Shohl, 1924;Moreno et al, 1960Moreno et al, , 1966Patel et al, 1974;Strates et al, 1957], and was approximately parallel to the track of the results from Gregory et al [1970], Patel et al [1974] and Moreno et al [1960Moreno et al [ , 1966 ( fig. 1 ).…”

Section: Discussionmentioning

confidence: 59%

“…Above this point, HAp is thought to be more stable. In contrast to the behaviour of HAp, the dissolution of DCPD has been reported to be congruent [Verbeeck et al, 1983], although experimental data suggest otherwise [Holt et al, 1925;Moreno et al, 1960Moreno et al, , 1966Gregory et al, 1970;Patel et al, 1974]. Reported solubility data for DCPD are mostly consistent ( fig.…”

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confidence: 59%

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Solubility of Dicalcium Phosphate Dihydrate by Solid Titration

Pan

Darvell

2009

Caries Res

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Solid-titration results for hydroxyapatite (HAp), octacalcium phosphate, β-tricalcium phosphate and tetracalcium phosphate have shown that the only stable phase in 100 mmol·l^-1 KCl at 37°C is HAp. In particular, dicalcium phosphate dihydrate (DCPD) did not form at pH <4.2 (where it is otherwise believed to be stable) except as a metastable phase under conditions of slight supersaturation. The behaviour of DCPD itself under the same conditions requires checking. Solid titration was used to determine the apparent solubility of DCPD in a 100-mmol·l^–1 KCl solution at 37.0 ± 0.1°C over the pH range 3.2–11.6. The constitution of the precipitate was determined by X-ray diffraction, particle morphology was observed by scanning and transmission electron microscopy, and the precipitate Ca/P ratio was calculated by energy-dispersive X-ray analysis. The titration curve for DCPD was substantially lower than the position reported elsewhere. DCPD was the only identified phase at equilibrium at pH 3.60 and 4.50, but HAp was formed after seeding with 1 mg HAp at DCPD equilibrium at pH 4.47, 3.60 and 3.30. It is concluded that the titration curve observed for DCPD corresponds to the solubility isotherm for the phase, but that this represents a metastable equilibrium. HAp is more stable than DCPD, particularly below pH 4.2. The implications for calcium phosphate studies are profound as the reverse is generally believed to be true. Thus, solubility results and the nature of the carious lesion need reconsideration.

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Section: Discussionmentioning

confidence: 59%

mentioning

confidence: 59%

Solubility of Dicalcium Phosphate Dihydrate by Solid Titration

Pan

Darvell

2009

Caries Res

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“…In addition to the work re ported here, we have re-examined solubility data obta ined a t 25°C in other studies [8][9][10] of hydroxyapatites pre pared in a manne r similar to the one used he re. The adjustm ent procedure [5,[11][12][13][14][15] used in treating the d ata is unusually ri gorous and provides a superior assessme nt of the re i iability of the de rived constants .…”

Section: Introductionmentioning

confidence: 99%

Solubility of Ca5{P04)3OH in the System Ca{OH)2-H3P04-H20 at 5, 15, 25, and 37 °C

McDowell¹,

Grégory²,

Brown³

1977

J. RES. NATL. BUR. STAN. SECT. A.

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406

166

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Solubility isothe nns of hydroxyapatite, Ca5(PO.h OH (OHAp) , pre pa red by titrating a boiling aqueous suspe nsion of Ca(O HJ, with 0 .5 M H3PO., we re detennined in the te rnary system Ca(OHJ,-H3PO.-H20 at 5, 15, 25, a nd 3 7°C in the pH ra nge 3 .7-6. 7 by equilibration with dilute H3PO. solutio ns. The solubility product K" dete rmi ned as a fun ct io n of te mpe rature by a gene ra lized least-squa res procedure from 4 1 ex pe rimenta l points, is g ive n by the equationThe values of K s and it s dis persion at 25 a nd 37°C a re 3.04 (0.25) a nd 2.35 (0.27) X 10-59 . The re is a max imum in K s near 16°C, whic h may be d ue to the fo rm of te mperature de pendence found earlier fo r the sta bilit y constants of the ion pa irs Ca H2POt a nd Ca HPO~.The re lati ve pos itio ns of the isothe rms s how that OHA p has a negati ve the rma l coeffi cient of solub ility. T hermod ynam ic fun ctions for the di sso lutio n of the sa lt a re report ed .T he so lubility data previous ly re pOl1ed by others fo r OHAp at 25°C were rev iewed . The solubility prod uc ts obta ined by three of these in vestigators were compara ble with our value of 3 .0 X 10-59 ; thei r data were reeva luated by the method desc ri bed he re. We conclude that the best value fo r the so lubility p rod uct at 25 °c is 4.7 (2 .0) X 10-59 . Key wo rd s: Dissolution; hydroxyapatite; ion pa irs; sol ubility; so lu b ilit y isothe rms; so lu bility prod uct; the rmal coeffi c ient of solubilit y; thermod ynamics; tooth mine ra l.

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“…The solubility behavior of DCPD has been examined by Brown and co-workers (17)(18)(19) when NaCl was added in the equilibration system), and a ␤ parameter of the modified extended Debye-Huckel equation. Since our objective was to determine the stability constants of these and other complexes that might be important under the experimental conditions used in apatite dissolution studies undertaken in our laboratory, the present experiments were conducted in acetate buffers with an ionic strength around 0.5 M.…”

Section: Solubility Of Dcpd In Suspensions At Various Phsmentioning

confidence: 99%

“…DCPD (CaHPO 4 ⅐ 2H 2 O) has the least complex solubility behavior among various calcium phosphate compounds, and its thermodynamic solubility has been intensively studied in dilute phosphoric acid solutions (17)(18)(19). DCPD solubility studies have been extended to solutions containing NaCl concentrations as high as 0.50 M (19).…”

Section: Introductionmentioning

confidence: 99%