The system CaHPO4·2H2O-CaSO4·2H2O: crystallizations from calcium phosphate solutions in the presence of SO2-4

Rinaudo, Caterina; Lanfranco, A. M.; Franchini-Angela, M.

doi:10.1016/0022-0248(94)90287-9

Cited by 17 publications

(18 citation statements)

References 11 publications

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“…Both crystallize in the monoclinic system with nearly identical unit cells, although the space group of brushite is Aa instead of A2/a. Therefore, it is reasonable that some authors (Rinaudo et al 1994(Rinaudo et al , 1996Hina et al 2001) have proposed the possibility of co-crystallizing both minerals to form oriented intergrowths or even solid solutions in which SO 4 2-substitutes for HPO 4 2-. When two solutes crystallize simultaneously and have similar structures, the formation of solid solutions and/or epitaxies is always a possibility, which is important not only from a fundamental point of view, but also from an applied perspective.…”

mentioning

confidence: 98%

Interaction of phosphate-bearing solutions with gypsum: Epitaxy and induced twinning of brushite (CaHPO4{middle dot}2H2O) on the gypsum cleavage surface

Pinto

Jiménez

Prieto

2009

American Mineralogist

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Under slightly acidic conditions and 25 °C, the interaction between phosphate-rich aqueous solutions and gypsum cleavage fragments results in the surface precipitation of brushite (CaHPO 4 ·2H 2 O) crystals, which grow epitaxially on the (010) surface of gypsum. Using an A-centered unit-cell setting for both brushite (Aa) and gypsum (A2/a), the epitaxial relationship implies matching of the planes (010) of both structures and correspondence between equivalent crystallographic directions within these planes. The crystal habit of the overgrowing brushite is thin tabular to laminar on {010} with {111} and {111} as side faces and a clear elongation on [101]. There are two orientations of the brushite plates on the gypsum surface related to each other by a twofold axis on [010]. Thus, the overgrowth is an aggregate of parallel brushite crystals that may be twin-related, with the twofold axis as the twin law. During the interaction, gypsum dissolution is coupled with brushite growth until saturation with respect to both minerals is reached. A model of this thermodynamically driven dissolution-crystallization process is presented using the geochemical code PHREEQC. The epitaxial relationships are explained by comparing the bond system and the crystallographic properties of both minerals.

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confidence: 98%

Interaction of phosphate-bearing solutions with gypsum: Epitaxy and induced twinning of brushite (CaHPO4{middle dot}2H2O) on the gypsum cleavage surface

Pinto

Jiménez

Prieto

2009

American Mineralogist

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“…This reflection is rather sharp, appears isolated (see Fig. 2) and can be attributed to the typical 040 spacing of natural ardealite and "ardealite-like" synthetic compounds 23 . that are missing in the pattern calculated by Sakae and co-workers 25 but are usually observed in natural ardealite 40 .…”

Section: Composition and Mineralogical Features Of The Precipitatesmentioning

confidence: 93%

“…In the case of brushite and gypsum, the possibility of co-precipitation to form solid solution crystals with anionic SO 4 2-/HPO 4 2-substitution was pointed out by a number of authors [23][24] , but an evaluation of the extent and character of this solid solution has yet to be performed.…”

Section: Introductionmentioning

confidence: 99%

The Link between Brushite and Gypsum: Miscibility, Dehydration, and Crystallochemical Behavior in the CaHPO₄·2H₂O–CaSO₄·2H₂O System

Pinto

Carneiro

Katsikopoulos

et al. 2011

Crystal Growth & Design

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The present study explores the mixing properties of the Ca(SO 4 ,HPO 4 ) . 2H 2 O solid solution and the role of the "double-salt" Ca 2 SO 4 HPO 4 ·4H 2 O (ardealite) by means of precipitation experiments carried out in a solution calorimeter at 25ºC. Moreover, the dehydration behavior of a number of solids with different compositions is studied by thermogravimetry and thermo-X-ray diffraction. The experimental results indicate the existence of two (sulfate-rich and phosphate-rich) ranges of solid solution which are separated by two miscibility gaps from a range around the midpoint (~50% molar) composition in which ardealite forms. On the phosphate-rich miscibility range, the structural (020) layers contract with the sulfate content, whereas the interlayer spacing expands. This contraction is consistent with the negative enthalpy of mixing determined from the calorimetric data. For the ardealite range of compositions, the strong contraction of the (020) layers resolves in a different stacking sequence (with double b-axis and (040) as elementary stacking layers). Therefore, ardealite is demonstrated to be not a member of the Ca(SO 4 ,HPO 4 ) . 2H 2 O solid solution, but a nearly stoichiometric compound with specific structural features. The thermogravimetric study indicates a specific dehydration behavior for ardealite, which again supports the idea that this phase is not a member of the solid solution. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 3 ABSTRACTThe present study explores the mixing properties of the Ca(SO 4 ,HPO 4 ) . 2H 2 O solid solution and the role of the "double-salt" Ca 2 SO 4 HPO 4 ·4H 2 O (ardealite) by means of precipitation experiments carried out in a solution calorimeter at 25ºC. Moreover, the dehydration behavior of a number of solids with different compositions is studied by thermogravimetry and thermo-X-ray diffraction.The experimental results indicate the existence of two (sulfate-rich and phosphate-rich) ranges of solid solution which are separated by two miscibility gaps from a range around the midpoint (~50% molar) composition in which ardealite forms. On the phosphate-rich miscibility range, the structural (020) layers contract with the sulfate content, whereas the interlayer spacing expands. This contraction is consistent with the negative enthalpy of mixing determined from the calorimetric data. For the ardealite range of compositions, the strong contraction of the (020) layers resolves in a different stacking sequence (with double b-axis and (040) as elementary stacking layers). Therefore, ardealite is demonstrated to be not a member of the Ca(SO 4 ,HPO 4 ) . 2H 2 O solid s...

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“…Regarding this topic, the possible synergic action of phosphate and sulfate-based pollutants toward the alteration of cement-based materials needs to be considered, due to the extensive literature devoted to the study of calcium phosphate and sulfate phases in solid solution [19][20][21][22]. Gypsum and brushite both belong to the monoclinic system and have similar structures, despite the fact that they are not isomorphous (a = 5.182 Å, b = 15.180 Å, c = 6.239 Å, β = 116.43°, sp.gr.…”

Section: Scientific Backgroundmentioning

confidence: 99%

“…I2/c for gypsum [21]). Although they have different sizes (the phosphate group is larger than the sulfate one), the substitution of sulfate and phosphate groups can occur within certain limits [20], and a solid solution between the two phases, which also comprehends the stoichiometric mineral ardealite (Ca 2 (SO 4 )(HPO 4 )·4(H 2 O), monoclinic system, Cc space group), can form. Furthermore, it has been demonstrated [22] that the relative proportions between the two end members of the solid solution have relevant influences on the dehydration behavior of the resulting compounds, being significantly different from the ones of the pure end members within certain composition intervals.…”

Section: Scientific Backgroundmentioning

confidence: 99%

Degradation processes of reinforced concretes by combined sulfate–phosphate attack

Secco

Lampronti

Schlegel

et al. 2015

Cement and Concrete Research

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The system CaHPO4·2H2O-CaSO4·2H2O: crystallizations from calcium phosphate solutions in the presence of SO2-4

Cited by 17 publications

References 11 publications

Interaction of phosphate-bearing solutions with gypsum: Epitaxy and induced twinning of brushite (CaHPO4{middle dot}2H2O) on the gypsum cleavage surface

Interaction of phosphate-bearing solutions with gypsum: Epitaxy and induced twinning of brushite (CaHPO4{middle dot}2H2O) on the gypsum cleavage surface

The Link between Brushite and Gypsum: Miscibility, Dehydration, and Crystallochemical Behavior in the CaHPO₄·2H₂O–CaSO₄·2H₂O System

Degradation processes of reinforced concretes by combined sulfate–phosphate attack

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The system CaHPO4·2H2O-CaSO4·2H2O: crystallizations from calcium phosphate solutions in the presence of SO2-4

Cited by 17 publications

References 11 publications

Interaction of phosphate-bearing solutions with gypsum: Epitaxy and induced twinning of brushite (CaHPO4{middle dot}2H2O) on the gypsum cleavage surface

Interaction of phosphate-bearing solutions with gypsum: Epitaxy and induced twinning of brushite (CaHPO4{middle dot}2H2O) on the gypsum cleavage surface

The Link between Brushite and Gypsum: Miscibility, Dehydration, and Crystallochemical Behavior in the CaHPO4·2H2O–CaSO4·2H2O System

Degradation processes of reinforced concretes by combined sulfate–phosphate attack

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The Link between Brushite and Gypsum: Miscibility, Dehydration, and Crystallochemical Behavior in the CaHPO₄·2H₂O–CaSO₄·2H₂O System