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Coatings 2019, 9(3), 169; https://doi.org/10.3390/coatings9030169

Diammonium Hydrogenphosphate Treatment on Dolostone: The Role of Mg in the Crystallization Process

1
Istituto per la Conservazione e la Valorizzazione dei Beni Culturali (ICVBC), Consiglio Nazionale delle Ricerche (CNR), Via R. Cozzi 53, 20125 Milan, Italy
2
Dipartimento di Scienze della Terra, Università degli Studi di Milano, Via Botticelli 23, 20133 Milan, Italy
*
Author to whom correspondence should be addressed.
Received: 28 January 2019 / Revised: 26 February 2019 / Accepted: 26 February 2019 / Published: 4 March 2019
(This article belongs to the Special Issue Ion-Substituted Calcium Phosphates Coatings)
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Abstract

The diammonium hydrogenphosphate (DAP, (NH4)2HPO4) reaction with calcite has been extensively investigated. The availability of free calcium ions in the reaction environment has been acknowledged as a crucial factor in the crystallization of calcium phosphates with a high (hydroxyapatite, Ca/P 1.67) or low Ca/P molar ratio (dicalcium phosphate dihydrate, Ca/P 1.00; octacalcium phosphate, Ca/P 1.33). On the contrary, no data are available on the DAP interaction at room temperature with dolomite in terms of reaction mechanism and composition of the reaction products. Here, a multi-analytical approach based on scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectrometry (EDS) and X-ray powder diffraction before and after heating treatments is proposed to explore how the formation of calcium phosphates occur on Mg-enriched substrates and if the presence of magnesium ions during the reaction influences the crystallization process of calcium phosphates. The DAP reaction with polycrystalline dolomite gives rise to the formation of struvite and of poorly crystalline hydroxyapatite. Calcium and magnesium ions mutually interfered in the crystallization of magnesium and calcium phosphates, respectively, whose effects influenced the properties (size, micro-morphology, composition and crystallinity) of the newly-formed phases. View Full-Text
Keywords: calcium phosphate; hydroxyapatite; magnesium phosphate; struvite; dolomite; consolidating treatment; cultural heritage; ammonium phosphate calcium phosphate; hydroxyapatite; magnesium phosphate; struvite; dolomite; consolidating treatment; cultural heritage; ammonium phosphate
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Possenti, E.; Conti, C.; Gatta, G.D.; Realini, M.; Colombo, C. Diammonium Hydrogenphosphate Treatment on Dolostone: The Role of Mg in the Crystallization Process. Coatings 2019, 9, 169.

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