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Mechanism of setting reaction in magnesia-phosphate cements

Soudee, E. / Pera, J.

This paper tries to explain the setting mechanism of magnesia-phosphate cements obtained by mixing equal qualities of magnesia (MgO) and monoammonium dihydrogen phosphate (NH₄H₂PO₄) or MAP. As soon as mixing water is added to the mixture, the MAP goes into solution till saturation while magnesia starts to be wetted. The drop in pH observed during this period leads to the dissociation of magnesia through an acid-base reaction. The kinetics of this reaction depends upon the MgO surface structure. Mg²⁺ ions present in solution are complexed into Mg (H₂O)₆²⁺ and can substitute to molecules of water and be adsorbed on the MgO surface. These complexes remain attached to the surface and recover it progressively. Ions PO₄^3- and NH₄⁺ and Mg(H₂O)₆²⁺ complexes can come close to the surface and develop a struvite network, owing to hydrogen bonds. This explanation results from analyses of solutions, X-ray diffractometry, and scanning electron microscopy.

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Mechanism of setting reaction in magnesia-phosphate cements

Soudee, E. / Pera, J.

This paper tries to explain the setting mechanism of magnesia-phosphate cements obtained by mixing equal qualities of magnesia (MgO) and monoammonium dihydrogen phosphate (NH₄H₂PO₄) or MAP. As soon as mixing water is added to the mixture, the MAP goes into solution till saturation while magnesia starts to be wetted. The drop in pH observed during this period leads to the dissociation of magnesia through an acid-base reaction. The kinetics of this reaction depends upon the MgO surface structure. Mg²⁺ ions present in solution are complexed into Mg (H₂O)₆²⁺ and can substitute to molecules of water and be adsorbed on the MgO surface. These complexes remain attached to the surface and recover it progressively. Ions PO₄^3- and NH₄⁺ and Mg(H₂O)₆²⁺ complexes can come close to the surface and develop a struvite network, owing to hydrogen bonds. This explanation results from analyses of solutions, X-ray diffractometry, and scanning electron microscopy.

Mechanism of setting reaction in magnesia-phosphate cements

Soudee, E. / Pera, J.

This paper tries to explain the setting mechanism of magnesia-phosphate cements obtained by mixing equal qualities of magnesia (MgO) and monoammonium dihydrogen phosphate (NH₄H₂PO₄) or MAP. As soon as mixing water is added to the mixture, the MAP goes into solution till saturation while magnesia starts to be wetted. The drop in pH observed during this period leads to the dissociation of magnesia through an acid-base reaction. The kinetics of this reaction depends upon the MgO surface structure. Mg²⁺ ions present in solution are complexed into Mg (H₂O)₆²⁺ and can substitute to molecules of water and be adsorbed on the MgO surface. These complexes remain attached to the surface and recover it progressively. Ions PO₄^3- and NH₄⁺ and Mg(H₂O)₆²⁺ complexes can come close to the surface and develop a struvite network, owing to hydrogen bonds. This explanation results from analyses of solutions, X-ray diffractometry, and scanning electron microscopy.

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Title:

Mechanism of setting reaction in magnesia-phosphate cements

Contributors:

Soudee, E. (author) / Pera, J. (author)

Published in:

Cement and Concrete Research ; 30 ; 315-321

Publication date:

2000

Size:

7 Seiten, 28 Quellen

ISSN:

DOI:

https://doi.org/10.1016/S0008-8846(99)00254-9

Type of media:

Article (Journal)

Type of material:

Print

Language:

English

Keywords:

Reaktionskinetik , Magnesiumoxid , Mikrostruktur , Wasserstoffbrücke , Röntgenbeugung , Röntgenanalyse , Rasterelektronenmikroskopie , Hydratisieren , Dissoziation , Wasserabbinden von Zement , Ammoniumphosphat

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