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Polyamorphism and frustrated crystallization in the acid-base reaction of magnesium potassium phosphate cements
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SYSNO ASEP 0491029 Document Type J - Journal Article R&D Document Type Journal Article Subsidiary J Článek ve WOS Title Polyamorphism and frustrated crystallization in the acid-base reaction of magnesium potassium phosphate cements Author(s) Viani, Alberto (UTAM-F) RID, ORCID, SAI
Mácová, Petra (UTAM-F) RID, SAI, ORCIDNumber of authors 2 Source Title CrystEngComm. - : Royal Society of Chemistry - ISSN 1466-8033
Roč. 20, č. 32 (2018), s. 4600-4613Number of pages 13 s. Publication form Print - P Language eng - English Country GB - United Kingdom Keywords cement ; potassium compounds ; crystalline materials ; reaction intermediates Subject RIV CF - Physical ; Theoretical Chemistry OECD category Physical chemistry R&D Projects LO1219 GA MŠMT - Ministry of Education, Youth and Sports (MEYS) UT WOS 000442612000011 EID SCOPUS 85051475594 DOI 10.1039/c8ce00670a Annotation Magnesium potassium phosphate cements are a class of acid−base cements for bioengineering and civil engineering applications. The kinetics of the chemical reaction was investigated in-situ with isothermal conduction calorimetry and with powder X-ray diffraction, quantifying amorphous and crystalline products. The first reaction step, dissolution of MgO, with apparent activation energy of 71 kJ/mol, dictates the time-evolution of two amorphous intermediate precursors and of the crystalline product. The early crystallization of the latter has been described with an Avrami equation with apparent activation energy of 81 kJ/mol, pointing to a mechanism of deceleratory nucleation and growth in one direction, compatible with the acicular crystal habit observed with electron microscopy. The observed polyamorph transformation is controlled by a complex interplay between kinetic and thermodynamic factors, in which the changes in chemical environment (increase in pH) driven by the MgO dissolution, play a crucial role. It is proposed that the onset of the amorphous-amorphous transformation hinders crystallization by decreasing ion mobility, raising the energy barriers to structural reorganization. The rate of MgO dissolution depends on the reactivity of the powder and parameters of the mix (such as the amount of liquid) and influences the reaction pathways, impacting on material performance. Workplace Institute of Theoretical and Applied Mechanics Contact Kulawiecová Kateřina, kulawiecova@itam.cas.cz, Tel.: 225 443 285 Year of Publishing 2019 Electronic address http://dx.doi.org/10.1039/C8CE00670A
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