Journal
CERAMICS INTERNATIONAL
Volume 43, Issue 8, Pages 6571-6579Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.ceramint.2017.02.087
Keywords
Sol-gel processes; Spectroscopy; MgO; Chemically-bonded ceramics
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Funding
- Ministry of Education, Youth and Sports National sustain ability programme I of Czech Republic [LO1219]
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Magnesium phosphate ceramics are chemically-bonded ceramics for bioengineering and civil engineering applications. Information about the nature of the reaction products, especially the amorphous fraction, and their role in the setting reaction, essential for linking reaction mechanisms to microstructure and performance of ceramics, is lacking. By exploiting H-1 and P-31 magic-angle spinning nuclear magnetic resonance spectroscopy, in addition to the crystalline reaction product (MKP), two amorphous phases, characterized by two distinct proton and phosphorous environments, have been identified. The results pointed to amorphous hydrated orthophosphate compounds which are the precursors of MKP. They show different H-1 spin-lattice relaxation dynamics, and, higher water mobility with respect to MKP. Although these amorphous precursors should not be crypto-structural variants of MKP, they likely host similar structural units. Conversion into MKP is thought to occur through relatively minor rearrangements, as in Ca phosphate hydrates. The new information provided in this work allows us to propose a model for the setting reaction based on an existing theory involving a densification process, analogue to sol-gel processing of ceramics, coherent with results from small angle neutron scattering and mechanisms predicted by reaction kinetics analysis.
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