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New insights into the nucleation of portlandite and the effects of polymeric additives

  • The crystallization of calcium hydroxide (Ca(OH)2, CH, portlandite) is a key process during the early stages of cement hydration. In the present work, we have revisited the formation of this mineral through nucleation and growth from supersaturated aqueous solutions, in the light of the currently emerging picture of multistage “non-classical” crystallization. To that end, we developed a titration-based assay, in which stock solutions of both relevant ions are added simultaneously into a reservoir, where supersaturation increases slowly at constant stoichiometry until nucleation occurs. This procedure allows both pre- and early post-nucleation phenomena to be analyzed quantitatively. Complementarily, the early stages of portlandite mineralization were probed by various advanced characterization techniques, including cryo-transmission electron microscopy (cryo-TEM), in-situ small-angle X-ray scattering (SAXS), pair distribution function (PDF) analysis of high-energy X-ray scatteringThe crystallization of calcium hydroxide (Ca(OH)2, CH, portlandite) is a key process during the early stages of cement hydration. In the present work, we have revisited the formation of this mineral through nucleation and growth from supersaturated aqueous solutions, in the light of the currently emerging picture of multistage “non-classical” crystallization. To that end, we developed a titration-based assay, in which stock solutions of both relevant ions are added simultaneously into a reservoir, where supersaturation increases slowly at constant stoichiometry until nucleation occurs. This procedure allows both pre- and early post-nucleation phenomena to be analyzed quantitatively. Complementarily, the early stages of portlandite mineralization were probed by various advanced characterization techniques, including cryo-transmission electron microscopy (cryo-TEM), in-situ small-angle X-ray scattering (SAXS), pair distribution function (PDF) analysis of high-energy X-ray scattering (HEXS) data, and analytical ultracentrifugation (AUC). The experimental data show that the formation of calcium hydroxide starts with the association of ions into complexes and clusters, which subsequently coalesce to form amorphous nanoparticles – much like what has been observed in the case of calcium carbonate and other prominent minerals. Subsequently, these particles aggregate and build networks, which eventually transform into hexagonal Ca(OH)2 crystals. The presence of a soluble polycarboxylate – as a known inhibitor of portlandite crystallization – does not change the main characteristics of this multistep nucleation pathway, but it proved capable of significantly extending the lifetime of the amorphous intermediate phase and thus delaying the transition to the final crystalline phase. Our observations confirm the notion that “non-classical” crystallization is a much more common phenomenon than initially believed – and that, for minerals forming in aqueous environments, it may actually be the rule rather than the exception.zeige mehrzeige weniger

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Autor*innen:B. Madeja, D. Gebauer, M. R. Marsiske, A. Ott, M. Rückel, R. Rosenberg, A. Baken, Tomasz M. Stawski, A. Fernandez-Martinez, A.E.S. Van Driessche, H. Cölfen, M. Kellermeier
Dokumenttyp:Zeitschriftenartikel
Veröffentlichungsform:Verlagsliteratur
Sprache:Englisch
Titel des übergeordneten Werkes (Englisch):Cement and Concrete Research
Jahr der Erstveröffentlichung:2023
Organisationseinheit der BAM:6 Materialchemie
6 Materialchemie / 6.3 Strukturanalytik
Verlag:Elsevier B.V.
Jahrgang/Band:173
Aufsatznummer:107258
Erste Seite:1
Letzte Seite:13
DDC-Klassifikation:Technik, Medizin, angewandte Wissenschaften / Ingenieurwissenschaften / Ingenieurwissenschaften und zugeordnete Tätigkeiten
Freie Schlagwörter:Building and Construction; General Materials Science
Themenfelder/Aktivitätsfelder der BAM:Material
DOI:10.1016/j.cemconres.2023.107258
ISSN:0008-8846
Verfügbarkeit des Dokuments:Datei im Netzwerk der BAM verfügbar ("Closed Access")
Datum der Freischaltung:06.09.2023
Referierte Publikation:Ja
Datum der Eintragung als referierte Publikation:06.09.2023
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