TY - JOUR

T1 - New insights into the nucleation of portlandite and the effects of polymeric additives

AU - Madeja, Benjamin

AU - Gebauer, Denis

AU - Marsiske, Maximilian R.

AU - Ott, Andreas

AU - Rückel, Markus

AU - Rosenberg, Rose

AU - Baken, Annet

AU - Stawski, Tomasz M.

AU - Fernandez-Martinez, Alejandro

AU - Van Driessche, Alexander E.S.

AU - Cölfen, Helmut

AU - Kellermeier, Matthias

N1 - Funding Information: The authors thank Dr. Michael Laumann and the Electron Microscopy Centre at the University of Konstanz for support during SEM studies, Elisabeth Wagner (BASF SE) for conducting TOC analyses, as well as Ralf Sander and Dr. Tobias Umbach (BASF SE) for carrying out nanoindentation experiments. Access to beamlines ID02 and ID15a at ESRF for SAXS and HEXS experiments through grant numbers ES 526 and ES 608, respectively, and support by ESRF experts is highly appreciated. AESVD and AFM acknowledge funding from the Spanish Ministerio de Ciencia y Innovacion through the Grant TED2021-130860B-I00 .

PY - 2023/11

Y1 - 2023/11

N2 - 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 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.

AB - 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 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.

KW - Amorphous precursors

KW - Analytical ultracentrifugation

KW - Calcium hydroxide

KW - Cryo-TEM

KW - Mineralization

KW - Non-classical crystallization

KW - Nucleation

KW - Pair distribution function analysis

KW - Polymer-controlled crystallization

KW - Potentiometric titration

KW - Pre-nucleation clusters

KW - SAXS

UR - http://www.scopus.com/inward/record.url?scp=85165032108&partnerID=8YFLogxK

U2 - 10.1016/j.cemconres.2023.107258

DO - 10.1016/j.cemconres.2023.107258

M3 - Article

AN - SCOPUS:85165032108

VL - 173

JO - Cement and concrete research

JF - Cement and concrete research

SN - 0008-8846

M1 - 107258

ER -