Despite a millennial history and the ubiquitous presence of cement in everyday life, the molecular processes underlying its hydration behavior, like the formation of calcium–silicate–hydrate (C–S–H), the binding phase of concrete, are mostly unexplored. Using time-resolved potentiometry and turbidimetry combined with dynamic light scattering, small-angle X-ray scattering, and cryo-TEM, we demonstrate C–S–H formation to proceed via a complex two-step pathway. In the first step, amorphous and dispersed spheroids are formed, whose composition is depleted in calcium compared to C–S–H and charge compensated with sodium. In the second step, these amorphous spheroids crystallize to tobermorite-type C–S–H. The crystallization is accompanied by a sodium/calcium cation exchange and aggregation. Understanding the formation of C–S–H via amorphous liquid precursors may allow for a better understanding of the topography of the nucleation in cement paste and thus the percolation of hydration products leading to the mechanical setting as well as the retarding effect of known chemical species like aluminum ions and polycarboxylate ethers.

Scale formation, the deposition of certain minerals such as CaCO3, MgCO3, and CaSO4·2H2O in industrial facilities and household devices, leads to reduced efficiency or severe damage. Therefore, incrustation is a major problem in everyday life. In recent years, double hydrophilic block copolymers (DHBCs) have been the focus of interest in academia with regard to their antiscaling potential. In this work, we synthesized well-defined blocklike PAA-PAMPS copolymers consisting of acrylic acid (AA) and 2-acrylamido-2-methyl-propane sulfonate (AMPS) units in a one-step reaction by RAFT polymerization. The derived copolymers had dispersities of 1.3 and below. The copolymers have then been investigated in detail regarding their impact on the different stages of the crystallization process of CaCO3. Ca(2+) complexation, the first step of a precipitation process, and polyelectrolyte stability in aqueous solution have been investigated by potentiometric measurements, isothermal titration calorimetry (ITC), and dynamic light scattering (DLS). A weak Ca(2+) induced copolymer aggregation without concomitant precipitation was observed. Nucleation, early particle growth, and colloidal stability have been monitored in situ with DLS. The copolymers retard or even completely suppress nucleation, most probably by complexation of solution aggregates. In addition, they stabilize existing CaCO3 particles in the nanometer regime. In situ AFM was used as a tool to verify the coordination of the copolymer to the calcite (104) crystal surface and to estimate its potential as a growth inhibitor in a supersaturated CaCO3 environment. All investigated copolymers instantly stopped further crystal growth. The carboxylate richest copolymer as the most promising antiscaling candidate proved its enormous potential in scale inhibition as well in an industrial-filming test (Fresenius standard method).

Monodisperse FePt@MnO nano-heteroparticles with different sizes and morphologies were prepared by a seed-mediated nucleation and growth technique. Both size and morphology of the individual domains could be controlled by adjustment of the synthetic parameters. As a consequence, different particle constructs, including dimers, dumbbell-like particles, and flowerlike particles, could be obtained by changing the polarity of the solvent. The FePt@MnO nano-heteroparticles were thoroughly characterized by high resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD) analyses and superconducting quantum interference device (SQUID) magnetometry. Due to a sufficient lattice match, the MnO nanoparticles (NPs) preferentially grow on the (111) surfaces of the fcc-FePt seeds. Furthermore, the surface spins of the antiferromagnetic MnO domains pin the magnetic moments of the ferromagnetic FePt NPs, which leads to an exchanged biased magnetic hysteresis.

The mechanisms by which amorphous intermediates transform into crystalline materials are still poorly understood. Here we attempt to illuminate the formation of an amorphous precursor by investigating the crystallization process of zinc phosphate hydrate. This work shows that amorphous zinc phosphate (AZP) nanoparticles precipitate from aqueous solutions prior to the crystalline hopeite phase at low concentrations and in the absence of additives at room temperature. AZP nanoparticles are thermally stable against crystallization even at 400 °C (resulting in a high temperature AZP), but they crystallize rapidly in the presence of water if the reaction is not interrupted. X-ray powder diffraction with high-energy synchrotron radiation, scanning and transmission electron microscopy, selected area electron diffraction, and small-angle X-ray scattering showed the particle size (≈20 nm) and confirmed the noncrystallinity of the nanoparticle intermediates. Energy dispersive X-ray, infrared, and Raman spectroscopy, inductively coupled plasma mass spectrometry, and optical emission spectrometry as well as thermal analysis were used for further compositional characterization of the as synthesized nanomaterial. (1)H solid-state NMR allowed the quantification of the hydrogen content, while an analysis of (31)P{(1)H} C rotational echo double resonance spectra permitted a dynamic and structural analysis of the crystallization pathway to hopeite.

The mechanisms by which amorphous intermediates transform into crystalline materials are not well understood. To test the viability and the limits of the classical crystallization, new model systems for crystallization are needed. With a view to elucidating the formation of an amorphous precursor and its subsequent crystallization, the crystallization of calcium oxalate, a biomineral widely occurring in plants, is investigated. Amorphous calcium oxalate (ACO) precipitated from an aqueous solution is described as a hydrated metastable phase, as often observed during low-temperature inorganic synthesis and biomineralization. In the presence of water, ACO rapidly transforms into hydrated whewellite (monohydrate, CaC2 O4 ⋅H2 O, COM). The problem of fast crystallization kinetics is circumvented by synthesizing anhydrous ACO from a pure ionic liquid (IL-ACO) for the first time. IL-ACO is stable in the absence of water at ambient temperature. It is obtained as well-defined, non-agglomerated particles with diameters of 15-20 nm. When exposed to water, it crystallizes to give (hydrated) COM through a dissolution/recrystallization mechanism.