Günne, Jörn Schmedt auf der
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Günne, Jörn Schmedt auf der
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Publication Access status: Metadata only , Cement hydration kinetics followed by electron spin resonanceCement hydration is driven by a complex system of chemical reactions of several hydraulic binders and water that influence each other. Here we establish a method to measure the hydration kinetics of an individual clinker phase by electron spin resonance spectroscopy. The hydration of a Mn(II) doped crystalline phase can be analyzed from the decay of signals coming from the starting material and the formed product. Transformation times can be determined by modeling the time series of the signal intensities. The host of the dopant could be identified by combining evidence from different analytical techniques including diffraction and electron microscopy. The results about the reaction kinetics are compared to those obtained from caloric measurements. The method opens a way to study the hydration of different hydraulic binders in complex systems selectively, which includes the determination of induction periods and transformation times from in-situ measurements.Source Type:Article1 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Combining NMR and impedance spectroscopy <i>in situ</i> to study the dynamics of solid ion conductorsUnwanted differences in the apparent ion mobilities as seen by NMR and impedance spectroscopy are removed by a setup that allows measuring both on the same, by which in situ studies of interface stability and phase transitions become possible.Source Type:Article2 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Echo pulses for background suppression by optimal controlMaterials used to construct magic‐angle‐spinning NMR probes can contain NMR active nuclei that produce a significant amount of background signal. Because these materials are located outside the sample coil, the use of spatially selective pulses to remove the background is a popular approach for background suppression. However, previously suggested spatially selective pulses suffer from limited excitation bandwidths, which may make them unsuitable for the acquisition of nuclei with a large chemical shift range. Here, a pulse (OC‐BACK) is presented, which has been developed by optimal control, which has a flat profile of ~120 kHz with respect to off‐resonance effects and extended pass and suppression bands with respect to the nominal nutation frequency. The presented solution is large enough to be effective for background suppression schemes in 19 F magic‐angle‐spinning NMR at medium and low magnetic fields.Source Type:ArticleDOI:10.1002/mrc.53541 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Influence of Mg on the Li ion mobility in Li<sub>4−2<i>x</i></sub>Mg<sub><i>x</i></sub>P<sub>2</sub>S<sub>6</sub>Mg as a roadblock for Li ion motion was investigated by NMR, impedance spectroscopy, quantum-chemical simulations and X-ray diffraction. Aliovalent substitution can cause substantial structural changes in solid ion conductors.Source Type:Article1 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Structure and phase changes of alumina produced by flame hydrolysisFumed alumina from the combustion of AlCl 3 produced nano pArticles with specific areas from 30 to 220 m 2 g −1 (BET) which were characterized by powder X-ray diffraction, 27 Al solid-state NMR and transmission electron microscopy.Source Type:Article4 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Synthesis and Characterization of Iron-Doped TiO2 Nanotubes (Fe/TiNTs) with Photocatalytic ActivityOne of the most significant global challenges for humans is environmental pollution. The technology to control this problem is the utilization of semiconductors as photocatalysts. In the current study, iron-doped titania nanotubes (Fe/TiNTs) with increased photocatalytic effect were synthesized via a modified hydrothermal method. The products were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy (TEM), gas adsorption, electron spin resonance (ESR) and UV–Vis diffuse reflectance spectroscopy (DRS). TEM results indicated that Fe/TiNTs have a tubular and uniform structure with an average outer diameter of 23–48 nm and length of 10–15 µm. ESR and DRS revealed that Fe3+ ions were successfully introduced into the TiNT structure by replacing Ti4+ ions. An enhanced light absorption in the range of 400–600 nm additionally indicated successful doping. The band gap was narrowed as iron wt% was increased. The photocatalytic activity was evaluated by the degradation of methyl orange (MO) in the presence of Fe/TiNTs and TiTNs by monitoring the degradation of MO under UV light irradiation. An acceleration on the hydration of Portland cement was observed in the presence of 2.0 wt% Fe/TiNTs. Fe/TiNTs can be used as a nanomaterial in cement-based building materials to provide self-cleaning properties to the surface of concrete even in indoor environments.Source Type:Article7
