Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (44) (entfernen)
Schlagworte
- Mechanochemistry (13)
- Polymorphism (6)
- Crystallization (5)
- SAXS (5)
- In situ (4)
- Synchrotron radiation (4)
- XRD (4)
- Cocrystal (3)
- Nifedipine (3)
- cocrystal (3)
- Acoustic levitation (2)
- Gas adsorption (2)
- Glasses (2)
- Luminescence (2)
- Metal phosphonate (2)
- Metal-organic frameworks (2)
- Milling (2)
- Nanolithography (2)
- Nanoparticle (2)
- Nanoparticles (2)
- Polymorphs (2)
- Raman spectroscopy (2)
- Specific surface area (2)
- Surface-enhanced Raman scattering (2)
- X-ray diffraction (2)
- in situ (2)
- mechanochemistry (2)
- AFM (1)
- AFM/TEM/SEM (1)
- Activation energy (1)
- Antimony clusters (1)
- Benzamide (1)
- Bismuth (1)
- Caffeine (1)
- Calibration (1)
- Calorimetry (1)
- Carbon dioxide (1)
- Catalytic applications (1)
- Co-crystal (1)
- Continuous flow (1)
- Dendrites (1)
- Dielectric liquids (1)
- Dielectric relaxation (1)
- Dissipation (1)
- ESEM (1)
- Evaporation of droplets (1)
- Force-Microscopy (1)
- Force-microscopy (1)
- Formation mechanisms (1)
- Friction (1)
- Gas-phase NMR spectroscopy (1)
- Glas (1)
- Glass transition (1)
- Glucose (1)
- Gold (1)
- Goldcluster (1)
- Green-chemistry synthesis (1)
- Growth mechanism (1)
- Height Calibration (1)
- Height calibration (1)
- Hexagons (1)
- In situ PXRD (1)
- In situ Raman spectroscopy (1)
- In situ WAXS (1)
- In situ reactions (1)
- In situ studies (1)
- Ion exchanged soda lime silicate glass (1)
- Ion-exchange (1)
- Liquid structure (1)
- MOF (1)
- MOF-14 (1)
- Metastable (1)
- Micro spot (1)
- Microstructured static mixer (1)
- Multiphoton fabrication (1)
- Nanoparticle formation mechanism (1)
- Nanophotonik (1)
- Nicotinamide (1)
- Nucleation (1)
- Organic compounds (1)
- Piezoelectric translator (1)
- Primary reference gas mixtures (1)
- Pyrazinamide (1)
- Quantitative NMR spectroscopy (1)
- RESS (1)
- ROY (1)
- Scanning probe microscope (1)
- Silicon (1)
- Silver (1)
- Silver nanoparticle growth (1)
- Silver nanoparticles (1)
- Single-crystal (1)
- Size control (1)
- Small-angle X-ray scattering (1)
- Sodium borohydride (1)
- Sol-gel processes (1)
- Supercooling (1)
- Supercritical fluids (1)
- Surface plasmon resonance (1)
- Thermoelectric applications (1)
- Tunneling microscopy (1)
- X-ray lithography (1)
- benzamide (1)
- caffeine (1)
- hydrate (1)
- milling (1)
- polymorphism (1)
- pyrazinamide (1)
- synchrotron X-ray diffraction (1)
- theophylline (1)
- µSpot (1)
Organisationseinheit der BAM
- 6 Materialchemie (3)
- 6.3 Strukturanalytik (3)
Tribological properties of amorphous and crystalline antimony nanoparticles studied by SFM and TEM
(2005)
Crystallization processes under different conditions are of fundamental interest in chemistry, pharmacy, and medicine. Therefore, we have studied the formation of micro- and nanosized crystals using water-caffeine (1,3,7-trimethyl-1H-purine-2,6(3H,7H)-dione) solutions under ambient conditions as a relevant model system. When droplets of an aqueous caffeine solution evaporate and eventually dry on surfaces (glass, polystyrene, and polyester), stable coffee tabletop rings with a perimeter of typically 3 mm are formed after 20 to 50 min. Using a micro focus X-ray beam available at the BESSY µSpot-beamline, the fine structure of different caffeine needles can be distinguished. Unexpectedly, both crystal modifications (α- and β-caffeine) are present, but locally separated in these rings. Furthermore, AFM studies reveal the presence of even smaller particles on a nanometer length scale. To eliminate influences of surface irregularities from the crystallization process, acoustic levitation of liquid samples was employed. Such levitated droplets are trapped in a stable position and only surrounded by air. The solvent in an ultrasonically levitated drop evaporates completely, and the resulting crystallization of caffeine was followed in situ by synchrotron X-ray diffraction. In this case, the diffraction pattern is in accordance with pure α-caffeine and does not indicate the formation of the room temperature polymorph β-caffeine. Hence, our investigations open new vistas that may lead to a controlled formation of cocrystals and novel polymorphs of micro- and nanocrystalline materials, which are of relevance for fundamental studies as well as for pharmaceutical and medical applications.
The crystallization of nifedipine was studied by means of synchrotron-X-ray diffraction, single-crystal X-ray structural analysis, and Raman spectroscopy. The results of slow evaporation (24 h in minimum) using dimethyl sulfoxide (DMSO) are presented. Since fast crystallization processes (typically minutes) in different solvents always led to the final formation of the thermodynamically most stable α-polymorph of nifedipine, we observed a novel pseudo-polymorph due to slow crystallization from DMSO. The single-crystal X-ray structure of the solvated species nifedipine·DMSO (1:1) is reported for the first time. In addition, the crystallization process on surfaces was followed by means of light microscopy and environmental scanning electron microscopy (ESEM) coupled with energy-dispersive X-ray spectroscopy (EDS) analysis. Different diffractions pattern and Raman spectra were observed for crystals grown from stock solution and those obtained by drying the solution on soda lime silicate surfaces.
The use of a fibre-based light sensor for the calibration of Scanning Probe Microscopy piezos
(1999)
The effect of the ball to reactant ratio on mechanochemical reaction times studied by in situ PXRD
(2017)
The effect of the reactant powder mass on reaction times for the mechanochemical formation of a soft matter model system was studied by in situ PXRD. The syntheses were performed at a constant ball mass in a shaker mill with and without glassy SiO2 as an inert additive. Reaction times decreased with the increase of the ball to reactant ratio (BRR). The kinetic influence of the SiO2 powder was excluded. The decrease in the reaction time with decreasing mass of reactants was related to the rise in the stress energy transferred to the powder by a higher ball impact. The BRR had no effect on the induction time. But the product conversion was accelerated by raising the BRR. While a certain temperature is needed for the activation of reactants in the induction phase, the conversion of soft matter reactants is rather controlled by impact than temperature.
The crystal structures and syntheses of four different copper(II) phenylphosphonates, the monophenylphosphonates α-, β-, and γ-Cu(O3PC6H5)·H2O (α-CuPhPmH (1) β-CuPhPmH (2) and γ-CuPhPmH (3)), and the diphosphonate Cu(HO3PC6H5)2·H2O (CuPhP2mH (4)), are presented. The compounds were synthesized from solution at room temperature, at elevated temperature, under hydrothermal conditions, and mechanochemical conditions. The structures of α-CuPhPmH (1) and CuPhP2mH (4) were solved from powder X-ray diffraction data. The structure of β-CuPhPmH (2) was solved by single crystal X-ray analysis. The structures were validated by extended X-ray absorption fine structure (EXAFS) and DTA analyses. Disorder of the crystal structure was elucidated by electron diffraction. The relationship between the compounds and their reaction pathways were investigated by in situ synchrotron measurements.
Two divalent manganese aminophosphonates, manganese mono (nitrilotrimethylphosphonate) (MnNP3) and manganese bis N-(carboxymethyl)iminodi(methylphosphonate)) (Mn(NP2AH)2), have been prepared by mechanochemical synthesis and characterized by powder X-ray diffraction (PXRD). The structure of the novel compound Mn(NP2AH)2 was determined from PXRD data. MnNP3 as well as Mn(NP2AH)2 exhibits a chain-like structure.
In both cases, the manganese atom is coordinated by six oxygen atoms in a distorted octahedron. The local coordination around Mn was further characterized by extended X-ray absorption fine structure. The synthesis process was followed in situ by synchrotron X-ray diffraction revealing a three-step reaction mechanism. The asprepared manganese(II) phosphonates were calcined on air.
All samples were successfully tested for their suitability as catalyst material in the oxygen evolution reaction.
The driving forces triggering the formation of co-crystals under milling conditions were investigated by using a set of multicomponent competitive milling reactions. In these reactions, different active pharmaceutical ingredients were ground together with a further compound acting as coformer. The study was based on new co-crystals including the coformer anthranilic acid. The results of the competitive milling reactions indicate that the formation of co-crystals driven by intermolecular recognition are influenced and inhibited by kinetic aspects including the formation of intermediates and the stability of the reactants.
The stability of different theophylline cocrystals under milling conditions was investigated by competitive cocrystal reactions. To determine the most stable cocrystal form under milling conditions, the active pharmaceutical ingredient theophylline was either ground with two similar coformers (benzoic acid, benzamide, or isonicotinamide), or the existing theophylline cocrystals were ground together with a competitive coformer. All competitive reactions were investigated by in situ powder X-ray diffraction disclosing the formation pathway of the milling processes. On the basis of these milling reactions, a stability order (least to most stable) was derived: tp/bs < tp/ba < tp/ina < bs/ina.