Datei im Netzwerk der BAM verfügbar ("Closed Access")
Filtern
Erscheinungsjahr
Dokumenttyp
Schlagworte
- Flame retardancy (7)
- Solid-state NMR (5)
- Geopolymers (4)
- NMR (3)
- Zinc borate (3)
- 11B (2)
- 25Mg (2)
- 29Si NMR (2)
- Acid resistance (2)
- Aluminium diethylphosphinate (2)
- Aryl phosphate (2)
- Calcined clays (2)
- Cement additive (2)
- Deadtime (2)
- Epoxy resin (2)
- Flame retardance (2)
- Kaolin (2)
- One-part geopolymers (2)
- Polycarbonate (PC) blends (2)
- Pozzolan (2)
- Probe background suppression (2)
- REDOR (2)
- Ringing suppression (2)
- SEBS (2)
- Synergy (2)
- Zeolite Na-A (2)
- (NH4)3InF6 (1)
- 115In and 19F solid state NMR (1)
- 13C (1)
- 13C NMR (1)
- 19F (1)
- 1H (1)
- 23Na (1)
- 27Al MAS NMR (1)
- 29Si MAS NMR (1)
- 29Si{27Al} TRAPDOR MAS NMR (1)
- 2D NMR (1)
- ATR-FTIR-spectroscopy (1)
- Abwasserinfrastruktur (1)
- Acid rock drainage (1)
- Al13 (1)
- Alkali activated materials (1)
- Alkali-activated materials (1)
- Alkaliaktivierte Bindemittel (1)
- Aluminium fluorine (1)
- Aluminium phosphate (1)
- Aluminosilicate inorganic polymers (1)
- Aluminosilicates (1)
- Aluminum (1)
- Ammonia plasma (1)
- Ammonium polyphosphate (1)
- Anion exchange (1)
- Apatite formation (1)
- Arsenic retention (1)
- Basaluminite (1)
- Benzamide (1)
- Beta-christobalite structure type (1)
- Biogene Schwefelsäurekorrosion (1)
- Bisphenol A bis(diphenyl)phosphate (BDP) (1)
- Bisphenol-A bis(diphenyl)phosphate (BDP) (1)
- Building-blocks (1)
- CPMAS NMR (1)
- Calcium phosphate (1)
- Carbon-fluorine bonds (1)
- Chemical durability (1)
- Computational chemistry (1)
- Crystalline aluminium isopropoxide fluoride (1)
- Degradation (1)
- Degree of reaction (1)
- Deuterated ammonia (1)
- Deuterated polyolefins (1)
- Drying (1)
- Etal-complexes (1)
- Faujasite-type zeolites (1)
- Fire residue (1)
- Flammability (1)
- Fluorescent dye labeling (1)
- Germylium ions (1)
- H-D exchange (1)
- Hexamethyldisiloxane plasma polymer (1)
- Hexatriacontane (1)
- High-cristobalite form (1)
- High-temperature resistance (1)
- Hydrochar (1)
- Hydrodefluorination (1)
- Hydrothermal carbonization (1)
- Hydroxyapatite (1)
- INADEQUATE (1)
- In situ reactions (1)
- Inorganic fillers (1)
- Lewis-acids (1)
- MAS (1)
- MAS NMR (1)
- Magnesium hydroxide (1)
- Mechanochemistry (1)
- Melamine poly(magnesium phosphate) (1)
- Melamine poly(metal phosphate) (1)
- Micro-computed tomography (1)
- Microcrystalline cellulose (1)
- NMR spectroscopy (1)
- NMR-spectroscopy (1)
- Nanochrystalline AlPO4 (1)
- Nicotinamide (1)
- Nuclear magnetic resonance (1)
- One-part formulation (1)
- One-part mix (1)
- PC/ABS (1)
- Phosphine-ligands (1)
- Phosphorus (1)
- Plasma polymerization (1)
- Poly(acrylic acid)-grafted particles (1)
- Poly(phenylene) oxide (1)
- Polycarbonate blends (1)
- Polyethylene (1)
- Polymer beads (1)
- Polymorphs (1)
- Polystyrene (1)
- Q4(mAl) sites (1)
- Qudrupolar nuclei (1)
- REPT-HMQC (1)
- Reparatursysteme (1)
- Room-temperature (1)
- SEM (1)
- Si-O-C bonds (1)
- Silica (1)
- Silica-cellulosic composites (1)
- Silicate (1)
- Silicon (1)
- Silicone rubber (1)
- Sol-gel derived silica (1)
- Sol-gel processes (1)
- Solid State NMR (1)
- Solid state NMR (1)
- Spectroscopy (1)
- Stabilization of high-temperature phase at RT (1)
- Stannosilicates (1)
- Sulfuric acid resistance (1)
- Surface analysis (1)
- Thermal properties (1)
- Vapor-phase hydrofluorination (1)
- Vinyl fluoride (1)
- XPS (1)
- XRD (1)
- Zeolites (1)
- qNMR of quadrupolar nuclei (1)
Organisationseinheit der BAM
The small-pore framework sodium stannosilicate AV-10, chemical composition Na2SnSi3O9⋅2H2O and known crystallographic structure, was synthesized by hydrothermal crystallization. This stannosilicate is built up of a three-dimensional network of corner-shared SiO4 tetrahedra and SnO6 octahedra. The SnO6 sites are linked to six SiO4 tetrahedra (Sn(6Si)) while each of the two crystallographically different SiO4 units are connected to two SnO6 and SiO4 units (Si(2Si,2Sn)). This material was used as model compound for developing a solid-state MAS NMR strategy aimed on the challenges and possibilities for structural studies, particularly considering the short and medium range order to verify the connectivity of SiO4 and SnO6 of such compounds despite the low natural abundances of 4.68% for 29Si and 8.59% for 119Sn nuclei as a real challenge. 29Si{119Sn} and 119Sn{29Si} REDOR (Rotational-Echo Double-Resonance) NMR measurements after 1H cross-polarization (CP) were carried out. The REDOR curves show a significant change after the “normal” quadratic short time evolution from which both (i) the shortest internuclear 29Si – 119Sn distances (and vice versa) and (ii) the number of corner-sharing SiO4 tetrahedra around the SnO6 octahedra (and vice versa) can be obtained. Based on these data, optimized 29Si {119Sn} and 119Sn{29Si} REPT-HMQC (Recoupled Polarization Transfer-Heteronuclear Multiple-Quantum Correlation, again after 1H CP) experiments were implemented, which directly show those heterogroup connectivity as correlation peaks in a 2D spectrum. This information was also obtained using 2D29Si{119Sn}-J-Coupling NMR experiments. Furthermore, 2D29Si INADEQUATE NMR experiments are also feasible, showing the connectivity of SiO4 tetrahedra. The combination of REDOR, REPT-HMQC, J-Coupling and INADEQUATE experiments yielded a complete analysis of the short and medium range structure of this microporous stannosilicate, in agreement with the previously published structure obtained Ab Initio from powder X-Ray diffraction data (XRD).
The layered silicophosphate Si(HPO4)(2) was prepared via a novel synthesis approach using silicon nanopowder and ortho-phosphoric acid at 150 degrees C providing a polycrystalline product. Silicophosphate compounds with sixfold coordinated silicon atoms obtained from pyrophosphoric acid H4P2O7 and tetraalkoxysilanes via a sol-gel route exhibit the same short-range order. The solid products were analyzed with XRD, elemental analysis (ICP-AES), and detailed NMR spectroscopic studies, including H-1, C-13, Si-29, and P-31 MAS-, P-31-Si-29-REDOR, HETCOR, and CP-RFDR experiments. DFT calculations support the structure of Si(HPO4)(2) consisting of layers of [SiO6] octahedra linked by [O3P(OH)] tetrahedra. The OH groups point to the neighboring layers and may be substituted by ethoxy or other groups.
Einkomponentige alkaliaktivierte Bindemittel (AAB), d. h. AAB, bei denen der Aktivator als Feststoff im Bindemittel vorliegt, weisen Vorteile hinsichtlich der praktischen Anwendung im Bauwesen gegenüber konventionellen AAB auf. Einkomponentige AAB lassen sich als Gemische aus reaktiver Silica und Natriumaluminat herstellen, wobei die Reaktionsprodukte von der eingesetzten Silica und den Verhältnissen Na2O/Al2O3/SiO2/H2O abhängen: Während Mikrosilica und ähnliche Reststoffe zu zeolithreichen Produkten führen, erhält man aus Reisschalenasche vollständig amorphe Gele (sog. «Geopolymere »). Mörtel auf Basis solcher Bindemittel entsprechen den Anforderungen von DIN 19573:2016-03 hinsichtlich des Widerstands gegen Schwefelsäureangriff (Prüfung bei pH = 1 für 70 d) und sind damit potentiell als Reparatursysteme für Abwasserinfrastruktur geeignet. Untersuchungen mittels 29Si-MAS-NMR und 1H-29Si-Kreuzpolarisations(CP)-MAS-NMR sowie REM-Aufnahmen von erhärteten und dem Schwefelsäureangriff ausgesetzten AAB zeigen, dass der hohe Säurewiderstand v. a. auf die Fällung von Silicagel an der Grenzfläche Mörtel/Säure zurückzuführen ist, wodurch der Korrosionsfortschritt in darunterliegenden Schichten verlangsamt wird.
Mixing and curing of geopolymers and related alkali-activated materials without storage and handling of highly alkaline solutions possesses advantages regarding safety and economic viability. One possible approach is to produce these materials from solid silica feedstocks and solid sodium aluminate, and subsequent mixing with water. We present a comparison between geopolymers and aluminosilicate gel-zeolite composites synthesized by this route from different silica feedstocks (by-product silica from chlorosilane production, microsilica, rice husk ash) and with different SiO2/Al2O3 ratios, using results from XRD, NMR, SEM, thermal analysis, mechanical and acid resistance testing. The use of rice husk ash favors formation of a fully amorphous geopolymer with high strength. Utilization of the other silica feedstocks leads to formation of aluminosilicate gel-zeolite composites, the amount and kind of zeolites depending on the feedstock and the SiO2/Al2O3 ratio. These composites show beneficial dehydration behavior, viz. no distinct dehydration step of thermal strain, with the phase assemblage after heating to 1000°C controlled by the starting composition. Mortars produced from both, the geopolymers as well as the composites, exhibit high resistance to sulfuric acid attack, making them promising materials for the construction and the repair of industrial and sewer structures.
One-part alkali-activated (geopolymer) mortars based on three different silica-rich starting materials and sodium aluminate, with and without ground granulated blast furnace slag (GGBFS) addition, were tested regarding sulfuric acid resistance according to DIN 19573:2016-03 (70 days at pH = 1). Corresponding pastes were characterized by XRD, SEM, chemical analysis, 29Si MAS NMR and 1H-29Si CPMAS NMR after water storage and after acid exposure. The mortars exhibited a high resistance against sulfuric acid attack, with the best ones conforming to the requirements of DIN 19573:2016-03. The analytical results showed that this was due to precipitation of silica gel at the acid-mortar interface, which formed a mechanically stable layer that protected the subjacent mortar and thus inhibited further degradation. The addition of GGBFS decreased the acid resistance via formation of expansive calcium sulfate phases.
Nanocrystalline basaluminite [Al4OH10(SO4)(H2O)3–5] and Aggregation of the e-Keggin polyoxocation [Al12(AlO4)(OH)24(H2O)12]7+, referred to as Al13, have both been described to form in acid mine Drainage environments. Although the chemical composition is quite similar, their crystalline varieties significantly differ, demonstrating that various types of Al-hydroxysulfates can form under similar conditions and that their respective formation is not fully understood yet. Here, we report the occurrence of nanocrystalline precipitates that form naturally in a small alpine catchment in Switzerland where an acidic mountainous stream (pH 4) is neutralized successively after mixing with several neutral tributaries. The stepwise neutralization in conjunction with the large amount of precipitates provide an ideal setting for obtaining new insights into (i) the structure of naturally forming Al-hydroxysulfates, (ii) their formation mechanism, (iii) their role in controlling the solubility of Al, and (iv) their ability to lower the mobility of As. Synchrotron-based high-energy X-ray diffraction and subsequent pair distribution function analyses demonstrate that these precipitates are structurally identical to basaluminite samples obtained from acid mine drainage sites. In contrast, only minor amounts of tetrahedrally coordinated Al, as present in Al13, were identified by nuclear magnetic resonance spectroscopy. The precipitates are further characterized by elevated As concentrations up to 600 lg/g, whereas other heavy metals are at background concentrations only. Given the low As concentrations in the stream from which precipitation occurs (<0.03 mg/L), high As concentrations confirm that basaluminite serves as a highly efficient As sink, which is attributed to its high anion-exchange capacity. Chemical analysis of streamwater samples in combination with geochemical modeling show that precipitation occurs instantaneously upon mixing with neutral streams.
Moreover, our data reveal that the precipitation of basaluminite exerts a strong solubility control on dissolved Al concentrations as manifested by the quasi-constant basaluminite ion activity product observed during neutralization from pH 5 to pH 5.9. We hypothesize that in our field system, high fluoride and sulfate concentrations on the order of 100 and 1–2 mg/L,
Geopolymer-zeolite composites were synthesized using a silica-rich industrial byproduct from chlorosilane production and sodium aluminate. Pastes were cured at 80 °C and 80% RH, and subsequently dried in two different climates: at 23 °C and 50% RH, and under vacuum. 1H MAS, 23Na MAS and 29Si MAS NMR and XRD measurements were performed after the drying procedures as well as after subsequent aging. Zeolite Na-A was found beside traces of faujasite-type zeolite and zeolite EMT as major crystalline phases in the cured composites; the fraction of geopolymeric gel in the reaction products was determined to be ~18% on a molar basis. Various water species could be distinguished using 1H MAS and 1H-29Si CP MAS NMR, applying rotorsynchronized echo experiments. The largest fraction of the pore water resides in the α-cages of the zeolite Na-A and in the geopolymeric gel; in addition, water exists in the β-cages of the zeolites and adsorbed at sodium ions. The water species in α-cages and in the pores of the geopolymeric gel exhibit slightly different chemical shifts of 4.7 ppm and 4.9 ppm, respectively, in the 1H MAS NMR spectra. Changes of the water content in the geopolymer pores of differently dried samples were observed and led to slightly varied chemical shifts in the 29Si MAS NMR spectra too. Measurements after more than 500 days revealed no significant aging effects of the composites, which confirm their chemical stability.
One-part geopolymers, synthesized from three different silica sources and sodium aluminate, were investigated regarding their microstructure and the evolution of their compressive strength on curing at slightly elevated temperatures. The effect of thermal treatment was studied up to 1000 °C and for the investigation of the chemical durability specific samples were treated with sulfuric acid (H2SO4, pH = 1).
Depending on the silica feedstock, different degrees of reaction were observed. One of the silicas had a significantly higher reactivity. For two of the silicas, significant amounts of zeolites occurred as reaction products besides geopolymeric gel, whereas the more reactive silica source lead to the formation of a rather fully condensed geopolymeric network.
The composites indicated promising behavior on heating in so far as no distinct shrinkage step occurred in the temperature range of dehydration. Up to 400 °C the residual strength of those mixes increased. Above 800 °C the samples underwent new phase formation. After exposure to sulfuric acid (pH 1; 70 d) specimens showed a residual compressive strength of about 77 % of the reference, indicating high acid resistance.
This paper reports the first successful synthesis and the structural characterization of nanocrystalline and stacking-disordered β-cristobalite AlPO4 that is chemically stabilized down to room temperature and free of crystalline impurity phases. Several batches of the title compound were synthesized and thoroughly characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray spectroscopy mapping in SEM, solid-state 31P nuclear magnetic resonance (31P-NMR) spectroscopy including the TRAPDOR method, differential thermal analysis (DTA), gas-sorption methods, optical Emission spectroscopy, X-ray fluorescence spectroscopy, and ion chromatography. Parameters that are critical for the synthesis were identified and optimized. The synthesis procedure yields reproducible results and is well documented. A high-quality XRD pattern of the title compound is presented, which was collected with monochromatic copper radiation at room temperature in a wide 2θ range of 5°–100°.
Catalytic C–F bond activation reactions of mono- and polyfluoroalkanes at Lewis acidic amorphous aluminum chlorofluoride (ACF) are presented. The hydrogen sources Et3GeH or Et3SiH control the selectivity of the conversions. The immobilization of Et3GeH at ACF resulted in catalytic dehydrohalogenation reactions to yield olefins under very mild conditions. In contrast, if Et3SiH is immobilized at ACF, C–C coupling occured and the formation of Friedel–Crafts products was observed. MAS NMR spectroscopic studies revealed information about the surface binding of the substrates.