β-alumina-14H and β-alumina-21R : two chromic Na2-δ(Al,Mg,Cr)17O25 polysomes observed in slags from the production of low-carbon ferrochromium

The crystal structures of unknown phases found in slags from the production of low-carbon ferrochromium were studied by powder and single-crystal X-ray diffraction. Two phases of Na2−δ (Al, Mg, Cr)17O25 composition were found to be composed of an alternating stacking of a spinel-type and a Na-hosting block. Similar structures are known for β-alumina and β”- alumina, NaAl11O17. However, the spinel-type block in Na2-δ(Al, Mg, Cr)17O25 is composed of five cation layers in contrast to three cation layers in the β-alumina spinel-block. The two new phases, β-alumina-14H, P63/mmc, a=5.6467(2), c=31.9111(12) Å, and β-alumina-21R, R m, a=5.6515(3), c=48.068(3) Å have a 14-layer and 21-layer stacking with a 2 × (cccccch) and a 3 × (ccccccc) repeat sequence of oxygen layers in cubic and hexagonal close packing, respectively.http://www.elsevier.com/locate/jssc2017-09-30hb2016Electrical, Electronic and Computer Engineerin

Metastable Corundum-Type In2O3: Phase Stability, Reduction Properties, and Catalytic Characterization

The phase stability, reduction, and catalytic properties of corundum-type rhombohedral In2O3 have been comparatively studied with respect to its thermodynamically more stable cubic In2O3 counterpart. Phase stability and transformation were observed to be strongly dependent on the gas environment and the reduction potential of the gas phase. As such, reduction in hydrogen caused both the efficient transformation into the cubic polymorph as well as the formation of metallic In especially at high reduction temperatures between 573 and 673 K. In contrast, reduction in CO suppresses the transformation into cubic In2O3 but leads to a larger quantity of In metal at comparable reduction temperatures. This difference is also directly reflected in temperature-dependent conductivity measurements. Catalytic characterization of rh-In2O3 reveals activity in both routes of the water-gas shift equilibrium, which gives rise to a diminished CO2-selectivity of 60% in methanol steam reforming. This is in strong contrast to its cubic counterpart where CO2 selectivities of close to 100% due to the suppressed inverse water-gas shift reaction, have been obtained. Most importantly, rh-In2O3 in fact is structurally stable during catalytic characterization and no unwanted phase transformations are triggered. Thus, the results directly reveal the application-relevant physicochemical properties of rh-In2O3 that might encourage subsequent studies on other less-common In2O3 polymorphs.(VLID)2581066Accepted versio

Energie- und Ressourceneinsparung durch Sanierung und Lehmziegelforschung

Zusammenfassung in englischer SpracheAufgrund des weltweit zunehmenden Energie- und Ressourcenverbrauchs ist es im Bausektor wichtig und notwendig, alternative Baustoffe zu untersuchen und die Energieeffizienz zu verbessern. Einer dieser alternativen Baustoffe ist meiner Einschätzung nach der Lehmziegel. Der Vorteil eines Lehmziegels liegt darin, dass dieser nicht gebrannt werden muss und somit die Herstellungsenergie deutlich niedriger als bei Ziegel und Beton ausfällt. Im Zuge meines Forschungsprojektes wurde ein tragender Lehmziegel entwickelt und dessen bauliche Anwendung in einem Pilotprojekt erarbeitet. Durch das Beimischen verschiedener Zuschlagsstoffe soll die Tragfähigkeit und Haltbarkeit des Lehmziegels verbessert werden, ohne seine vielen positiven Eigenschaften zu beeinträchtigen. Der Lehmziegel selbst wurde von mir im Labor der Firma Wienerberger im Modellmaßstab entwickelt und geprüft. Des Weiteren untersucht diese Arbeit als Grundlagenforschung die Beschaffenheit eines historischen Wohngebäudes mit anschließendem Wirtschaftstrakt und behandelt thermische Sanierungsstufen im Altbestand. Aufgrund der Bestandsituation und der zukünftigen geänderten funktionellen Anforderungen an das Gebäude, stellte sich im Zuge dieser Arbeit heraus, dass ein kleiner Anbau erforderlich wurde. An diesem Zubau wird auch gezeigt, wie der tragende Lehmziegel eingesetzt werden kann.Due to the increasing consumption of energy and resources worldwide it is essential in the building sector to prospect alternative building materials in order to improve their energy efficiency. One of those alternative building materials in my opinion is a brick made of clay. The advantage of clay bricks is that they are not being fired and this results in a lower energy consumption compared to fired bricks or concrete. In the course of my research project a load-bearing clay brick was being developed and its constructional usage possibilities were formulated in a pilot project. Through various additions of aggregates to the clay the brick's supporting properties and endurance were supposed to improve without compromising its many already existing positive attributes. The clay brick itself was developed and tested in model scale at the brick company 'Wienerberger'. Furthermore, the present work explores the constructional condition of a historical residential building with a connected farm block as a fundamental research project as well as its step by step thermal refurbishment. Due to the building's present situation and the prospectively functional requirements it was becoming clear that a small annex to the existing building would be necessary. This building extension is a good opportunity to display the use of the supporting clay brick.11

Structural, spectroscopic and computational studies on the monoclinic polymorph form I of potassium hydrogen disilicate KHSi2O5

Hydrothermal treatment of quartz with 2 M K2CO3 solutions at 623 K and 1 kbar resulted in the formation of single crystals of the monoclinic polymorph of potassium hydrogen disilicate KHSi2O5 or KSi2O4 OH . Basic crystallographic data of this so called phase I at room conditions are as follows space group C2 m, a 14.5895 10 , b 8.2992 3 , c 9.6866 7 , b 122.756 10 , V 986.36 10 3, Z 8. The structure was determined by direct methods and refined to a residual of R F 0.0224 for 892 independent observed reflections with I gt; 2s I . The compound belongs to the group of chain silicates. It is based on crankshaft like vierer double chains running parallel to [010]. The H atoms are associated with silanol groups. Hydrogen bonding between neighbouring double chains results in the formation of 5 A amp; 730; wide slabs. The three crystallographically independent K cations with six to eight O ligands provide linkage 1 between the chains of a single slab or 2 between adjacent slabs. Structural investigations have been supplemented by micro Raman spectroscopy. The interpretation of the spectroscopic data including the allocation of the bands to certain vibrational species has been aided by DFT calculation

Rb2Ca2Si3O9 the first rubidium calcium silicate

The crystal structure of Rb2Ca2Si3O9 has been characterized by X ray diffraction techniques and Raman spectroscopy. Crystal growth was performed by the flux method in closed platinum capsules using a polycrystalline ceramic precursor as well as RbCl as a mineralizer. The crystal structure was solved from a single crystal diffraction data set acquired at 23 C and refined to a final residual of R F 0.022 for 1871 independent reflections. Basic crystallographic data are as follows monoclinic symmetry, space group type P1n1, a 6.5902 3 , b 7.3911 3 , c 10.5904 4 , amp; 946; 93.782 3 , V 514.72 3 3, Z 2. With respect to the silicate anions the compound can be classified as a sechser single chain silicate. The undulated chains run parallel to [ 101] and are connected by Rb and Ca cations, which are distributed among four crystallographically independent sites. In a first approximation the coordination polyhedra of the two different calcium ions in the asymmetric unit can be described by distorted trigonal prisms and tetragonal pyramids, respectively. The two rubidium sites exhibit more irregular coordination spheres with eight to nine next neighbors. Structural investigations on the new phase are completed by solid state micro Raman spectroscopy. DFT calculations were employed for the interpretation of the spectroscopic data including the allocation of the bands to certain vibrational specie

Water-Gas Shift and Methane Reactivity on Reducible Perovskite-Type Oxides

Comparative (electro)catalytic, structural, and spectroscopic studies in hydrogen electro-oxidation, the (inverse) water-gas shift reaction, and methane conversion on two representative mixed ionic–electronic conducting perovskite-type materials La0.6Sr0.4FeO3−δ (LSF) and SrTi0.7Fe0.3O3−δ (STF) were performed with the aim of eventually correlating (electro)catalytic activity and associated structural changes and to highlight intrinsic reactivity characteristics as a function of the reduction state. Starting from a strongly prereduced (vacancy-rich) initial state, only (inverse) water-gas shift activity has been observed on both materials beyond ca. 450 °C but no catalytic methane reforming or methane decomposition reactivity up to 600 °C. In contrast, when starting from the fully oxidized state, total methane oxidation to CO2 was observed on both materials. The catalytic performance of both perovskite-type oxides is thus strongly dependent on the degree/depth of reduction, on the associated reactivity of the remaining lattice oxygen, and on the reduction-induced oxygen vacancies. The latter are clearly more reactive toward water on LSF, and this higher reactivity is linked to the superior electrocatalytic performance of LSF in hydrogen oxidation. Combined electron microscopy, X-ray diffraction, and Raman measurements in turn also revealed altered surface and bulk structures and reactivities

Temperature- and moisture-dependent studies on alunogen and the crystal structure of meta-alunogen determined from laboratory powder diffraction data

Starting from a synthetic sample with composition Al2(SO4)3·16.6H2O, the high-temperature- and moisture-dependent behavior of alunogen has been unraveled by TGA measurements, in situ powder X-ray diffraction as well as by gravimetric moisture sorption/desorption studies. Heating experiments using the different techniques show that alunogen undergoes a first dehydration process already starting at temperatures slightly above 40 C. The crystalline product of the temperature-induced dehydration corresponds to the synthetic equivalent of meta-alunogen and has the following chemical composition: Al2(SO4)3·13.8H2O or Al2(SO4)3(H2O)12·1.8H2O. At 90 C a further reaction can be monitored resulting in the formation of an X-ray amorphous material. The sequence of “amorphous humps” in the patterns persists up to 250 C, where a re-crystallization process is indicated by a sudden appearance of a larger number of sharp Bragg peaks. Phase analysis confirmed this compound to be anhydrous Al2(SO4)3. Furthermore, meta-alunogen can be also obtained from alunogen at room temperature when stored at relative humidities (RH) lower than 20 %. The transformation is reversible, however, water sorption of meta-alunogen to alunogen and the corresponding desorption reaction show considerable hysteresis. For RH values above 80 %, deliquescence of the material was observed. Structural investigations on meta-alunogen were performed using a sample that has been stored at dry conditions (0 % RH) over phosphorus pentoxide. Powder diffraction data were acquired on an in-house high-resolution diffractometer in transmission mode using a sealed glass capillary as sample holder. Indexing resulted in a triclinic unit cell with the following lattice parameters: a = 14.353(6) Å, b = 12.490(6) Å, c = 6.092(3) Å, = 92.656(1), = 96.654(1), = 100.831(1), V = 1062.8(8) Å3 and Z = 2. These data correct earlier findings suggesting an orthorhombic cell. Ab-initio structure solution in space group P 1~~~, using simulated annealing, provided a chemically meaningful structure model. The asymmetric unit of meta-alunogen contains three symmetry independent SO4-tetrahedra and two Al(H2O)6 octahedra. The polyhedra are isolated, however, linkage between them is provided by Coulomb interactions and hydrogen bonding. In addition to the water molecules which directly belong to the coordination environment of the aluminum cations there are two additional zeolitic water sites (Ow1 and Ow2). If both positions are fully occupied meta-alunogen corresponds to a 14-hydrate. Structural similarities and differences between the previously unknown structure of meta-alunogen and alunogen are discussed in detail. Since hydrous aluminum sulfates have been postulated to occur in Martian soils, our results may help identifying meta-alunogen by X-ray diffraction not only on the surface of the Earth but also using the Curiosity Rovers ChemMin instrument.(VLID)454130

Temperature and moisture dependent powder X ray diffraction studies of kanemite NaSi2O4 OH x 3H 2 O

The high temperature and moisture dependent behaviour of synthetic kanemite NaSi2O4 OH 3H2O or SKS 10 has been studied by in situ powder X ray diffraction. Heating experiments in the range between ambient temperatures and 250 C confirm earlier investigations that the dehydration of kanemite occurs in two steps. According to our results the two different reactions start at amp; 8764;30 and 75 C. The dehydration products have the following compositions NaSi2O4 OH H2O monohydrate and NaSi2O4 OH , respectively. The crystal structures of both phases have been solved at ambient conditions ab initio from laboratory powder diffraction data using samples that have been carefully dehydrated at 60 and 150 C, respectively, and refined subsequently by the Rietveld method. Both compounds belong to the group of single layer silicates based on Si2O4 OH sheets. The sodium cations are located between the tetrahedral sheets and are surrounded by oxygen atoms from silicate anions and or water molecules. Depending on the dehydration step the coordination numbers of the alkali ions vary between six kanemite and five NaSi2O4 OH . Kanemite and its two dehydration products show structural similarities which are discussed in detail. Moisture dependent diffraction studies at ambient temperatures indicate that kanemite is stable between 10 and at least 90 relative humidity. Below the lower threshold a transformation to the monohydrate phase was observed. Dehydration and rehydration as a function of humidity is reversible. However, this process is combined with a significant loss of crystallinity of the sample