Asbestos-containing pottery shards collected in the northeast of Corsica (Cap Corse) and dating from the 19th century, or earlier, have been analyzed by SEM-EDS, XRPD, FTIR and Raman ...microspectroscopy. Blue (crocidolite) and white (chrysotile) asbestos fiber bundles are observed in cross-sections. Most of the asbestos is partly or totally dehydroxylated, and some transformation to forsterite is observed to occur, indicative of a firing above 800 °C. Examination of freshly fractured pieces shows a nonbrittle fracture with fiber pull-out, consistent with a composite material behavior, which makes these ceramics the oldest fiber-reinforced ceramic matrix composite. Residues indicate the use of this pottery as a crucible for gold extraction using cyanide.
Representative ‘Bluespeckled’ (13–16th centuries) and ‘Brownspeckled’ (13–21st century) wares recovered from the excavations in Qalhât or collected around Bahlâ city (Sultanate of Oman) were ...characterized by XRPD, SEM-EDS, Raman/optical microspectroscopy, and thermal expansion. Minerals present in the body (quartz, augite and albite as major phases, calcite, dolomite, rutile, anatase, phosphate, hematite and magnetite as minor phases) were identified by XRPD and/or Raman spectroscopy. SEM-EDXS microanalysis was performed on the glazes in order to compare their composition, especially the type of flux. The firing temperatures measured from the thermal expansion curves range between 1080°C and 1150°C. This preliminary study confirms that the first differentiation can be made by considering non-invasive Raman technique and thermal expansion measurement is sufficient to get an extensive comparison of the wares. A local place of production is likely for the body of all samples but importation of the glazes of ‘Bluespeckled’ wares is questioned. Modern Bahlâ productions cannot be considered to have inherited the Qalhât ones. Ba-rich, cassiterite-opacified glaze corresponding to the Late Islamic Arabic Period appears as a new technology without a connection to the ancient one.
Las mercancías representativas ‘moteadas de azul’ (siglos XIII-XVI) y ‘moteadas de marrón’ (siglos XIII-XXI) recuperadas de las excavaciones en Qalhât o recolectadas alrededor de la ciudad de Bahlâ (Sultanato de Omán) se caracterizaron por microscopía XRPD, SEM-EDS, Raman, microscopía y expansión térmica. Los minerales presentes en el cuerpo (cuarzo, augita y albita como fases principales, calcita, dolomita, rutilo, anatasa, fosfato, hematita y magnetita como fases menores) se identificaron mediante espectroscopía XRPD y/o Raman. Se realizó un microanálisis SEM-EDXS en los esmaltes para comparar su composición, especialmente el tipo de flujo. Las temperaturas de cocción medidas a partir de las curvas de expansión térmica oscilan entre 1080° C y 1150° C. Este estudio preliminar confirma que la primera diferenciación se puede hacer considerando la técnica Raman no invasiva y la medición de la expansión térmica es suficiente para obtener una comparación extensa de las mercancías. Es probable que haya un lugar de producción local para el cuerpo de todas las muestras, pero se cuestiona la importación de los esmaltes de las mercancías “moteadas de azul”. No se puede considerar que las producciones modernas de Bahlâ hayan heredado las de Qalhât. El esmalte opacificado con casiterita, rico en Ba correspondiente al último período árabe islámico, aparece como una nueva tecnología sin conexión con la antigua.
Crystal structure of K3EuSi2O7 Kovac, Sabina; Dabic, Predrag; Kremenovic, Aleksandar
Journal of the Serbian Chemical Society,
01/2021, Volume:
86, Issue:
7-8
Journal Article
Peer reviewed
Open access
As part of research on the flux technique for growing alkali rare-earth elements (REE) containing silicates, tripotassium europium disilicate, K3EuSi2O7, was synthesized and characterized by ...single-crystal X-ray diffraction. It crystallizes in the space group P63/mcm. In the crystal structure of the title compound, one part of the Eu cations are in a slightly distorted octahedral coordination and the other part are in an ideal trigonal prismatic coordination environment. The disilicate Si2O7 groups connect four EuO6 octahedra and one EuO6 trigonal prism. Three differently coordinated potassium cations are located between them. Silicates containing the larger rare earth elements usually crystallize in a structure that contains the rare-earth cation in both a slightly distorted octahedral and an ideal trigonal prismatic coordination environment.
The behaviour and stability of arsenopyrite largely depend on its crystal structure, but studies of crystallography and structural defects are scarce. For clarification, we investigated a series of ...natural arsenopyrite crystals from the polymetallic Pb-Zn-(±Cu,Ag,Au,Sb,Bi,W) Šumadija-Kopaonik ore district (Serbia) by powder X-ray diffraction (XRPD). Among them, samples from the Drenjak gold mineralisation showed near-stoichiometric FeAsS composition and were further investigated by conventional and high-resolution transmission electron microscopy methods. TEM revealed abundant planar crystallographic defects and epitaxial surface oxide layer formation upon air exposure. Our findings present the fundamental work on the prototype arsenopyrite structure and have further implications for studies on ion incorporation into FeAsS structure and its environmental stability and oxidation mechanisms as a source of anthropogenic As release into the environment.
Magnetic structure of ZnFe2O4 normal spinel is re-examined. Antiferromagnetic structure non-collinear model is established within Ca2 space group having four different crystallographic/magnetic sites ...for 32 Fe3+ spins within magnetic unit cell.
•Magnetic structure of ZnFe2O4 normal spinel is re-examined.•Antiferromagnetic non-collinear structure model is established within Ca2 space group.•Four different crystallographic/magnetic sites contain 32 Fe3+ spins within magnetic unit cell.
•Polymeric Co(II) complex with anion of H6mell was synthesized and characterized.•3D supramolecular network is comprised of supramolecular and water layers.•Contribution of noncovalent interactions ...and their energies were determined by DFT.
Orange single crystals of new polymeric cobalt(II) complex {Co(bipy)(H2O)42Co(μ-mell)(H2O)2·10H2O}n, 1, were synthesized by slow evaporation method at room temperature (bipy = 2,2′-bipyridine, mell = hexaanion of mellitic acid) and its crystal structure was determined by single-crystal X-ray diffraction. The complex 1 was characterized based on elemental analysis, FTIR spectroscopy and thermal (TG/DTA) analysis followed by computational analysis of noncovalent interactions and quantum chemical calculations of interaction energies. In 1, two crystallographically different Co(II) atoms adopt a deformed octahedral geometry, while bridging mell acts as a tetrakis monodentate ligand allowing the development of wavy-like anionic chains running along 100 direction. The 3D supramolecular network of 1 is composed of alternating supramolecular and water layers connected by hydrogen bonds. The supramolecular layer is formed of ionic interactions between complex cations and polymeric complex anions, established mainly through O–H···O hydrogen bonds, as well as stacking interactions between bipy ligands, while the water layers are comprised of hydrogen bonded lattice water molecules. Upon heating up to 1200 °C in nitrogen and air atmosphere, complex 1 showed multiple-step degradation that resulted in the formation of Co and Co3O4, respectively. Computed Hirshfeld surfaces and 2D fingerprint plots indicated that O–H···O hydrogen bonds are the most dominant in the crystal structure, while the shape index and curvedness mapped on the Hirshfeld surfaces of 1 revealed that stacking interactions have an important role in the stabilization of the crystal packing. Quantum chemical calculations showed that, aside from ionic hydrogen-bonded interaction between cation and anionic polymer, the important role in the stability of supramolecular structure of 1 is played by hydrogen bonds of cation and anionic polymer with lattice water, as well as by stacking interactions between bipy ligands.
The 3D supramolecular network of a polymeric {Co(bipy)(H2O)42Co(μ-mell)(H2O)2·10H2O}n complex is composed of alternating supramolecular and water layers connected by hydrogen bonds. According to the quantum-chemical studies, the hydrogen bonds are the most dominant, while stacking interactions contribute to stabilization of the crystal packing of the complex. Display omitted
This study employed a novel synthetic approach involving a modified reverse co-precipitation method utilizing glacial acetic acid to synthesize α-Bi2O3. X-ray powder diffraction and scanning and ...transmission electron microscopy analyses revealed the formation of a rod-like α-Bi2O3 microstructure. The prepared material was utilized to modify a glassy carbon paste (GCP) electrode for the development of an electrochemical sensor for acetaminophen (APAP) detection using differential pulse voltammetry (DPV). Cyclic voltammetry studies revealed that the GCP@Bi2O3 electrode exhibited enhanced electrochemical properties compared to the bare GCP. The designed GCP@Bi2O3 sensor detected APAP in the linear concentration range from 0.05 to 12.00 µM, with LOQ and LOD of 36 nM and 10 nM, respectively. Additionally, the developed sensor demonstrated sufficient precision, repeatability, and selectivity toward APAP detection. The recovery values between the declared and found APAP content in a pharmaceutical formulation (Caffetin®) displayed the advantageous accuracy, precision, and applicability of the GCP@Bi2O3 sensor and the developed DPV method for real-time APAP detection in pharmaceuticals, with minimal interference from the matrix effect.
Pure, crystalline, ∼10 nm lithium ferrite phase (Li0.5Fe2.5O4), was successfully synthesized at very low temperature using a modified combustion method. The crystal structure and microstructure ...evolution of this system upon annealing were monitored by a careful investigation of X-ray diffractograms collected on a synchrotron source. Comparative analysis of the results obtained from the full profile Rietveld method (in reciprocal space) and the pair distribution function method (in direct space) was carried out. Nanocrystalline samples exhibit similar crystal structure, on average, with a partial ordering of Li+ and Fe3+ ions between octahedral 4b and 12d sites on the spinel crystal lattice (space group P4332). After annealing at 973 K, cation distribution changes to a completely ordered, resembling that which is seen in the bulk lithium ferrite. The PDF analysis reveals abnormally high values of oxygen atomic displacement parameters in tetrahedral 8c sites (O1) indicating a significant disordering of the O1 network and suggests migration of lithium ions from 4b sites to the outer layers of nanoparticles. Analysis of room temperature Mössbauer spectra has shown that the hyperfine field for Fe3+ ions in tetrahedral 8c sites is the most sensitive on increasing the particle size and improving the crystallinity. From the differential thermal analysis, it was found that a lower driving force is required to induce an order−disorder phase transition in nanocrysalline samples, compared to the bulk-like sample, presumably due to the higher crystal disordering in these samples.
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