Showing papers on "Tridymite published in 2014"

Atomic Layer Deposition of Aluminum Phosphate Based on the Plasma Polymerization of Trimethyl Phosphate

Abstract: Aluminum phosphate thin films were deposited by plasma-assisted atomic layer deposition (ALD) using a sequence of trimethyl phosphate (TMP, Me3PO4) plasma, O2 plasma, and trimethylaluminum (TMA, Me3Al) exposures. In situ characterization was performed, including spectroscopic ellipsometry, optical emission spectroscopy, mass spectrometry and FTIR. In the investigated temperature region between 50 and 320 °C, nucleation delays were absent and linear growth was observed, with the growth per cycle (GPC) being strongly dependent on temperature. The plasma polymerization of TMP was found to play an important role in this process, resulting in CVD-like behavior at low temperatures and ALD-like behavior at high temperatures. Films grown at 320 °C had a GPC value of 0.37 nm/cycle and consisted of amorphous aluminum pyrophosphate (Al4P6O21). They could be crystallized to triclinic AlPO4 (tridymite) by annealing to 900 °C, as evidenced by high-temperature XRD measurements. The use of a TMP plasma might open up the ...

Ab Initio Calculations of the Energy Dependence of Si–O–Si Angles in Silica and Ge–O–Ge Angles in Germania Crystalline Systems

Abstract: Cristobalite is the only corner-sharing tetrahedral framework that can maintain perfectly regular SiO4 tetrahedra throughout the entire 180° range of Si–O–Si angles. It is, thus, the ideal system for a study of the energy dependence of the Si–O–Si angle in a crystalline framework. Using the VASP first principles density functional code, we have derived energy versus Si–O–Si angle curves for pure silica and versus Ge–O–Ge angles for pure germania models of cristobalite. In addition, the frameworks of quartz, tridymite, and the zeolites sodalite (SOD) and metavariscite (BCT) were studied. The range of angles with low energies is larger for silica, though the lowest-energy Ge–O–Ge angle is always lower than the corresponding lowest-energy Si–O–Si angle in the same framework type. We discuss which framework types are possible for pure-silica and pure-germania based on a rigid tetrahedron model.

Photo-induced change of dielectric response in BaCoSiO4 stuffed tridymite

Abstract: The photodielectric effect is demonstrated in Mott-insulator BaCoSiO4 with a stuffed-tridymite-type structure under irradiation of visible light at 365 nm. The real part of dielectric permittivity is enhanced by ∼300% with little increase of tan δ in a low-frequency region. Results of diffuse reflectance spectroscopy, first-principles calculations and dielectric measurements suggest that the photodielectric effect stems from a response of photo-excited electrons in an unoccupied upper-Hubbard band for 3d-orbitals of cobalt, which have significantly small mobility due to the unique configuration of Co ions in the stuffed-tridymite-type structure.

Phase states of Na/W/Mn/SiO2 composites at temperatures of catalytic oxidative coupling of methane

Abstract: This paper analyzes phase states in the Na2O-WO3-MnO-Mn2O3 and Na2O-WO3-Mn2O3-SiO2 systems at temperatures of oxidative coupling of methane (OCM). The results indicate that, in the case of effective OCM, Na/W/Mn/SiO2 composite catalysts are in melt-Mn2O3 -tridymite (cristobalite) equilibrium.

Effect of soda-lime-silica glass addition on the physical properties of ceramic obtained from white rice husk ash

Abstract: This study reports on the effect of soda-lime-silica (SLS) glass on the physical properties of the ceramic material obtained from white rice husk ash (WRHA). The crystallisation behaviour of samples was investigated by XRD analysis after different heat treatments. The bulk density and linear shrinkage (LS) of the samples were determined using Archimedes’ method and direct geometric measurement, respectively. The residual pore contents of the specimens were determined using SEM micrographs. The results show that the bulk density and LS of the samples increased and the porosity decreased as the sintering temperature increased. The XRD analysis results show the formation of cristobalite to be a major phase and some tridymite phase was detected in the specimens.

Structural changes and microstructures in stuffed tridymite-type compounds Ba1−xSrxAl2O4

Abstract: Crystal structures and microstructures in Ba1−xSrxAl2O4 solid solutions between the end members of BaAl2O4 and SrAl2O4 have been carefully investigated by powder X-ray diffraction, electron diffraction and transmission electron microscopy (TEM) imaging experiments. With the help of fast Fourier transform (FFT) calculation, high-resolution TEM images suggested that diffuse streaks along three equivalent 〈110〉 directions in the (001) plane, which appear in the P63 structure of Ba1−xSrxAl2O4 for x = 0.4, originate from the large structural fluctuation of the AlO4 tetrahedral network. On the other hand, the monoclinic P21 structure in Ba1−xSrxAl2O4 with x = 0.7 was found to consist of a modulated structure with . The present experimental results reveal that a structural phase boundary exists at approximately x = 0.6 between the P63 structure with a large structural fluctuation and a monoclinic P21 phase with the single-q modulated structure.

Effect of calcium phosphate addition on sintering of El-Oued sand quartz raw materials

Abstract: This work addresses the development of an eventual low cost ceramic insulating or microfiltration membrane supports from inexpensive raw materials such Eloued quartz sand (EQS) and calcium phosphate (CP) using uniaxially dry compaction method. The prepared samples were sintered at different temperatures ranging between 1200 and 1550 oC. Subsequently, the effects of sintering temperature and amount of CP on samples proprieties were investigated. It is observed that X-ray diffracion measurements confirmed that EQS was transformed into cristobalite and tridymite phases when both sintering temperature and holding time were increased. This transformation is favored with increasing amount of CP, it is observed also formation of CaSiO3 and Ca(Fe)(Al)PO4. The SEM images of the samples sintered at different temperatures illustrate that silica grains, CP grains, intergranular phase contents (Si, Ca, P, and O) and an important open porosity depend on the sintering temperature. The porosity ratio changes in the range between 37% and 34% according to sintering temperature and to CP content; these values are in good agreement with SEM images. The thermal expansion behavior shows a weak expansion in the range of temperature between 600 and 1000 oC which is situated between 1.27% and 1.33% (variation of 0.05% at 400 oC).

Structural Phase Transition and Microstructures in Stuffed Tridymite-Type Compounds; Ba(Al, Fe)2O4

Abstract: We have investigated structural phase transition and changes of microstrucrtures in BaAl2O4 with the tridymite tetrahedral framework structure by transmission electron microscopy experiments in the temperature range between 100 K and 298 K. In our polycrystalline samples the transition from the paraelectric phase with the P6322 space group to the ferroelectric (FE) phase took place around 250 K, which accompanies with the appearance of the modulated structure with the three equivalent modulation wave vectors, q = 1/2 . Real-space images revealed that the FE phase should consist of nanodomains with the 10 ∼ 20 nm size. In addition, it is revealed that partial substitution of Fe3+ for Al3+ in BaAl2O4 induced structural phase transition to the modulated structure with q = 1/3 around x ∼ 0.50 in Ba(Al1-xFex)2O4.

Phase equilibria studies of the “MnO”–Al2O3–SiO2 system in equilibrium with metallic alloy. Part 1: Development of the technique and determination of liquidus isotherms between 1 423 K and 1 523 K

Abstract: Phase equilibria in the "MnO"-AlO-SiO pseudo-ternary system in equilibrium with metallic alloy have been experimentally investigated in the temperature range from 1423 K to 1523 K. This study is a part of a broader research program on the phase equilibria in the AlO-CaO-LiO- "MnO"-SiO system, which is of importance to the slags used in a novel pyrometallurgical process for recycling of electric car batteries. The experimental procedures involve equilibration of high purity powder mixtures at high temperatures, rapid quenching, and accurate measurement of phase compositions using electron probe X-ray microanalysis, which allow the slag liquidus temperatures to be determined. This paper is part 1 of a series of two papers and focuses on the improvement of the experimental methodology. A number of elementary reactions taking place in the samples have been identified, including the formation of a tridymite ring around the alloy particles, manganese oxidation and manganese vaporization. This enabled relevant modifications to the experimental methodology to be introduced. The liquidus at 1423 K, 1473 K and 1523 K in the high silica area and the solid solubility data in the tridymite and rhodonite phases have been reported.

Siliceous composition and method for obtaining same

Abstract: A powdered composition made from silica for ceramic welding, in particular by spraying, comprising - 10 to 90 % of a phase of porous siliceous particles comprising at least 80 % by weight of cristobalite and at most 15% by weight of tridymite, relative to the total weight of the composition, - 90 to 10 % by weight of conventional additives forming a binder phase, relative to the total weight of said composition, said siliceous particles having a d 50 of between 350 and 800 μm, and preferably between 400 and 500μm.

Major element and oxygen isotope geochemistry of vapour-phase garnet from the Topopah Spring Tuff at Yucca Mountain, Nevada, USA

Abstract: Twenty vapour-phase garnets were studied in two samples of the Topopah Spring Tuff of the Paintbrush Group from Yucca Mountain, in southern Nevada. The Miocene-age Topopah Spring Tuff is a 350 m thick, devitrified, moderately to densely welded ash-flow tuff that is zoned compositionally from high-silica rhyolite to latite. During cooling of the tuff, escaping vapour produced lithophysae (former gas cavities) lined with an assemblage of tridymite (commonly inverted to cristobalite or quartz), sanidine and locally, hematite and/or garnet. Vapour-phase topaz and economic deposits associated commonly with topaz-bearing rhyolites (characteristically enriched in F) were not found in the Topopah Spring Tuff at Yucca Mountain. Based on their occurrence only in lithophysae, the garnets are not primary igneous phenocrysts, but rather crystals that grew from a F-poor magma-derived vapour trapped during and after emplacement of the tuff. The garnets are euhedral, vitreous, reddish brown, trapezohedral, as large as 2 mm in diameter and fractured. The garnets also contain inclusions of tridymite. Electron microprobe analyses of the garnets reveal that they are almandine-spessartine (48.0 and 47.9 mol.%, respectively), have an average composition of (Fe1.46Mn1.45Mg0.03Ca0.10)(Al1.93Ti0.02)Si3.01O12 and are comparatively homogeneous in Fe and Mn concentrations from core to rim. Composited garnets from each sample site have δ18O values of 7.2 and 7.4‰. The associated quartz (after tridymite) has δ18O values of 17.4 and 17.6‰, values indicative of reaction with later, low-temperature water. Unaltered tridymite from higher in the stratigraphic section has a δ18O of 11.1‰ which, when coupled with the garnet δ18O values in a quartz-garnet fractionation equation, indicates isotopic equilibration (vapour-phase crystallization) at temperatures of ~600°C. This high-temperature mineralization, formed during cooling of the tuffs, is distinct from the later and commonly recognized low-temperature stage (generally 50–70°C) of calcite, quartz and opal secondary mineralization, formed from downward-percolating meteoric water, that locally coats fracture footwalls and lithophysal floors.

Powdered composition made from porous silica for ceramic welding and method for obtaining same

Abstract: A powdered composition made from porous silica for ceramic welding, in particular by spraying, comprising 10 to 90 % of a phase of porous siliceous particles comprising at least 80 % by weight of cristobalite and at most 15% by weight of tridymite and residual amorphous phase, relative to the total weight of the composition, and 90 to 10 % by weight of conventional additives forming a binder phase, relative to the total weight of said composition, said porous siliceous particles having a d50 of between 200 and 1000 μm, and preferably between 350 and 800μm.

Анализ структуры ксерогелей на основе жидкого стекла в рамках модели хаотически разориентированных кристаллитов

Abstract: The atom arrangement in short-range order for the initial and modifi ed by cobalt xerogels based on water glass is analyzed. The model is a mixture of randomly disoriented small blocks having different composition and structure. For the initial sample arrangement of atoms in the short-range order is a mechanical mixture of ultra-small (a few unit cells) optically disconnected blocks in proportion: 80 % Na2Si3O7, 10 % SiO2 (3 % cristobalite and 7 % tridymite), 8 % – α-Na 2 Si 2 O 5 и 2 % – β-Na 2 Si 2 O 5 . The structure of modifi ed sample describes by a set of phases: 61 % mechanical mixture of Na 2 Si 3 O 7 (11 % – SiO 2 cristobalite, 24 % – SiO 2 tridymite, 28 % – α-Na 2 Si 2 O 5 , 7 % – β-Na 2 Si 2 O 5 and 30 % Na 2 Si 3 O 7 ); 31 % – a layer of CoO unit cells (wurtzite type, 5×1×5 size) and 8 % – CoO (NaCl type, 2×2×2 size).

The Application of Electron Backscatter Diffraction to a Tridymite-Diopside-Enstatite Crystal Aggregate in Mason Gully (H5): Understanding its Formation and Implications for Metamorphism

Abstract: ENSTATITE CRYSTAL AGGREGATE IN MASON GULLY (H5): UNDERSTANDING ITS FORMATION AND IMPLICATIONS FOR METAMORPHISM. K. A. Dyl, A. Halfpenny, N. E. Timms, S. M. Reddy, and P. A. Bland. Department of Applied Geology, Curtin University, GPO Box U1987, Perth, WA 6845, Australia. Email: katie.dyl@curtin.edu.au. CSIRO Earth Sciences and Resource Engineering, 26 Dick Perry Avenue, Kensington, Perth, WA 6151, Australia.

Synthesis, crystal structure and property of a new tridymite-type iodoargentate

Abstract: A new compound, Cd(en)3Ag2I4 (1), has been synthesized by self-assembly reaction, and characterized by elemental analysis, IR spectra, PXRD, and single-crystal X-ray diffraction. The compound contains a three-dimensional framework built by AgI4 tetrahedra with tridymite topology, and the discrete Cd(en)3 2+ cations are located in the channels. The thermal property of the compound has also been investigated.

Effects of Different Content of TiO2 on Crystallization Behavior and Properties of Li2O-ZnO-SiO2 Glass-Ceramics

Abstract: Glass-ceramic materials of the Li2O-ZnO-SiO2 system, with various amounts of TiO2 added, have been prepared The appropriate heat treatment temperatures were selected according to the information provided by the differential thermal analysis (DTA) X-ray diffraction (XRD) analysis demonstrated that in the LZS glass-ceramics system, the main phases are Li2ZnSiO4, cristobalite, tridymite and quartz The scanning electron microscopy (SEM) revealed that crystals appear as lamellar and spherical particles in the glass-ceramics samples In addition, the average coefficient of the thermal expansion (CTE) values first decreased, then increased and finally tended to flatten When the content of TiO2 increased to 6%, the CTE value decreased to 915×10-6/K, reached the lowest value When the content of TiO2 increased to 10%, the CTE value reached highest value 1390×10-6/K

Ferroindialite (Fe 2+ ,Mg) 2 Al 4 Si 5 O 18 , a new beryl-group mineral from the Eifel volcanic region, Germany

Abstract: A new mineral, ferroindialite, a Fe2+-dominant analog of indialite, has been found in a pyrometamorphosed xenolith of pelitic rock hosted in alkaline basalts. Associated minerals are phlogopite, sanidine, sillimanite, pyroxenes of the enstatite-ferrosilite series, wagnerite, fluorapatite, tridymite, zircon and almandine. Ferroindialite forms brown-purple to gray with a violet-blue tint short prismatic or thick tabular hexagonal crystals up to 1.5 mm in size. The new mineral is brittle, with a Mohs’ hardness of 7. Cleavage is not observed. Dmeas = 2.66(1), Dcalc = 2.667 g/cm3. IR spectrum shows neither H2O nor OH groups. Ferroindialite is anomalously biaxial (−), α = 1.539(2), β = 1.552(2), γ = 1.554(2), 2Vmeas = 30(10)°. The mineral is weakly pleochroic, ranging from colorless on X to pale violet on Z. Dispersion is weak, r < v. The chemical composition (electron microprobe, mean of five point analyses, wt %) is as follows: 0.14 Na2O, 0.46 K2O, 4.95 MgO, 1.13 MnO, 12.66 FeO, 2.64 Fe2O3, 30.45 Al2O3, 47.22 SiO2, total is 99.65. The distribution of total iron content between Fe2+ and Fe3+ was carried out according to structural data. The empirical formula of ferroindialite is: (K0.06Na0.03)(Fe1.122+Mg0.78Mn0.10)Σ2.00(Al3.79Fe0.213+)Σ4.00Si4.98O18. The simplified formula is: (Fe2+,Mg)2Al4Si5O18. The crystal structure has been refined on a single crystal, R = 0.049. Ferroindialite is hexagonal, space group P6/mcc; a = 9.8759(3), c = 9.3102(3) A, V = 786.40(3) A3, Z = 2. The strongest lines in the X-ray powder diffraction pattern [d, A (I, %) (hkl)] are: 8.59 (100) (100), 4.094 (27) (102), 3.390 (35) (112), 3.147 (19) (202), 3.055 (31) (211), 2.657 (12) (212), 1.695 (9) (224). The type specimen of ferroindialite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, registration number 4400/1.