Showing papers on "Tridymite published in 2019"

Experimental Liquidus Studies of the Pb-Fe-Si-O System in Air

Abstract: Phase equilibria of the Pb-Fe-Si-O system have been investigated at 958-1913 K (685-1640 °C) for oxide liquid in equilibrium with air and solid oxide phases: (a) quartz, tridymite or cristobalite SiO2; (b) hematite Fe2O3; (c) spinel Fe3O4+x; (d) complex lead-iron silicates (melanotekite PFS = PbO·FeO1.5·SiO2, barysilite P9−xFxS6 = (9 − x)PbO·xFeO1+y·6SiO2, “P5FS” = 5PbO·FeO1.5·SiO2, and “P6FS” = 6PbO·FeO1.5·SiO2); (e) lead silicates (alamosite PS = PbO·SiO2, P2S = 2PbO·SiO2, P11S3 = 11PbO·3SiO2, P5S = 5PbO·SiO2); (f) lead ferrites (magnetoplumbite PbO·12FeO1.5, plumboferrite PbO·(5 + x)FeO1.5, 1:1 lead ferrite PbO·(1 ± x)FeO1.5); and (g) lead oxide (PbO, massicot). High-temperature equilibration on primary phase or inert metal (platinum, gold) substrates, followed by quenching and direct measurement of Pb, Fe and Si concentrations in the phases with the electron probe x-ray microanalysis (EPMA) has been used to accurately characterize the system in equilibrium with air. All results are projected onto the PbO-“FeO1.5”-SiO2 plane for presentation purposes. The present study is the first systematic characterization of liquidus over a wide range of compositions in this system in equilibrium with air.

Murashkoite, FeP, a new terrestrial phosphide from pyrometamorphic rocks of the Hatrurim Formation, South Levant

Abstract: Murashkoite, FeP, is a new mineral found in pyrometamorphic rocks of the Hatrurim Formation, South Levant. It is a typical accessory phase in the marbles and paralavas in the southern Negev Desert, Israel and on the Transjordan Plateau, Jordan. Murashkoite occurs as grains and aggregates up to 2 mm closely associated with barringerite, (Fe,Ni)2P, and zuktamrurite, FeP2. The rock-forming minerals include pyroxenes of the diopside-hedenbergite series, anorthite with subordinate gehlenite, tridymite, cristobalite, pyrrhotite, fluorapatite, chromite, magnetite, hematite, merrillite and late hydrothermal carbonates, silicates and sulfates. Macroscopically, murashkoite is yellowish-grey in colour and has a metallic lustre. In reflected light, the mineral is white with a beige tint and it is non-pleochroic. The anisotropy is distinct, from yellow-grey to greyish-blue. Selected reflectance values [Rmax–Rmin, % (λ, nm)] are: 42.7–40.8 (400), 42.0–40.6 (500), 44.5–43.4 (600), 48.0–47.7 (700). It is brittle. VHN20 = 468 kg mm−2. The holotype material has the chemical composition (electron microprobe): Fe 63.82; Ni 0.88; P 35.56; total 100.26 wt.%. The empirical formula calculated on the basis of 2 apfu is (Fe0.99Ni0.01)1.00P1.00 corresponding to FeP. Murashkoite is orthorhombic, space group Pnma, unit cell parameters refined from the single-crystal data are: a 5.099(2), b 3.251(2), c 5.695(2) A, V 94.41(8) A3, Z = 4, Dx = 6.108(5) g cm−3. The crystal structure was solved and refined to R1 = 0.0305 on the basis of 131 unique reflections with I > 2σ(I). The strongest lines of the powder X-ray diffraction pattern [(d, A) (I, %) (hkl)]: 2.831(75)(002,011); 2.548(22)(200); 2.477(46)(102,111); 1.975(47)(112); 1.895(100)(202,211); 1.779(19)(103); 1.632(45)(013,301,020). The mineral is named in honour of Dr. Mikhail Nikolaevich Murashko (born 1952), for his contributions to the mineralogy of the Hatrurim Formation. Murashkoite is a natural counterpart of synthetic FeP, the compound widely used in heterogeneous catalysis and electrocatalysis.

Distributions of Ag, Bi, and Sb as minor elements between iron-silicate slag and copper in equilibrium with tridymite in the Cu-Fe-O-Si system at T = 1250 °C and 1300 °C (1523 K and 1573 K)

Abstract: New experimental data on the distributions of silver (Ag), bismuth (Bi), and antimony (Sb) between liquid iron-silicate slag and liquid copper metal in equilibrium with tridymite in the Cu-Fe-O-Si system at T = 1250 °C and 1300 °C (1523 K and 1573 K) have been obtained. The experimental methodology involved high-temperature equilibration, rapid quenching of the equilibrated phases, followed by direct measurement of the equilibrium phases with electron probe X-ray microanalysis (EPMA) for measurement of major element concentrations and laser ablation inductively coupled plasma mass spectrometry (LAICPMS) for the measurement of minor element concentrations. The 4-point test approach was employed to confirm the achievement of chemical equilibrium in the current study. Open-system equilibration on quartz substrates in controlled gas atmospheres (CO/CO2/Ar) and closed-system equilibration in sealed quartz ampoules were used. The new experimental data resolve significant discrepancies found in previous studies and can be used as input for the development of thermodynamic databases for copper-making processes.

Experimental Liquidus Studies of the Binary Pb-Cu-O and Ternary Pb-Cu-Si-O Systems in Equilibrium with Metallic Pb-Cu Alloys

Abstract: Phase equilibria of the Pb-Cu-Si-O system have been investigated in the range 933-1938 K (660-1665 °C) for oxide liquid (slag) in equilibrium with solid Cu metal, liquid Pb-Cu alloy, or both solid and liquid metals, and solid oxide phases: (a) quartz, tridymite, cristobalite (SiO2); (b) cuprite (Cu2O); (c) lead silicates (PbSiO3, Pb2SiO4, Pb11Si3O17); (d) lead oxide (massicot, PbO); and (e) copper plumbite (Cu2PbO2). High-temperature equilibration on silica or copper substrates, followed by quenching and direct measurement of Pb, Cu and Si concentrations in the liquid and solid phases with the electron probe x-ray microanalysis (EPMA) has been used to accurately characterize the system in equilibrium with Cu or Pb-Cu metal. All results are projected onto the PbO-“CuO0.5”-SiO2 plane for presentation purposes. The present study is a continuation of the previous investigation of this system by the authors in a part of the silica and cuprite primary phase fields. Present data were later used to develop the thermodynamic models for all phases in this system.

Experimental liquidus studies of the Zn–Fe–Si–O system in air

Abstract: The liquidus of the ternary system ZnO-\FeO"-SiO in air has been experimentally investigated in the tridymite and cristobalite, spinel, and zincite primary phase fields in the temperature range 1 623 - 1 923 K (1 350 - 1 650 8C). Slags containing up to 65 mol.% \FeO" have been studied for the first time. The slag-spinel-zincite eutectic in the binary ZnO-\FeO" system in air has been estimated by extrapolation of the low-SiO part of the ternary system to x(SiO) = 0. High-temperature equilibration on primary phase (silica) or inert metal (platinum) substrates, followed by quenching and direct measurement of Zn, Fe and Si concentrations in the equilibrium phases with electron probe X-ray microanalysis has been used to accurately characterize the system in equilibrium with air. The discrepancies of the previous experimental work in this system have been resolved. The obtained data have been used to reoptimise the existing thermodynamic model.

Using powder XRD and pair distribution function to determine anisotropic atomic displacement parameters of orthorhombic tridymite and tetragonal cristobalite.

Abstract: Determination of the crystal structures of low-temperature tridymite and cristobalite using single-crystal XRD has been challenging because they generally occur as metastable fine-grained crystals in the geological environment. Therefore, using powder diffraction and scattering techniques is critical to study the low-temperature crystals. Synchrotron powder X-ray diffraction (XRD), pair distribution function (PDF) and transmission electron microscopy were used to investigate the structure of orthorhombic tridymite with C2221 symmetry and tetragonal cristobalite with P41212 symmetry, including their anisotropic atomic displacement parameters (ADPs). Rietveld refinement was used to determine the unit-cell parameters, fractional coordinates and isotropic atomic displacement parameters (Uiso) of the tridymite and cristobalite. The PDF method was used to determine ADPs for each atom. The results suggest that the crystal structure with high quality ADP values can be obtained using the combined methods of XRD and PDF analyses. The method can be used for characterizing crystals that are not suitable for single-crystal XRD.

Crystal structures, dielectric properties and ferroelectricity in stuffed tridymite-type BaAl(2-2x)(Zn0.5Si0.5)2xO4 solid solutions.

Abstract: BaAl(2-2x)(Zn0.5Si0.5)2xO4 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) solid solutions with weak ferroelectricity were prepared using a conventional solid-state reaction method. Zn atoms preferentially occupied the 6c-Wyckoff site of Al1 and the 2b-Wyckoff site of Al4, whereas Si atoms filled the 6c-Wyckoff site of Al2 and the 2b-Wyckoff site of Al3. As such, the cell volume shrank abnormally as the number of larger [Zn0.5Si0.5]3+ compared to Al3+ increased. There were two anomalous peaks in the dielectric constant. One peak at low temperature represented a second-order ferroelectric transition. Relaxor-like behaviour and a stable dielectric constant against temperature from -50 °C to 400 °C were observed at x = 0.4. This result was attributed to disorder in the 2b-Wyckoff site Al/(Zn0.5Si0.5) and distortion in the tetrahedron.

Experimental Liquidus Study of the Binary PbO-CaO and Ternary PbO-CaO-SiO 2 Systems

Abstract: Phase equilibria of the binary PbO-CaO and ternary PbO-CaO-SiO2 systems have been investigated at 870-1655 °C for oxide liquid in equilibrium with air and solid oxide phases: tridymite or cristobalite SiO2, pseudowollastonite CaSiO3, dicalcium silicate (Ca,Pb)2SiO4, tricalcium silicate (Ca1−xPbx)3SiO5 (x < 0.03), new phase tricalcium-lead silicate (Ca0.8Pb0.2)3SiO5 (Ca12Pb3Si5O25), lime CaO, and calcium plumbate Ca2PbO4, covering the ranges of concentrations not studied before. High-temperature equilibration on primary phase or inert metal (platinum, gold) substrates, followed by quenching and direct measurement of the Pb, Ca and Si concentrations in the phases with the electron probe x-ray microanalysis (EPMA) has been used to accurately characterize the system. Liquidus phase equilibrium data of the present authors for the PbO-CaO-SiO2 system are essential to obtain a self-consistent set of parameters of thermodynamic models for all phases.

Experimental Liquidus Study of the Ternary CaO-ZnO-SiO 2 System

Abstract: Phase equilibria of the ternary CaO-ZnO-SiO2 system have been investigated at 1170 °C to 1691 °C for oxide liquid in equilibrium with air and solid oxide phases: tridymite or cristobalite SiO2 (up to two immiscible liquids), pseudowollastonite (CS) CaSiO3, rankinite (C3S2) Ca3Si2O7, dicalcium silicate (C2S) (Ca, Zn)2SiO4, tricalcium silicate (C3S) (Ca, Zn)3SiO5, lime (Ca, Zn)O, zincite (Zn, Ca)O, willemite Zn2SiO4 and hardystonite (melilite) Ca2ZnSi2O7, covering the ranges of concentrations not studied before. High-temperature equilibration on primary phase (silica) or inert metal (platinum) substrates followed by quenching and direct measurement of the Ca, Zn and Si concentrations in the phases with the electron probe X-ray microanalysis (EPMA) has been used to accurately characterize the system. Liquidus phase equilibrium data of the present authors for the CaO-ZnO-SiO2 system are essential to obtain a self-consistent set of parameters of thermodynamic models for all phases.

Experimental investigation of gas/slag/matte/tridymite equilibria in the Cu–Fe–O–S–Si system in controlled gas atmosphere at T = 1 200 °C and P(SO2) = 0.1 atm

Abstract: The effects of partial pressure of sulphur dioxide on the gas/slag/matte/tridymite equilibria in the Cu-Fe-O-S-Si system at 1 200 degrees C have been experimentally investigated and compared with the previous studies at various P(SO2). The experimental procedure includes equilibration of the sample and silica substrate at high temperature for the designated time, rapid quenching to preserve the equilibrium phases, followed by measuring the composition of the condensed phases with electron probe X-ray microanalysis. A set of graphs were constructed to present the compositions of slag and matte as a function of copper concentration in matte. The present study confirmed that the chemically dissolved copper and sulphur for the given Cu in matte are independent of the partial pressure of SO2. However, the experimentally measured liquidus (Fe/SiO2) are different for various P(SO2). The new data provide an important, accurate and reliable quantitative foundation for improvement of the thermodynamic databases for the chemical systems containing copper matte and slag. The present study is a part of a broader overall research program on the characterisation of the multi component (Cu-Fe-O-S-Si-Al-CaMg), multi-phase (gas/slag/matte/metal/solids) systems with minor elements.

Structural and optical properties of Ba(Co1-xZnx)SiO4 (x = 0.2, 0.4, 0.6, 0.8)

Abstract: Structural characterization and X-ray reference powder pattern determination have been conducted for the Co- and Zn-containing tridymite derivatives Ba(Co1−xZnx)SiO4 (x = 0.2, 0.4, 0.6, 0.8). The bright blue series of Ba(Co1−xZnx)SiO4 crystallized in the hexagonal P63 space group (No. 173), with Z = 6. While the lattice parameter “a” decreases from 9.126 (2) A to 9.10374(6) A from x = 0.2 to 0.8, the lattice parameter “c” increases from 8.69477(12) A to 8.72200(10) A, respectively. Apparently, despite the similarity of ionic sizes of Zn2+ and Co2+, these opposing trends are due to the framework tetrahedral tilting of (ZnCo)O4. The lattice volume, V, remains comparable between 626.27 A3 and 626.017 (7) A3 from x = 0 to x = 0.8. UV-visible absorption spectrum measurements indicate the band gap of these two materials to be ≈3.3 and ≈3.5 eV, respectively, therefore potential UV photocatalytic materials. Reference powder X-ray diffraction patterns of these compounds have been submitted to be included in the Powder Diffraction File (PDF).

Raman spectra of tridymite modifications: MC, MX–1, and PO–10

Abstract: In order to facilitate identification of tridymite modifications using micro–Raman spectroscopy, the Raman spectra of synthetic and natural tridymite modifications (MC, MX–1, and PO–10) including low frequency region (ν = 15–200 cm−1) are measured. The Raman spectrum of MX–1 is reported for the first time. All modifications revealed the characteristic peaks below 150 cm−1. Using the compiled Raman spectra, tridymite modifications of the reported Raman spectra from meteorites in the literature were identified. It revealed that not only MC, but PO–10 modification exists in the meteorites.

Pyrometamorphic Rocks in the Molinicos Basin (Betic Cordillera, SE Spain): Insights into the Generation of Cordierite Paralavas

Abstract: A singular thermal anomaly occurred in the Molinicos Miocene, lacustrine, intramontane basin (Betic Cordillera). This gave place to vitreous vesicular materials (paralavas) and baked rocks (clinker) inside of a sequence of marly diatomites and limestones. The chemical composition of the paralavas (SiO2 = 52–57, Al2O3 ≈ 20, Fe2O3 = 10–20, K2O + Na2O 4% in weight) of dark clay layers and the existence of tectonic fractures give the right context for a combustion process. Short-term heating favoured the generation of paralavas, clinker and marbles. Thermodynamic modelling constrains the onset of melting at 870–920 °C for <10 MPa at equilibrium conditions. However, the presence of tridymite and/or cristobalite in clinker and paralavas and the compositional variation in both rock types suggests that the temperature at which first melting occurred ranged between 870 °C and 1260 °C due to melt fractionation processes.

Preparation of Binderless Silicoaluminophosphates by Vapor-Phase Crystallization of Kaolin–Phosphoric Acid Grains

Abstract: Transformations of granules based on kaolin and phosphoric acid under conditions of vapor-phase crystallization in a mixture of water vapor and a structure-directing agent have been studied. It has been shown that silicoaluminophosphate granules obtained in the presence of dipropylamine, triethylamine, or tetramethylammonium hydroxide as a structure-directing agent consist of a shell formed by dense nonporous cristobalite, tridymite, and berlinite phases and the core made mainly of microporous crystalline silicoaluminophosphates. The formation of the shell, which ensures the strength of the silicoaluminophosphate granules, is due to the interaction of steam with the material of the granules at the initial stages of vapor-phase crystallization. It has been established that the selectivity of the structure-directing action of the amines under vapor-phase crystallization conditions basically corresponds to the template hydrothermal synthesis. It has been assumed that the specific features of the structure-directing action of dimethylamine during vapor-phase transport synthesis are due to its low boiling point, which ensures the primary contact of the granules with template, rather than water molecules. As a result, the products of the transformation of granules in the presence of a mixture of dimethylamine and water do not contain dense nonporous phases and are cocrystallized silicoaluminophosphate and calcium aluminosilicate with the gismondine structure.

Experimental Determination of the Effect of CaO and Al2O3 in Slag Systems Related to the Conversion Process of High Copper Matte Grade

Abstract: The slags generated in the conventional copper conversion process are mainly composed of Cu2O–Fe2O3–SiO2 with CaO, Al2O3, and MgO compounds—in concentrations up to 10 wt %. The present work contributes to the knowledge of the conversion process, generating experimental data for the phase diagrams of the Cu2O–Fe2O3–SiO2–Al2O3 and Cu2O–Fe2O3–SiO2–CaO systems. The experiments were carried out in a tubular furnace at temperatures of 1150 °C and 1200 °C, under a condition of saturation with tridymite and spinel. Once the equilibrium was reached, the samples were immediately quenched in water. The phases in the samples were observed through a scanning electron microscope (SEM) and the elemental composition of the phases were analyzed by means of energy-dispersive X-ray spectroscopy (EDS) detectors. The addition of Al2O3 and CaO into the Cu2O–Fe2O3–SiO2 system resulted in an appreciable displacement of the liquidus lines, corresponding to an expansion of the liquid in the tridymite primary phase field. The addition of CaO and Al2O3 combined was evaluated on industrial slags and from samples obtained in a Peirce–Smith furnace, with increasing amounts of CaO in the flux.

Innovation of Building Materials: Ecological Bricks, Characterization of Complementary Inorganic Raw Materials

Abstract: Morphological, chemical and mineralogical characterization of inorganic raw materials (pumicite and heavy clay) was carried out by SEM-EDS, XRF and XRD. It was found that pumicite shows the following composition; 71.78% SiO2, 14.83% Al2O3, 2.57% Fe2O3, 2.32% FeO, 2.37% Na2O, 4.12% K2O, 1.51% CaO and 0.5% P2O5. The major phase corresponds to Sanidine and as minor phases are Berlinite, Alkaline calcium and sodium ferritesilicoaluminate and Tridymite. For heavy clay, there was a chemical composition of 63.0% SiO2, 19.9% Al2O3, 6.2% Fe2O3, 1.5% Na2O, 2.1% K2O, 3.9% CaO, 2.5% MgO and 0.9% TiO2. Also are present in some contents of Illite, Kaolinite and Tridymite; Quartz, Hematite, Vermiculite and Montmorillonite are presented as minor phases. Additionally, the Atterberg number and the thixotropy were determined to heavy clay, finding values of 31.31 ± 9.45% and 2.87 ± 1.64%, respectively.