Showing papers on "Tridymite published in 2018"

Experimental Liquidus Studies of the Pb-Fe-Si-O System in Equilibrium with Metallic Pb

Abstract: Phase equilibria of the Pb-Fe-Si-O system have been investigated at 943 K to 1773 K (670 °C to 1500 °C) for oxide liquid in equilibrium with liquid Pb metal and solid oxide phases: (a) quartz, tridymite, or cristobalite; (b) (fayalite + tridymite) or (fayalite + spinel); (c) spinel (Fe3O4); (d) complex lead-iron silicates (melanotekite PbO·FeO1.5·SiO2, barysilite 8PbO·FeO·6SiO2, 5PbO·FeO1.5·SiO2, and 6PbO·FeO1.5·SiO2); (e) lead silicates (Pb2SiO4, Pb11Si3O17); (f) lead ferrites (magnetoplumbite Pb1+x Fe12−x O19−x solid solution range); and (g) lead oxide (PbO, massicot). High-temperature equilibration on primary phase or iridium substrates, followed by quenching and direct measurement of Pb, Fe, and Si concentrations in the phases with the electron probe X-ray microanalysis, has been used to accurately characterize the system in equilibrium with Pb metal. All results are projected onto the PbO-“FeO”-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 metallic Pb.

Experimental Phase Equilibria Studies of the PbO-SiO2 System

Abstract: Phase equilibria of the PbO-SiO2 system have been established for a wide range of compositions: (a) liquid in equilibrium with silica polymorphs (quartz, tridymite and cristobalite) between 740°C and 1580°C, at 60-90 mol.% SiO2; (b) with lead silicates (PbSiO3, Pb2SiO4 and Pb11Si3O17) and lead oxide (PbO) between 700°C and 810°C. A high-temperature equilibration/quenching/electron probe X-ray microanalysis (EPMA) technique has been used to accurately determine the compositions of the phases in equilibrium in the system. Significantly, no liquid immiscibility has been found in the high-silica range, and the liquidus in this high-silica region has been accurately measured. The phase equilibria information in the PbO-SiO2 system is of practical importance for the improvement of the existing thermodynamic database of lead-containing slag systems (Pb-Zn-Fe-Cu-Si-Ca-Al-Mg-O). This article is protected by copyright. All rights reserved.

Non-invasive Raman identification of crystalline and glassy phases in a 1781 Sèvres Royal Factory soft paste porcelain plate

Abstract: A Raman study of a Sevres soft paste (frit) porcelain plate allowed the identification of both the crystalline and amorphous phases. Cristobalite and pseudowollastonite gave main Raman signatures in the body where also tridymite, amorphous alkali silicate glass and lead arsenate apatite were detected. Na0.4K0.1Ca0.5Pb4(AsO4)3 lacunar apatite is identified as opacifier in blue and green overglaze enamel. Pb-Sb-reach pyrochlore (Naples Yellow) pigment was found in yellow and green overglaze enamels. The orange hue is obtained by superposing a hematite bearing red paint stroke over the yellow. These results are compared to those previously obtained by detailed OM, SEM, XRD and XRF analyses. Some of the phases identified by XRD (quartz, tridymite) are hardly detected by Raman and vice versa cristobalite was not found by XRD, most probably due to its low amount.

Structure Analysis of Fe3O4@SiO2 Core Shells Prepared from Amorphous and Crystalline SiO2 Particles

Abstract: This article reports the results synthesis of crystalline (Fe3O4@c-SiO2) and amorphous (Fe3O4@a-SiO2) nanoparticles from natural resources (iron sand and silica sand). The synthesis of Fe3O4 and SiO2 nanoparticles used co-precipitation and hydrothermal-coprecipitation methods with polyethylene glycol (PEG) 4000 as a template. The XRD data analysis presented that the amorphous SiO2 particles were successfully produced using hydrothermal and co-precipitation methods. The XRD data analysis also presented that the crystalline phases were formed in quartz and tridymite phases after calcination process of the amorphous phase. SEM images exhibited that the amorphous phase had different particle size and morphology from the crystalline phase. FTIR spectra presented some absorption peaks of new functional groups indicating the existence of Si-O-Si (silanol), Fe-O, C-N, and Fe-O-Si as new functional groups.

The Effect of CaO on Gas/Slag/Matte/Tridymite Equilibria in Fayalite-Based Copper Smelting Slags at 1473 K (1200 °C) and P (SO 2 ) = 0.25 Atm

Abstract: Fundamental experimental studies have been undertaken to determine the effect of CaO on the equilibria between the gas phase (CO/CO2/SO2/Ar) and slag/matte/tridymite phases in the Cu-Fe-O-S-Si-Ca system at 1473 K (1200 °C) and P(SO2) = 0.25 atm. The experimental methodology developed in the Pyrometallurgy Innovation Centre was used. New experimental data have been obtained for the four-phase equilibria system for fixed concentrations of CaO (up to 4 wt pct) in the slag phase as a function of copper concentration in matte, including the concentrations of dissolved sulfur and copper in slag, and Fe/SiO2 ratios in slag at tridymite saturation. The new data provided in the present study are of direct relevance to the pyrometallurgical processing of copper and will be used as an input to optimize the thermodynamic database for the copper-containing multi-component multi-phase system.

Lunar and Martian Silica

Abstract: Silica polymorphs, such as quartz, tridymite, cristobalite, coesite, stishovite, seifertite, baddeleyite-type SiO2, high-pressure silica glass, moganite, and opal, have been found in lunar and/or martian rocks by macro-microanalyses of the samples and remote-sensing observations on the celestial bodies. Because each silica polymorph is stable or metastable at different pressure and temperature conditions, its appearance is variable depending on the occurrence of the lunar and martian rocks. In other words, types of silica polymorphs provide valuable information on the igneous process (e.g., crystallization temperature and cooling rate), shock metamorphism (e.g., shock pressure and temperature), and hydrothermal fluid activity (e.g., pH and water content), implying their importance in planetary science. Therefore, this article focused on reviewing and summarizing the representative and important investigations of lunar and martian silica from the viewpoints of its discovery from lunar and martian materials, the formation processes, the implications for planetary science, and the future prospects in the field of “micro-mineralogy”.

Experimental Liquidus Studies of the Pb-Cu-Si-O System in Equilibrium with Metallic Pb-Cu Alloys

Abstract: Phase equilibria of the Pb-Cu-Si-O system have been investigated in the temperature range from 1073 K to 1673 K (800 °C to 1400 °C) for oxide liquid (slag) in equilibrium with solid Cu metal and/or liquid Pb-Cu alloy, and solid oxide phases: (a) quartz or tridymite (SiO2) and (b) cuprite (Cu2O). High-temperature equilibration on silica or copper substrates was performed, followed by quenching, and direct measurement of Pb, Cu, and Si concentrations in the liquid and solid phases using the electron probe X-ray microanalysis has been employed 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 the first-ever systematic investigation of this system to describe the slag liquidus temperatures in the silica and cuprite primary phase fields.

Structural Characterization of the Body Frame and Spicules of a Glass Sponge

Abstract: The nanostructure (atomic-scale structure) and water species in the body frame and spicules of the marine glass sponge, Euplectella aspergillum, collected from the sea floor around Cebu Island was characterized in detail by thermogravimetric differential thermal analysis, nuclear magnetic resonance spectroscopy, Raman and infrared spectroscopies, and X-ray diffraction method. The structural features of the nanostructure in the body frame and spicules were essentially similar to each other, although these were different from those of inorganic amorphous silica materials, such as silica gel and silica glass. In addition, the averaged short and medium range structures of the sponge may be similar to those of tridymite. The water content and water species included in the body frame and spicules were almost the same. More than half of the contained water was physisorbed water molecules, and the rest was attributed to Q3 and Q2 silanol groups. Most of the water species may be present at the surface and involved in hydrogen bonding.

Characterization of Silica Sand Due to The Influence of Calcination Temperature

Abstract: The characterization of natural silica from Tanah Datar region has been done due to variation of calcination temperature. Characterization is done using X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD). The results of the XRF test show that the content of silica content is 88.957%. Based on XRD test it is found that temperature increase causes structural changes in natural silica. At a temperature of 26 ° C the silica has a quartz phase and in the temperature range of 800 ° C to 1000 ° C there is a new phase, cristobalite. As for the temperature of 1100 °C appears a tridymite phase. Furthermore, the higher the given temperature causes of the crystal size of the crystal be small. In addition to phase and crystal size, there is also a change of lattice parameters.

Phase Transformation of Amorphous Rice Husk Silica

Abstract: This work aims at assessing the crystallization process of amorphous silica from rice husk (RH) by in situ X-ray diffraction, upon heating up to 1450 °C in a high-temperature chamber. The study includes microstructural characterization by transmission electron microscopy. The work was conducted on rice husk ash (RHA), obtained by combustion of RH at 650 °C with and without leaching in 1 N HCl solution, obtaining samples with variable impurity content. The results showed that crystallization of RHA amorphous silica upon continuous heating occurred at higher temperatures compared to the isothermal one, considering the sample purity. The type of polymorph silica identified in the samples during continuous heating consisted of cristobalite or a combination of cristobalite and tridymite depending on the impurity levels in the samples. The study revealed silica crystallites with spherical shape nucleated by a dominant homogeneous mechanism. The size of crystallites ranges from around 2 nm to 20 nm. Larger particles nucleated on impurities and constituted by combinations of P, Ca, K, Mg, and Na were also observed.

Liquid phase deposition of iron phosphate thin films

Abstract: Liquid phase deposition (LPD) has been applied for the synthesis of iron phosphate thin films as an example of an effective methodology for the thin film growth of other polyanionic compounds The prepared films were highly uniform, free of cracks, pure and successfully applied to cover various substrates such as soda-lime glass and stainless steel The thickness of these films can be easily tailored in the range of 80 nm to 27 μm by the deposition time The chemical equilibria for the hydrolysis of [PF6]− species and the formation of iron phosphate were studied by 19F-NMR and 31P-NMR spectroscopy to get insight into the formation mechanism of iron phosphate thin films Hydrolysis of [PF6]− occurs very slowly and a longer induction period favors the hydrolysis The as-prepared FePO4·2H2O films on conductive stainless steel substrates are shown to be electrochemically active for the intercalation of Li+ ions Two polymorphs of FePO4 with crystal structures identical to hexagonal tridymite AlPO4 and monoclinic FeAsO4 were identified upon heat treatment of the as-prepared powders

Pedogenic Siliceous Features

Abstract: This chapter deals with the micromorphological characteristics and interpretation of pedogenic siliceous features in soils and regoliths. Pedogenic siliceous features occur as crystalline forms, such as quartz, tridymite, and cristobalite, and as poorly ordered or non-crystalline forms, such as opal-A and opal-CT. Silica may be concentrated in varying degrees through weathering, vertical and lateral translocation, and precipitation and dissolution, resulting in the formation of cemented horizons (silcretes and duripans) and non-cemented or poorly cemented horizons (fragipans). Typic coatings, infillings, and nodules, mainly consisting of opal, are commonly observed in fragipan thin sections. In duripans and silcretes, the most common pedofeatures are typic and laminar coatings and infillings with various silica phases such as opal, opal-CT, cristobalite, chalcedony, and non-fibrous microcrystalline quartz. Transformation of poorly ordered to more crystalline forms with aging is frequently observed. Dissolution of quartz is commonly observed in strongly weathered materials.

Specific Features of Formation of Crystalline Silicoaluminophosphates in Grains Based on Kaolin and Phosphoric Acid

Abstract: Transformations of granules based on kaolin and phosphoric acid under the conditions of vapor-phase crystallization at 170°C were studied. Specific features of the individual and cooperative action of a water vapor and a template dipropylamine on the granules were determined. It is shown that the regulation of competing processes of formation of dense non-porous phases (tridymite, cristobalite, berlinite) and microporous crystalline silicoaluminophosphates of structural types ATL and ATN can be carried out by creating transport pores in the volume of the initial granules. The formation of transport pores was provided by using of porogens (hydroxyethyl cellulose and carbon nanospheres) with the subsequent calcination of the granules. The presence of 40- and 60- nm macropores in the porous structure favored intensification of mass-exchange processes occurring within the granules under the vapor-phase crystallization conditions. This led to an increase in the selectivity of crystallization of the materials with crystal structure types AEL and ATN. The morphology of the crystals with the AEL and ATN structure and their chemical composition depend on the porogen used to prepare the starting granules.

Effect of CaO Addition on Synthesis of Tridymite Phase from Amorphous Silica

Abstract: The crystallization and transformation behaviors from amorphous and crystalline silica to tridymite were investigated. Silica glass and precipitated silica as an amorphous silica and quartz as a crystalline silica were used for silica source. These silica were well mixed with tridymite as a seed crystal and fired at a temperature from 1100°C to 1400°C for 4, 6 and 12 h to form tridymite phase. The effect of CaO as a dopant on the formation of tridymite was also examined. Regardless to the presence or absence of CaO, the seed crystal tridymite was needed for phase transformation from amorphous silica or quartz to tridymite. In addition, it was found that silica glass was easier to transform to tridymite phase than precipitated silica and quartz. For samples without CaO, tridymite could be directly achieved from amorphous silica without the assistance of liquid phase. For samples doped with CaO, on the other hands, the dominant reaction for transformation to tridymite was the precipitation from liquid phase that was caused by the reaction between doped CaO and cristobalite crystallized from amorphous silica. The significant behaviors that occurred in the samples with CaO were (1) the formation of cristobalite and CaSiO3 which reduced tridymite amount and (2) the liquid phase formation which led the precipitation of tridymite.

Correlation between thermoluminescence emission and phase transitions of tridymite

Abstract: Tridymite exhibits a complex 400 nm-induced thermoluminescence spectra consisting of five groups of components at (i) 90 and 130°C (due mainly to oxygen vacancies, substitution and interstitial atoms and/or impurities that create localized charge losses), (ii) 200°C (linked to a partial phase transition), (iii) 230°C (associated probably with alkali ions moving away from Al that leads to [AlO4]° hole-like or [GeO4/Li]° centers) and (iv) 320°C (caused by both phase transition and electron recombination with the unstable holes trapped at oxygen vacancies next to Al sites). The application of the Tm–Tstop protocol confirms a continuum in the trap structure not only because of the successive shifting of the maxima with the increase of the temperature, but also with the enhancement of the activation energy values that have been assessed by means of the initial rise method.

Preparation, Thermal Diffusivity, and Thermal Conductivity of Phosphate Ceramics with the Tridymite Structure

Abstract: We have synthesized powders of the CsMIIPO4 (MII = Mg, Mn, Co) phosphates with the β-tridymite structure. Phosphate ceramics were produced by conventional cold pressing with inorganic sintering aids, followed by programmed annealing, and by an innovative method: high-speed spark plasma sintering. The thermal diffusivity and thermal conductivity (0.3–0.4 W/(m K)) of the CsMIIPO4 ceramics indicate that they are heat insulators with a high working temperature.

Dense Mulliteceramic Sintered by SPS and Its Behavior Under Thermal Shock

Abstract: This article studies the influence of raw material, sintering temperature, particle size, and Al2O3 content on densification of mullite ceramics. Thermal cycle treatments were conducted to evaluate thermal shock resistance of samples. Microstructures of samples were also investigated to reveal effects of various parameters and thermal test. Flexural strength retention rises while density decreases, resulting from increasing extra space for stress release. Tridymite precipitation is found to be harmful in improving thermal shock resistance.

Characterization at High Temperature of the Porcelanite Mineral Phases from the Gafsa-Metlaoui Basin and Valuation in the Ceramic Domain

Abstract: In a bid to test the potential use of the porcelanites of the Gafsa-Metloui basin in the ceramic manufacturing domain, three porcelanites were collected from three different areas: the Kef el Ghiss, Oued Thelja and Kef Eddour. These porcelanites were treated at 800, 1000 and 1200 °C for three to six hours. The aim has been to understand their relating phase transformations at high-temperature, by simple calcination and activated calcination with an alkaline flux (Na2CO3). The treated and raw samples were analyzed through various techniques (XRD, X-ray Fluorescence). All samples were discovered to be opal C/T-rich. The Oued Thelja and Kef Eddour samples appear to be carbonate-rich, while the Kef el Ghiss’s sample turns out to be rather clayey and contain trace amounts of quartz, francolite and feldspars. Following calcination, all samples have appeared to lose a large part of their mineralogical constituents (clay minerals, calcite, dolomite, quartz, francolite, hematite and feldspars), while the opal C/T proved to transform into cristobalite and tridymite. Thus, the activated calcination, within the ranges of 1000–1200 °C, of the samples of Oued Thelja and Kef Eddour proved to yield cristobalite and tridymite. The same mineral phases were obtained with enstatite and/or diopside, following a simple 1200 °C calcination process. The administered ceramic tests appear to reveal that the Kef Eddour and Kef el Ghiss associated samples are not suitably fit for ceramic applications. As for the Oued Thelja relevant sample, it proves to display satisfactory properties (in terms of shrinkage, porosity and loss on ignition), and could therefore be valued in ceramics manufacture through applying it in formulas of up to 20% in range, in conformity with the following formula: 20% Opal C/T + 12% Tabarka clay + 30% feldspars + 38% clay from Ukraine.