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This study, investigates how adaptable silica made from rice husks could be used in energy storage applications. It is show that rice husk silica (SiO2) can be used in a variety of applications with the right processing. Cold plasma is used to prepare the silica samples in a variety of structural phases which improves their electrochemical characteristics. Using (X-ray diffraction analysis) XRD, Raman spectroscopy, (Fourier-transform infrared spectroscopy) FTIR, (Field emission scanning Electron microscopy) FESEM, and (Energy Dispersive spectroscopy) EDS techniques are used to investigate and evaluate the differences in their structural, morphological, and chemical composition. A three-electrode system is used to assess the material's electrochemical performance. Surprisingly, it is found that after plasma treatment, amorphous silica materials have a large increase in specific capacitance (297 F/g) as a result of an increase in functional groups and better adhesion characteristics. These silica samples also have an outstanding electron reversibility and coulombic efficiency. The effect of the various properties of the silica on super capacitance and catalyst performances in metal air battery is discussed. [ABSTRACT FROM AUTHOR]

Copyright of Refractories / Naihuo Cailiao is the property of Naihuo Cailia (Refractories) Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

It is urgently necessary for environmental resource utilization of copper slag with incremental quantities of stacked copper slag. In this paper, copper slag has been used as mineralizer and raw material to prepare silica refractory. The effect of copper slag on phase composition, microstructure, mechanical, and load deformation performance has been investigated. The results indicate that the components of copper slag as mineralizer promote the formation of tridymite. Simultaneously, copper slag promotes the densification of silica refractory and glass phase increases due to the mineralizer and impurities in copper slag. The increased glass phase promotes the cold crushing strength and cold modulus of rupture for silica refractory, while the hot modulus of rupture slightly decreases by 1.5 MPa for 6 wt% copper slag. In addition, the load softening temperature and high‐temperature creep attains 1632.6°C and ‐5.5%, respectively. It is estimated that the potential application of silica refractory with copper slag on upper part of copper stove (low‐temperature and low‐load region) is acceptable in consideration of environmental utilization of solid waste. [ABSTRACT FROM AUTHOR]

The absorbance efficiency of local kaolin clay from Tanzania (Pugu kaolin) has been enhanced to improve its utilization in removal of textile dyes from water. The clay was acid-activated using H2SO4, after calcination at 750 ℃. Characterization by XRF, XRD, ATR-FTIR and Porosimeter showed kaolinite [Al2Si2O5(OH)4], silica (SiO2) and microcline [KAlSi3O8] as the main phases. Upon acid treatment, silica increased from 44.18% to 58.81% due to the appearance of tridymite, and alumina decreased from 26.70% to 12.74% due to disappearance of the kaolinite. Surface area increased from 15.36 to 149.61 m²/g due to removal of acid-soluble impurities. The chemical composition showed decrease of Fe2O3 and increase of other major oxides. The impact of acid-activation on contact time, temperature, adsorbent dose, initial pH and absorbate concentration was investigated through batch adsorption technique using basic blue 9 (BB9) and direct red 28 (DR28) dyes. The results at optimal conditions of 3 hours contact time, 27oC temperature, 0.9 g adsorbent dose, initial pH of 11 and initial adsorbate concentration of 90 mg/L, showed that acid modification of the clay increased its capacity to adsorb BB9 from 96.82% to 99.91%, and DR28 from 86.33% to 95.04%. These findings established the influence of modifying the raw clay for its dye removal applications. [ABSTRACT FROM AUTHOR]

Alternative sources of silica, most abundant in the earth's crust, are converted into useful hightemperature crystalline phases. In this study, temperature dependent phase transformations of silica sand and rice husk sourced silica with and without the addition of 10 % by weight elemental iron were investigated. For this purpose, firstly, the initial silica sources were calcined at 700 °C for 2 hours, ground into fine powder and placed on a carbon substrate and heat treated in a tube furnace at 1500 °C for 2 hours in argon atmosphere. The phase transformation characteristics of the final material were made by XRD and SEM analysis. A mixture of cristobalite-tridymite and high purity cristobalite was observed in rice husk ash with and without Fe addition, respectively. In the same order, XRD phase pure tridymite and cristobalite phases were observed in silica sand. As a result, XRD phase pure or tailored transformations of these crystalline phases were obtained depending on the Fe addition and silica source. [ABSTRACT FROM AUTHOR]

The study of silica polymorphs in impactites is important for determining the pressure and temperature of impact rock formation. Silica modifications in impact melt rocks of the Janisjärvi impact structure (Karelia, Russia) are presented by tridymite, cristobalite, quartz, trace stishovite and coesite. Silica modifications were characterized and studied by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and Raman and cathodoluminescent spectroscopy. Investigations were carried out in order to clarify polymorphs formation mechanisms and search for signs of the transition of certain structural modifications to others. For the first time, a description of tridymite with a ballen-like texture from impact melt rock is given. A sequence of silica modification and textural transformation in impact rocks after the impact event is suggested. We conclude that the pressure of 40 GPa and a temperature of more than 900 °C were achieved in the impact structure. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Novel silica bricks were made of crystalline silica with ferrosilicon nitride as the mineralizer. The phase, microstructure, pore characteristics and high-temperature properties of the novel silica bricks prepared by adding 1%, 1.5% and 2% ferrosilicon nitride were characterized. The results showed that, compared to conventional silica bricks (with mineralizers of calcium hydroxide and iron scale), the novel silica bricks with the addition of ferrosilicon nitride contained less calcium oxide, less residual quartz and more tridymite. The ferrosilicon nitride was gradually oxidized to form SiO 2 and Fe 2 SiO 4 during the firing stage of the silica bricks. After adding ferrosilicon nitride, the degree of particle breakage was reduced, and the pore size of interconnected pores increased. With the increase in ferrosilicon nitride content, the silica brick structure gradually densified. The silica brick sample with 2% ferrosilicon nitride achieved better creep resistance at high temperature (1550 °C, 0.2 MPa), but the refractoriness under load of the bricks was slightly reduced by using ferrosilicon nitride as a mineralizer. An optimization model of ferrosilicon nitride as a mineralizer was established. [ABSTRACT FROM AUTHOR]

Abstract: Silica bricks with cemented silica and crystalline silica as raw materials show different properties. In this paper, the phase and structural characteristics of different kinds of silica raw materials and silica bricks after heat treatment at different temperatures are explored by the means of XRD, SEM and CT, and the formation mechanism of tridymite in the silica bricks is clarified. Results show that the liquid phase formed by impurities in both crystalline silica and cemented silica raw material cannot promote the transformation of quartz to tridymite at high temperatures. The phase composition of both cemented silica and crystalline silica after heat treatment at 1460 and 1550 °C is cristobalite. [ABSTRACT FROM AUTHOR]

The efficiency of the production of foundry products depends on the reliable operation of the melting furnace including, therefore, the durability of its lining. The most common material adopted for the production of an acid furnace crucible lining is quartzite, in which during the pretreatment (heating to 800 °C followed by holding), a tridymite phase appears that maintains a constant volume at 840–1470 °C for a long time and provides high lining durability of 300–350 melts, but only when using melting temperature regimes not exceeding 1500 °C. However, the absence of iron scrap leads to the smelting of synthetic iron from only one steel scrap using higher melting temperatures (1550–1570 °C), which sharply reduces the lifetime of the lining to 220 melts. This work is devoted to research aimed at establishing technology for the pretreatment with the original quartzite, which ensures the formation of a phase state that successfully withstands elevated temperatures for a long time. The studies were carried out using a Bruker D8 ADVANCE diffractometer and a Shimadzu XRF-1800 X-ray wave-dispersive spectrometer. The work consisted of drying samples of the original quartzite at temperatures of 200 and 800 °C with subsequent exposure to temperatures of 200, 400, 600, 870, 1000, 1200, 1470 and 1550 °C. As a result, the conditions for pretreatment of quartzite were established, during which during its further use, a cristobalite phase can be obtained, which makes it possible manufacture a high-temperature lining that ensures its high durability. The introduction of this technology will ensure the efficiency of the production of foundry products for enterprises operating induction crucible furnaces at industrial frequency. [ABSTRACT FROM AUTHOR]

The study of silica polymorphs in impactites is important for determining the pressure and temperature of impact rock formation. Silica modifications in impact melt rocks of the Janisjärvi impact structure (Karelia, Russia) are presented by tridymite, cristobalite, quartz, trace stishovite and coesite. Silica modifications were characterized and studied by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and Raman and cathodoluminescent spectroscopy. Investigations were carried out in order to clarify polymorphs formation mechanisms and search for signs of the transition of certain structural modifications to others. For the first time, a description of tridymite with a ballen-like texture from impact melt rock is given. A sequence of silica modification and textural transformation in impact rocks after the impact event is suggested. We conclude that the pressure of 40 GPa and a temperature of more than 900 °C were achieved in the impact structure.

The gas-slag-matte-tridymite equilibria in the Cu–Fe–O–S–Si system at 1200°C have been experimentally studied. An improved experimental technique was used, which includes high temperature equilibration of sulfide-oxide mixtures on silica substrates at p(SO2) = 0.6 atm, preservation of the equilibrium phases by rapid quenching, and direct compositional analysis of the phases using microanalysis techniques. The new data have enabled the effects of sulfur dioxide partial pressure between 0.1 and 0.6 atm on the equilibria to be accurately determined. Whilst, for a given matte grade, the dissolved copper in slag is not sensitive to sulfur dioxide partial pressure, the Fe/SiO2 in slag in equilibrium with tridymite was found to increase with increasing p(SO2). This latter observation has implications for fluxing practice in industrial copper smelting operations. [ABSTRACT FROM AUTHOR]

Experimental measurements have been made of the compositions of slag, matte and tridymite phases in chemical equilibrium in the Cu-Fe-O-S-Si system at 1300°C, p(SO2) = 0.25 atm and selected oxygen partial pressures. The high temperature equilibration experiments were conducted using silica substrates under controlled CO-CO2-SO2-Ar gas atmospheres. The resulting phases obtained from the equilibrations were retained at room temperature through rapid quenching of the samples. The condensed phase compositions from the equilibrium experiments were measured by Electron Probe X-ray Microanalysis (EPMA). The data obtained in the present study, combined with those from previous studies, have enabled the liquidus slag temperature to be accurately described as a function of Fe/SiO2 ratio at p(SO2) = 0.25 atm for temperatures between 1200 and 1300oC and mattes containing from ∼44 to ∼ 78 wt pct Cu. [ABSTRACT FROM AUTHOR]

High thermal conductivity dense silica bricks have the higher thermal conductivity than ordinary silica bricks, which is conducive to the realization of energy saving and emission reduction in the iron and steel industry. The performance of ordinary silica bricks and high thermal conductivity dense silica bricks was compared, and the high thermal conductivity mechanism was analyzed. The results show that (1) compared with ordinary silica bricks, high thermal conductivity dense silica bricks have the characteristics of higher thermal conductivity, lower apparent porosity, higher tridymite content, higher compressive strength, and higher thermal expansion; (2) by increasing the tridymite content and reducing the porosity, the close packing of honeycomb α-tridymite improves the density and continuity of the SiO2 frame structure of the silica bricks, and the larger area perpendicular to the heat transfer direction improves the thermal conductivity of the bricks; (3) the densification of the silica bricks also increases the thermal expansion of the bricks, but they still meet the standard requirements. [ABSTRACT FROM AUTHOR]

Opaline mudstone (OM) composed of opal-CT (SiO2·nH2O) has high potential use as a cesium (Cs) adsorbent, due to its high specific surface area (SSA). The objective of this study was to investigate the Cs adsorption capacity of chemically activated OM and the adsorption mechanism based on its physico-chemical properties. We used acid- and base-activation methods for the surface modification of OM. Both acid- and base- activations highly increased the specific surface area (SSA) of OM, however, the base-activation decreased the zeta potential value more (− 16.67 mV), compared to the effects of acid-activation (− 6.60 mV) or non-activation method (− 6.66 mV). Base-activated OM showed higher Cs adsorption capacity (32.14 mg/g) than the others (acid: 12.22 mg/g, non: 15.47 mg/g). These results indicate that base-activation generates pH-dependent negative charge, which facilitates Cs adsorption via electrostatic attraction. In terms of the dynamic atomic behavior, Cs cation adsorbed on the OM mainly exist in the form of inner-sphere complexes (IS) containing minor amounts of water molecules. Consequently, the OM can be used as an effective Cs adsorbent via base-activation as an economical and simple modification method. [ABSTRACT FROM AUTHOR]

Silica refractory has excellent high-temperature performance, but its apparent porosity is relatively high. In this work, samples obtained before and after creep testing of silica brick (1550 °C, 50 h), from used silica checker brick (existing only tridymite and amorphous) and from used dome brick (existing only cristobalite and amorphous) were investigated using a three-dimensional structure model based on X-ray computed tomography (CT). The results show that the porosity of silica brick was high but consisted mainly of interconnected pores, with a very small proportion of closed pores (smaller after long-term use). During the use of silica brick, the morphology and phase transformation caused large particles to rupture, and the mineralizer became liquid at high temperature. The broken particles and interconnected pores provided channels for the migration of the liquid in the brick at high temperature. The silica brick presented a homogeneous ceramic structure during long-term operation. Tridymite or cristobalite presented a solid frame leading to an excellent creep performance of the silica brick (the creep rate of the checker brick was −0.16% at 1550 °C for 50 h). Results were discussed, compared with literature and a model for the transformation of the silica brick from a refractory structure to a homogeneous ceramic structure was established in this paper. [ABSTRACT FROM AUTHOR]

This article provides data on cristobalite and tridymite from the Arsenatnaya active fumarole of the Tolbachik volcano, Kamchatka, Russia. The minerals occur in associations with fumarolic sylvite, sanidine, cassiterite, hematite, pseudobrookite, johillerite, tilasite, and badalovite. Fumarolic cristobalite is tetragonal (α-modification); the unit-cell parameters for one sample are: а = 4.975 (7) Å, с = 6.944 (13) Å, and V = 171.89 Å3. There are two types of tridymite, that is, monoclinic (MC) and orthoorthorhombic (PO-10), in the Arsenatnaya fumarole. The unit-cell parameters of these tridymite modifications are: a = 18.553 (5) Å, b = 5.006 (1) Å, с = 25.952 (10) Å, β = 117.68 (2)°, V = 2134.3 (11) Å3 (MC); a = 9.941 (2) Å, b = 17.165 (4) Å, с = 82.362 (18) Å, and V = 14053.4 (29) Å3 (PO-10). Mineral assemblages of cristobalite and tridymite indicate high-temperature formation conditions of these minerals not lower 450–500°С with considerable participation of HCl and HF in process of basalt alteration by fumarolic gas. The surrounding basalt was a source of silicon. This element was probably transported in the form of SiX4, where X = F, Cl. [ABSTRACT FROM AUTHOR]

Textures and whole-rock chemistry, as well as mineral composition, were analyzed in megaspherulites (high-temperature crystallization domains [HTCDs]) that formed in different geographical and geotectonic contexts and during different geological periods (Silver Cliff, CO, USA—Paleogene; El Quevar, Argentina—Miocene; Meissen Volcanic Complex, Germany—Late Carboniferous). All of these megaspherulites have formed exclusively in rhyolitic lava, and their mineral composition is dominated by K-feldspar (sanidine) and SiO2 phases (quartz, cristobalite, tridymite). All megaspherulites represent composite HTCDs, comprising three zones: inner domain (ID), outer domain (OD), and a marginal domain (MD). Early evolution of megaspherulites is characterized by either central cavities and sector- to full-sphere spherulites or dendritic quartz-sanidine domains. The latter consist of bundles of fibrils each radiating from a single point reflecting relatively high growth rates. A common feature of OD and MD of all three megaspherulite occurrences is autocyclic banding. It mainly comprises fibrous (≤ 100 μm length), radially oriented sanidine and quartz, which formed at a temperature close to glass transition temperature (Tg). The termination of megaspherulite growth is marked by centimeter-sized sector-sphere spherulites on the surface. Megaspherulite formation requires limited nucleation, which is probably related to the low phenocryst content of the hosting lava. Latent heat from overlying crystallizing lithoidal rhyolite maintained low undercooling conditions keeping nucleation density low and facilitating high diffusion and growth rates. Late megaspherulite growth and its termination under low diffusion conditions is controlled by cooling close to Tg. Calculations based on literature data suggest that the megaspherulite growth presumably lasted less than 60 years, perhaps 30 to 40 years. [ABSTRACT FROM AUTHOR]

In August 2015, the Curiosity Mars rover discovered tridymite, a high‐temperature silica polymorph, in Gale crater. The existing model for its occurrence suggests erosion and detrital sedimentation from silicic volcanic rocks in the crater rim or central peak. The chemistry and mineralogy of the tridymite‐bearing rocks, however, are not consistent with silicic volcanic material. Using data from Curiosity, including chemical composition from the Alpha Particle X‐ray Spectrometer, mineralogy from the CheMin instrument, and evolved gas and isotopic analyses from the Sample Analysis at Mars instrument, we show that the tridymite‐bearing rocks exhibit similar chemical patterns with silica‐rich alteration halos which crosscut the stratigraphy. We infer that the tridymite formed in‐place through hydrothermal processes and show additional chemical and mineralogical results from Gale crater consistent with hydrothermal activity occurring after sediment deposition and lithification. Plain Language Summary: In August 2015, the Curiosity Mars rover discovered tridymite, an unexpected mineral phase, in Gale crater. The existing model for its occurrence suggests erosion and deposition from silicon‐rich volcanic rocks in the crater rim or central peak. The chemistry and mineralogy of the tridymite‐bearing rocks, however, are not consistent with silicon‐rich volcanic material. Using data from Curiosity's instrument suite, we show that the tridymite‐bearing rocks exhibit similar chemical patterns with silicon‐rich alteration zones which crosscut the layered sediments. We infer that the tridymite formed in‐place through hydrothermal processes and show additional chemical and mineralogical results from Gale crater consistent with hydrothermal activity occurring after sediment deposition and lithification. Key Points: Chemical and mineralogical data from the Curiosity Mars rover suggest a history of hydrothermal alteration within Gale craterSilica‐rich alteration halos and tridymite‐bearing deposits exhibit similar chemical signatures, suggesting related formation processesWe propose the in situ formation of tridymite through hydrothermal processes as an alternative to a detrital origin [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Development of silica microcrystals is inferred from morphology and local probe data. • Cristobalite and tridymite can nucleate from iron oxide not requiring alkali metals. • Morphology of silica microcrystals can hide intergrowths and paramorphic phases. • Cristobalite hexagonal plates and dendrites show a tridymite external growth front. Different methods have been historically used to identify silica-polymorph microcrystals in various contexts. However, in the existing literature there is a substantial lack of correlation between local probe analytical data and the corresponding images showing crystal morphologies. Here we demonstrate that such correlation is attainable through an approach based on the characterization of samples prepared as polished thin sections combining optical microscope images with local probe techniques (synchrotron through-the-substrate X-ray microdiffraction and confocal micro-Raman). We report the characterization of different morphologies of silica microcrystals embedded in lead glazes from glazed pottery produced in Jouques (France) in the mid-19th century. Among the eight identified morphologies, are worthy of note cristobalite-coated quartz, paramorphic quartz after cristobalite, cristobalite-tridymite intergrowths or cristobalite twinned crystals. Elusive tridymite has been identified and mapped using μ-Raman and locates predominantly at the borders of some morphologies suggesting a growth front of tridymite that turns to cristobalite. [ABSTRACT FROM AUTHOR]

The purpose of this study was to find an alternative application for chrysotile asbestos, given that there is a complete structure of extraction and production of this class of serpentine minerals, but its use is banned for many applications. The idea was to obtain a compound that could immobilize phosphate by triggering a reaction between the magnesium oxide and hydroxide contained in the mineral, without causing phosphate leaching. To this end, chrysotile (Mg3SiO5(OH)4) was treated with phosphoric acid (H3PO4) in a molar ratio of 1:3 in an aqueous medium at 85 °C until the solvent evaporated, resulting in two different solid compounds, which were prepared in a similar manner. The first compound (cri/H3PO4 1:3)1, was obtained by rinsing and then heat-treating it at 150 °C for 6 h, while the second one, (cri/H3PO4 1:3)2, was rinsed after the heat treatment. Compound (cri/H3PO4 1:3)1 underwent partial leaching, while compound (cri/H3PO4 1:3)2 showed a mass increase of 48%, with the formation of crystalline magnesium pyrophosphate mixed with amorphous SiO2. The latter compound adsorbed N–NH3 at pH 10, following the pseudo-first-order model (activation energy = 8329 ± 1696 J mol−1). Equilibrium experiments, which were performed following Hill's sigmoidal type S2 isotherm model, indicated that the adsorption phenomenon was governed by two processes, i.e., complexation up to the inflection point (KH between 10.0 mg L−1 at 40 °C and 13.6 mg L−1 at 25 °C) followed by adsorption. The qmax varied from 18.0 to 19.6 mgN g−1 and the adsorbent was reusable, maintaining its initial adsorbent capacity during its first reuse. This material, which was tested on real effluents, presented a N–NH3 removal rate similar to that shown by the test solutions. The treatment of chrysotile with H3PO4 conducts it to a composite that adsorbs ammoniacal nitrogen at pH 10 and it is reusable maintaining the adsorption capacity.

Structural changes in tridymite have been investigated by molecular dynamics simulation. Two thermal processes were carried out, one cooling from the high-temperature hexagonal structure of tridymite (HP-tridymite) and the other heating from the low-temperature monoclinic structure of tridymite (MX1-tridymite). The former process showed that HP, LHP (low-temperature hexagonal structure), OC (orthorhombic structure with C2221 symmetry) and OP (orthorhombic structure with P212121 symmetry)-like structures appeared in sequence. In contrast, the latter process showed that MX1, OP, OC, LHP and HP-like structures appeared in sequence. Detailed analysis of the calculated structures showed that the configuration underwent stepwise changes associated with several characteristic modes. First, the structure of HP-tridymite determined from diffraction experiments was identified as a time-averaged structure in a similar manner to β-cristobalite, thus indicating the important role of floppy modes of oxygen atoms at high temperature – one of the common features observed in silica crystals and glass. Secondly, the main structural changes were ascribed to a combination of distortion of the six-membered rings in the layers and misalignment between layers. We suggest that the slowing down of floppy oxygen movement invokes the multistage emergence of structures with lower symmetry on cooling. This study therefore not only reproduces the sequence of the main polymorphic transitions in tridymite, except for the appearance of the monoclinic phase, but also explains the microscopic dynamic structural changes in detail.

Elastic and anelastic properties of a ceramic sample of elasticoluminescent SrAl2O4:Eu have been characterized as a function of temperature by resonant ultrasound spectroscopy. Both the bulk (K) and shear (G) moduli show changes attributable to the influence of the P6322→P63 (3A)→P21 sequence of structural phase transitions. Softening of K and stiffening of G at the P6322→P63 (3A) transition (Tc≈1135 K) is consistent with weak strain/order parameter coupling and tricritical character. In marked contrast, the first order P63 (3A)→P21 transition near 930 K is accompanied by stiffening such that G is ∼50% larger at room temperature than the value for a P6322 structure extrapolated directly from high temperatures and K is ∼15% larger. Softening of G at high temperatures is consistent with the existence of a soft acoustic mode. Both the P63 (3A) and P6322 phases show an increasing acoustic dissipation with increasing temperature and there is an additional peak in the dissipation behavior below ∼650 K. Landau theory has been used to analyze the overall strain and elastic behavior of SrAl2O4:Eu. The stability of the P21 structure is considered in terms of coupling between order parameters with Γ6 and M2 symmetry, though it could also be stabilized by pairwise coupling of order parameters corresponding to irreps Γ4+M2, Γ4+M3, Γ6+M3, and M2+M3. Twin walls in this material should have interesting properties, which are quite distinct from those of the bulk material and could contribute differently to the elasticoluminescent properties. [ABSTRACT FROM AUTHOR]

Intergrowth oxides, like Aurivillius, Ruddlesden–Popper phase, comprise functional layers and exhibit interesting physical properties. The hitherto known intergrowth structures mainly were composed of closed‐packing of oxygen ions, and it is very challenging to develop new types of intergrowth structures. We proposed the possible match between the tridymite and grossite, both of which are purely tetrahedra‐based structures. We synthesized Ca2PbGa8O15 ((Ca0.5Pb0.5Ga2O4)2(CaGa4O7)) and its structure was solved by ab‐initio method. Pb2+ is vitally important to stabilize this first example of tetrahedra‐based intergrowth oxide. The appropriate size difference between Pb2+ and Ca2+ causes the layered type cationic ordering, and reduced the thermodynamic potential, in addition, the high hybridization between Pb 6s6p and O 2p orbitals further consolidate the covalency of the tetrahedra‐base framework. [ABSTRACT FROM AUTHOR]

Abstract Phase equilibria of the binary PbO-ZnO and ternary PbO-ZnO-SiO 2 systems have been experimentally investigated at 1033–1898 K (760–1625 °C) for oxide liquid in equilibrium with air and solid oxide phases: tridymite or cristobalite (SiO 2), willemite (Zn 2 SiO 4), zincite (ZnO), larsenite (PbZnSiO 4) and lead-zinc melilite (Pb 2 ZnSi 2 O 7) covering the ranges of concentrations not studied before. High-temperature equilibration on primary phase or inert metal (platinum) substrates, followed by quenching and direct measurement of the Pb, Zn and Si concentrations in the phases with the electron probe X-ray microanalysis (EPMA) has been used. Liquidus phase equilibrium data is essential for the development of the thermodynamic model. [ABSTRACT FROM AUTHOR]

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. Anisotropic atomic displacement parameters of orthorhombic tridymite and tetragonal cristobalite can be determined accurately using the combined methods of powder XRD and pair distribution function analysis. [ABSTRACT FROM AUTHOR]

Abstract The Mars Science Laboratory's Chemistry and Camera (ChemCam) instrument suite on-board the Curiosity rover has analysed ∼1200 sedimentary targets during the mission up to sol 1482. These targets have included sedimentary rock, diagenetic features (e.g., fracture-associated alteration halos, mineral veins, nodules, and erosion resistant raised ridges), active aeolian fines, soils and float. We have isolated ChemCam geochemical trends relating to diagenetic features and alteration products from those of the sedimentary rock in order to identify the compositional characteristics of Gale crater's sediment source regions. The effects of grain size variation on sedimentary unit geochemistry have been taken into account by grouping and analysing geological units according to grain size. With obvious diagenetic features removed from the database, and predominately isochemical aqueous alteration inferred for the Mt Sharp Group samples, we propose that source region composition is a stronger source of geochemical change between the Bradbury and Mt Sharp Groups than open-system alteration. Additionally, a lack of correlation between the Chemical Index of Alteration (CIA) values and SiO 2 , MgO or FeO T indicates that the slight increase in chemical weathering of the Mt Sharp Group sediments was insufficient to overprint sediment source compositional signatures. This has led to the identification of five unique igneous endmember compositions which we hypothesise to have contributed to Gale crater's stratigraphic record. These endmembers are: (1) a subalkaline basalt, compositionally similar to the tholeiitic Adirondack Class basalts of Gusev crater, and dominant within the finer grained units up to the base of Mt Sharp; (2) a trachybasalt, mostly identified within conglomerate units from the Darwin waypoint to the base of Mt Sharp; (3) a potassium-rich volcanic source, determined from strong potassium enrichment and a high abundance of sanidine that is most dominant in the fluvial sandstones and conglomerates of the Kimberley formation; (4) a highly evolved, silica-rich igneous source that correlates with the presence of tridymite, and is recorded in the lacustrine mudstone of Mt Sharp's Marias Pass locality; and, (5) a fractionated, relatively SiO 2 -rich subalkaline basalt, seen to have influenced the composition of mudstone deposited in the lower part of the Mt Sharp Group. Endmembers (1), (2), (3), and (4) have previously been identified at specific waypoints along the rover's traverse, but we show that their influence extends throughout Gale's stratigraphic record. The occurrence of detected endmembers is also strongly correlated with stratigraphic position, which suggests changing sediment source regions with time. We conclude that Gale sediment provenances were much more varied than suggested by the largely homogenous, globally-distributed Martian basalt inferred from orbit, showing that complex magmatic assemblages exist within the ancient highland crust surrounding Gale. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract BaAl 2 O 4 is a stuffed tridymite used as a long-lasting phosphor. The thermoluminescence of BaAl 2 O 4 prepared by solution-combustion is reported. Analysis of the sample using X-ray diffraction shows that it formed as a single phase compound with a hexagonal structure following annealing at 1200 °C. A broad photoluminescence emission band between 300 and 650 nm was detected due to excitation at 248 nm. The phosphor showed a natural TL peak at 102 °C for measurement at 1 oCs−1 and, when beta irradiated to 100 Gy, two broad peaks at 123 and 318 °C also for heating at 1 oCs−1. The analysis of the main glow peak at 123 °C suggests that it is a combination of several collocated peaks, that is, peaks embedded within each other. We resolved four such components labelled peaks 1 to 4. The thermoluminescence decreases with heating rate in a way consistent with thermal quenching whose activation energy was determined as ∼0.65eV using peak 3. Interestingly, this value of the activation energy for thermal quenching for BaAl 2 O 4 , a stuffed derivative of silica, is similar to literature values for quartz (a silica), suggesting that the recombination centre in the two cases may be similar. Highlights • Thermoluminescence (TL) of BaAl 2 O 4 , a stuffed tridymite, is reported. • The TL glow curve has peaks at 123 and 318 °C for heating at 1 oCs−1. • The main peak at 123 °C studied comprises at least four collocated peaks. • The TL is affected by thermal quenching with activation energy ∼0.65eV. • Similarities of the stuffed tridymite to quartz, a silica, are pointed out. [ABSTRACT FROM AUTHOR]

A Raman study of a Sèvres 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. Na 0.4 K 0.1 Ca 0.5 Pb 4 (AsO 4 ) 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. [ABSTRACT FROM AUTHOR]

We report for the first time the complete set of elastic coefficients of the mechanoluminescent material SrAl2O4 stuffed tridymite determined by the first-principles plane-wave pseudopotential total energy method. We calculate other mechanical properties (i.e., bulk modulus, Young’s modulus, and Poisson’s ratio) of this material from the elastic coefficients determined, and compare them with the corresponding experimental and calculated results of typical oxides, indicating that SrAl2O4 stuffed tridymite is a relatively soft ceramic oxide. In addition, we investigate the crystal structure of SrAl2O4 stuffed tridymite at elevated hydrostatic pressures up to 10 GPa and confirm anisotropic deformation in the SrAl2O4 lattice. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The use of low-temperature quartz modifications in pulverized form creates additional risks in the manufacture of molds, since polymorphic transformations decrease their crack resistance. In practice, individual layers of the shell wall or the mold as a whole often crack and even disintegrate. In many casting shops, the lining is preliminarily roasted. That may somewhat improve the consequences of polymorphic transformations in the quartz, but steady heating of the molds through the filler to reduce the odds of cracking prolongs the process and increases the energy consumption. The best-known approach to minimizing the cracking and disintegration of shell molds on roasting is to replace the filler: instead of quartz dust, it is possible to use disperse quartz sand of polyfractional composition, sillimanite, pulverized alumosilicate, globular corundum, or fused quartz. However, those materials are expensive and their use is inconsistent with the requirements of resource conservation in casting. A possible material might be silica-based ceramic cullet from the shells used in steel and aluminum investment casting. At present, such cullet is not recycled. It is dumped or used as filler in the flasks used for shaping shells. Chemical and phase analysis shows that the ceramic cullet formed after removing the steel and aluminum castings contains not only quartz and high-temperature tridymite and cristobalite phases (the base) but also 5-10% iron and iron scale and 3-5% aluminum and its oxides. The use of such ceramic cullet in shell production eliminates repeated polymorphic transformation of the quartz in roasting and sealing the molds, which would change the volume, density, and crystal lattice of the material. That increases the crack resistance and strength of the shells and minimizes the waste of the castings produced. Residual iron and aluminum and their oxides improve the utility of the mold. Tests of this recycling method in production conditions confirm its effectiveness. [ABSTRACT FROM AUTHOR]

Silica nanoparticles (SiO 2 NPs) have found applications in many advanced areas. In this study, we report a powder technology route as a low cost, simple and safe method for the fabrication of SiO 2 NPs. It is a promising method as it has high throughput (91.7%) for different applications. The SiO 2 NPs were prepared by an ultra-sonication technique and an alkali wet chemical etching process (one step), starting from commercial silicon powder. The main factors that affect the production of crystalline (quartz, cristobalite, and tridymite) and amorphous SiO 2 NPs from crystalline silicon are the etching solution (KOH) concentration and the sonication time. The particle size of the SiO 2 NPs is inversely related to the sonication time for 3 wt % KOH but directly proportional to the sonication time for 6 wt % KOH. The synthesized nanoparticles were systematically characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy and scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Abstract We demonstrate a new modulation for a high-temperature polymorph of BaSrFe 4 O 8 via synchrotron powder X-ray diffraction and transmission electron microscopy (TEM) experiments. Although the powder X-ray diffraction pattern was successfully analyzed using a structure model of space group Pnna , an unusually large isotropic atomic displacement parameter ( U iso ) was observed for the O1 atom. A split atom model that was applied to the O1 site and the adjacent Ba/Sr site, both of which are on the two-fold axis along the c -axis, indicated that positional disorder occurred in these atoms along the c -axis. The electron diffraction pattern and high-resolution TEM observations combined with the structure refinements revealed an incommensurate structure with a modulation vector q = 0.4270 ( 1 ) a * and a displacement vector perpendicular to the a -axis, which gave rise to the large U iso value of the O1 atom. The modulation observed in this study may be a signature of structural instability, which has commonly been discussed in the stuffed tridymite-type oxides. Graphical abstract The modulation of q = 0.4270 ( 1 ) a * observed in the high-temperature polymorph of the stuffed tridymite-derivative BaSrFe 4 O 8. fx1 Highlights • The crystal structure of the high-temperature polymorph of BaSrFe 4 O 8 was reinvestigated via synchrotron powder X-ray diffraction and transmission electron microscopy. • The high-temperature polymorph of BaSrFe 4 O 8 exhibits a modulation of q = 0.4270 ( 1 ) a * . • The modulation observed in this study may be a signature of structural instability, which has commonly been discussed for stuffed tridymite-type oxides. [ABSTRACT FROM AUTHOR]

To assist in the optimization of copper smelting and converting processes, accurate new measurements of the phase equilibria of the Cu-Fe-O-S-Si system have been undertaken. The experimental investigation was focused on the characterization of gas/slag/matte/tridymite equilibria in the Cu-Fe-O-S-Si system at 1523 K (1250 °C), P(SO2) = 0.25 atm, and a range of P(O2)s. The experimental methodology, developed in PYROSEARCH, includes high-temperature equilibration of samples on substrate made from the silica primary phase in controlled gas atmospheres (CO/CO2/SO2/Ar) followed by rapid quenching of the equilibrium condensed phases and direct measurement of the phase compositions with electron-probe X-ray microanalysis (EPMA). The data provided in the present study at 1523 K (1250 °C) and the previous study by the authors at 1473 K (1200 °C) has enabled the determination of the effects of temperature on the phase equilibria of the multicomponent multiphase system, including such characteristics as the chemically dissolved copper in slag and Fe/SiO2 ratio at silica saturation as a function of copper concentration in matte. The new data will be used in the optimization of the thermodynamic database for the copper-containing systems. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The majority of primary pyrometallurgical copper making processes involve the formation of two immiscible liquid phases, i.e., matte product and the slag phase. There are significant gaps and discrepancies in the phase equilibria data of the slag and the matte systems due to issues and difficulties in performing the experiments and phase analysis. The present study aims to develop an improved experimental methodology for accurate characterisation of gas/slag/matte/tridymite equilibria in the Cu-Fe-O-S-Si system under controlled atmospheres. The experiments involve high-temperature equilibration of synthetic mixtures on silica substrates in CO/CO/SO/Ar atmospheres, rapid quenching of samples into water, and direct composition measurement of the equilibrium phases using Electron Probe X-ray Microanalysis (EPMA). A four-point-test procedure was applied to ensure the achievement of equilibrium, which included the following: (i) investigation of equilibration as a function of time, (ii) assessment of phase homogeneity, (iii) confirmation of equilibrium by approaching from different starting conditions, and (iv) systematic analysis of the reactions specific to the system. An iterative improved experimental methodology was developed using this four-point-test approach to characterize the complex multi-component, multi-phase equilibria with high accuracy and precision. 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-Ca-Mg), multi-phase (gas/slag/matte/metal/solids) systems with minor elements (Pb, Zn, As, Bi, Sn, Sb, Ag, and Au). [ABSTRACT FROM AUTHOR]

Experimental studies were undertaken to determine the gas/slag/matte/tridymite equilibria in the Cu-Fe-O-S-Si system at 1473 K (1200 °C), P(SO) = 0.25 atm, and a range of P(O)'s. The experimental methodology involved high-temperature equilibration using a substrate support technique in controlled gas atmospheres (CO/CO/SO/Ar), rapid quenching of equilibrium phases, followed by direct measurement of the chemical compositions of the phases with Electron Probe X-ray Microanalysis (EPMA). The experimental data for slag and matte were presented as a function of copper concentration in matte (matte grade). The data provided are essential for the evaluation of the effect of oxygen potential under controlled atmosphere on the matte grade, liquidus composition of slag and chemically dissolved copper in slag. The new data provide important accurate and reliable quantitative foundation for improvement of the thermodynamic databases for copper-containing systems. [ABSTRACT FROM AUTHOR]