Search

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]

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]

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]

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]

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]

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]

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]

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]

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]

Temperature-induced phase transitions for stuffed tridymite A Ga 2 O 4 ( A = Sr, Ca) were investigated by experimental and theoretical calculations. A simple annealing of SrCO 3 and Ga 2 O 3 led to the formation of γ-SrGa 2 O 4 ( P 2 1 /n ) below 1200 °C, and transform to β-SrGa 2 O 4 ( P 2 1 /c ) when heated at 1200 °C. A similar phenomenon was found for CaGa 2 O 4 , and the temperature boundary between α-CaGa 2 O 4 ( Pna 2 1 ) and the high temperature polymorph β-CaGa 2 O 4 ( P 2 1 /c ) was about 1350 °C. Rietveld refinements provided detailed structural information for these polymorphs and suggest that the driving force of these phase transitions is the under-bonded nature of the alkaline earth cations. In other words, the need of larger space for Sr 2+ /Ca 2+ in the high temperature β-phase forces the 6-membered-ring channel expand through increasing the Ga-O-Ga angles. Density functional theory calculations proved the formation energies for γ-SrGa 2 O 4 and α-CaGa 2 O 4 were both lower than their high temperature β-polymorphs, in accordance with the experimental observations. [ABSTRACT FROM AUTHOR]

Synthesis and thermomechanical characterization of polyethylene glycol-silica cristobalite composites have been successfully performed. Commercial Polyethylene glycol (PEG) 4000 and natural-silica-sand-derived cristobalite (SiO) powders were used in this research. The cristobalite ceramic powder was produced by a coprecipitation method using silica sand from Tanah Laut, South Kalimantan as the raw material. XRD data analysis for the cristobalite powder showed that it contained 98.8 wt% cristobalite and 1.2 wt% tridymite - both are polymorphs of silica. The PEG-cristobalite composition was varied in the composites at PEG weight fraction of 100, 80, 60 and 40 %. PEG and cristobalite dry powders were simply mixed and then uniaxially pressed before a heat treatment at 50 °C to form dense composite prior to characterization. Further FTIR and XRD data analyses for the densed samples showed the success of the formation of the composite. The thermomechanical properties was characterised using Dynamic mechanical analysis (DMA) instrument with shear mode. In general, at all measurement temperatures, the storage modulus ( G') of the composites was significantly improved with the addition of cristobalite, e.g. its values for 60 % cristobalite sample was 13 times that of the pure PEG sample. The pure samples showed a rubbery plateau behaviour which was not found in the composite samples. It was also found that by increasing the amount of cristobalite, the glassy transition temperature ( T ) increase from 56 °C for the pure and 68 °C for the 60 % cristobalite samples respectively. [ABSTRACT FROM AUTHOR]

Pink-orange crystals of a composition within the ferri-obertiite compositional space were found in vesicles in a pale beige silicate vein found from a basalt quarry at Mount Rothenberg, Eifel district, Germany. Associated minerals are potassic feldspar, alpha quartz paramorphic after beta quartz, eifelite (the second occurrence after the Caspar quarry at Bellerberg volcano, Eifel region), tridymite, rutile, roedderite and other amphiboles. The ideal formula of ferri-obertiite is ANaBNa2C(Mg3Fe3+Ti)TSi8O22WO2; the empirical formula derived for the holotype specimen from Mount Rothenberg from the results of electron-microprobe analysis and single-crystal structure refinement is A(Na0.76K0.22)Σ0.98B(Na1.61Ca0.35Mn2+0.04)Σ2.00C(Mg3.58Mn2+0.11Fe3+0.62Ti4+0.66Cr3+0.01Zn0.01Ni0.01)Σ5.00T(Si7.82Ti4+0.12Al0.06)Σ8.00O22W[O1.26F0.55(OH)0.19]Σ2.00. The unit-cell dimensions are a = 9.7901(7), b = 17.9354(13), c = 5.2892(4) Å, β = 104.142(2)°, V = 900.58 (11) Å3. The space group is C2/m, Z = 2. Ferri-obertiite is biaxial (+), with α = 1.664, β = 1.680, γ = 1.722, all ±0.002 and 2V (meas.) = 66.4(3)°, 2V (calc.) = 64.7°. The strongest eight reflections in the powder X-ray pattern [d values (in Å), I, (hkl)] are: 2.704, 100, (151); 3.116, 76, (310); 3.388, 72, (131); 8.931, 72, (110); 2.529, 67, (2̅02); 2.583, 39, (061); 2.160, 38, (261); 3.260, 37, (240). Both the mineral and the name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2015-079); the rock specimen has been deposited at the Museo di Mineralogia, Dipartimento di Scienze della Terra e dell'Ambiente, Università degli Studi di Pavia, under the code 2015-02. [ABSTRACT FROM AUTHOR]

Treatment of alumina bound MTW zeolite extrudates with H 3 PO 4 causes conversion of the binding matrix from Al 2 O 3 to tridymite AlPO 4 and we show the crystalline AlPO 4 coats the surface of the MTW zeolite crystals. In this transformation, the surface area and pore volume of the catalyst decrease precipitously, but the MTW crystallinity remains largely intact. Similar, but less specific behavior was observed when using NH 4 H 2 PO 4 as the phosphorus source. After phosphate treatment, the interaction of P with zeolite framework Al is a major effect reducing acidity of the zeolite. These two effects allow for selectivity control during oligomerization of propylene and butenes. Increasing the phosphorus content of the catalyst from 0 to 10 wt% causes a decrease in the amount of liquid product heavier than gasoline from 15 wt% to 3 wt%. Concomitantly, the selectivity to triisobutylenes increases to almost 50%. Thus we attain catalytic performance similar to traditional solid phosphoric acid catalyst, but with a significant yield of triisobutylenes. [ABSTRACT FROM AUTHOR]

Through use of in situ Raman spectroscopy and single-crystal/powder X-ray diffraction, we resolve the “C0” phase structure discovered recently in the H2 + H2O system. This phase forms at ∼400 MPa and 280 K with the nominal composition (H2O)2H2 and three formula units per unit cell. The hexagonal structure is chiral, consisting of interpenetrating spiral chains of hydrogen-bonded water molecules and rotationally disordered H2 molecules, and shows topological similarities with the mineral quartz. Like other clathrate hydrates and forms of ice, the protons of H2O molecules within C0 are disordered. The large zeolite-like channels accommodate significant amounts of hydrogen (5.3% by weight) in a unique hydrogen-bonded lattice, which might be applicable to the thermodynamic conditions found on icy planetary bodies. [ABSTRACT FROM AUTHOR]

Red loess and black-rice husk ash (B-RHA) composite was investigated for its compressive strength. The loess was collected in Khon Kaen University and sieved through mesh No.60. Clay components of red loess were enhanced up to 9% by gravitational settling. This oriented loess was then mixed with black-rice husk ash (B-RHA) at a dry solid weight ratio of 1:1. The mixture was casted in a cylindrical mold with a diameter and height of 1.7 cm and 3.4 cm, respectively. The green bodies were fired under different fixed temperatures of 900, 1000, 1100, and 1200°C. Tridymite and cristobalite were dominant silica polymorphism found under the applied firing temperatures especially at 1200°C. Uniaxial compression tests were performed on un-oriented loess, unmixed oriented loess, and oriented loess/B-RHA composite. The oriented loess was found to be more rigid than the un-oriented loess and the loess composite. The elastic modulus of the oriented loess was found to be as high as 4 GPa, which is twice as much compared to that of the un-oriented loess at the same firing temperature of 1200°C. It can be surmised that the structural network of red ferric oxide-clay loess stabilizes the strength of the material when finegrained silica is reduced, resulting in a higher strength of loess after orientation. Fired bodies of loess/B-RHA composite showed a significant decrease in its elastic modulus which is approximately 45 times less compared to that of the unmixed oriented loess. This is a result of an increased amount of voids of the composite due to the incineration of B-RHA. In addition to the reduction of its elastic modulus and compressive strength, the composite also shows extreme brittleness. However, the relationship of both yield strength and elastic modulus of the composite as a function of temperature shows a strong linear behavior in contrast to that of the un-oriented loess and unmixed oriented loess. It can be inferred that B-RHA in the composite decomposes into voids at a similar rate that quartz transforms to higher phases during the firing process. [ABSTRACT FROM AUTHOR]

The effect of repeated nonisothermal heating to 1500°C on shrinkage and crystallization of quartz ceramic with added alkali (0.5% NaO) and monolithic fuzed quartz is studied. Marked (up to 10%) tridymite formation is detected in specimens with added alkali and with a predominant cristobalite content. Some properties are provide for specimens after single-stage heating to 1500°C. Depending on additive content specimens have open porosity of 6 - 9% and ultimate strength in compression of 130 - 185 MPa. [ABSTRACT FROM AUTHOR]

Tridymite, a low-pressure, high-temperature (>870 °C) SiO2 polymorph, was detected in a drill sample of laminated mudstone (Buckskin) at Marias Pass in Gale crater, Mars, by the Chemistry and Mineralogy X-ray diffraction instrument onboard the Mars Science Laboratory rover Curiosity. The tridymitic mudstone has ~40 wt.% crystalline and ~60 wt.% X-ray amorphous material and a bulk composition with ~74 wt.% SiO2 (Alpha Particle X-Ray Spectrometer analysis). Plagioclase (~17 wt.% of bulk sample), tridymite (~14 wt.%), sanidine (~3 wt.%), cation-deficient magnetite (~3 wt.%), cristobalite (~2 wt.%), and anhydrite (~1 wt.%) are the mudstone crystalline minerals. Amorphous material is silica-rich (~39 wt.% opal-A and/or high-SiO2 glass and opal-CT), volatile-bearing (16 wt.% mixed cation sulfates, phosphates, and chlorides−perchlorates−chlorates), and has minor TiO2 and Fe2O3T oxides (~5 wt.%). Rietveld refinement yielded a monoclinic structural model for a well-crystalline tridymite, consistent with high formation temperatures. Terrestrial tridymite is commonly associated with silicic volcanism, and detritus from such volcanism in a "Lake Gale" catchment environment can account for Buckskin's tridymite, cristobalite, feldspar, and any residual high-SiO2 glass. These cogenetic detrital phases are possibly sourced from the Gale crater wall/rim/central peak. Opaline silica could form during diagenesis from high-SiO2 glass, as amorphous precipitated silica, or as a residue of acidic leaching in the sediment source region or at Marias Pass. The amorphous mixed-cation salts and oxides and possibly the crystalline magnetite (otherwise detrital) are primary precipitates and/ or their diagenesis products derived from multiple infiltrations of aqueous solutions having variable compositions, temperatures, and acidities. Anhydrite is post lithification fracture/vein fill. [ABSTRACT FROM AUTHOR]

The heat capacity measurements of the crystalline phosphate CsCoPO 4 with a β-tridymite structure were performed between T = (6 and 650) K. Phase transitions were found at T = (313.40, 486.9 and 514.4) K. They correspond to the polymorphic transformations between two monoclinic and two orthorhombic modifications of CsCoPO 4 , respectively. Thermodynamic functions C p ,m o / R , Δ 0 T H m o / RT , Δ 0 T S m o / R and Φ m o / R were calculated over the range of T = (0 and 650) K from experimental values and the fractal dimension D fr evaluated. Standard entropy of formation at T = 298.15 K was estimated to be (−386.40 ± 1.38) J · K −1 · mol −1 for crystalline phosphate CsCoPO 4 . [ABSTRACT FROM AUTHOR]

Water assisted phase transformation process from crystalized AlPO 4 -5 to AlPO 4 -tridymite was studied by the combination of X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and in situ multinuclear MAS NMR. It is found that water first activates the residue amorphous aluminophosphate in crystalized AlPO 4 -5 sample through hydrolysis and condensation reactions. Then the activated aluminophosphate species reassemble into AlPO 4 -tridymite crystalline. Meanwhile, AlPO 4 -5 transforms into orthorhombic phase during heating process. With further crystallization of AlPO 4 -tridymite, the amorphous phase is gradually consumed, and mass transportation between AlPO 4 -5 and AlPO 4 -tridymite is established through gradually amorphization of AlPO 4 -5. Finally, most of the AlPO 4 -5 transforms into the thermodynamically stable dense phase AlPO 4 -tridymite. [ABSTRACT FROM AUTHOR]

Silica refractories with cristobalite–tridymite ratios between 0.83–0.86 and 1.43–1.47 and porosities of 13–17% are characterized by impulse excitation up to 1200 °C and by dilatometry up to 1300 °C. During heating, Young’s moduli start to decrease from their room temperature values (9–12 GPa) to about 5–7 GPa at 200 °C, followed by a very steep increase at around 230 °C to values higher than the room temperature values and a nonlinear increase to their final high-temperature values. During cooling, Young’s moduli increase even further, exhibit a maximum and a nonlinear decrease that does not follow the heating curve, a very steep decrease at around 200 °C and a final increase to the intial room temperature values, so that a closed loop results during thermal cycling. Dilatometric measurements confirm that the strong increase of the Young’s modulus at around 230 °C (during heating) can be attributed to the phase transition between low- and high-temperature cristobalite, while the more gentle—but still very significant—changes in Young’s moduli below 200 °C are due to the more diffuse transitions between tridymite subpolymorphs. Microcracks are identified as the primary cause of the low Young’s moduli and their increase with temperature. [ABSTRACT FROM AUTHOR]

The unexpected detection of ∼16 wt.% monoclinic tridymite, a high-temperature silica polymorph, within an otherwise lacustrine mudstone in Gale crater, Mars raises significant questions about its formation and the extent of magmatic evolution on that planet. The rock sample, analyzed by the X-ray diffractometer onboard the Curiosity rover, also contained feldspar, cristobalite, and opaline silica (±Si-glass). Monoclinic tridymite is extremely rare on Earth, and has only been discovered in silicic volcanic environments, high-temperature impact settings, and extraterrestrial rocks. We review the most common formation pathways of natural tridymite and run thermodynamical models to investigate possible formation mechanisms. We consider the broader context of the sample to propose a formation and transport mechanism based on: (1) the mineralogical assemblage of the mudstone and rocks in the vicinity, (2) the composition of the mudstone layer, and (3) the overall geological context. Based on the large amount of tridymite, the high SiO 2 and low Al 2 O 3 concentration of the mudstone, and the low temperature context within distal lacustrine mudstone, we propose that an explosive eruption released Si-rich ashes, which were deposited into Gale crater's watershed as a tridymite-rich ashfall along with cristobalite, feldspar, Ti-oxide, and Si-rich glass, when Gale was still a lake (Hesperian). The dissolution of Si-rich glass and mineral sorting during transport would have concentrated tridymite, caused opaline silica precipitation, and relatively lowered the Al 2 O 3 concentration. This scenario implies that explosive volcanism on Mars occurred during the Hesperian and might not be restricted to basaltic eruptions, revealing the complexity of Mars magmatism. • One layer of lacustrine mudstone in Gale contains high temperature silicic minerals. • Tridymite and plagioclase could have co-crystallized from a rhyolitic magma. • The rhyolitic magma is consistent with evolution of observed igneous rock sources. • The Buckskin sample is detrital from tridymite-bearing ash in Gale lake's watershed. • At least one silicic explosive eruption occurred on Mars in the Hesperian. [ABSTRACT FROM AUTHOR]

Cesium-containing phosphates CsMgPO, CsZr(PO), and CsMgZr(PO) of framework structure were synthesized. The chemical stability of the crystalline phosphates in neutral, acidic, and alkaline media was studied. Quantitative data on the chemical stability in a wide pH range and on the ion-exchange capacity of phosphates containing cesium, magnesium, and zirconium ions were obtained by potentiometric titration. The Cs leach rates from the ceramic samples upon long contact with water were from 3 × 10 to 4 × 10 g cm day. The phosphates CsZr(PO) and CsMgZr(PO) are thermally stable in the temperature range from-268 to 1000°C, and CsMgPO undergoes a low-temperature phase transition at-37°C without break of chemical bonds in the structure. The stability of ceramic and powdered samples of CsMgPO, CsZr(PO), and CsZrMg(PO) was studied in different aspects, and these materials proved to be promising for cesium consolidation. High cesium content of CsMgPO allows its use as a material of the active core of Cs/Ba sources. [ABSTRACT FROM AUTHOR]

Effects of element substitution on the phase transition between different pyroelectric phases of the stuffed-tridymite-type oxide, BaZnGeO 4 , are examined by dielectric measurements on BaZn 1− x M x GeO 4 ( M =Ni, Co, and Mn) with x =0.05 and 0.10. The Ni 2+ -substitution is found to suppress strongly the phase transition, in marked contrast to the cases of Co 2+ and Mn 2+ that have only subtle influences on the transition temperature. Internal distortions of M O 4 tetrahedra due to the Jahn–Teller effect might play a major role in the variation of transition temperature induced by the element substitution. [ABSTRACT FROM AUTHOR]

EET 87720 is a polymict ureilite breccia known to contain numerous nonindigenous fragments. We have discovered a microgranitic clast in an interior chip of Elephant Moraine ( EET) 87720. The clast consists of a granophyre-like intergrowth of a pure SiO2 phase (tridymite) and albite, mantling a zoned oligoclase phenocryst. In the intergrowth, the tridymite occurs as thin elongate vermicular blebs within larger albite crystals. The granophyre-like intergrowth and the oligoclase phenocryst share a common margin, suggesting that the clast was originally part of a larger fragment. An estimate of its bulk composition is equivalent to that of granite (77 wt% SiO2). Patches of high-Si K-bearing glass occur interstitially within the clast; they have high concentrations of SO3 (11-12 wt%) and contain Cl (0.6 wt%), suggesting that the clast formed on a volatile-rich parent body perhaps resembling early Mars. The mean oxygen isotope composition of the feldspar and tridymite in the clast is very different from the oxygen isotope compositions of ureilites, and is similar to those of silicate inclusions in IIE and IVA irons. Thus, the clast is not indigenous to the ureilite parent body, but it provides evidence for the formation of evolved melts on an unknown parent body in the early solar system. [ABSTRACT FROM AUTHOR]

Using a conventional solid-state reaction method SiO 2 ceramics with addition of Li 2 TiO 3 were synthesized and their phase evolution, chemical reactions, microstructure and microwave dielectric properties were studied. The microwave dielectric properties of SiO 2 ceramics with addition of Li 2 TiO 3 strongly depend on the formation and the decomposed of Li 2 (TiO)(SiO 4 ) intermediate phase. The tridymite phase was formed for all samples sintered above 1150 °C and its microwave dielectric properties were reported for the first time ( ϵ r = 2.58, Q × f = 25,800 GHz , τ f = −17.8 ppm/°C). The promising ceramics of 0.945SiO 2 –0.055Li 2 TiO 3 sintered at 1050 °C were found to possess good microwave dielectric properties: ϵ r = 3.21, Q × f = 10,180 GHz and τ f ∼ 0.17 ppm/°C. [ABSTRACT FROM AUTHOR]

Classical molecular dynamics (MD) study was performed in order to explain a different wettability of silanized silica-glass surfaces prepared by using two different precursors - dichlorodimethylsilane (DCDMS) and dimethyldiethoxysilane (DMDES), respectively. Whereas the modified surface prepared by DCDMS becomes hydrophobic (contact angle (CA) of water >90°), DMDES-modified surface stays partially hydrophilic (CA ∼39°). In order to explain the observed discrepancy, several models of surfaces of trydimite with different coating by (CH3)2-Si= units were constructed and treated by water nanodroplets in the MD simulations. The models of surfaces differ by a different degree of surface coverage and/or oligomerized (CH3)2-Si= units in a lateral dimension. The simulations showed that incomplete coverage leads to a decrease of the computed CA, whereas upon lateral oligomerization the CA increases. This variation of the CA is directly related to the accessible amount of the hydroxyl groups on the surfaces and can be a possible explanation of the difference in wettability between DCDMS- and DMDES-treated glass surfaces. [ABSTRACT FROM AUTHOR]

There is a conflict of evidence with regard to the structure of the silica polymorph known as opal-CT. The current widely accepted interpretation of the structure views opal-CT as made up essentially of a disordered interlayering of crystalline cristobalitic and tridymitic stacking units, in about equal proportions where the d spacing of the diffraction maximum is close to 4.11 Å, but becoming progressively more ordered and cristobalitic as this spacing decreases in value and approaches the d (101) reflection at 4.04 Å of α -cristobalite. The most compelling evidence for this interpretation comes from matching calculated and experimental XRD profiles, HRTEM lattice images and SAED patterns. This interpretation is here described as the “crystalline” model. However, the crystalline model is not supported by a variety of spectroscopic techniques that can be used to probe both long-range and short-range order. In general, these techniques which include FTIR, Raman, NMR and XANES spectroscopies are more consistent with a structure, especially where the diffraction maximum approaches 4.11 Å, as being dominated by disordered material similar to amorphous opal (opal-A) but containing a small volume of crystalline stacking units which are mainly (sometimes exclusively) of a tridymitic nature. This interpretation is referred to as the “paracrystalline” model. From a critical review of the literature, suggestions are made as to how these two conflicting strands of evidence can be reconciled, as well as matters concerning appropriate nomenclature of opaline materials. [ABSTRACT FROM AUTHOR]

Thermoluminescence (TL) emission of tridymite, a quartz-like mineral, could be used for a variety purposes, including basic research, ceramic technology, traditional/medical industry, and dating. The current study focused on the investigation of the thermal effects on both the luminescence emission and structural properties of natural tridymite. Thermally stimulated luminescence of beta and UVC irradiated samples exhibits complex glow curves indicating simultaneous physical-chemistry processes such as phase transitions, dehydration, dehydroxylation or redox reactions involving intrinsic defects (O vacancies giving rise to F+ and F-type centers, Schottky and Frenkel defects), extrinsic defects (dopants) and structural defects (stacking fault defects, linear and planar defects or dislocations). TL glow curves can be analyzed despite the complexity by assuming that photon emission can be fitted to 1st order kinetics. The structural changes observed using thermal X-ray diffraction up to 200 °C indicate that the Miller indices (204) and (321) have only a reversible behavior in the range of 26–29° 2θ. Tests based on the TL also corroborate such reversibility. • Thermal stability of the tridymite structure was evaluated by T-XRD. • UVC and beta dose response were investigated by TL technique. • The reusability of the natural tridymite was investigated. • Activation energy (E) and figure of merit (FOM) were calculated using CGCD method. [ABSTRACT FROM AUTHOR]

The framework host (CuZn(CN)4], a coordination polymer composed of tetrahedral Cu(I) and Zn (II)ions and CN bridges, exhibits a reversible reconstructive transition in the solid-state between a cristobalite-like framework and a tridymite-like one induced by guest exchange between water and acetonitrile molecules. [ABSTRACT FROM AUTHOR]

Rhodiumcatalysts exhibited higher dispersion with tridymite-typeAlPO4supports than with Al2O3duringthermal aging at 900 °C under an oxidizing atmosphere. The localstructural analysis via X-ray photoelectron spectroscopy, transmissionelectron microscopy, X-ray absorption fine structure, and infraredspectroscopy suggested that the sintering of AlPO4-supportedRh nanoparticles was significantly suppressed because of anchoringvia a Rh–O–P linkage at the interface between the metaland support. Most of the AlPO4surface was terminated byphosphate P–OH groups, which were converted into a Rh–O–Plinkage when Rh oxide (RhOx) was loaded.This interaction enables the thin planar RhOxnanoparticles to establish close and stable contact with theAlPO4surface. It differs from Rh–O–Al bondingin the oxide-supported catalyst Rh/Al2O3, whichcauses undesired solid reactions that yield deactivated phases. TheRh–O–P interfacial linkage was preserved under oxidizingand reducing atmospheres, which contrasts with conventional metaloxide supports that only present the anchoring effect under an oxidizingatmosphere. These experimental results agree with a density functionaltheory optimized coherent interface RhOx/AlPO4model. [ABSTRACT FROM AUTHOR]