Showing papers on "Tridymite published in 2012"
28 Sep 2012-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, the pseudo-binary phase diagrams in the Cu-O-Si system in equilibrium with air and metallic copper have been constructed, and the effects of CaO, MgO, Al2O3, and Fe 2O3 on the liquidus isotherms of tridymite with metallic copper at temperatures of 1473 K and 1573 K (1200 −C and 1300 −C).
Abstract: The pseudo-binary phase diagrams in the Cu-O-Si system in equilibrium with air and metallic copper have been constructed. Equilibration at high temperature in an appropriate containment material, followed by rapid quenching and measurement of phase compositions using an electron probe x-ray microanalysis (EPMA) technique, was carried out to obtain the phase equilibria data. The investigation has been extended to characterize the effects of CaO, MgO, Al2O3, and “Fe2O3” on the liquidus isotherms of tridymite in equilibrium with metallic copper at temperatures of 1473 K and 1573 K (1200 °C and 1300 °C).
40 citations
TL;DR: In this paper, the authors used the integrated areas of the X-ray diffraction peaks associated with both the crystalline and amorphous components to calculate the relative proportions of groundmass crystallites and groundmass material from both glassy and devitrified material, and a detailed calibration indicates a linear relationship among the ratio of the integrated counts and bulk crystallinity.
Abstract: Devitrification of silicic volcanic rocks is a relatively common process, resulting in the production of microcrystalline silica and feldspar components. Here we investigate how the products of pervasive devitrification may be characterized using the combined techniques of X-ray powder diffraction, electron microprobe analysis, and X-ray fluorescence analysis to provide a new calibrated approach to calculating the crystallinity and mineral modes in both glassy vitrophyre and devitrified volcanics. Using the integrated areas of the X-ray diffraction peaks associated with both the crystalline and amorphous components, the relative proportions of groundmass crystallites and amorphous material from both glassy and devitrified material can be calculated. A detailed calibration indicates a linear relationship among the ratio of the integrated counts and bulk crystallinity. Mineral proportions are also calculated from X-ray fluorescence measurements of whole-rock and groundmass separates and are well correlated to crystallinities calculated from both X-ray diffraction and electron microprobe image analysis for vitrophyre samples. Devitrification products in a pervasively devitrified sample are tridymite, quartz, sanidine, and a Ca-rich aluminosilicate component. Mineral analysis and X-ray mapping by electron microprobe analysis indicates that the Ca-rich aluminosilicate component appears to be the dominant metastable or amorphous phase in the devitrified sample with proportions calculated from X-ray mapping (~32%) in reasonable agreement with the calculated proportion of amorphous material determined by means of X-ray diffraction (~38%). These results demonstrate the robustness of this combined X-ray diffraction and electron microprobe imagery technique for quantifying and characterizing crystallization in complex samples.
28 citations
07 Feb 2012
TL;DR: In this article, the effect of heating on the granulometry of chert was analyzed. But the results showed that the results were not applicable to diatomite and showed that a new mode appeared systematically, between 0.1?n and 1?m, for all thermal treated samples with alkaline flux.
Abstract: The cherty rocks of the Chouabine Formation of the Gafsa-Metlaoui basin (south-western Tunisia), that is composed by biogenic silica, are treated using thermal treatment at 1000?C with flux calcination method in order to prepare a specific filter aids of melting sulfur filter used for the production of sulfuric acid. This work presents the effect of heating on the granulometry of chert. The mineralogical composition of natural starting chert is composed by opal CT (cristobalite/tridymite) and by the mineral mixture of quartz, smectite clay minerals, palygorskite-sepiolite fibrous clay minerals, calcite and hematite. After thermal treatment, at 1000?C, the crystallinity of chert increases significantly and the opal-CT, transforms mostly to opal-C. The comparison of infrared spectra of untreated and treated cherts shows systematic variation of the wavenumber and the intensity of the absorption bands, due to the apparition of 619, 795, 1094 and 1202 cm?1 absorption bands of cristobalite in the infrared spectrum of chert treated sample, which is similar to diatomite. Granulometric analysis show that the natural untreated chert sample displays unimodal distribution, whereas the treated chert sample display bimodal distribution, as same as diatomite. Thus, a new mode appears systematically, between 0.1 ?n and 1 ?m, for all thermal treated samples with alkaline flux as observed for diatomite.
17 citations
Patent•
22 Feb 2012
TL;DR: In this paper, a silica-based castable castable refractory is obtained by adding, to 100 mass% of the raw material mixture of fused quartz and fired silica, 3.0-9.3 mass% (expressed in terms of solid SiO) of colloidal silica and 0.04-0.30mass% of sodium silicate.
Abstract: PROBLEM TO BE SOLVED: To provide a silica-based castable refractory which has excellent thermal shock resistance during heating, suppresses shrinkage under load at high temperatures, exhibits good creep resistance at high temperatures, and hardens within a proper time.SOLUTION: A silica-based castable refractory is obtained by adding, to 100 mass% of a silica-based refractory raw material mixture comprising fused quartz and fired silica stone, 3.0-9.3 mass% (expressed in terms of solid SiO) of colloidal silica and 0.04-0.30 mass% (expressed in terms of solid NaO) of sodium silicate. The fired silica stone consists mainly of tridymite, blending percentages of fused quartz and fired silica stone are 40-100 mass% of fused quartz and 0-60 mass% of fired silica stone, and a total addition amount of sodium components is 0.06-0.32 mass% (expressed in terms of solid NaO) externally relative to 100 mass% of the composition. The fired silica stone may consist mainly of tridymite and cristobalite. In this case, blending percentages of fused quartz and fired silica stone are set to 60-100 mass% of fused quartz and 0-40 mass% of fired silica.
16 citations
TL;DR: Buseckite (IMA 2011-070), (Fe,Zn,Mn)S, is the Fe-dominant analog of wurtzite, discovered in Zaklodzie, and an ungrouped enstatite-rich achondrite as discussed by the authors.
Abstract: Buseckite (IMA 2011-070), (Fe,Zn,Mn)S, is the Fe-dominant analog of wurtzite, a new member of the wurtzite group discovered in Zaklodzie, and an ungrouped enstatite-rich achondrite. The type material occurs as single-crystal grains (4–20 μm in size) in contact with two or more of enstatite, plagioclase, troilite, tridymite, quartz, and sinoite. Low-Ni iron, martensitic iron, schreibersite, keilite, cristobalite, and graphite, which are also present in the type sample, are not observed to be in contact with buseckite. Buseckite is black under diffuse illumination and nearly opaque grayish brown in transmitted light. The mean chemical composition of buseckite, as determined by electron microprobe analysis of the type material, is (wt%) S 35.84, Fe 28.68, Zn 23.54, Mn 10.04, Mg 1.18, sum 99.28, leading to an empirical formula calculated on the basis of 2 atoms of (Fe_(0.46)Zn_(0.32)Mn_(0.16)Mg_(0.04))_(Σ0.99)S_(1.01). Electron backscatter diffraction patterns of buseckite are a good match to that of synthetic (Zn_(0.558)Fe_(0.442))S with the P6_3mc structure, showing a = 3.8357, c = 6.3002 A, V = 80.27 A3, and Z = 2. Buseckite is likely derived from the breakdown of high-temperature pyrrhotite to form troilite and buseckite following the solidification of sulfide-rich liquids produced during impact melting of an enstatite-rich rock.
16 citations
06 Dec 2012
TL;DR: In this paper, the strength of Hi-NicalonTM-S SiC fibers was measured after oxidation in wet air between 700 deg and 1300 deg C. The results showed that the fiber strength increased by approximately 10% for SiO2 scale thickness up to 100 nm, and decreased for thicker scales.
Abstract: : The strengths of Hi-NicalonTM-S SiC fibers were measured after oxidation in wet air between 700 deg and 1300 deg C. The oxidation and scale crystallization kinetics were also measured. Thicknesses of amorphous and crystalline scale were measured by TEM. Oxidation initially produces an amorphous scale that starts to crystallize to cristobalite and tridymite in 100 hours at 1000 deg C or in one hour at 1300 deg C. Crystallization kinetics for oxidation in wet air were slightly slower than those for dry air. The activation energy of 249 kJ/mol for parabolic oxidation to uncrystallized SiO2 scale in wet air was indistinguishable from that for dry air oxidation, but the pre-exponential factor was 2x higher. SiC fiber strength changes with oxidation in dry and wet air were very similar. The fiber strength increased by approximately 10% for SiO2 scale thickness up to 100 nm, and decreased for thicker scales. No significant strength degradation was observed for amorphous scales. All fibers with significantly degraded strength had crystallized or partially crystallized scales.
15 citations
01 Jan 2012
TL;DR: In this paper, the oxidation characteristics of metal and ceramics were studied by synchrotron radiation diffraction, neutron diffraction and secondary-ion mass spectrometry (SIMS) experiments.
Abstract: MAX phases display a unique combination of characteristics of both metals and ceramics, and unusual mechanical, electrical and thermal properties. In this chapter, the oxidation characteristics of Ti 3 AlC 2 , Ti 3 SiC 2 and Ti 2 AlC over the temperature range 500–1400 °C were studied by synchrotron radiation diffraction, neutron diffraction, secondary-ion mass spectrometry (SIMS) and nuclear magnetic resonance (NMR) experiments, which provided elemental and phase compositional depth profiles over this range as well as evidence of glassy phase formation. Evidence for the outward diffusion of Al or Si during oxidation was shown for the first time by the complementary SIMS and NMR results, suggesting amorphous Al or Si at low temperature oxidation, which is vital for strong adherent oxide scales during oxidation. During oxidation, anatase formed at 500 °C, which transformed to rutile at 600 °C and was completed by 900 °C. The crystalline phase α-Al 2 O 3 was detected at 900 °C in Ti 3 AlC 2 or Ti 2 AlC. Tridymite and cristobalite were detected at 1000 and 1350 °C respectively in Ti 3 SiC 2 .
12 citations
TL;DR: Browneite (IMA 2012-008), MnS, is a new member of the sphalerite group, discovered in Zaklodzie, an ungrouped enstatite-rich achondrite as discussed by the authors.
Abstract: Browneite (IMA 2012-008), MnS, is a new member of the sphalerite group, discovered in Zaklodzie, an ungrouped enstatite-rich achondrite The type material occurs as one single crystal (~16 μm in size) in contact with and surrounded by plagioclase; enstatite and troilite are nearby Low-Ni iron, martensitic iron, tridymite, quartz, cristobalite, sinoite, schreibersite, buseckite, keilite, and graphite, are also present in the type sample Browneite is yellowish brown and translucent The mean chemical composition, as determined by electron microprobe analysis of the type material, is (wt%) S 3646, Mn 6231, Fe 062, Ca 010, sum 9949, leading to an empirical formula calculated on the basis of 2 atoms of (Mn_(0993)Fe_(0010)Ca_(0002))S_(0995) Electron back-scatter diffraction patterns of browneite are a good match to that of synthetic β-MnS with the F43m structure, showing ɑ = 5601 A, V = 17571 A^3, and Z = 4 Browneite is a low-temperature (<200 °C) phase, metastable relative to alabandite, that postdates the impact melting and subsequent crystallization of an enstatite-rich rock
12 citations
TL;DR: In this article, six transparent glass frits were prepared based on the poudretteite (K Na2 B3 Si12 O30) glass composition, and three catalysts were experimented on the base glass composition as nucleation catalysts.
Abstract: Based on the poudretteite (K Na2 B3 Si12 O30) glass composition, six transparent glass frits were prepared. TiO2, LiF and Cr2O3 were experimented on the base glass composition as nucleation catalysts. Only cristobalite and tridymite were developed through the sintering process of the glasses between 900 and 1100 °C. LiF enhances mainly tridymite with traces of cristobalite and in the opposite side the parent and both TiO2 and Cr2O3 containing glasses catalyzed mainly cristobalite with traces of tridymite. The microstructure of the glass samples heat-treated at 1000 °C showed backbone-like, small rods, quadrant-, hexagonal crystals referred to the cristobalite and tridymite. The EDS microanalysis shows the presence of both alkalis, i.e. Na + and K + , in the cristobalite crystal structure while the residual glass contains K + . The infrared spectroscopy indicates the band patterns of cristobalite and tridymite.
11 citations
TL;DR: In this article, high-temperature IR spectra of the orthorhombic modifications of CsZnPO 4 and CsNiPO 4 are presented and assigned.
Abstract: Caesium-bearing phosphates with the β -tridymite structure are considered as storage container for radioactive Cs. In this context, double phosphates of caesium and divalent cations, CsM 2+ PO 4 where M 2+ = Zn, Co, Mn, Mg, and Ni, have been synthesised by the precipitation method as powders and investigated by infrared spectroscopy in combination with factor-group analyses for band assignment. Comparison of the IR pattern of CsZnPO 4 and CsCoPO 4 confirms that they are isomorphic (space group P 1 2 1 / a 1 at room conditions). Both undergo T -induced phase transitions: one at 260 °C ( Pn 2 1 a) and another one at 310 °C ( Pnma ). High-temperature IR spectra of the orthorhombic modifications of CsZnPO 4 are presented and assigned. Comparison of the IR-spectrum of CsMnPO 4 with that of CsZnPO 4 ( Pn 2 1 a ) confirms that it crystallizes in the orthorhombic structure at room conditions ( Pn 2 1 a) . CsMgPO 4 crystallizes at room conditions in the orthorhombic space group Pnma , however, it tends to hydrate immediately after quenching in air forming the cubic hydrate CsMgPO 4 ·6H 2 O (space group F 43 m ). The liability to hydration is also characteristic for CsNiPO 4 . Temperature-dependent IR spectroscopy, X-ray diffraction, thermal analyses (TGA, DTA) and second-harmonic generation (SHG) revealed that pure anhydrous CsMgPO 4 (space group Pnma ) can only be stored in air at temperatures higher than 150 °C. Our study proves that CsM 2+ PO 4 , where M 2+ = Zn, Co, Mn, may be stable containers for radioactive Cs at room temperatures. However, CsMgPO 4 and CsNiPO 4 can only be used as crystalline matrices for the immobilisation of radioactive Cs when stored at temperature higher than 150 °C due to their hydrolytic instability in air. The difference in the structures of CsMg phosphate and Cs phosphates with Zn, Co, and Mn is caused by the different liability of these cations to form either ionic or covalent chemical bonds.
10 citations
TL;DR: In this article, a solution-based synthesis route is developed to produce off-stoichiometric amorphous silica (SiO2 with x < 2) by using sonochemical reduction of silica-based materials in the presence of sodium.
Abstract: Reduction of silica (SiO2) in the bulk form is quite challenging because the bulk silica in both the amorphous and crystalline states is a highly stoichiometric material. In this work, a solution-based synthesis route is developed to produce off-stoichiometric amorphous silica (SiOx with x < 2) by using sonochemical reduction of silica-based materials in the presence of sodium. The resulting amorphous SiOx materials are found to crystallize after annealing at temperatures higher than ∼800 °C under Ar or vacuum environment, resulting in off-stoichiometric silica crystals. The main crystal phase is cristobalite, and a small amount of tridymite was also included. The thus obtained silica crystals exhibit a broad photoluminescence (PL) emission peaking at ∼500 nm, characterized by the PL decay constant on the time scale of microseconds. The spin forbidden emission of oxygen vacancies in a silica crystal lattice is likely to be responsible for the observed broad visible PL emission. The present sonochemical re...
TL;DR: In this article, complex phosphates CsMg1 − xMxPO4 (M = Mn, Co, Cu, Zn), containing cesium and metals in the oxidation state +2, have been synthesized, and their structure and thermal behavior have been studied.
Abstract: Complex phosphates CsMg1 − xMxPO4 (M = Mn, Co, Cu, Zn), containing cesium and metals in the oxidation state +2, have been synthesized, and their structure and thermal behavior have been studied. Continuous solid solutions (0 ≤ x ≤ 1) of the β-tridymite structure type are formed in the CsMg1 − xMnxPO4, CsMg1 − xCoxPO4, and CsMg1 − xZnxPO4 systems, whereas limited solid solutions (0 ≤ x ≤ 0.4) are formed in the CsMg1 − xCuxPO4 system. Based on DTA data, phase transitions have been revealed in the cobalt-, copper-, and zinc-containing phosphates, and the orthorhombic or monoclinic crystal system has been identified. Unit cell parameters of the solid solutions have been calculated. Thermal expansion of the CsMPO4 phosphates has been studied.
Proceedings Article•
01 Jan 2012TL;DR: It is shown that quartz and cristobalite have smooth three-dimensional configuration spaces, but ideal high tridymite is a singular configuration with a six-dimensional tangent space, and the topology around this singularity is explicitly described.
Abstract: Building upon and complementing recent results on the rigidity theory of periodic bar-and-joint frameworks, this paper studies tetrahedral structures modeled on specific crystalline materials: quartz, cristobalite and tridymite. The general theory predicts at least three infinitesimal degrees-of-freedom. Here, we investigate the actual deformations of these structures. We show that quartz and cristobalite have smooth three-dimensional configuration spaces, but ideal high tridymite is a singular configuration with a six-dimensional tangent space. The topology around this singularity is explicitly described.
TL;DR: The opal-like hydrogenated phase assemblage of amorphous phase, cristobalite and tridymite thus formed have a minimum band gap at ca.
Abstract: Amorphous SiO2 powders having two kinds of medium range order (MRO) were subjected to pulse laser ablation in water (PLAL) for X-ray diffraction, transmission electron microscopy and spectroscopy characterization. The powders fragmented down to 10-20 nm in size are mainly hydrogenated amorphous phase retaining Si-2nd O but not Si-2nd Si MRO. There are minor co-existing crystallites of beta-cristobalite, H2Si2O5 as well as additional alpha-tridymite and Na2SiO3 when water is spiked with NaCI for PLAL. Na-signature also caused lower vibration frequency of the hydrogenated silica network. The opal-like hydrogenated phase assemblage of amorphous phase, cristobalite and tridymite thus formed have a minimum band gap at ca. 5 eV for potential optoelectronic and catalytic applications in UV range and shed light on natural occurrence in dynamic settings such as meteorite impact and lightening strike on silicate-enrich crustal rocks.
Journal Article•
TL;DR: In this paper, the phase transformation and melting behaviors of different silica fumes were related to the parti-cle size distribution and the Na2O and K2O content, and the analysis by XRD revealed that silica in all the samples appeared amorphous when heated at 800 ℃, and then became cristobalite and tridymite after heated at 900 and 1 200
Abstract: The morphology,particle size distribution,phase transformation,and melting behaviors of three kinds of silica fumes at room temperature and heated at 800-1 200 ℃ for 3 h were investigated by X-ray fluorescence spectrometry,field emission scanning electron microscope,energy dispersive spectrometry,X-ray diffractometer(XRD) and laser particle size analysis,respectively.At room temperature,they are spherical particles with the size of 1 μm,which contain some smaller distinguished spheres in the range of 30-50 nm.The smaller spheres are adhered onto the surface of larger particles.The particles with the size of 1 μm are mostly the agglomerates.The analysis by XRD revealed that silica in all the samples appeared amorphous when heated at 800 ℃,and then be-came cristobalite and tridymite after heated at 900 ℃ and 1 200 ℃,respectively.The cohering phenomenon occurred when heated at 800 ℃,and then the deformation and softening phenomena took place with the further increase of temperature.All the samples melted after heated at 1 200 ℃ for 3 h.The phase transformation and melting behaviors of the different silica fumes were related to the parti-cle size distribution and the Na2O and K2O content.Tetragonal zirconia appeared in the ZrO2 containing silica fume after heated at 900 ℃ for 3 h,and thereafter there existed no further phase transformation when heated at a higher temperature.
27 Sep 2012
TL;DR: In this paper, the authors examined the rapid thermal annealing process of single crystal Si(0,0,1) substrates in oxygen ambient, where a crystalline interlayer was observed between the amorphous silicon oxide (SiO x ) film and Si( 0,0,1) substrate.
TL;DR: In this article, palm petiole ash (PPA) in Thailand was calcined in different temperatures and their structures and compositions were analyzed using a melt-quenched technique and investigated their optical and physical properties.
Abstract: In this paper, palm petiole ash (PPA) in Thailand was calcined in different temperatures and their structures and compositions were analyzed. The glasses from each PPA were prepared by melt-quenched technique and investigated their optical and physical properties. The results show that, the major compositions of PPA are SiO2 and CaO, MgO, K2O and P2O5. The structures of PPA are low-quartz phase in all calcining temperatures. The tridymite phase was appeared at 800 and 1,000°C. Glasses from PPA were produced and showed light yellow-brown color. The results are similar in all samples, correspond with absorption spectra from UV-Visible spectrophotometer.
Journal Article•
TL;DR: The analysis of diffraction patterns has shown that in these glasses, besides an amorphous phase forming a weakly structured background, there are microscopic crystalline inclusions of sassolite with a diffraction size of 26 ± 3 nm and of α-quartz with a characteristic size of 6 ± 1 nm as mentioned in this paper.
Abstract: Microscopic structure of three types of porous glasses with the average pore diameter of 5, 7 and 140 nm obtained by chemical etching was studied by neutron diffraction. The analysis of diffraction patterns has shown that in these glasses, besides an amorphous phase forming a weakly structured background, there are microscopic crystalline inclusions of sassolite with a diffraction size of 26 ±3 nm and of α -quartz with a characteristic size of 6 ±1 nm. Microcrystalline inclusions sizes do not depend on the average pore size diameter. It is shown that in these samples a tridymite phase does not make a significant contribution to observed scattering and a relative sassolite contribution decreases substantially with the average pore size increasing from 5 to 140 nm.