Showing papers on "Tridymite published in 2008"
TL;DR: Seifertite as discussed by the authors is a dense orthorhombic polymorph of silica with the scrutinyite (α-PbO2) type structure that was found as lamellae occurring together with dense silica glass lamlae in composite silica grains in the heavily shocked Martian meteorite Shergotty.
Abstract: Seifertite is a dense orthorhombic polymorph of silica with the scrutinyite (α-PbO2) type structure that was found as lamellae occurring together with dense silica glass lamellae in composite silica grains in the heavily shocked Martian meteorite Shergotty. The mineral is also intergrown in some grains with minor stishovite and a new unnamed monoclinic dense silica polymorph with a ZrO2-type structure. Seifertite has also been found in the Martian shergottite Zagami and is a minor constituent in other Martian shergottites. Chemical analyses of seifertite in Shergotty indicate major SiO2 with minor concentrations of Al2O3 and Na2O. Selected-area electron diffraction (SAED) and X-ray diffraction can be interpreted in terms of an orthorhombic pattern from a scrutinyite (α-PbO2) structure. The cell parameters are a = 4.097(1) A, b = 5.0462(9) A, c = 4.4946(8) A, V = 92.92 A3, Z = 4, and the space group is Pbcn or Pb 2 n . Density is (calc.) = 4.294 g/cm3 (with pure SiO2), 4.309 g/cm3 (with empirical formula). It is inferred that seifertite was formed by shock-induced solid-state transformation of either tridymite or cristobalite on Mars at an estimated minimum equilibrium shock pressure in excess of 35 GPa. The new mineral is named after Friedrich A. Seifert (b. 1941), founding Director of the Bayerisches Geoinstitut, Universitat Bayreuth, Germany, for his seminal contributions to high-pressure geoscience.
79 citations
TL;DR: Two novel framework compounds have been synthesized by a self-assembly reaction and contain an unexpected framework, Ag2I4(2-) with tridymite topology, and the discrete M(en)3(2+) cations are located in the channels.
Abstract: Two novel framework compounds, Zn(en)3Ag2I4 (1) and Ni(en)3Ag2I4 (2), have been synthesized by a self-assembly reaction. Both of them contain an unexpected framework, Ag2I42− with tridymite topolop...
70 citations
TL;DR: In this article, the authors used 29Si and 31P MAS-NMR to characterize the structure of both glass and glass-ceramic samples and found that phosphorus is mainly present in the form of ortho-(Q0) and pyrophosphate (Q1) structural units and variation of ZnO content did not have much effect on these resonances.
47 citations
TL;DR: In this paper, the complex microstructural evolution in mixtures of kaolinite clay, quartz, nepheline syenite, and soda-lime-silica (SLS) glass has been revisited.
Abstract: The complex microstructural evolution in mixtures of kaolinite clay, quartz, nepheline syenite, and soda–lime–silica (SLS) glass has been revisited. Detailed descriptions of reactions leading to dense whiteware bodies backed by semi-quantitative X-ray diffraction analysis reveal that ternary mixtures containing nepheline syenite differ from those containing SLS glass, as new crystalline phases develop inside and at the interfaces among SLS glass particles and decomposed clay and quartz. In SLS glass-fluxed mixtures, tridymite formation was hindered and cristobalite formed at ≥750°C followed by wollastonite at ≥800°C. Albite and plagioclase formed from interaction between clay and molten SLS glass above 800°C. Wollastonite was not present ≥1100°C, leaving only cristobalite in the surrounding regions. Quartz partially dissolves at temperatures ≥1000°C after interacting with molten SLS glass. In quaternary mixtures containing 6.25 wt% SLS glass and 17.25 wt% nepheline syenite fluxes, formation of types II and III secondary mullite was more pronounced than in the fully SLS glass-fluxed mixture. The more fluid liquid from nepheline syenite enhances the growth kinetics of mullite. The body fired at the optimum firing temperature (1100°C) has a microstructure containing primary type I and secondary types II and III mullites, remnant cristobalite, plagioclase, and partially dissolved quartz embedded in the glassy phase. Providing a roadmap for microstructural design in clay-based systems may have significant commercial impact in the emerging technology of use of waste materials in clay-based ceramics.
41 citations
TL;DR: The morphology and dimensions of the hematite particle influenced the shade of red pigments obtained as mentioned in this paper, and both fine ( 250 nm in length) acicular shapes gave poor red shades.
35 citations
TL;DR: In this paper, the influence of Ta 2 O 5 additions on the thermal properties and non-isothermal crystallization kinetics of this glass, including nucleation rate maxima and activation energies for crystallization, has been determined by differential scanning calorimetry and X-ray diffraction.
Abstract: The lithium zinc silicate glass exhibits two crystallization exotherms corresponding to the formation of Li 2 ZnSiO 4 and silica phases, respectively. The silica phases include tridymite and cristobalite. The influence of Ta 2 O 5 additions on the thermal properties and non-isothermal crystallization kinetics of this glass, including nucleation rate maxima and activation energies for crystallization, has been determined by differential scanning calorimetry and X-ray diffraction. It has been found that Ta 2 O 5 affects the crystallization behavior markedly, inhibiting the crystallization of high thermal expansion silica phases at lower concentrations, whilst at higher concentrations also suppressing crystallization of the Li 2 ZnSiO 4 phase. At the higher concentrations, these phases are replaced by small amounts of LiTaO 3 and LiTaSiO 5 .
23 citations
TL;DR: In this paper, a single phase KAlSiO4 was obtained as a substantially single phase after heating at 1000°C for one day; the crystal structure from powder X-ray-diffraction data in space group P 1211 [MM = 158.17 g/mol, b 9.669(2), c 8.621(1)°, V 1223.5 A3, Z = 12, Dx = 2.57 g cm−3, RB = 0.080].
Abstract: Dry synthesis of KAlSiO4 at temperatures from 900 to 1500°C yielded products with slightly different powder X-ray-diffraction patterns. “Orthorhombic” K x Al x Si2− x O4- O1 with x ≈ 1 was obtained as a substantially single phase after heating at 1000°C for one day; we refined its crystal structure from powder X-ray-diffraction data in space group P 1211 [MM = 158.17 g/mol, a 15.669(2), b 9.057(1), c 8.621(1) A, β 90.16(1)°, V 1223.5 A3, Z = 12, Dx = 2.57 g cm−3, RB = 0.080]. It is composed of a relatively open [AlSiO4] framework that is a topological variant of tridymite (t) having the supercell (s) metric a s ≈ 3 a t, b s ≈ a t + 2 b t, c s ≈ c t. The space group P 1211 allows for Al–Si ordering, and refinement of distance-least-squares restrained models, although problematic owing to the pronounced pseudosymmetry, indicates preference for an ordered pattern where Al and Si are distributed on alternating tetrahedra [ d Si–O/ d Al–O = 1.628(1)/1.719(1) A], so that every SiO4 tetrahedron is coordinated to four AlO4 tetrahedra and vice versa . The alternating distribution was independently inferred from 29Si and 27Al MAS NMR spectroscopic data, and the framework model obtained from Rietveld refinement with Si on tetrahedron T 1 could be used to successfully simulate the observed Si(Al4) doublet peak in the 29Si spectrum. Electron diffraction showed that triple twinning with a rotation of 120° around c of the metrically almost hexagonal P 1211 cell is ubiquitous and enhances, in the diffraction experiment, the pseudosymmetry inherited from the tridymite subcell. Furthermore, the diffraction aspect of single individuals ( P *21*) confirms that the screw axes 21-- and --21 of the orthorhombic supergroup P 212121 are only approximated.
18 citations
TL;DR: The existence of a disordered silica polymorph dominated by tridymite-like stacking is implied by the long-held interpretation of opaline silica as disordered intergrowths of cristobalitic-like and tridymitic-like domains as discussed by the authors.
Abstract: The existence of a disordered silica polymorph dominated by tridymite-like stacking is implied by the long-held interpretation of opaline silica as disordered intergrowths of cristobalite-like and tridymite-like domains. The currently accepted model for diagenetic transformation of amorphous silica also predicts that early formed structures will be dominated by tridymite stacking. Although the cristobalitic end-member (opal-c) and intermediate structures (opal-ct) have long been acknowledged, the tridymitic end-member has not yet been recognized. Evidence for such an end-member is found in 54 Twiggs clay samples examined by X-ray diffraction (XRD). The mineralogy of the samples is dominated by smectite and disordered silica. The silica phase is biogenic in origin and presents an XRD signature consistent with that of line-broadened tridymite, with a broad primary reflection near 4.107 A (21.6 °2𝛉), additional broad peaks of lower intensity at approximately 4.328 A (20.5 °2𝛉) and 2.50 A (35.9 °2𝛉), and lacking diagnostic cristobalite peaks at 3.14 A (28.5 °2𝛉) and 2.84 A (31.5 °2𝛉). At present, the most widely used classification of disordered silica is a threefold system that recognizes an amorphous phase (opal-a), a cristobalite-like end-member (opal-c), and intermediate structures incorporating both cristobalite and tridymite domains (opal-ct) (Jones and Segnit 1971). This classification does not accommodate a dominantly tridymite-like structure as is observed in the Twiggs clay. The silica phase in these samples is more accurately described as “disordered tridymite.” A new term “opal-t” is proposed to describe this end-member phase.
12 citations
Patent•
17 Sep 2008
TL;DR: In this article, a nano-sized composite silica brick and a production method for nano-size composite bricks was proposed. But the method is based on the existing production process of the silica bricks and introduces compound nanopowders in optimal proportions in the production process.
Abstract: The invention relates to a nano-sized composite silica brick and a production method thereof. The invention is characterized in that: raw materials and binder of the silica brick are as follows: silica granules and fine powders, waste silica brick granules, calcium carbonate nanoparticles, iron oxide nanoparticles, silicon dioxide nanoparticles, fluorite powders, lime and sulfite pulp wastes. The production method is based on the existing production process of the silica brick, and introduces compound nanopowders in optimal proportions in the production process of the silica brick after high-efficiency dispersion, to produce nano-sized composite silica bricks. With the addition of nanopowders, the performance of silica brick is significantly improved, and manifested as follows: 1) the particle size fraction is more reasonable, the accumulation is compact and the texture is uniform; 2) the slurry has good plasticity and moldability and the production efficiency is improved; 3) the burning temperature is decreased to 20 DEG C, thus realizing energy conservation and discharge reduction; 4) the tridymite is superior in crystallization conversion and has low content of quartz residues; 5) the number of closed pores is increased, the number of opened pores are reduced, the porosity is reduced, and the strength and refractoriness under load are increased; and 6) the final product has good appearance, smooth end surface and good bonding property, and the rate of qualified products is increased.
10 citations
TL;DR: In this paper, the crystal structure of all the phases, I-IV, in CsCoPO4 was studied by synchrotron-radiation X-ray powder diffraction.
Abstract: A new phase transition (III–IV) was found at 311 K in CsCoPO4 by DSC measurements. The crystal structure of all the phases, I–IV, in CsCoPO4 was studied by synchrotron-radiation X-ray powder diffraction. The diffractometry revealed that CsCoPO4 had the same crystal structure as that of corresponding phases in CsZnPO4. An extremely large particle size effect was found on III–IV phase transition in CsCoPO4; the phase transition enthalpy decreases with decreasing the particle size around 0.1 mm. Such large particle size effects had been also observed in CsZnPO4. However, no III–IV phase transition was observed in the particle smaller than 0.1 mm of CsZnPO4, while such a critical size was not found in CsCoPO4.
9 citations
TL;DR: A detailed mineralogical study and single-crystal X-ray analysis were carried out on K-Mg osumilite from high temperature pyrometamorphic rocks as discussed by the authors.
Abstract: A detailed mineralogical study and single-crystal X-ray analysis were carried out on K-Mg osumilite from high temperature pyrometamorphic rocks. These rocks were generated during spontaneous combustion of coal-bearing spoil-heaps in the South Urals, Russia. The osumilite-bearing metapelitic rocks – clinkers – contain K-Na- and K-Na-Ca feldspars, tridymite, mullite as main phases and magnesian K-bearing cordierite, corundum, native iron, pyrrhotite, cohenite, graphite, black carbon, and iron phosphide as minor phases. The composition of pyrometamorphic osumilites approaches the synthetic compound KMg 2 Al 3 (Al 2 Si 10 )O 30 . Pyrometamorphic alterations of sedimentary protolith during coal combustion proceeded at atmospheric pressure. The osumilite-bearing parageneses are formed under the conditions of low f O2 and water activity, at temperatures above 900 °C and below the melting point for the osumilite-bearing associations. The crystal structure of osumilite was refined from X-ray single-crystal data. Its crystal-chemical formula is K 0.83 C Na 0.10 B′ (Mg 1.78 Fe 0.16 Mn 0.03 Ti 0.03 ) A (Al 2.88 Fe 0.12 ) T2 (Al 1.91 Si 10.09 ) T1 O 30 . K cations occupy the standard 12-coordinated C site, whereas Na cations populate the B′position, located between three 6-membered double rings above the A position. The comparative crystal-chemical analysis shows that in the structure of osumilite, in contrast to cordierite, potassium not only compensates for the framework charge, but also stabilizes the structure. The role of sodium in cordierite and osumilite is similar and consists in a charge compensating function.
09 Jul 2008
TL;DR: The nonintegral phase in tridymite was found in the range 150° to 190 °C as discussed by the authors, and the average amplitude was estimated to be about 0.3 A from the intensity dependence on sin ϑ/λ.
Abstract: The non‐integral phase in tridymite was found in the range 150° to 190 °C. The distance between main and satellite reflection along the a*‐axis changed continuously depending on temperature. The non‐integral satellites result from wavy shift of the atomic positions. The average amplitude is estimated to be about 0.3 A from the intensity dependence on sin ϑ/λ. The symmetry operations in four‐dimensional space are as follows: (0,0,0,0), (1/2,1/2,0,0,)+x, y,z,ξ, x, ȳ, 1/2−z, ξ, x, y, z, ?, x, ȳ, 1/2+z, ?. The structure is refined using a newly‐developed program. The non‐weighted R for 81 reflections is 0.16. Atomic displacements tend to form a ditrigonal six‐membered ring in reference to the low temperature structure.
01 Oct 2008
TL;DR: The chemical behavior of chrysotile and its dissolution in the presence of dipalmitoylphosphatidylcholine (DPPC) were investigated in physiological conditions and it is proposed that under physiological conditions, the mechanism of brucite dissolution is based on its interaction with hydrogen ions and that the mechanisms of tridymite dissolution are based on a hydrolysis process.
Abstract: It is known that Brazilian chrysotile is rapidly removed from the lungs, but quantitative studies about the influence of lung surfactants on chrysotile dissolution have not been investigated. In this work, the chemical behavior of chrysotile and its dissolution in the presence of dipalmitoylphosphatidylcholine (DPPC) were investigated in physiological conditions. The dissolution was investigated through quantification of magnesium and silicon released by chrysotile. At 37 degrees C, the magnesium concentration is similar to control (without DPPC), which is about 2.0x10(-4)molL(-1), meaning that the dissolution process is not affected by the presence of this surfactant. The same was observed for silicon. The silicon concentration released by chrysotile is similar in all media tested. It is known that the dissolution mechanisms of brucite and tridymite layers are different. From our results, we propose that under physiological conditions, the mechanism of brucite dissolution is based on its interaction with hydrogen ions and that the mechanism of tridymite dissolution is based on a hydrolysis process.
TL;DR: In this article, a new method for the synthesis of tridymite is reported, where amorphous SiO2 is treated with ethylene glycol for 3 h at 196°C and then filtered and washed with distilled water.
Abstract: A new method for the synthesis of tridymite is reported in this article. When amorphous SiO2 is treated with ethylene glycol for 3 h at 196°C and then filtered and washed with distilled water, tridymite is obtained. The transmission electron microscopy equipped with energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) are used to characterize the crystal materials. The EDX shows the material is pure silica and The XRD pattern shows this silica is tridymite phase. In order to study the formation process of tridymite, all sorts of reaction conditions are discussed in detail. The products obtained at different conditions are characterized by XRD techniques. Finally, a reasonable mechanism is proposed.
Patent•
20 Dec 2008
TL;DR: In this article, the authors used clinoptilolite containing rocks to purify effluent water and prevent secondary contamination of the filtrate, improved ecological situation during production.
Abstract: FIELD: chemistry. ^ SUBSTANCE: proposed method involves treatment of effluent water with a chemical reagent, mixing, holding and separation of the solid phase. The reagent used is clinoptilolite containing rocks - silicate zeolitic or carbonate silicate zeolitic rocks, containing the following minerals: clinoptilolite, calcite, opal, cristobalite, tridymite and quartz. The above mentioned rocks have the following chemical content in terms of oxides, in wt %: for silicate zeolitic rocks - SiO2 69.0-69.81, Al2O3 4.22-7.61, TiO2 0.25-0.52, Fe2O3 1.3-2.0, MgO 0.15-0.54, CaO 5.0-5.3, Na2O 0.2-1.4, K2O 1.49-2.27, P2O5 0.33-0.42; for carbonate silicate zeolitic rocks - SiO2 45.0-47.0, Al2O3 1.5-1.95, TiO2 0.1-0.2, Fe2O3 0.5-0.57, MgO 2.0-3.0, CaO 20.0-22.3, Na2O 0.6-0.7, K2O 0.55-0.58, P2O5 0.8-0.87. Treatment is carried out with the mass ratio of rocks to effluent water equal to 1:5-1:7, and the water is held for 20-30 minutes. ^ EFFECT: increased efficiency of purifying effluent water and prevention of secondary contamination of the filtrate, improved ecological situation during production. ^ 3 ex
01 Jan 2008
TL;DR: In this article, the crystallization process of nanometer SiO 2 powder under high pressure and high temperature was investigated, and it was shown that SiO2 powder crystallizes to α-cristobalite with a little tridymite under normal pressure at 1 000~1 600 ℃,crystallizes to ǫ-quartz under 2.0~3.5 GPa and 320~1 100 Ω(ǫ)
Abstract: The crystallization process of nanometer SiO 2 powder under high pressure and high temperature was investigated.The experiment results show that nanometer SiO 2 powder crystallizes to α -cristobalite with a little tridymite under normal pressure at 1 000~1 600 ℃,crystallizes to α -quartz under 2.0~3.5 GPa and 320~1 100 ℃,and crystallizes to coesite under 3.9 GPa and 320~1 100 ℃.The temperature of coesite formation from nanometer SiO 2 is much lower than that from common α -quartz.
TL;DR: In this paper, the authors used the opacities of various polymorphs of silica and their amorphous versions computed from earth-based laboratory measurements to model the silica emission features in mid-infrared spectra of a few T Tauri stars taken with the IRS on board the Spitzer Space Telescope.
Abstract: Mid-infrared spectra of a few T Tauri stars (TTS) taken with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope show prominent narrow emission features indicating silica (crystalline silicon dioxide). Silica is not a major constituent of the interstellar medium; therefore, any silica present in the circumstellar protoplanetary disks of TTS must be largely the result of processing of primitive dust material in the disks surrouding these stars. We model the silica emission features in our spectra using the opacities of various polymorphs of silica and their amorphous versions computed from earth-based laboratory measurements. This modeling indicates that the two polymorphs of silica, tridymite and cristobalite, which form at successively higher temperatures and low pressures, are the dominant forms of silica in the TTS of our sample. These high temperature, low pressure polymorphs of silica present in protoplanetary disks are consistent with a grain composed mostly of tridymite named Ada found in the cometary dust samples collected from the STARDUST mission to Comet 81P/Wild 2. The silica in these protoplanetary disks may arise from incongruent melting of enstatite or from incongruent melting of amorphous pyroxene, the latter being analogous to the former. The high temperatures of 1200K-1300K and rapid cooling required to crystallize tridymite or cristobalite set constraints on the mechanisms that could have formed the silica in these protoplanetary disks, suggestive of processing of these grains during the transient heating events hypothesized to create chondrules.
TL;DR: In this article, two novel framework compounds, Zn(en)3Ag2I4 (1) and Ni(en)-3Ag 2 I4 (2), have been synthesized by a self-assembly reaction.
Abstract: Two novel framework compounds, Zn(en)3Ag2I4 (1) and Ni(en)3Ag2I4 (2), have been synthesized by a self-assembly reaction. Both of them contain an unexpected framework, Ag2I42− with tridymite topolop...