Synthesis and characterization of Cu2O·TeO2 and CuI·Cu2O·TeO2 glasses

Cu₂O·TeO₂ and CuI·Cu₂O·TeO₂ glasses were synthesized and characterized by complex impedance measurement, Raman spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy techniques. Samples of the binary and the ternary systems are found to have both Cu⁺ and Cu²⁺ with their relative concentration being composition dependent. Bonds like -O-Cu²⁺-O-, leading to the formation of bridging oxygen are found to form in the binary system. Structural units like (Te₃O₈ ^4–)_n are also found to form when Cu₂O content is high in the binary system. Phase separation is observed in the ternary system. The glass structure and hence the ionic conduction behavior are found to depend upon chemical composition. When CuI content exceeds 60 mol%, the crystalline phase of -Cul gets stabilized at room temperature, thus causing the enhancement in conductivity.     

X-ray powder diffraction and IR study of NaMg(H2O)2[BP2O8]·H2O and NH4Mg(H2O)2[BP2O8]·H2O

NaMg(H₂O)₂[BP₂O₈]·H₂O was prepared by hydrothermal synthesis and was characterized by X-ray powder difraction and IR method. The title compound was synthesized from MgCl₂·6H₂O, NaBO₃·4H₂O, and (NH₄)₂HPO₄ with variable molar ratios using hydrothermal method by heating at 165 °C for 3 days. The X-ray powder diffraction data was indexed in hexagonal system, the unit cell parameters were found to be as a = 9.428, c = 15.82 Å, Z = 4 and the space group is P6₁22. It is isostructural with M^lM^ll(H₂O)[BP₂O₈] type compounds where M^l = Na, K; M^ll = Mg, Mn, Fe, Co, Ni and Zn. In addition NH₄Mg(H₂O)₂[BP₂O₈]·H₂O was also synthesized the first time in this research. Its unit cell parameters and hkl values were in good agreement with the sodium magnesium compound. The unit cell parameters are a = 9.529, c = 15.736 Å. The indexed X-ray powder diffraction data of both compounds which were not reported in the literature is presented in this work. The IR data of NaMg(H₂O)₂[BP₂O₈]·H₂O is also reported.     

Phase Relations in the Na2O–Al2O3–Nb2O5and CaO–Al2O3–Nb2O5Systems

Phase relations in the Na₂O–Al₂O₃–Nb₂O₅and CaO–Al₂O₃–Nb₂O₅systems were studied. The Na₂O system was found to contain neither ternary compounds nor niobate–aluminate solid solutions. In the CaO system, a ternary compound of composition 4CaO · Al₂O₃·Nb₂O₅was identified (cubic structure, a= 7.628 Å, Z= 2, _meas= _x= 4.43 g/cm³).     

Synthesis and Study of Sr[HSiUO6]2·2H2O and Ba[HSiUO6]2·2H2O

Uranosilicates of the general formula M^{I I}[HSiUO₆]₂·2H₂O (M^{I I} = Sr, Ba) were prepared by hydrothermal synthesis. Previously unknown intermediate crystal hydrates were separated and studied by X-ray diffraction (XRD), IR spectroscopy, and thermal analysis. Polymorphic transitions -Sr[HSiUO₆]₂ -Sr[HSiUO₆]₂ and -Ba[HSiUO₆]₂ -Ba[HSiUO₆]₂ were revealed at 700 and 780°C, respectively.     

Effects of Y2O3 and La2O3 addition on the crystallization of Li2O·Al2O3·4SiO2 glass-ceramic

Effects of adding Y₂O₃ and La₂O₃ on the crystallization of -quartz solid solution (ss) and the subsequent -quartz ss to -spodumene transformation of Li₂O·Al₂O₃·4SiO₂ glass-ceramic were investigated. Adding 4 mol% YO_3/2 or 8 mol % LaO_3/2 effectively improved the control of the crystallization process of the glass. Y₂O₃ did not effectively induce bulk crystallization of -quartz ss, but can reduce the rate of surface crystallization. La₂O₃ completely suppressed the surface crystallization and promoted a uniform, bulk crystallization of -quartz ss. For both the Y₂O₃- and La₂O₃-doped glasses, the kinetics for glass crystallization to -quartz ss was delayed as the doping level increased. Except for the 8 mol % LaO_3/2-doped glass in which no -spodumene was formed, the kinetics for the -quartz ss to -spodumene transformation for the doped glasses was enhanced compared with that for the undoped glass. For the 4 and 8 mol % YO_3/2-doped compositions, the relative amount of -spodumene to -quartz revealed an anomalous decrease trend with heating temperature in a particular temperature range. This can be explained by the surface crystallization characteristic, which induced an overlap of crystallization and -quartz ss to -spodumene transformation. Glass doped with 8 mol % LaO_3/2 exhibited an Avrami exponent of about 2.4 and an activation energy for crystal growth of -quartz ss of about 418 kJ mol^–1.     

Surface crystallization and second-order optical non-linearity in Gd2O3–Bi2O3–B2O3 glasses

Some ternary Gd₂O₃–Bi₂O₃–B₂O₃ glasses are prepared, and crystallization behavior and second harmonic intensity are examined to develop new non-linear optical crystallized glasses. The glasses with Gd₂O₃ contents of 8–14 mol% have large densities of over 6 g/cm³ and large refractive indices of ～ 1.9. Transparent surface crystallized glasses consisting of two kinds of crystalline phases with different morphologies, i.e. plate shape and needle shape crystals, are fabricated by heat-treatment at temperatures between glass transition and crystallization temperatures. From second harmonic generation microscope observations, micro-Raman scattering spectra and XRD analyses, plate shape crystals are determined to be non-linear optical Gd_xBi_1KxBO₃ and needle shape crystals are Bi₃B₅O₁₂ having no second-order optical non-linearity. Since crystallized glasses consisting of Gd_xBi_1KxBO₃ crystals exhibit relatively strong SHGs, they have a high potential for application to light control devices.     

Photoluminescence and scintillation properties of Eu2O3–BaO–Nb2O5–TeO2 glass and glass ceramics

Journal of Materials Science: Materials in Electronics - 1Eu2O3–3BaO–20Nb2O5–76TeO2 glass and the corresponding glass-ceramics were synthesized with the aim to investigate the...     

Surface crystallization and second-order optical non-linearity in Gd2O3–Bi2O3–B2O3 glasses

Some ternary Gd₂O₃–Bi₂O₃–B₂O₃ glasses are prepared, and crystallization behavior and second harmonic intensity are examined to develop new non-linear optical crystallized glasses. The glasses with Gd₂O₃ contents of 8–14 mol% have large densities of over 6 g/cm³ and large refractive indices of ∼1.9. Transparent surface crystallized glasses consisting of two kinds of crystalline phases with different morphologies, i.e. plate shape and needle shape crystals, are fabricated by heat-treatment at temperatures between glass transition and crystallization temperatures. From second harmonic generation microscope observations, micro-Raman scattering spectra and XRD analyses, plate shape crystals are determined to be non-linear optical Gd_xBi_1−xBO₃ and needle shape crystals are Bi₃B₅O₁₂ having no second-order optical non-linearity. Since crystallized glasses consisting of Gd_xBi_1−xBO₃ crystals exhibit relatively strong SHGs, they have a high potential for application to light control devices.     

Effect of Bi2O3 on structural and optical properties of Li2O·PbO·Bi2O3·B2O3 glasses

Journal of Materials Science: Materials in Electronics - The quaternary glass system has a composition of 30Li2O·20PbO·xBi2O3·(50-x)B2O3 (where x?=?0, 10, 20, 30, and...     

Wetting behaviour of SiC ceramics: Part II—Y2O3/Al2O3 and Sm2O3/Al2O3

Wettability is the most significant phenomenon in SiC liquid phase sintering. The wetting of Y₂O₃/Al₂O₃ and Sm₂O₃/Al₂O₃ on SiC was analysed by the “Sessil drop” method. The wetting of liquid on solid during liquid phase sintering is very important. The behaviour of the additive on the SiC plate was observed using an imaging system with a CCD camera, and the contact angle measurements were analysed by Qwin Leica software. The samples were cut transversally and characterized by scanning electron microscopy and X-ray spectrometry (SEM/EDS). The wetting was found to be strongly influenced by the temperature; the SiC/additive contact angle decreased with increasing temperature. The YA and SA additives presented low contact angle values, indicating their good wetting on SiC in the argon atmosphere. The contact angle could not be measured when the test was performed in the nitrogen atmosphere because bubbles formed in the liquid during the test. The best atmosphere for this sintering was found to be argon, which allows uniform spreading.     

Phase relations in the systems ZrO2Y2O3Nd2O3 and ZrO2Y2O3CeO2

The phase relations of ZrO₂Y₂O₃Nd₂O₃ and ZrO₂Y₂O₃CeO₂ systems have been studied at 1100–1600°C. The single region of the fluorite phase was intensively examined using the relation between lattice parameter and composition. In the ZrO₂Y₂O₃Nd₂O₃ system, 37 mol% Nd₂O₃ is soluble in Y₂O₃-stabilized zirconia (fluorite phase) at 1100°C and 42 mol% Nd₂O₃ at 1600°C. In the ZrO₂Y₂O₃CeO₂ system, 40 mol% CeO₂ dissolves into the stabilized zirconia at 1600°C.     

HIP-sinteredβ- and mixedα-β sialons densified with Y2O3 and La2O3 additions

Various fully dense sialon materials sintered by the glass-encapsulated hot isostatic pressing technique were synthesized using Y₂O₃ and/or La₂O₃ as sintering aids. Constant molar amounts of the oxide mixtures were added in the ratios Y₂O₃/La₂O₃:100/0, 75/25, 50/50, 25/75, 0/100. The samples were sintered at two different temperatures, 1550 and 1825° C. At the lower temperature, unreacted-Si₃N₄ was present in the samples in addition to-sialon and secondary phases. The samples sintered at 1825° C showed that yttrium but not lanthanum favoured-sialon formation. The amount of intergranular phase increased by about 50% when Y₂O₃ was replaced by La₂O₃. The La-sialon ceramics have as good an indentation fracture toughness as the Y-sialon ceramics, about 5 MPam^–1/2, but the Vicker's hardness is slightly lower, being 1400 kg mm^–2 at a 98 N load.     

Sintering of pseudo-boehmite and γ-Al2O3

Sintering of pseudo-boehmite, acicular-Al₂O₃ produced by dehydration of pseudo-boehmite, and-Al₂O₃ ex alum was investigated. The sintering process was studied by X-ray diffraction, transmission electron microscopy with selected area electron diffraction and BET surface area measurements. The solid state reaction to-Al₂O₃ causes a steep drop of the surface area to less than 10 m²g^–1. The acicular pseudo-boehmite and-Al₂O₃ supports exhibit an intermediate state where the acicular particles assume a rod-like shape and the surface area falls from about 300 to 100 m²g^–1. It was established that reaction to -Al₂O₃ and, hence, sintering proceeds via a nucleation and growth mechanism. The rate-limiting step is nucleation of -Al₂O₃. Consequently, the contacts between the elementary alumina particles dominate the sinter process. The contact between the acicular elementary particles of pseudoboehmite and-Al₂O₃ studied leads to the reaction to -Al₂O₃ to be almost complete after keeping samples for 145 h at 1050 °C. Decomposition of alum produces very small particles showing negligible mutual contacts. Consequently an elevated thermal stability is exhibited. Treatment of the alumina ex alum with water and drying results in a xerogel in which contact between elementary particles is much more intimate. Accordingly, treatment at 1050 °C causes a sharp drop in surface area.     

Study of Na2O-SiO2-Fe2O2-Y2O3 glass by Mössbauer and EPR spectroscopy

Mössbauer, EPR and magnetization experiments have been carried out on the glass composition Na₂O-SiO₂-Fe₂O₂-Y₂O₃ in which yttrium iron garnet (YIG) can be precipitated by suitable heat-treatment. The measurements have been carried out on the as-quenched sample as well as samples heat-treated for 4 h at 400, 500, 600, 650, 700, 750, 810 and 850 C. Mössbauer spectra from the as-quenched sample as well as the first six samples showed a quadrupole splitting while the last two samples, as well as the sample heat-treated (i) by a two-stage process at 600 C and then at 750 C for 4 h each, and (ii) at 700 C for 40 h, showed a hyperfine as well as quadrupole splitting. The behaviour of the isomer shift (IS) and quadrupole splitting (E) with the heat-treatment temperature show significant changes at the glass transition and crystallization temperatures. The Mössbauer data have been found consistent with optical and electron micrographs which show a large variation in particle size of the precipitated magnetic phase. This has been further correlated with EPR and magnetization data.     

Oxidation of FeCrAl foils at 500–900°C in dry O2 and O2 with 40% H2O

Abstract

High temperature resistant FeCrAl alloys are frequently used in high temperature applications such as heating elements and metal based catalytic converter bodies. When exposed to high temperatures an adherent, slowly growing, dense aluminium oxide layer forms on the surface, which protects the underlying alloy from severe degradation. The composition, structure and properties of the formed oxide layer are strongly dependent on the alloy composition, temperature and oxidation environment. In this study, the Sandvik 0C404 FeCrAl alloy, in the form of 50 μm thick foils, was exposed isothermally in the temperature range 500–900°C for 168 hours in dry O₂ and in O₂ with 40 vol.% H₂O. The surface morphology, composition and microstructure of the grown oxide scales were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), grazing incidence X-ray diffraction (GIXRD), Auger electron spectroscopy (AES), and time of flight secondary ion mass spectrometry (TOF-SIMS). The oxidation process was faster at 900°C than at 500 and 700°C. At 500°C a thin (10–20 nm) mixed oxide of Fe, Cr and Al was formed. Exposure at 700°C resulted in a similar (40–50 nm) duplex oxide, in both dry O₂ and in O₂ with 40 vol.% H₂O. These oxide scales consisted of an inner and an outer relatively pure alumina separated by a Cr-rich band. This type of duplex oxide scale also formed at 900°C with a thin inward growing α–Al₂O₃ at the oxide/metal interface and an outward growing layer outside a Cr-rich band. However, at 900°C the outward growing layer showed two types of oxide morphologies; a thin smooth base oxide and a much thicker nodular oxide grown on top of substrate ridges. In dry O₂ atmosphere, the main part of this outward growing layer had transformed to α–Al₂O₃. Only in the outer part of the thick oxide nodules, metastable alumina was found. When exposed in the presence of water vapour the main part of the metastable alumina remained untransformed.     

Self-assembly,microstructure and photoluminescence properties of nanocomposite mesoporous silica loaded with In2O3 and In2O3–SnO2

Abstract

The mesoporous nanocomposite fabricated by self-assembly has many unique properties compared with the original materials. In₂O₃ (IO) and In₂O₃–SnO₂ (ITO) in mesoporous silica were studied in the present paper. They were self-assembled in a nanoscale mesoporous silica by an adsorption–annealing process. The composite of IO and ITO in mesoporous silica was characterised by transmission electron microscopy, atomic force microscopy and nitrogen sorption isotherms. Photoluminescence spectra of the samples were measured by a fluorescence spectrophotometer. The results show that the composite was synthesised from IO and ITO in a nano-scale mesoporous silica with assembly structure, and bulk mesoporous silica is easier to be loaded by the particles than the sheet one, but the specific surface area decreases with increasing atomic weight of the substances loaded in silica mesoporous. The results also show that the mesoporous composite doped with some substance may enhance the effect of photoluminescence. For instance, the mesoprous composite of IO/SiO₂ has an enhancement in the effect of photoluminescence, and that of the mesoprous nanocomposite of ITO/SiO₂ is greater. Mesoporous nanocomposite is a promising photoluminescence material in the application to industry.     

EPR and magnetic susceptibility studies of Cr2O3–Bi2O3–GeO2 glasses

Electron paramagnetic resonance (EPR) and magnetic susceptibility measurements have been performed on xCr2O3(1–x)[Bi2O3·GeO2] glasses with 0相似文献   

High-pressure high-temperature transitions in nanocrystallineγ Al2O3,γ Fe2O3 and TiO2

We report first observation of new polymorphs of Al₂O₃ and Fe₂O₃ in specimens of xerogelγ Al₂O₃ andγ Fe₂O₃ quenched from high pressures and temperatures. At about 5 GPa and 1400°C, xerogel gamma alumina (XGA) transformed into a polymorphic mixture of phasesα Al₂O₃, B Al₂O₃ and C Al₂O₃, while XGA containing 1 wt% Cr₂O₃ transformed into a mixture of phasesαAl₂O₃, H Al₂O₃ and k′ Al₂O₃. The phases B Al₂O₃, C Al₂O₃ and H Al₂O₃ have the monoclinic-, cubic- and hexagonal-rare earth sequioxide (Ln₂O₃) type structure, respectively. At 5·2 GPa and 1450°C, XGA yielded a mixture ofα Al₂O₃ and hexagonalμ Al₂O₃. At STP, the phaseμ Al₂O₃ was found to transform to another hexagonal phaseλAl₂O₃ over a 10 week period. At 5·2 GPa and 900°C,γ Fe₂O₃ showed transition to a new phase H Fe₂O₃ which probably has an 8 layer close packed structure. In nanocrystalline TiO₂, only the anatase to rutile transition was found. The results are discussed using the free energy vs temperature diagram for xerogel and nanocrystalline materials.