Mn4+ Luminescence in 2MgO · GeO2 and 2MgO · GeO2 · MgF2

The oxidation state of the Mn activator in 2MgO · GeO₂, 2MgO · GeO₂ · MgF₂ was shown to be 4+. The observed luminescence behavior of these phosphors was accounted for by a large crystal-field splitting. The²T₁ and²E excited states of Mn⁴⁺ were found to be close in lifetime (100-120 ώs). The slower luminescence decay in magnesium fluorogermanate is attributable to the energy transfer between the activator and electron traps through the conduction band.     

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.     

The role of fluorine in the devitrification of SiO2·Al2O3·P2O5·CaO·CaF2 glasses

A series of eight glasses based on a glass system with the generic composition 1.5(5–Z)SiO₂·(5–Z) Al₂O₃·1.5P₂O₅·(5–Z)CaO·ZCaF₂ were studied where Z = 2, 1.75, 1.5, 1.25, 1, 0.5, 0.25, 0. These glasses were characterised using differential scanning calorimetry (DSC) and x-ray powder diffraction (XRD). Glasses with high fluorine contents were found to crystallise readily to fluorapatite via a homogeneous nucleation route probably involving prior amorphous phase separation. These results are explained in terms of an approach which views glasses as being inorganic polymers where the presence of fluorine disrupts the glass network and thereby reduces the energy barrier to homogeneous nucleation and crystallisation of fluorapatite.     

Sintering and crystallization of (SrO·SiO2)-(SrO·Al2O3·2SiO2) glass-ceramics

In the ternary SrO-Al₂O₃-SiO₂ system the pseudobinary join composition of 50 wt % SrO·SiO₂–50 wt % SrO·Al₂O₃·2SiO₂ (SS-SA2S) showed a glass melting temperature of 1500 °C and a crystallization peak temperature of 1100 °C. The (SS-SA2S) glass-ceramic pellets prepared by cold pressing and pressureless sintering, showed very low porosity. The (SS-SA2S) glass-ceramics containing B₂O₃ and those containing B₂O₃ and TiO₂ revealed crystallization peak temperatures of 1000 °C and unexpectedly high porosity. By applying Kissinger analyses to the DTA data the activation energy values for crystallization of the three glass-ceramics were determined to range from 196 to 255 kJ/mol. The Ozawa analyses on the DTA data gave the Avrami parameter values at 3.69 to 3.95. The X-ray diffraction (XRD) patterns from the three glass-ceramics revealed formation of the equilibrium crystalline phases of SrO·SiO₂ and SrO·Al₂O₃·2SiO₂ (monocelsian).     

Sintering and crystallization of off-stoichiometric SrO·Al2O3·2SiO2 glasses

Glass-ceramics with the celsian-corundum binary join composition of 88.8 wt% SrO·Al₂O₃·2SiO₂ – 11.2 wt% Al₂O₃, (SA2S-A), were fabricated by pressureless sintering and investigated for their sintering and crystallization behaviors. The (SA2S-A) glass powder showed crystallization peak and melting temperatures of 1059 and 1550 °C, respectively and high sintering ability. The (SA2S-A) glass powders containing B₂O₃, (SA2S-A)B and those containing B₂O₃ and TiO₂, (SA2S-A)BT showed lowered crystallization peak temperatures of 1033 and 997 °C, respectively. By applying Kissiger analyses to the DTA data of the (SA2S-A), (SA2S-A)B and (SA2S-A)BT glass powders, the activation energy values for crystallization were determined as 488, 370 and 333 kJ/mol, respectively. The Ozawa analyses on the DTA data gave the Avrami parameter values at 1.2, 1.1 and 1.9, respectively for the (SA2S-A), (SA2S-A)B and (SA2S-A)BT glass powders. The x-ray diffraction (XRD) patterns of the (SA2S-A) glass-ceramics, crystallized at 1100 °C for 4 h, showed formation of both the monocelsian and hexacelsian phases. The (SA2S-A)B and (SA2S-A)BT glass-ceramics crystallized at 1100 °C for 1 h, showed formation of the phase-pure monocelsian and did not show any evidence of the hexacelsian formation prior to the monocelsian formation.     

Preparation and electrochemical properties of SrCe 0·4 Zr 0·4 Yb 0·2 O 2·9 electrolyte

The perovskite Yb-doped strontium cerate–zirconate material, SrCe_0·4Zr_0·4Yb_0·2O_2·9, was prepared by solid-state reaction and the structure was characterized by X-ray diffraction. The calcination process of the powder was investigated by thermogravimetric/differential thermal analysis (TG–DTA). The high temperature conductivities were measured by d.c. four-probe technique in the temperature range from 500 to 950°C in wet hydrogen and effect of temperature on conductivity was investigated. The conductivity increased with the elevation of temperature from 500 to 950°C. The highest conductivity of 4·4 × 10^???2 S· cm^???1 was observed for SrCe_0·4Zr_0·4Yb_0·2O_2·9 at 950°C. The current–voltage (I–V) and current–power (I–P) characteristics of the single cell (H₂, Pt/SrCe_0·4Zr_0·4Yb_0·2O_2·9/Pt, O₂) at temperature range from 600 to 850°C were tested. With the temperature increasing from 600 to 850°C, the open circuit voltage (OCV) decreased from 1·164 to 1·073 V and the ionic transfer number decreased from 0·996 to 0·946. At 850°C, the maximum power density of 25·2 mW· cm^???2 was observed.     

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...     

Creep activation energy of flow process in Bi2Te2·8Se0·2 single crystals

Temperature dependence of the Vickers microhardness of Bi₂Te_2·8Se_0·2 single crystals has been studied. Loading time dependence of microhardness at different temperatures has been used for creep study in the temperature range 303 K-373 K. The activation energy for indentation creep of the crystals has been evaluated.     

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.     

High resolution TEM study of ceramic BaO·Pr2O3·4TiO2

Ceramic specimens of BaO·Pr₂O₃·4TiO₂ (Ba_4.5Pr₉Ti₁₈O₅₄) were prepared by the mixed oxide-route. The single phase products were examined by High Resolution Transmission Electron Microscopy (HRTEM). Orthorhombic symmetry, with cell parameters a22.2 Å, b12.2 Å and c7.6 Å, was confirmed. On the basis of space group pnam (No. 62) and the crystal structural data of Rawn et al., good agreement was obtained between the experimental HRTEM images and images simulated by the multislice method.     

Thermal decomposition of CuCrO4·2CuO·2H2O and phase relations in the Cu-Cr-O system

The compound, CuCrO₄·2CuO·2H₂O has been synthesized by precipitating it from the aqueous solution containing chromium (VI) oxide and basic copper (II) carbonate. Thermal decomposition of CuCrO₄·2CuO·2H₂O has been studied by thermogravimetry and differential scanning calorimetry in flowing air and pure oxygen between 298 and 1373 K. The formation of different phases after each stage of decomposition were identified by X-ray diffraction analysis. The compound CuCrO₄ was found to be non-stoichiometric. Based on the results obtained in this study and those reported earlier, the isothermal section of the phase diagram of the Cu-Cr-O ternary system has been composed at 600 and 1150 K. Scanning electron microscopy studies of CuCrO₄·2CuO·2H₂O precipitate showed rectangular plate-like morphology. The decomposition of CuCrO₄·2CuO·2H₂O at 798 K in air resulted in the formation of a mixture of fine powder of CuCr₂O₄+CuO (Adkin's catalyst) having a uniform spherical geometry and a particle size less than 0.1 m.     

Phase Relations in the BaO · 2B2O3–La2O3 · 3B2O3 System

The BaO · 2B₂O₃–La₂O₃ · 3B₂O₃ join of the ternary system BaO–La₂O₃–B₂O₃ is studied using differential thermal analysis, x-ray diffraction, and density measurements. The join is shown to be pseudobinary, with eutectic phase relations. In the composition range 5–99.8 mol % La₂O₃ · 3B₂O₃, glassy materials are obtained, which seems to be associated with the existence of the congruently melting compound BaO · La₂O₃ · 5B₂O₃.     

Fabrication and properties of SiC fibre-reinforced Li2O·Al2O3·6SiO2 glass-ceramic composites

Ta₂O₅, Nb₂O₅ and TiO₂ were used separately as additives to a Li₂O·Al₂O₃·6SiO₂ glass-ceramic composition, to act as nucleating dopants and to aid the formation of an interfacial carbide layer (TaC and NbC) between the fibre and matrix in SiC fibre uniaxially reinforced glass-ceramic composites, The composites exhibited high modulus of rupture (>800 MPa) and fracture toughness (K _IC > 15 MPam^1/2). The interfacial amorphous carbon rich layer and carbide layer were responsible for lowered interfacial shear strength but permitted high composite fracture toughness. The composite with the TiO₂ additive in the matrix showed a lower flexural strength (<500MPa) and a smaller K _IC (-11 MPam^1/2) which resulted from the high interfacial shear strength between the SiC fibre and the matrix due to the formation of the interfacial TiC layer.     

Antibacterial and bioactive silver-containing Na2O·CaO·2SiO2 glass prepared by sol–gel method

The antibacterial effect of addition of silver oxide to Na2O x CaO x 2SiO2 glass have been studied. Silver containing and silver free Na2O x CaO x 2SiO2 glasses have been prepared by sol-gel synthesis using tetramethil orthosilicate, sodium ethoxide, calcium nitrate tetrahydrate and silver nitrate as starting materials and methyl ethyl ketone as solvent. The gel was examined by differential thermal analysis, thermo gravimetric analysis, FTIR spectroscopy and X-ray diffraction analysis. Antibacterial and bioactive tests on gel glass powders, obtained after a heat treatment of 2 h at 600 degrees C of the dried gel, were carried out. High antimicrobial effects of samples against Escherichia coli and Streptococcus mutans were found. FTIR measurements and SEM micrographs have ascertained the formation of a hydroxyapatite layer on the surface of samples soaked in a simulated body fluid for different times.     

Phase Diagrams of Two Binary Sections 4MnO·Nb_2O_52MnO·SiO_2 and MnO·Nb_2O_5—SiO_2 in the Ternary System MnO-Nb_2O_5-SiO_2

1.IntroductionIn previous papers[1,2],it has beenpointed out that the study of the phase dia-gram for the system Nb_2O_5—MnO—SiO_2 issignificant from both practical and theoreti-cal viewpoint.The new compound4MnO·Nb_2O_5 has been ascertained in thebinary system MnO—Nb_2O_5[1].Presence ofthree stable compounds 4MnO·Nb_2O_5,MnO·Nb_2O_5 and 2MnO·SiO_2 in theternary system predicts the possibility ofthree stable binary sections[2].The binary     

Creep of Pb–2·5Sb–0·2Sn alloy at low stresses

Abstract

The creep of a Pb–2·5Sb–0·2Sn alloy has been studied at stresses up to 6·5 MN m^?2 in the temperature range 318–348 K (0·53–0·58T_m) using helical specimens. At 333 K, a transition in the stress exponent from ~1 to 3 occurred at ~3 MN m^?2. The observed good agreements below the transition stress, both for experimental dE/do and predictions for Coble diffusional creep of lead, and for measured activation energy for creep and the activation energy for grain boundary self-diffusion in lead, suggest that grain boundary diffusional creep is the dominant mechanism. at low stresses. The presence of antimony does not seem to affect the magnitude of dE/do appreciably, and the results suggest that the grain boundary self-diffusivity of lead is not influenced by the presence of segregated antimony on the grain boundaries. The diffusional creep occurred above a threshold stress of magnitude ~0·5 MN m^?2, and its temperature dependence was characterised by an activation energy of ~20 kJ mol^?1, similar to the value of 23 ± 7 kJ mol^?1 typical of pure metals in the temperature range investigated. The stress exponent of ~3 observed for the power law regime suggests control by viscous glide of dislocations constrained by dragging of solute atmospheres. Preliminary tests on sagging beam specimens of as-worked material at an applied stress of 2·5 MN m^?2 and a test temperature of 333 K has provided the first direct evidence that anisotropic grain shape affects Coble creep. The specimen with the longest grain dimension along the stress axis underwent slower creep than the specimen with the longest grain dimension perpendicular to the stress axis. This observation is in qualitative agreement with theoretical predictions.

MST/1139     

有向图2k·_5及2k·_7的优美性

杜之亭（１９９４）中提出的猜想：在ｎＣ２ｐ＋１（ｐ∈Ｎ）,在ｎ≡０（ｍｏｄ２）时是优美图。证明了,当ｐ＝２,３时为真     

Phase separation of CaO·Al2O3 ·SiO2 glasses induced by electric field

By means of S-4200 SEM, phase separation of CaO-Al₂O₃-SiO₂ glasses upon application of an electric field is investigated. The experimental results show that externally applied electric field promotes the phase separation of the glass, and it leads to a different size of the droplet phase. In the vicinity of the anode of the glass, the smaller droplet phase is induced compared with the cathode of the glass. The accelerating phase separation of the glass in the presence of an electric field is due to the decrease in the free energy forming a critical nucleus size. The different size of the droplet phase of the cathode is due to the increase in the driving force of nucleation and decrease in the viscosity of the glass compared with that of the anode of the specimen.     

MgCl_2·6H_2O热分解机理的研究

利用综合热分析仪、电阻炉煅烧、X射线衍射、扫描电镜、能谱分析和化学分析,研究了MgCl2.6H2O的热分解机理及中间产物形貌.研究发现:MgCl2.6H2O热分解过程分为六步,在69℃时生成MgCl2.4H2O,129℃时生成MgCl2.2H2O,167℃时生成MgCl2.nH2O(1≤n≤2)和MgOHCl,203℃时MgCl2.nH2O(1≤n≤2)水解与脱水同时进行生成Mg(OH)Cl.0.3H2O,235℃时Mg(OH)Cl.0.3H2O脱水转变为MgOHCl,415℃时MgOHCl直接分解生成MgO.MgOHCl颗粒形状不规则,为多孔结构,Mg(OH)Cl.0.3HO颗粒表面平整.