Non-isothermal kinetic studies for binary TeO2-P2O5 glass system

A study of TeO₂–P₂O₅ glass system has been carried out by Differential Thermal Analysis (DTA) to elucidate the kinetics of crystallization for these glassy samples. The results of DTA performed at different heating rates are discussed. The values of the glass transition temperature, T _g , as well as the glass crystallization temperature, T _c , are found to be dependent upon the heating rate. From this dependence, the values of activation energy for both the glass transition and crystallization are evaluated and discussed     

In vivo behaviour of glasses in the SiO2-Na2O-CaO-P2O5-Al2O3-B2O3 system

Sixteen glasses in the SiO₂-Na₂O-CaO-P₂O₅-Al₂O₃-B₂O₃ system were studied. The glasses were implanted in rabbit tibia. According to theirin vivo behaviour, they were divided into five groups. A phenomenological equation for thein vivo behaviour was developed. The solubility of the glasses was determinedin vitro as weight loss in Tris buffer solution. The tissue response is discussed in relation to the glass composition and the solubility. For bone-bonding glasses calcium phosphate formation takes place within a silica-gel at the glass surface. The gel must be sufficiently hydrated and flexible to allow calcium phosphate to build up. The results suggest that alumina can inhibit bone bonding by retarding the formation rate of a silica-rich layer, by stabilizing the silica structure enough to prevent calcium phosphate build-up within the layer, or by either disturbance of the bone mineralization or bone incompatibility of an alumina-containing calcium- and phosphorus-rich surface layer. The mechanism responsible for the lack of bone adherence is determined by the glass composition. Up to about 1.5 wt % Al₂O₃ can be included in the glass without destroying the bioactivity.     

Sintering behaviour of lithium ferrites containing Nb2O5 and V2O5

Lithium ferrite toroids with various compositions and with various amounts of Nb₂O₅ or V₂O₅, have been prepared by a powder compacting method, and their sintering behaviours, microstructures and weight-loss characteristics have been investigated. The rate of sintering is higher in an Fe₂O₃-deficient lithium ferrite than in an Fe₂O₃-excess lithium ferrite due to the presence of excess oxygen vacancy in the Fe₂O₃-deficient lithium ferrite during sintering. The presence Of LiNbO₃ or LiVO₃, which is formed by Nb₂O₅ or V₂O₅, on the surface of lithium ferrite grains causes an increase in oxygen activity of the lithium ferrite and a decrease in the rate Of lithium evaporation during sintering, resulting in a strong enhancement in the sintering rate. The enhancing effect of V₂O₅ in the sintering Of lithium ferrite is stronger than that of Nb₂O₅ due to the possible formation of liquid V₂O, before the formation of LiVO₃.     

Preparation and characterization of binary V2O5-Bi2O3 glasses

Characterization of the binary V₂O₅-Bi₂O₃ glasses prepared by rapidly quenching the melt has been made from the studies of X-ray diffraction, scanning electron microscopy, infrared absorption, differential thermal analysis, electron paramagnetic resonance, chemical analysis, density and electrical properties. Stable glasses are obtained for 95 to 75 mol % V₂O₅ by quenching on a stainless steel substrate, while quenching on a copper substrate extends the glass formation range from 95 to 70 mol % V₂O₅. The V-O bond vibration in the glasses occurs at 1020 cm^–1 and the V^5% ion exists in six-fold coordination as in crystalline V₂O₅. All the glasses appear to be in single phase. The spin concentration in the glasses is found to be independent of temperature. A second heat-treatment at 255° C develops crystalline phase in the glasses. Unlike infrared absorption, electron paramagnetic resonance, density and chemical compositions, the electrical and thermal (DTA) properties are found to be slightly sensitive to the thermal history of preparation of the glasses. The high-temperature (300 to 500 K) conduction in the glasses seems to be due to adiabatic hopping of polarons. The thermopower is observed to be independent of temperature and provides evidence for small polaron formation in the glasses.     

Electrical behaviour of the MnO2-doped ZnO-Bi2O3 system

The electrical behaviour of xwt% MnO₂-(100-x) (95wtx% ZnO-5wt% Bi₂O₃) is investigated. Addition of MnO₂ retards grain growth in the ZnO-Bi₂O₃ system. It is observed that the MnO₂ dopant decreases the leakage current, while it increases the non-linearity coefficient and the grain boundary resistance of ZnO-Bi₂O₃ ceramics. In addition, the noise spectrum of MnO₂-doped ZnO-Bi₂O₃ deviates from 1/f behaviour. The deviation is, however, less enhanced for samples with more MnO₂ dopant.     

Grain growth of ZnO in binary ZnO-V2O5 ceramics

Grain growth of ZnO during liquid-phase sintering of binary ZnO-V₂O₅ ceramics has been studied for V₂O₅ contents from 0.5 to 4 mol% and sintering from 900°C to 1200°C. The results are discussed and compared with previous studies in terms of the phenomenological kinetic grain growth expression: G ⁿ – G _o ⁿ = K _o t exp(–Q/RT).Addition of V₂O₅ is found to decrease the ZnO grain growth exponent, n, as well as the apparent activation energy, Q. The activation analysis also reveals a change in the rate-controlling mechanism for ZnO grain growth. Following a low-V₂O₅-content (2 mol%) of nearly constant Q values of about 88 kJ/mol, further V₂O₅ additions cause an increase of the Q value to about 115 kJ/mol. Consistent with accepted models of liquid-phase sintering, it is concluded that the rate-controlling mechanism of ZnO grain growth during liquid-phase sintering in the presence of V₂O₅ changes from one of a phase-boundary reaction at low V₂O₅ levels to one of diffusion through the liquid phase at more than 2 mol% V₂O₅ levels.     

Phase equilibrium relations in the binary system Bi2O3-ZnO

Phase equilibria in the binary system Bi₂O₃-ZnO were studied by quenching technique. Heat-treated compositions were subjected to X-ray diffraction for phase identification, and differential thermal analysis, optical and scanning electron microscopy were used to determine the solid-liquid equilibria occurring in this system. The data thus obtained revealed that incorporation of a small amount of ZnO to the high-temperature face-centered cubic lattice of Bi₂O₃ leads to the formation of a body-centered cubic solid solution (-Bi₂O₃), which extends up to a composition of 2.2 mol% ZnO at a temperature near 750°C. On cooling, the -Bi₂O₃ solid solution undergoes a eutectoid transformation at a temperature of 710°C to yield the low-temperature monoclinic polymorph of Bi₂O₃ (-Bi₂O₃) and Bi₃₈ZnO₅₈. The eutectoid occurs at a composition of 1.8 mol% ZnO. The compound Bi₃₈ZnO₅₈ has a crystal structure analogous to the body-centered cubic -Bi₂O₃ solid solution and melts incongruently at a temperature near 753 ± 2°C to yield -Bi₂O₃ and liquid. A binary eutectic occurs between Bi₃₈ZnO₅₈ and ZnO at a composition near 25 ± 1.0 mol% ZnO with a melting temperature of 738 ±2°C. Based on the data obtained in this study, a revised phase diagram of the binary system Bi₂O₃-ZnO is proposed.     

Photo-luminescence characteristics of binary P2O5–CaO glass ceramic

ABSTRACT

To explore excellent colour display materials, the binary phosphate glass ceramics doped with R (R?=?Tm³⁺, Tb³⁺, Eu³⁺, Sm³⁺, and Mn²⁺) ions were prepared. The X-ray diffraction, transmission electron microscope, absorption, excitation, and emission spectra of the glass ceramics had been studied in detail. It was found that Ca₂P₂O₇ and CaP₂O₆ had excited in the glass ceramics, which can improve the luminescent characteristics of the materials. The results show that the binary phosphate glass ceramics can display abundant colours, which is very helpful for developing the luminescent materials for colour display.     

Phase equilibrium in the TeO2-B2O3-V2O5 system

Journal of Materials Science Letters -     

New low loss microwave dielectric ceramics in the BaO-TiO2-Nb2O5Ta2O5 system

Microwave ceramic dielectric resonator materials in the BaO-TiO₂-Nb₂O₅Ta₂O₅ system such as BaTiNb₄O₁₃, BaTiTa₂Nb₂O₁₃, BaTiTa₄O₁₃, Ba₃Ti₄Nb₄O₂₁, Ba₃Ti₄Ta₄O₂₁, Ba₃Ti₅Nb₆O₂₈, Ba₃Ti₅Ta₆O₂₈ and Ba₃Ti₅Nb₃Ta₃O₂₈ have been prepared by the conventional solid state ceramic route. They have relatively high dielectric constant and high quality factor. The resonator materials are characterized by X-ray diffraction and scanning electron microscopy (SEM) methods. The BaTiNb₄O₁₃Ba₃Ti₅Nb₆O₂₈ and Ba₃Ti₅Nb₃Ta₃O₂₈ have small temperature variation of the resonant frequency and are possible microwave dielectric resonator materials for practical applications.     

Preparation and characterization of new niobophosphate glasses in the Li2O-Nb2O5-CaO-P2O5 system

In the present work we describe the synthesis, spectroscopy, thermal and chemical durability properties of the vitreous system Li₂O-Nb₂O₅-CaO-P₂O₅ (LNCP). Investigations of the short-range order by Fourier transform infrared, Raman, UV-VIS and ³¹P MAS-NMR spectroscopies suggest that the network former glass consists of Nb octahedra linked to pyro/orthophosphate units through Nb—O—P bonds. The presence of modifier cations (Li⁺ and Ca²⁺) promotes depolymerization of the P—O—P chains, yielding pyro/orthophosphate units. The presence of this kind of structure accounts for the improvement of the chemical durability at low pH when the Nb content in the LNCP glass composition is high. The density and linear refractive indices of LNCP glasses increased linearly as the Nb₂O₅/P₂O₅ molar ratio increased, as a consequence of P₂O₅ substitution by Nb₂O₅ as the glassformer. The dependence of the glass transition temperature, the softening temperature and the crystallization temperature on the Nb₂O₅/P₂O₅ ratio exhibits the same behavior. On the other hand, the thermal expansion coefficient decreases with the increased Nb₂O₅/P₂O₅ ratio.     

Oxidation behaviour of the sintered Si3N4-Y2O3-Al2O3 system

The oxidation behaviour of silicon nitride composed of Si₃N₄, Y₂O₃, Al₂O₃, AlN and TiO₂ was investigated in dry and wet air at 1100–1400 °C. The oxidation rates were confirmed to obey the parabolic law. An activation energy of 255 kJ mol^–1 was calculated from the Arrhenius plots of the results of oxidation in an air flow. In still air the oxidation rate was larger than that in an air flow, but the oxidation rate in flowing air was not affected by the air flow rate. -cristobalite and Y₂O₃·2SiO₂ were formed in oxidized surface layers. These crystal phases increased with increasing oxidation temperature. In particular, a higher content of -cristobalite was obtained in still air oxidation. The existence of water vapour in flowing air greatly promoted the oxidation.Concurrent with Kanagawa Academy of Science and Technology.