Non-isothermal crystallization kinetics of V 2 O 5-MoO 3-Bi 2 O 3 glasses (original) (raw)
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Journal of Alloys and Compounds, 2009
Different glasses with nominal compositions of (70 − x)V 2 O 5 -xPbO-20Li 2 O-10Fe 2 O 3 (0 ≤ x ≤ 12.5 mol.%) were successfully obtained by the melt quenching technique. Crystallization kinetics of these glasses was studied under non-isothermal conditions using the formal theory of transformations for heterogeneous nucleation. The procedure was applied to the experimental data obtained by differential thermal analysis, using several measurements at different heating rates. In addition, from the heating rate dependence of the glass transition temperature, the glass transition activation energy was derived. The crystallization results are analyzed and both the activation energy of crystallization process and the crystallization mechanism are characterized in terms of Gao-Wang method. The phases at which the glass crystallizes after the thermal process have been identified by X-ray diffraction. The diffractogram of the transformed material indicates the presence of microcrystallites of LiV 15 O 35.5 , Pb 3 (VO 4 ) 2 and PbO 2 beside the remaining an additional amorphous matrix.
Role of V2O5 in structural properties of V2O5-MnO2-PbO-B2O3 glasses
Glass samples of compositions xV 2 O 5-(20-x) MnO 2-20PbO-60B 2 O 3 with x varying from 0 to 15 % mole fraction are prepared by melt quench technique. The structural analysis of glasses is carried out by XRD, FTIR and density measurement techniques. The FTIR spectral studies have pointed out the conversion of structural units of BO 3 to BO 4 with the presence of VO 4 and VO 5 structural units of vanadium in these glasses. Due to the formation of BO 4 groups, an increase in density from 3.52 to 4.33 g•cm −3 for MnO 2-PbO-B 2 O 3 glasses is observed with an increase in V 2 O 5 content.
Crystallization kinetics of Li2O–PbO–V2O5 glasses
Physica B: Condensed Matter, 2009
Lead vanadate glasses of the system 5Li 2 OÀ(45Àx) PbOÀ(50+x) V 2 O 5 , with x ¼ 0, 5, 10, and 15 mol% have been prepared and studied by differential scanning calorimetry (DSC). The crystallization kinetics of the glasses were investigated under non-isothermal conditions applying the formal theory of transformations for heterogeneous nucleation to the experimental data obtained by DSC using continuous-heating techniques. In addition, from dependence of the glass-transition temperature (T g ) on the heating rate, the activation energy for the glass transition was derived. Similarly the activation energy of the crystallization process was determined and the crystallization mechanism was characterized. The results reveal the increase of the activation energy for glass transition which was attributed to the increase in the rigidity, the cross-link density and the packing density of these glasses. The phases into which the glass crystallizes have been identified by X-ray diffraction. Diffractograms of the transformed material indicate the presence of microcrystallites of Li 0.30 V 2 O 5 , Li 0.67 O 5 V 2 , LiV 6 O 15 , Li 4 O 4 Pb, and O 7 Pb 2 V 2 in a remaining amorphous matrix.
Effect of V 2 O 5 addition on the crystallisation of glasses belonging to the CaO–ZrO 2–SiO 2 system
The crystallisation of CaO-ZrO 2 -SiO 2 glasses doped with V 2 O 5 (0.1-5 mol%) has been investigated in terms of microstructure and thermal parameters. Results indicate that crystallisation is predominantly controlled by a surface nucleation mechanism, even though a partial bulk nucleation has been encountered in compositions containing more than 2 mol% of doping oxide. As detected from differential thermal analysis curves, glass transition temperature and crystallisation temperature, are strongly dependent upon V 2 O 5 content varying from 0.0 to 2.0 mol%, while the crystallisation activation energy values decrease with a parabolic trend from B-glass (0.0 mol% V 2 O 5 content, 495 AE 7) to V-0.7 (0.7 mol% V 2 O 5 content, 420 AE 6) composition, increasing again to 442 AE 5 kJ/mol K with higher amount of V 2 O 5 . The microstructure of the glass-ceramic materials clearly showed a marked dependence upon the amount of V 2 O 5 , also due to the presence of phase separation for content higher than 0.7 mol%. Wollastonite, CaO Á SiO 2 , and a calcia-zirconia-silicate, 2CaO Á 4SiO 2 Á ZrO 2 , are the main crystalline phases whose ratio slightly varies with vanadium oxide content. The glass ceramics obtained from the studied materials are greenish and bluish coloured, so it is possible to use the studied glasses as coloured frits for tile glazes.
Kinetic characterization of TeO 2 –Bi 2 O 3 –V 2 O 5 –Na 2 O –TiO 2 glass system
In continuation of our earlier work on (the mechanical and thermal properties of TeO2–Bi2O3 –V2O5 – Na2O– TiO2 glass system), in this study, we have investigated the kinetic parameters of this system as a function of increasing TiO2 mol% by using differential scanning calorimetry (DSC) data under non-isothermal (isochronal) conditions. The thermodynamic fragility (F) and the glass forming tendency (Kg), ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ Tg Tm factors of the present glass have been evaluated to determine the relationship between the change in the structure and the thermal stability of the glass. The activation energies of both glass transition (Eg) and crystallization (Ec) processes have been evaluated by the methods of Kissinger and Ozawa by the data obtained from (DSC) at heating rates (β) 10, 15, 20 and 25 K/min. The quantitative interpretation of these kinetic parameters has been carried out by coupling with the previous estimated elastic moduli. The kinetic Avrami coefficient (n) was also calculated by several estimation methods to determine and confirm the mechanism of the crystallization process.
Study Of Some Physical And Optical Properties Of Bi2o3-Teo2-V2o5 Glasses
In This paper an experimental studying for Preparation of a glass series consisting of four samples with different composition of 60Bi2O3-(40-X) (TeO2)-X (V2O5), where (x=0, 5, 10 and15mol %)were fabricated by conventional melt-quenching technique. We have fabricated from high-purity raw materials by the melting 950 ºC and then annealing at350 ºC .The main objective of the present study the effect different content of V2O5on the optical and physical properties of the prepared glass. The an amorphous nature of the prepared glasses was determined by X-ray diffraction (XRD) analysis. The physical properties (density, molar volume and oxygen packing density) were determined and calculated. At room temperature by UV-Vis analysis the optical properties of the glasses in this work were determined in the wavelength range 380–800 nm. The results showed that the fundamental absorption edge shifts to higher wavelengths as the amount of V2O5 increases. An optical energy band gap direct transition í µí° í µí°¨í µí°©í µí° í µí° , indirect transition í µí° í µí°¨í µí°©í µí° í µí°í µí° § , ΔE, and refractive index values of these glasses has been determined.The optical band gap energy values corresponding to the direct and indirect allowed transitions decreases while the Urbach energy increases. By using Lorentz–Lorentz formula the polarizability of oxide ion have been evaluated. Metallization criterion M has been calculated on the basis of refractive indexn and energy gap.Based on relation proposed by Duffy and Ingram optical basicity Λ of the glasses is estimated. Molar refraction RM have been calculated and explained on the basis of structural changes.
Non-isothermal crystallization kinetics of SiO 2-B 2 O 3-V 2 O 5-Fe 2 O 3-Sm 2 O 3 glass and glass-ceramics are investigated using experimental and theoretical approaches. In order to gain insight into the thermal behaviour of the glasses, Sm 2 O 3 is systematically replaced with Fe 2 O 3 in the glass composition. Differential thermal analysis (DTA) curves of glass and glass-ceramics are obtained at various heating rates. The DTA-derived characteristic temperatures are used as inputs for different theoretical models. Sm 2 O 3 addition in place of Fe 2 O 3 increases the tendency of surface to bulk crystallization with glass formation tendency in the present samples. The highest activation energy of crystallization is observed for the 40SiO 2-40B 2 O 3-10V 2 O 5-10Fe 2 O 3 (SM-0) sample. The activation energy is observed in the range of 220-425 kJ/mol. It is comparable to other glasses.
Crystallization kinetics of semiconducting vanadium borate glass using DSC
Physica Scripta, 2010
The glass transition temperature was studied via differential thermal analysis of glasses in the system (100 -x) TeO 2 -5Bi 2 O 3 -xZnO and (100x)TeO 2 -10Bi 2 O 3 -xZnO where x = 15, 20, 25 in mol%. The crystallization behavior and microstructure development of the 0.7TeO 2 /0.1Bi 2 O 3 / 0.2ZnO glass during annealing were investigated by nonisothermal differential thermal analysis (DTA), X-ray diffractometry, and transmission electron microscopy. The glass transition temperature, crystallization temperature, and the nature of crystalline phases formed were determined. From the heating rate dependence of the glass transition temperature, the glass transition activation energy was derived. From variation of DTA peak maximum temperature with heating rate, the activation energies of crystallization were calculated to be 305.8 and 197 kJ mol -1 for first and second crystallization exotherms, respectively. Moreover, synthesized crystalline Bi 3.2 Te 0.8 O 6.4 , Bi 2 Te 4 O 11 , and Zn 2 Te 3 O 8 were investigated. In addition, the change in particle size with increasing annealing time was observed by high-polarized optical microscope.
Crystallization of Glasses in the MoO 3 Bi 2 O 3 System
Advanced Materials Research, 2008
a reni_11@abv.bg, b margi71@abv.bg, c astoy@abv.bg Abstract. α-Bi 2 Mo 3 O 12 and β-Bi 2 Mo 2 O 9 crystal phases have been synthesized by crystallization of a glass for a short time. Amorphous samples with the compositions corresponding to the alpha and beta bismuth molybdates have been obtained at high cooling rates (10 4 -10 5 K/s). XRD, DTA and SEM studies were performed to examine the phase formation, thermal behavior of the glasses and the microstructure of obtained crystalline products. By scanning electron microscopy it was shown that the obtained bismuth molybdates consist of dense agglomerates, containing uniform distributed crystals with submicron size.