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1.
K. A. Aly A. Dahshan Yasser B. Saddeek 《Journal of Thermal Analysis and Calorimetry》2010,100(2):543-549
The present paper reports on the effect of MoO3 on the glass transition, thermal stability and crystallization kinetics for (40PbO–20Sb2O3–40As2O3)100−x
–(MoO3)
x
(x = 0, 0.25, 0.5, 0.75 and 1 mol%) glasses. Differential scanning calorimetry (DSC) results under non-isothermal conditions
for the studied glasses were reported and discussed. The values of the glass transition temperature (T
g) and the peak temperature of crystallization (T
p) are found to be dependent on heating rate and MoO3 content. From the compositional dependence and the heating rate dependence of T
g and T
p, the values of the activation energy for glass transition (E
g) and the activation energy for crystallization (E
c) were evaluated and discussed. Thermal stability for (40PbO–20Sb2O3–40As2O3)100−x
–(MoO3)
x
glasses has been evaluated using various thermal stability criteria such as ΔT, H
r
, H
g and S. Moreover, in the present work, the K
r(T) criterion has been considered for the evaluation of glass stability from DSC data. The stability criteria increases with
increasing MoO3 content up to x = 0.5 mol%, and decreases beyond this limit. 相似文献
2.
The present work demonstrates application of electrical conductivity (σ)–temperature (T) cycles to investigate thermal properties viz., crystallization and glass transition kinetics in AgI–Ag2O–V2O5–MoO3 superionic glasses. The σ–T cycles are carefully performed at various heating rates, viz., 0.5, 1, 3, 5, and 7 K/min. The conductivity in Ag+ ion conducting glasses exhibit anomalous deviation from Arrhenius behavior near glass transition temperature (T
g) followed by a drastic fall at crystallization (T
c). The temperature corresponding to maximum rate of crystallization (T
p) is obtained from the derivative of σ–1/T plots. With increasing heating rates, the characteristic temperatures (T
g, T
p) are found to be shifting monotonically toward higher temperatures. Thus, activation energy of structural relaxation E
s, crystallization E
c and other thermal stability parameters have been obtained from σ–T cycles using Kissinger equation and Moynihan formulation. For a comparative study, these kinetics parameters have also been
calculated from differential scanning calorimetry plots. The parameters obtained from both the methods are found to be comparable
within experimental error. 相似文献
3.
Iordanova R. Lefterova E. Uzunov I. Dimitriev Y. Klissurski D. 《Journal of Thermal Analysis and Calorimetry》2002,70(2):393-404
Characteristic temperatures, such as T
g (glass transition), T
x (crystallization temperature) and T
l (liquidus temperature) of glasses from the V2O5-MoO3-Bi2O3 system were determined by means of differential thermal analysis (DTA). The higher content of MoO3 improved the thermal stability of the glasses as well as the glass forming ability. The non-isothermal crystallization was
investigated and following energies of the crystal growth were obtained: glass #1 (80V2O5·20Bi2O3) E
G=280 kJ mol-1, glass #2 (40V2O5·30MoO3·30Bi2O3) E
G=422 kJ mol-1 and glass #3 (80MoO3·10V2O5·10Bi2O3) E
G=305 kJ mol-1. The crystallization mechanism of glass #1 (n=3) is bulk, of glass #3 (n=1) is surface. Bulk and surface crystallization was supposed in glass #2. The presence of high content of a vanadium oxide
acts as a nucleation agent and facilitates bulk crystallization.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
P. Mošner K. Vosejpková L. Koudelka L. Beneš 《Journal of Thermal Analysis and Calorimetry》2012,107(3):1129-1135
The effect of TeO2 additions on the thermal behaviour of zinc borophosphate glasses were studied in the compositional series (100 − x)[0.5ZnO–0.1B2O3–0.4P2O5]–xTeO2 by differential scanning calorimetry, thermodilatometry and heating microscopy thermal analysis. The addition of TeO2 to the starting borophosphate glass resulted in a linear increase of glass transition temperature and dilatometric softening
temperature, whereas the thermal expansion coefficient decreased. Most of glasses crystallize under heating within the temperature
range of 440–640 °C. The crystallization temperature steeply decreases with increasing TeO2 content. The lowest tendency towards crystallization was observed for the glasses containing 50 and 60 mol% TeO2. X-ray diffraction analysis showed that major compounds formed by annealing of the glasses were Zn2P2O7, BPO4 and α-TeO2. Annealing of the powdered 50ZnO–10B2O3–40P2O5 glass leads at first to the formation of an unknown crystalline phase, which is gradually transformed to Zn2P2O7 and BPO4 during subsequent heating. 相似文献
5.
A number of samples of sodium and silver phosphate glasses doped with
various compositions of some transition metals viz. iron, manganese and zinc
chlorides alongwith undoped samples of sodium and silver phosphate glasses
were synthesized and characterized by X-ray diffraction, IR spectral, electrical
conductivity and differential scanning calorimetry (DSC). The glass transition
temperature (T
g)
and crystallization temperature (T
c)
values obtained from DSC curves were found to increase with increasing concentration
of the dopant Fe/Mn/Zn chlorides in both sodium and silver phosphate glasses
and the following sequence is observed:
T
g(–FeCl3)>T
g(–MnCl2)>T
g(–ZnCl2)
T
c(–FeCl3)>T
c(–MnCl2)>T
c(–ZnCl2)
The increase in T
g
and T
c values indicate
enhanced chemical durability of the doped glasses. The electrical conductivity
values and the results of FTIR spectral studies have been correlated with
the structural changes in the glass matrix by the addition of different transition
metal cations as dopants. 相似文献
6.
Thermal behaviour of the glass series (100-x)[50ZnO-10B2O3-40P2O5]·xSb2O3 (x=0-42 mol%) and (100-y)[60ZnO-10B2O3-30P2O5]·ySb2O3 (y=0-28 mol%) was investigated by DSC and TMA. The addition of Sb2O3 results in a decrease of the glass transition temperature and crystallization temperature in both compositional series. All
glasses crystallize on heating in the temperature range of 522–632°C. Thermal expansion coefficient of the glasses monotonously
increases with increasing Sb2O3 content in both series and varies within the range of 6.6–11.7 ppm °C−1. From changes of thermal capacity within the glass transition region it was concluded that with increasing Sb2O3 content the ‘fragility’ of the studied glasses increases. 相似文献
7.
A linear relationship exists between the glass transition temperature (T
g) and the quadrupole splitting (Δ) of Fe(III). The linear relationship, termed ‘T
g-Δ rule’, has been verified in 60CaO·(40-x)Al2O3·xFe2O3, 60CaO·10BaO·(30-x) Al2O3·xFe2O3, 60CaO·(40-x)Ga2O3·xFe2O3, and 50CaO·(50-x)Ga2O3·xFe2O3 glasses. In these glasses, both theT
g and Δ decrease linearly with an increasing content of Fe2O3 (≈40 mol%). The slope of the straight line, obtained from the plot of theT
g vs. Δ, was calculated to be 670≈700, °C/(mm·s−1), revealing that the Fe(III) constitutes the skeleton of aluminoferrate and galloferrate glasses. 相似文献
8.
The glass transition temperature (Tg), density, refractive index, Raman scattering spectra, and X-ray photoelectron spectra (XPS) for xZnO-yBi2O3-zB2O3 glasses (x=10-65, y=10-50, z=25-60 mol%) are measured to clarify the bonding and structure features of the glasses with large amounts of ZnO. The average electronic polarizability of oxide ions (αO2−) and optical basicity (Λ) of the glasses estimated using Lorentz-Lorenz equation increase with increasing ZnO or Bi2O3 content, giving the values of αO2−=1.963 Å3 and Λ=0.819 for 60ZnO-10Bi2O3-30B2O3 glass. The formation of BOBi and BOZn bridging bonds in the glass structure is suggested from Raman and XPS spectra. The average single bond strength (BMO) proposed by Dimitrov and Komatsu is applied to the glasses and is calculated using single bond strengths of 150.6 kJ/mol for ZnO bonds in ZnO4 groups, 102.5 kJ/mol for BiO bonds in BiO6 groups, 498 kJ/mol for BO bonds in BO3 groups, and 373 kJ/mol for BO bonds in BO4 groups. Good correlations are observed between Tg and BMO, Λ and BMO, and Tg and Λ, proposing that the average single bond strength is a good parameter for understanding thermal and optical properties of ZnOBi2O3B2O3 glasses. 相似文献
9.
Thermal behaviour and structure of glasses from the SiO2–P2O5–K2O–MgO–CaO system modified by Fe2O3 addition were studied by DSC, XRD and FTIR methods. It has been found that the replacement of MgO and CaO modifiers by Fe2O3 in the structural network of silicate–phosphate glass results in decrease of the glass transition temperature (T
g) and heat capacity change (ΔC
p) accompanying the glass transformation. Simultaneously, the ability for crystallization, its course and the type of the forming
phases depend on the relative proportions between iron and phosphorus as components forming the silicate–phosphate structure.
The type of the crystal phases forming in the course of heating the considered glass has been found to be in agreement with
the character of the domains occurring in this glass, confirmed by FTIR examinations. 相似文献
10.
Silicate-phosphate glasses of SiO2–P2O5–K2O–MgO–CaO system containing manganese cations were investigated to obtain information about the influence of manganese ions
on the thermal behavior of such glasses. Amorphous state of glasses and the course of phase transformation and crystallization
taking place during their heating were investigated by DSC, XRD, and FTIR methods. It was shown that an increasing content
of manganese replacing calcium and magnesium in the structure of analyzed glasses causes decrease of glass transition temperature
(T
g) and heat capacity change (Δc
p) accompanying the glass transformation. Simultaneously, thermal stability of the glasses increased. Products of multistage
crystallization of glasses containing up to 8 mol% of MnO2 were: marokite (CaMn2O4), phosphate of Ca9MgK(PO4)7 type, and diopside (CaMgSi2O6). Product of crystallization of glasses containing higher amount of manganese was braunite (Mn7O8SiO4). This was accompanied by change of structure of magnesium calcium silicates from diopside-type structure to akermanite-type
silicates (Ca2MgSi2O7). The data interpretation was based on bonds and chemical interactions of the individual components forming the glass structure. 相似文献
11.
Thermal behaviour of the
glass series (100–y)[0.5ZnO·0.1B2O3·0.4P2O5]·yTiO2
(with y=0–39 mol% TiO2)
was investigated by DSC and TMA. The addition of TiO2
results in a non-linear increase of glass transition temperature. The compositional
dependences of thermal stability, evaluated by two criteria exhibit two maxima
for the glasses doped with 10.7 and 35.9 mol% TiO2.
All the glasses crystallize on heating in the temperature range of 576–670°C.
The crystallization mechanism was studied at the glasses with 19.4 and 35.9
mol% TiO2 and the results showed that surface nucleation
mechanism prevails in these glasses over the internal one. 相似文献
12.
Thermal
and structural properties of model silicate-phosphate glasses containing the
different amounts of the glass network modifiers, i.e. Mg2+
and Ca2+ were studied. To explain the changes of
the parameters characterizing the glass transition effect (Tg, Δcp) and the crystallization
process (Tc, ΔH) depending on the cations modifiers additions,
analysis of the bonds and chemical interactions of atoms in the structure
of glasses was used.
31P
MAS-NMR spectra of SiO2–P2O5–MgO(CaO)–K2O glasses show that the phosphate complexes are mono- and diphosphate. It
has been found that increasing amounts of Mg2+
or Ca2+ cations in the structure of glasses causes
the reduction of the degree of polymerization of the phosphate framework (Q1→Q0).
The influence of increasing of modifiers in the structure of silicate- phosphate
glasses on the number of non-bridging oxygens per SiO4
tetrahedron and density of glasses was presented. 相似文献
13.
L. Stoch 《Journal of Thermal Analysis and Calorimetry》2004,77(1):7-16
Thermochemistry and structural mechanism of crystallization of MgO-Al2O3-SiO2 glasses with TiO2 as crystallization activator were studied. Thermal and HREM investigation proved that near the T
g temperature crystallization is going by rearrangement of glass structure elements and part of its components redistribution
like at disorder — order phase transition in solid bodies. Nanocrystals of Mg-titanate and high quartz structure solid solution
are formed then. Next enstatite and cordierite are crystallizing. Thermochemical and chemical bonds strength analysis indicate
that during multistage crystallization of glasses, kind and order of crystal phase formation, is determined by the glass structure
decomposition progress and its particular components release accompanying increase of temperature. It has been proved that
molar heat capacity change (ΔC
p) accompanying the glass transition is the significant measure of degree of changes in the structure of glass preceding crystallization.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
M. M. A. Imran D. Bhandari N. S. Saxena 《Journal of Thermal Analysis and Calorimetry》2001,65(1):257-274
Results of phase transformations, enthalpy released and specific heat of Ge22Se78–xBix(x=0, 4 and 8) chalcogenide glasses, using differential scanning calorimetry (DSC), under non-isothermal condition have been reported and discussed. The glass transition temperature, T
g, is found to increase with an average coordination number and heating rates. Following Gibbs—Dimarzio equation, the calculated values of T
g (i.e. 462.7, 469.7 and 484.4 K) and the experimental values (i.e. 463.1, 467.3 and 484.5 K) increase with Bi concentration. Both values of T
g, at a heating rate of 5 K min–1, are found to be in good agreement. The glass transition activation energy increases i.e. 102±2, 109±3 and 115±8 kJ mol–1 with Bi concentration. The demand for thermal stability has been ensured through the temperature difference T
c–T
g and the enthalpy released during the crystallization process. Below T
g, specific heat has been observed to be temperature independent but highly compositional dependent. The growth kinetic has been investigated using the Kissinger, Ozawa, Matusita and modified JMA equations. Results indicate that the crystallization ability is enhanced, the activation energy of crystallization increases with increasing the Bi content and the crystal growth of these glasses occur in 3 dimensions.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
15.
Glasses with compositions 60Bi2O3–(40?x)B2O3–xGa2O3 (x = 5, 10, 15, 20 mol%) are prepared by conventional melting method. The thermal properties are investigated by differential thermal analysis (DTA) and the structures of the glasses were probed by Infrared, Raman and X-ray photoelectron spectroscopy (XPS). The results show that density, refractive index and optical basicity increase with the increase of Ga2O3. The glass transition temperature (Tg), the onset crystallization temperature (Tx), ΔT (Tx?Tg) decrease with the content of Ga2O3. The cut-off edges in ultraviolet and infrared shift to longer wavelength with the increase of Ga2O3. On the other hand, the addition of Ga2O3 causes a progressive coordination number change of the boron atom from 3 to 4. XPS result indicates both Bi5+ and Bi3+ exist in 5 mol% Ga2O3 content, while Bi5+ amounts decrease with the increase of Ga2O3 contents. The glass is mainly composed of [BiO6], [BO3], [BO4] and [GaO4] polyhedra. Glasses are supposed to have layer structure. [BO3] triangle and [BO4] tetrahedra may be located between the [GaO4] tetrahedral and [BiO6] octahedra to prevent crystallization and to compensate electric charge. 相似文献
16.
Glass transition effect of mixed network AlPO4–BPO4–SiO2 glasses was studied. DTA/DSC and TMA measurements has been applied in the research. It has been found that glass transition
effect has structurally sensitive properties. Glass transition temperature T
g, changes of specific heat (Δc
p)and thermal expansion coefficient (α) accompanying the process depend on the nature and the number of components forming
the glassy framework. Character of chemical bonds combining them into the glass structure has an influence on the glass transition
effect. Its course is dependent on the flexibility of the structure of glasses.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
DTA was used to study thermal properties and thermal stability of (50-x)Li2O-xTiO2-50P2O5 (x=0–10 mol%) and 45Li2Ot-yTiO2-(55-y)P2O5 (y=5–20 mol%) glasses. The addition of TiO2 to lithium phosphate glasses results in a non-linear increase of glass transition temperature. All prepared glasses crystallize
under heating within the temperature range of 400–540°C. The lowest tendency towards crystallization have the glasses with
x=7.5 and y=10 mol% TiO2. X-ray diffraction analysis showed that major compounds formed by annealing of the glasses were LiPO3, Li4 P2O7, TiP2O7 and NASICON-type LiTi2(PO4)3. DTA results also indicated that the maximum of nucleation rate for 45Li2O-5TiO2-50P2O5 glass is close to the glass transition temperature. 相似文献
18.
The high-resolution
transmission electron microscopy HRTEM study of the atomic scale mechanism
of crystal structure organization within the amorphous polymeric structure
of the model multicomponent glass TiO2–MgO–Al2O3–SiO2– in the glass transformation temperature range has been
undertaken. In the glass transition (T
g)
temperature range, glass transforms from the solid of rigid amorphous structure
into viscoelastic state of weakened chemical bonds. This is an example of
nuclei formation and crystal growth in the polymeric amorphous structure of
low atomic scale homogeneity due to middle range ordering. It has been demonstrated
that in this case crystal structure formation proceeds by successive displacement
and local ordering of atoms in the amorphous structure, like disorder-order
transformation in crystalline solid bodies. As the consequence in the crystallization
by parent structure reorganization mechanism, traditional model of glass crystallization
as well as kinetic models of reactions in solid bodies according Avrami or
others, are worthy to be revised. 相似文献
19.
Marcin Środa 《Journal of Thermal Analysis and Calorimetry》2009,97(1):239-243
Glasses have been synthesized in the system SiO2–Al2O3–Na2O–AlF3–LaF3–Er2O3. A base glass (in mol% 67SiO2–9Al2O3–20Na2O–Al2F6–3La2F6) was modified by 0.5, 0.75, 1, 1.25, 1.5, 2 and 5 mol% Er2O3, respectively. Glasses were prepared by conventional fusion method from 20 g batches. The glass transition temperature (T
g), the jump-like changes of the specific heat (ΔC
p) accompanying the glass transition and the enthalpy of crystallization (ΔH) were calculated. DTA measurements clearly reveal that the increase of the Er2O3 content in the glass changes the effects of crystallization and diminishes the thermal stability of the glassy network. In
the same time the changes in the transition temperature are observed. The formation of NaLaF4 and Na1.45La9.31(SiO4)6(F0.9O1.1) as a main phase was confirmed. The diminishing of the thermal stability was connected with erbium which incorporated into
Na1.45La9.31(SiO4)6(F0.9O1.1) structure. 相似文献
20.
Thermal behavior of xGa2O3–(50 − x)PbO–50P2O5 (x = 0, 10, 20, and 30 mol.% Ga2O3) and xGa2O3–(70 − x)PbO–30P2O5 (x = 0, 10, 20, 30, and 40 mol.% Ga2O3) glassy materials were studied by thermo-mechanical analysis (TMA) and differential thermal analysis (DTA). Replacement of
PbO for Ga2O3 is accompanied by increasing glass-transition temperature (263 ≤ T
g/°C ≤ 535), deformation temperature (363 ≤ T
d/°C ≤ 672), crystallization temperature (396 ≤ T
c/°C ≤ 640) and decreasing of coefficient of thermal expansion (5.1 ≤ CTE/ppm K−1 ≤ 16.7). Values of Hruby parameter were determined (0.1 ≤ K
H ≤ 1.3). The thermal stability of prepared glasses increases with increasing of concentration of Ga2O3. 相似文献