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2.
Fluorozirconate-phosphate glasses of the ZrF4–BaF2–NaPO3(LiPO3) and ZrF4–BaF2–LaF3–AlF3–LiPO3 systems doped with EuF3, ErF3, and NdF3 were studied by the differential-thermal (DTA) and X-ray diffraction (XRD) analysis, luminescence spectroscopy, scanning and transmission electron microscopy (SEM and TEM) methods. Addition of the phosphate component up to 20 mol % decreases the glass transition temperature and increases the glass stability to crystallization. Heat treatment in the range >Tg–Tc1 of glass transition and first maxima of crystallization temperatures causes crystallization of nanosized β-BaZrF6 particles. At LiPO3 (NaPO3) concentrations of more than 80 mol %, glasses containing a crystalline phase are formed during the synthesis process. 相似文献
3.
The crystallization behavior of the 70GeS 2–20In 2S 3–10CsI glass introduced with 2 mol% Ag 2S system has been studied under non-isothermal condition. The beginning of transmission is shifted toward longer wavelength as a function of annealing temperature. Thermal properties were measured by the differential scanning calorimeter. From the heating rate dependence of crystallization temperature, the activation energy ( E c) for crystallization and the crystallization rate constant ( K) were calculated. The K value of 2.44 × 10 9 for the In 2S 3 phase is about 28 times larger than the second CP, this is why the controllable crystallization to transparent chalcogenide glass-ceramics with sole In 2S 3 crystallites can be achieved. By heat treatment with various temperatures, the hardness of the glass enhanced from 204 to 230.8 kg mm ?2, while retained the transmittance of the 8–11 μm. 相似文献
4.
The understanding of molecular level structural information of phosphate glasses is very much essential. The unique microwave-absorbing ability of NaH 2PO 4·2H 2O was found to be very useful for preparing crystal and glassy sodium super ionic conductors (Nasicon's) as a component of batch mixtures. In this work NaPO 3 glass was prepared by both conventional melt quench and microwave heating from NaH 2PO 4·2H 2O as a starting material. The structure of NaPO 3 glass and their structural evolution upon heating through glass transition were probed by combination of complementary techniques like differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) and thermo-Raman spectroscopy.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
5.
Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used to study the thermal behaviour of (50- x)Na 2O- xTiO 2-50P 2O 5 and 45Na 2O-yTiO 2-(55- y)P 2O 5 glasses. The addition of TiO 2 to the starting glasses ( x=0 and y=5 mol% TiO 2) resulted in a nonlinear increase of glass transition temperature and dilatation softening temperature, whereas the thermal
expansion coefficient decreased. All prepared glasses crystallize under heating within the temperature range of 300–610°C.
The contribution of the surface crystallization mechanism over the internal one increases with increasing TiO 2 content. With increasing TiO 2 content the temperature of maximum nucleation rate is also gradually shifted from a value close to the glass transition temperature
towards the crystallization temperature. X-ray diffraction measurements showed that the major compounds formed by glass crystallization
were NaPO 3, TiP 2O 7 and NaTi 2(PO 4) 3. The chemical durability of the glasses without titanium oxide is very poor, but with the replacement of Na 2O or P 2O 5 by TiO 2, it increases sharply. 相似文献
6.
Na-Gd phosphate glasses doped with Ce 3+ are intensively studied due to their high intensity radioluminescence. Crystallization kinetics of glass with nominal composition
of NaGd(PO 3) 4 was investigated using non-isothermal DTA at heating rates between 10 and 115 K min −1 and evaluated by the Kissinger and Ozawa peak methods. The activation energy for crystallization was determined for heating
rates lower than 72 Kmin −1 as 789.91 and 802.77 kJ mol −1 by using the Kissinger and Ozawa methods, respectively. Formation of nuclei, their dimensions and movement of the crystallization
front were observed using isothermal optical thermomicroscopy. 相似文献
7.
A composition of the products of interaction in the system (NaPO 3) 3-Fe under heating was studied by X-ray analysis and calculation of Δ G T ○ . Possible pathways of the formation of iron phosphides of different chemical composition and other co-products during heating of sodium and iron cyclotriphophate to 1000°C were described on the basis of thermodynamic and X-ray data. The conditions for obtaining individual types of iron phosphides Fe 3P, Fe 2P, and FeP by interaction of sodium cyclotriphophate with metallic iron under heating were found. 相似文献
8.
Characteristic temperatures, such as T
g (glass transition), T
x (crystallization temperature) and T
l (liquidus temperature) of glasses from the V 2O 5-MoO 3-Bi 2O 3 system were determined by means of differential thermal analysis (DTA). The higher content of MoO 3 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 (80V 2O 5·20Bi 2O 3) E
G=280 kJ mol -1, glass #2 (40V 2O 5·30MoO 3·30Bi 2O 3) E
G=422 kJ mol -1 and glass #3 (80MoO 3·10V 2O 5·10Bi 2O 3) 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
9.
Two glasses based on lithium disilicate (LS 2), with and without fluorapatite (FA), were synthesised in the Li 2O-SiO 2-CaO-P 2O 5-CaF 2 system with P 2O 5: CaO: CaF 2 ratios corresponding to fluorapatite. Glass-ceramics have then been prepared by thermal treatment. The mechanism and kinetics
of crystallization as functions of grain size and rate of heating were investigated using thermal analysis methods. The smaller
particles crystallize preferentially by surface crystallization, which is replaced by volume crystallization at larger particle
sizes. Inclusion of FA in the LS 2 favours crystallization through the surface mechanism. The onset limit for volume crystallization replacing the surface mechanism
is at about 0.3 mm for pure LS 2 glass and 0.9 mm for glass containing FA. The calculated activation energies of the glasses ( 299 ± 1 kJ mol-1 for pure LS 2 glass and 288 ± 7 kJ mol −1 for glass containing FA according to Kissinger, or 313 ± 1 kJ mol-1 for pure LS 2 glass and 303 ± 8 kJ mol-1 for glass containing FA according to Ozawa) indicate that the tendency of the glasses to crystallize
is supported by the FA presence. Bioactivity of all samples has been proved in vitro by the formation of new layers of apatite-like
phases after soaking in SBF.
相似文献
10.
The present article deals with the differential scanning calorimetric (DSC) study of Se?CTe glasses containing Sn. DSC runs are taken at four different heating rates (10, 15, 20 and 25?K?min ?1). The crystallization data are examined in terms of modified Kissinger, Matusita equations, Mahadevan method and Augis and Bennett approximation for the non-isothermal crystallization. The activation energy for crystallization ( E c) is evaluated from the data obtained at different heating rates. Activation energy of glass transition is calculated by Kissinger??s relation and Moynihan theory. The glass forming tendency is also calculated for each composition. The glass transition temperature and peak crystallization temperature increases with the increase in Sn % as well as with the heating rate. 相似文献
11.
The crystallization of K 2O·TiO 2·3GeO 2 glass under non-isothermal condition was studied. In powdered glass with particle sizes less than 0.15 mm, surface crystallization
was dominant and an activation energy of crystal growth of E
a,s=327±50 kJ mol −1 was calculated. In the size range 0.15 to 0.45 mm, both surface and volume crystallization occurred. For particle sizes >0.45
mm, volume crystallization dominated with spherulitic morphology of the crystals growth and E
a,v=359±64 kJ mol −1 was calculated. 相似文献
12.
In this work, the crystallization process of a SiO 2–3CaO·P 2O 5–MgO glass was studied by non-isothermal measurements using differential thermal analysis carried out at various heating rates. X-ray diffraction at room and high temperature was used to identify and follow the evolution of crystalline phases with temperature. The activation energy associated with glass transition, ( E g), the activation energy for the crystallization of the primary crystalline phase ( E c), and the Avrami exponent ( n) were determined under non-isothermal conditions using different equations, namely from Kissinger, Matusita & Sakka, and Osawa. A complex crystallization process was observed with associated activation energies reflecting the change of behavior during in situ crystal precipitation. It was found that the crystallization process was affected by the fraction of crystallization, ( x), giving rise to decreasing activation energy values, E c(x), with the increase of x. Values ranging from about 580 kJ mol ?1 for the lower crystallized volume fraction to about 480 kJ mol ?1 for volume fractions higher than 80 % were found. The Avrami exponents, calculated for the crystallization process at a constant heating rate of 10 °C min ?1, increased with the crystallized fraction, from 1.6 to 2, indicating that the number of nucleant sites is temperature dependent and that crystals grow as near needle-like structures. 相似文献
13.
Crystallization, morphology and mechanical properties of a spodumene-diopside glass ceramics with adding different amount
of CaO and MgO in Li 2O-Al 2O 3-2SiO 2 were investigated. With CaO and MgO addition, the crystallization temperature ( T
p) decreased, the value of Avrami constant ( n) decreased from 3.2±0.3 to 1.4±0.2, the activation energy ( E) increased from 299±3 kJ mol −1 to 537±5 kJ mol −1. The crystalline phases precipitated were h-quartz solid solution, β-spodumene and diopside. The mechanism of crystallization of the glass ceramics changed from bulk
crystallization to surface crystallization. The grain sizes and thermal expansion coefficients increased while flexural strength
and fracture toughness of the glass-ceramics increased first, and then decreased. The mechanical properties were correlated
with crystallization and morphology of glass ceramics. 相似文献
14.
The effect of In impurity on the crystallization kinetics and the changes taking place in the structure of (Se 7Te 3) have been studied by DTA measurements at different heating rates (α=5 deg·min ?1, 10 deg·min ?1, 15 deg·min ?1 and 20 deg·min ?1). From the heating rate dependence of the values of T g, T c and T p, the glass transition activation energy ( E t) and the crystallization activation energy ( E c) have been obtained for different compositions of (Se 7Te 3) 100?xIn x (0≤×≤20). The variation of viscosity as a function of temperature has been evaluated using Vogel-Tamman-Fulcher equation. The crystallization data are analysed using Kissinger's and Matusita's approach for nonisothermic crystallization. It has been found that for samples containing In=0, 10, 15, 20 at%, three dimensional nucleation is predominant whereas for samples containing In=5 at%, two dimensional nucleation is the dominant mechanism. The compositional dependence of T g and crystallization kinetics are discussed in terms of the modification of the structure of the Se?Te system. 相似文献
15.
Results of differential scanning calorimetry (DSC) at different heating rates on Se 2Ge 0.2Sb 0.8 chalcogenide glass are reported and discussed. As the heating rate ( ) changed, also the glass transition temperature ( T
g) and onset temperature of crystallization ( T
c) changed. As the value of the transition activation energy E
t changed, the crystallization fraction (), heat flow ( q and the crystallization peak temperature ( T
p) also changed. The value of the effective activation energy of crystallization E
c
was calculated by means of six different methods. The Se 2Ge 0.2Sb 0.8 chalcogenide glass has two crystallization mechanisms, a one-dimensional and an other surface crystallization growth. The average value of E
t for Se 2Ge 0.2Sb 0.8 is equal to 194.95±3.9 kJ·mol –1 and the average value of E
c
is equal to 164±3.3 kJ·mol –1. 相似文献
16.
The induction period for the onset of crystallization was determined in poly(ethylene terephthalate) in the presence and absence of small metallic particles. Two kinds of substrates were used: single microcrystals “transplanted” from the water-soluble inorganic polymer (NaPO 3) x and powders of the same metals (Au, Pt, and Ir). The nucleating activity ? of the substrates was determined on the basis of classical nucleation theory. Values of ? obtained for PET are compared with the corresponding values in the (NaPO 3) x melt and with theoretical concepts. 相似文献
17.
The formation of nano-quasicrystals on isothermal annealing of melt-spun ribbons of Zr 69.5Al 7.5Ni 11Cu 12 metallic glass has been investigated using transmission electron microscopy (TEM). The crystallization study of this metallic glass has been carried out using differential scanning calorimetry (DSC) in non-isothermal (linear heating) mode. It exhibits two-stage crystallization where the first stage corresponds to the precipitation of icosohedral nano-quasicrystalline phase. This has been confirmed with the help of TEM investigations. The crystallization parameters like the activation energy ( E
c) and frequency factor ( k
0) have been derived using the Kissinger peak shift analysis. The activation energies for the first and second crystallization peak are found to be 278 and 295 kJ mol –1, respectively. The frequency factors obtained for the two peaks are respectively 7.16·10 19 and 1.42·10 20 s –1. E
c, k
0 and the Avrami exponent ( n) have also been derived by fitting the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation for the transformed volume fraction ( x) to the crystallization data. JMAK results of E
c for the first and second crystallization peak turn out to be 270 and 290 kJ mol –1 respectively. However, k
0 and n are found to be heating rate dependent as reported in similar studies. The values of n for the first crystallization stage ranges between 1.66 and 2.57 indicating diffusion-controlled transformation in agreement with earlier reports. 相似文献
18.
The study of crystallization kinetics of amorphous alloys has been a matter of great interest for material researchers for past few decades, since it provides information about the kinetic parameters i.e., activation energy of crystallization and the frequency factor. These kinetic parameters can be calculated by model-free isoconversional methods. Isoconversional methods allow calculating the activation energy as a function of degree of conversion, α. Hence, these methods provide accurate results for multistep processes like crystallization. Model-free methods are categorized as linear and non-linear isoconversional methods. Linear methods are further classified as linear differential and linear integral isoconversional methods. In present work, we have used these isoconversional methods to study the effect of non-linear heating rate, employed by modulated differential scanning calorimetry (MDSC), on the non-isothermal crystallization kinetics of Ti 20Zr 20Cu 60 metallic glass. For Ti 20Zr 20Cu 60, MDSC curves clearly indicate a two-step crystallization process. Both crystallization peaks were studied based on the modified expressions for isoconversional methods by non-linear heating rate. The term corresponding to non-linearity comes out to be ( A T ω/2 β) 2. The effect of non-linear heating rate on measurement of kinetic parameters by isoconversional methods is studied. The activation energy of crystallization is calculated for Ti 20Zr 20Cu 60 metallic glass for various degrees of conversion by linear integral isoconversional methods i.e., Ozawa–Flynn–Wall, Kissinger–Akahira–Sunose, and also with Friedman method which is a linear differential isoconversional method. 相似文献
19.
The crystallization and microstructure of Li 2O-Al 2O 3-SiO 2 (LAS) glass ceramic with complex nucleating agents (TiO 2 + ZrO 2 + P 2O 5 +/or F −) are investigated by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the effects of P 2O 5 and F − on the crystallization of LAS glass are also analyzed. The introduction of both P 2O 5 and F − promotes the crystallization of LAS glass by decreasing the crystallization temperature and adjusting the crystallization kinetic parameters, allows a direct formation of β-spodumene without the transformation of LiAl(SiO 3) 2 into β-spodumene and as a result, increases the crystal size and crystallinity of LAS glass ceramic. 相似文献
20.
The crystallization kinetics of glassy Se 98Ag 2 alloy is studied at different heating rates (5, 10, 15, and 20?K?min ?1) using differential scanning calorimetric technique. Endothermic and exothermic peaks are obtained at glass transition ( T g) and crystallization temperature ( T c). Four iso-conversional methods (Kissinger?CAkahira?CSunose (KAS), Flynn?CWall?COzawa (FWO), Tang and Straink) were used to determine the various kinetic parameters (crystallization temperature T ?? , activation energy of crystallization E ??, order parameter n) in non-isothermal mode. 相似文献
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