Crystallization Kinetics of Glass-Ceramics by Differential Thermal Analysis (original) (raw)
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Transparent fluorphlogopite based glasses were prepared using talc, glass sand and phosphate raw material. The effect of TiO 2 , ZrO 2 , phosphate or combinations of either B 2 O 3 -phosphate or TiO 2 -ZrO 2 on the crystallization of fluorphlogopite base glass was examined. X-ray diffraction analysis showed formation of fluorphlogopite at 765°C in the base glass. Addition of ZrO 2 or 5 wt% phosphate did not affect the monophase crystallization. However, when the amount of phosphate was increased to 10 wt%, fluorapatite was crystallized together with fluorphlogopite. TiO 2 and TiO 2 -ZrO 2 addition enhance the formation of enstatite together with fluorphlogopite. Thermal treatment of ZrO 2 -containing glasses was found to induce crystallization of fluorphlogopite as a main phase. The addition of TiO 2 alone or mixed with ZrO 2 catalyzed crystallization of enstatite and fluorphlogopite above 1000°C. SEM analysis showed that glasses containing fluorphlogopite acquired fine-grained micr...
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The MgO-Al 2 O 3-SiO 2-TiO 2 glass system was prepared by melting method. The crystallization behavior and crystallization kinetics of a sample with glass ceramic composition were examined. DTA and XRD analyses revealed the crystallization of Ca 0.965 Mg 2 Al 16 O 27 cordierite (Mg 2 Al 4 Si 5 O 18) and Fe 2 TiO 5 phases. The activation energy for the crystallization of cordierite phase has been evaluated, and the crystallization mechanism has been studied by applying DTA measurements performed at various heating rates. The results indicate that the dominant crystallization mechanism for this system is bulk crystallization dominated by three-dimensional growth. The average calculated values of crystallization and viscous flow for the formation of crystal phases from the glass matrix were measured to be 410 and 390 kJ mol-1 , respectively.
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The paper presents the kinetic study of the crystallization processes which take place in basalt glasses containing variable amount of nucleation agent (CaF 2 , 3÷10%). The activation energies have been calculated using Kissinger's equation and verified with the Ozawa-Flynn-Wall equation. In this order, the DTA curves have been registered with different heating rates, between 4 and 20 degrees/min. A correlation equation between the activation energy and the amount of nucleation agent (% of CaF 2) was established. By X-ray diffraction it was proved that the crystalline phase formed in the crystallization process represents a pyroxenic solid solution, Ca(Mg,Fe)SiO 3 .
Journal of Thermal Analysis and Calorimetry, 2018
In this study, the influence of Bi 2 O 3 on the crystallization kinetics of the MgO-Al 2 O 3-SiO 2-TiO 2 glass ceramics system produced from industrial waste was investigated. The Bi 2 O 3-added MgO-Al 2 O 3-SiO 2-TiO 2 glass ceramics systems were prepared by melting method. The crystallization behaviour and crystallization kinetics of a sample with glass ceramic composition were examined. DTA and XRD analysis revealed the crystallization of Ca 0.965 Mg 2 Al 16 O 27 cordierite (Mg 2-Al 4 Si 5 O 18) and Fe 2 TiO 5 phases. The activation energy for the crystallization of cordierite phase has been evaluated, and the crystallization mechanism has been studied by applying DTA measurements taken at various heating rates. The results indicate that the dominant crystallization mechanism for this system is bulk crystallization dominated by three-dimensional growth. At 2.5, 5 and 10% Bi 2 O 3 addition, the crystallization activation energy was calculated to be 336 ± 4, 218 ± 1 and 170 ± 3 kJ mol-1 , and the viscous flow activation energy was measured to be 377 ± 2, 403 ± 7 and 407 ± 21 kJ mol-1 , respectively.
Journal of the European Ceramic Society, 1997
This work deals with preparation and characterization of Er-doped lithium-yttrium phosphate glass and study of the influence of the particle size in samples on the crystallization process and its kinetics. Two types of prepared samples were used-powder with particle size fractions 90-106 and 200-212 lm and the bulk one. These glassy samples were studied by non-isothermal DSC measurements at heating rates from 2 to 40 K min-1 under nitrogen atmosphere. Obtained data were used for evaluation of the influence of the particle size on the activation energies of the crystallization process by seven the most widely used methods. Activation energies for both powder and bulk samples calculated by model-free methods (Kissinger, Augis-Bennett, and Matusita-Sakka) were similar and independent on the particle size. On the contrary, the influence of the particle size on the activation energy was well described by isoconversional methods (Kissinger-Akahira-Sunose, Starink, Tang, and Flynn-Wall-Ozawa). Moreover, the prepared glassy samples were calcined at temperature over the crystallization temperature and characterized by powder X-ray diffraction analysis.
Crystallization kinetics of SiO2-MgO-3CaO-P2O5-Al2O3-ZrO2 glass
Materials Science-poland, 2007
The crystallization behaviour of SiO2–MgO–3CaO–P2O5–Al2O3–ZrO2 glass was studied using glass samples prepared by melting reagent grade SiO2, MgO, Ca5(PO4)3OH, P2O5, Al2O3 and ZrO2. DTA and XRD analysis revealed the crystallization of whitlockite, anorthite and baddeleyite phases. The crystallization kinetics was studied by applying the DTA measurements carried out at various heating rates. The activation energies of crystallization and viscous flow were measured as 209 kJ·mol –1 and 356 kJ·mol –1 , respectively. The resultant SiO2–MgO–3CaO–P2O5–Al2O3–ZrO2 glass-ceramics revealed very fine and homogenous microstructure.
Mechanism and kinetics of glass-ceramics formation in the LiO2-SiO2-CaO-P2O5-CaF2 system
Central European Journal of Chemistry, 2009
Two glasses based on lithium disilicate (LS2), with and without fluorapatite (FA), were synthesised in the Li2O-SiO2-CaO-P2O5-CaF2 system with P2O5: CaO: CaF2 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 LS2 favours crystallization through the surface mechanism. The onset limit for volume crystallization replacing the surface mechanism is at about 0.3 mm for pure LS2 glass and 0.9 mm for glass containing FA. The calculated activation energies of the glasses (299 ± 1 kJ mol-1 for pure LS2 glass and 288 ± 7 kJ mol−1 for glass containing FA according to Kissinger, or 313 ± 1 kJ mol-1 for pure LS2 glass and 303 ± 8 kJ mol-1 fo...
A study of the primary crystallization of a mixed anion silicate glass
Journal of Non-Crystalline Solids, 2008
This paper presents the results of a study of the primary crystallization of a multicomponent mixed anion silicate glass. The primary phase, leucite, and the secondary phase, diopside, were formed by surface crystallization, while the secondary phase, phlogopite, was formed by volume crystallization. The influence of the particle size of glass powder samples in the range 0-1 mm on the temperature of the DTA crystallization peak, T p , the height of the peak, (dT) p , and the parameter T 2 p /(DT) p was studied. The behaviors of the parameters (dT) p and T 2 p /(DT) p depend only on the change in the surface-to-volume nuclei ratio, as is the case with polymorphic crystallization. However, the particle size ranges in which the surface, volume and mixed crystallization mechanism dominate are considerably narrower for this glass. The influence of the duration of a pre-DTA heat treatment on the parameters T p , (dT) p , and DT p for fixed temperatures in the range T = 550-750°C was investigated. The T p of the samples thermally treated for different times, at fixed temperatures, decreased up to t = 5 h and then increased to a value close to that of an as-quenched sample, after which the value remained constant. The curves of (dT) p , and DT p as a function of time for fixed temperatures show a maximum. The influence of the temperature of the pre-DTA heat treatment on the parameters T p , (dT) p, and DT p for fixed times of t = 1À5 h was also investigated. On increasing the pre-DTA heat treatment time, the curves changed significantly. The curves for 3 and 5 h in the temperature range 580-660°C were similar to the nucleation curve, which indicated that the volume nucleation process proceeded in this temperature range. The behavior of these parameters, as a result of the simultaneous action of different nucleation mechanisms and crystal growth differ from those previously reported for the case of polymorphic crystallization.
Crystal Growth of F-Phlogopite from Glasses of the SiO 2 -Al 2 O 3 -MgO-K 2 O-F System
Journal of the American Ceramic Society, 2015
A study on the devitrification of fluorophyllosilicate glass precursors is presented. The research has been focused on the early stages of the crystallization process and shows the variation in the crystallization mechanism with increasing the fluorine content. The devitrification process has been studied by means of differential scanning calorimetry (DSC) and field emission scanning electron microscopy (FESEM). These complementary techniques established that both surface (heterogeneous nucleation) and volume (internal homogeneous nucleation) mechanisms are present in the crystallization process of fluorophlogopite-based glasses, the latter being predominant. By increasing the percentage of fluorine in the parent glass, a variation in the location of the first crystals developed from the internal volume of the glass towards the external surface was observed. Such an alteration in the crystallization mechanism was also checked by examining the microstructure of crystallized samples prepared under short time treatments.
Crystallization of leucite as the main phase in aluminosilicate glass with low fluorine content
2000
The paper presents the results of the study of aluminosilicate glass that contains 0.77 wt% of F − anions. The results show that the critical size of glass particles at which the surface mechanism of crystallization changes to volume crystallization is in the vicinity of 0.075 mm in this glass. The temperature of the maximum nucleation rate was determined to be T n = 680 • C, and it is higher than the transformation temperature T g . At crystallization temperatures up to T c = 950 • C, the crystal phase of leucite is formed, alone. Above this temperature, besides the main phase of leucite, two other phases, diopside and phlogopite appear. The activation energy of crystallization E a = 319 ± 23 kJ/mol was determined. The results also show that the activation energy does not depend on the crystallization mechanism in this glass. The value of the Avrami parameters is n = 1.45. Microstructural studies confirmed the fact that volume crystallization of leucite takes place in this glass. The leucite crystals grow in form of equiaxial dendrites with pronounced anisotropy along the direction 001 . Kinetical and microstructural studies show that the process of leucite crystal growth occurs at the smooth atomic scale-faceted crystal/glass interfaces and that it is controlled by volume diffusion. During the isothermal heat treatment the structure of dendrites changes. C 2000 Kluwer Academic Publishers