Non-isothermal free-models kinetic analysis on crystallization of europium - doped phosphate glasses (original) (raw)
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Science of Sintering
Crystallization kinetics of 22.5Li 2 O•10Al 2 O 3 •30GeO 2 •37.5P 2 O 5 (mol%) glass was studied under non-isothermal condition using the differential thermal analysis (DTA). The study was performed by using the first crystallization peak temperature (T p1) which belongs to the precipitation of LiGe 2 (PO 4) 3 phase in the glass. The activation energy of glass crystallization (E a) was determined using different isokinetic methods. The dependence of E a on the degree of glass-crystal transformation (α) was studied using model-free isoconversional linear integral KAS (Kissinger-Akahira-Sunose) and FWO (Flynn-Wall-Ozawa) methods. It was shown that the E a varies with α and hence with temperature and consequently the glass/crystal transformation can be described as a complex process involving different mechanisms of nucleation and growth.
Journal of Materials Science, 2014
The crystallization kinetics and phase transformation of a transparent Tb 3?-doped lithium-aluminum phosphate glass, prepared by melt quenching, were investigated. The energy associated to the glass transition and the crystallization parameters (activation energy for crystallization and Avrami exponent) were evaluated by different methods using the experimental data obtained by differential thermal analysis performed at different heating rates. Using an isoconversional method to determine the change of the activation energy for crystallization with the fraction of crystallization, it was verified that with the increase in the fraction of crystallization from 0.1 to 0.9, the value of the activation energy decreased slightly from *370 to *310 kJ mol-1 and that the Avrami exponent varied from 0.8 to 1, suggesting a surface crystal growth mechanism. Observation of the microstructural evolution of heat-treated glass samples confirmed a surface crystallization process revealing spherulitic crystals constituted mainly by aluminum metaphosphate.
Differential scanning calorimetry (DSC) was used in this work to study the effect of La2O3 addition on crystallization mechanism of barium–lead–zinc phosphate glasses. Bulk glasses from two different routes (using P2O5 and H3PO4 as starting materials) presented only one crystallization peak. An assessment of glass-forming ability (GFA) was performed from recent theory that is connected to glass stability (GS), and is also correlated to critical cooling rate, qcr. Systems with high La2O3 content presented some of the highest GS values and estimated critical cooling rates (qcr) lower than 0.079 K/s. For both routes were determined the activation enthalpies for crystallization, that were 126±12 kJ/mol (for P2O5) and 110±32 kJ/mol (for H3PO4). The calculated Avrami n parameters, based on exothermic crystallization peaks, were 3.50±0.33 (for P2O5) and 3.09±0.91 (for H3PO4), considering data from the lowest heating rate (5 K/min). These values suggest that the DSC peaks should be associated to volume crystallization, due to La2O3 influence, and crystallization did not change significantly using different routes.
Journal of Thermal Analysis and Calorimetry, 2019
Preparation and thermal properties of Er 3+-doped lithium-yttrium meta-phosphate glasses with a nominal composition of Er:LiY(PO 3) 4 were studied as a new scintillating material for neutron detection. The glassy Er:LiY(PO 3) 4 ingots 10 × 10 × 25 mm 3 in size were prepared by quenching of the molten mixture of the starting lithium carbonate, yttrium phosphate, and phosphorus oxide in stoichiometric relations. Crystallization kinetics was experimentally studied on powder samples with particle sizes ranging from 96 to 106 μm, 200 to 212 μm, and on bulk glassy samples using the non-isothermal differential scanning calorimetry. The evaluation of the measured data was performed using the Johnson-Mehl-Avrami, Matusita and Augis-Bennett models, and the y(α) and z(α) functions. In the case of the powder samples, the model analysis of the measured data showed that the crystallization mechanism was primarily performed through volume nucleation followed by 2D and 3D growth and in the bulk one by the surface and volume nucleation with 1D growth. Obtained kinetic parameters were used for reconstruction of the crystallization peaks using various models and compared with actual experimental data.
Structure and crystallization kinetics of Li2O modified sodium-phosphate glasses
Journal of Molecular Structure, 2015
h i g h l i g h t s Density of glasses depends on the field strength of various cations. 15 mol% Li 2 O contained glass shows higher thermodynamic and kinetic stability. FTIR and Raman study confirmed the higher polymerization in 15 mol% Li 2 O glass. As Li 2 O increases phosphate structural units changes from Q 3 ? Q 2 ? Q 1 ? Q 0 .
This work aims to investigate the prepared glasses within the 20Li2O−(50−x)Li2WO4−xTiO2−30P2O5 system, with 0≤x≤15 mol%. The bonds constituting the framework of these glasses were studied by Raman spectroscopy. The data analysis of the chemical durability showed that the dissolution rates depend on the composition of each glass. Thermal analysis by DSC technique was used to determine the activation energy of crystallization, it found in the glass of composition (x= 5) that Ec= 184.482 kJ/mol. The determinate Avrami parameter is around 1.7 which allows suggesting the mechanism is surface crystallization. The crystallization process of the prepared glasses is carried out by heating samples at 550°c for 4 hours and 12 hours. The crystallized phases are identi ed by XRD. The results of X−ray diffraction analysis con rm that TiO2 acts mainly as network forming units. The crystalline phases Li2WO4 (JCPDS# 01−072−0086) and (JCPDS# 01−087−0409) are formed during the crystallization process. The formation of these crystalline phases into the glasses depends on the time of heating at xed crystallization temperature. FTIR spectra of the glass-ceramics show nearly the same IR vibrational modes as their parent glasses.
The analysis of the nucleation process of the lithium germanium phosphate glass
Science of Sintering, 2022
The nucleation process of lithium germanium-phosphate glass was studied to determine the temperature range of nucleation and the temperature of the maximum nucleation rate. The differential thermal analysis (DTA), and scanning electron microscope (SEM) were used to reveal the nonisothermal and isothermal process of nucleation, respectively. The crystallization process occurred at a high homogeneous nucleation rate and the spherulitic crystal growth morphology. Nanostructured samples were obtained.
Crystallization and microstructure of Eu3 +-doped lithium aluminophosphate glass
2014
A transparent Eu 3+-doped lithium aluminophosphate glass was prepared by melt-quenching technique. The thermal behavior of the glass was investigated by differential thermal analysis (DTA), the structure was studied by X-ray diffraction (XRD) and the morphology was observed by optical polarization microscopy and scanning electron microscopy (SEM). The activation energy of glass transition and the activation energy of crystallization and Avrami exponent have been evaluated under non-isothermal conditions from the data obtained by DTA at different heating rates. DTA curves exhibited an endothermic peak associated with the glass transition and two exothermic peaks. The mean value calculated for the activation energy of glass transition was 545 kJ mol −1. The activation energy of crystallization was~400 kJ mol −1 for the first exothermic peak and~170 kJ mol −1 for the second peak. The Avrami exponent was~1 for both peaks indicating surface crystallization. XRD results showed that the main crystalline phase, aluminum metaphosphate, Al(PO 3) 3 , and aluminum phosphate, AlPO 4 , were formed together with lithium barium phosphate, Li 3 Ba(PO 3) 7 , during the first exothermic peak and together with barium pyrophosphate, Ba 2 P 2 O 7 , during the second peak. Morphological study of heat-treated glass samples revealed microstructural features that confirmed a surface crystallization process.
Crystallization study of molybdate phosphate glasses by thermal analysis
Journal of Non-Crystalline Solids, 2009
Vitreous samples were prepared in the binary system NaPO 3-MoO 3 and their characteristic temperatures were determined by Differential Scanning Calorimetry. Glasses with high amounts of MoO 3 (>45 mol%) exhibit an intense crystallization peak and the composition 50 NaPO 3-50 MoO 3 was chosen for the crystallization study. Two different methods based on thermal analyzes were used to determine the mechanism of crystallization in these molybdenum-phosphate glasses. In the first procedure, thermal analyses by DTA were performed on samples with different grain sizes and the crystallization tendency deduced in function of superficial area. The second method used the classical non-isothermal crystallization study: DSC measurements were performed under several heating rates to access activation energy for crystallization and Avrami parameter n. Critical cooling rate was calculated and compared with experimental data obtained from DTA analysis upon cooling.
Crystallization of silico-phosphate glasses
Journal of Thermal Analysis and Calorimetry, 2008
Silico-phosphate glasses of Ca 3/2 PO 4 -SiO 2 and NaCaPO 4 -SiO 2 systems have been the topic of our studies. Microscopic and EDX investigations which have been carried out have shown that liquation occurs only in the case of glasses belonging to the NaCaPO 4 -SiO 2 system. Additionally, it has been found that there are significant differences in the chemical compositions of the matrix and the inclusions. Based on the spectroscopic investigations it has been shown that the glasses of both series are characterized by complex domain composition and the structure of domains is close to that of the corresponding crystalline phase. Interpretation of the DTA results has been based on the knowledge of the texture and the structure of the materials studied. It has been found that liquation of the glasses is a multi-step process in which the matrix and the inclusions crystallize separately. Multi-step crystallization of the glasses belonging to the NaCaPO 4 -SiO 2 system has been confirmed by the high temperature XRD investigations.