Non-isothermal crystallization kinetics of MgO–BaO–B2O3–Al2O3–SiO2 glass

5MgO–9BaO–33B₂O₃–33Al₂O₃–20SiO₂ (mol%) glass was prepared by the melt quenching method at 1823 K for 2 h. Dilatometry and differential scanning calorimetry (DSC) curves of the glass have been investigated. Fragility index F was used to estimate glass formability. The crystallization kinetics of the glass was described by the activation energy (E) for crystallization and numerical factors (n, m) depending on the nucleation process and growth morphology. XRD and SEM analysis were also used to describe the crystals’ types and morphology precipitated from the MgO–BaO–B₂O₃–Al₂O₃–SiO₂ glass. The results show that the effective activation energy of the crystallization process E was 45.19 kJ/mol, and n up to 4.05. Two crystals phases, i.e. Al₄B₂O₉ and Al₂₀B₄O₃₆ were observed in the crystallized samples. SEM results were consistent with crystallization kinetics.     

The nucleation and crystallization of MgO-B2O3-SiO2 glass

The nucleation and crystallization of MgO-B₂O₃-SiO₂ (MBS) glass were studied by means of a non-isothermal, thermal analysis technique, X-ray diffraction and scanning electron microscopy. The temperature range of the nucleation and the temperature of the maximum nucleation rate for MBS glass were determined from the dependences of the inverse temperature at the DSC peak (1/T_p) and the maximum intensity of the exothermic DSC crystallization peak ((δT)_p) on the nucleation temperature (T_n). For MBS glass the nucleation occurred at 600-750 °C, with the maximum nucleation rate at 700 °C, whereas the nucleation and crystal growth processes overlapped at 700 °C < T ≤ 750 °C. The analyses of the non-isothermal data for the bulk MBS glass using the most common models (Ozawa, Kissinger, modified Kissinger, Ozawa-Chen, etc.) revealed that the crystallization of Mg₂B₂O₅ was three-dimensional bulk with a diffusion-controlled crystal growth rate, that n = m = 1.5 and that the activation energy for the crystallization was 410-440 kJ/mol.     

Structural, thermal and crystallization kinetics of ZnO–BaO–SiO2–B2O3–Mn2O3 based glass sealants for solid oxide fuel cells

Glass compositions in the system 40SiO₂–30BaO–20ZnO–(x)Mn₂O₃–(10 − x)B₂O₃ glasses have been synthesized and the thermal, structural and crystallization kinetic properties characterized. The lower concentration of Mn₂O₃ in place of B₂O₃ acts as a network former and suppressed the tendency of phase separation in glasses. On the other hand, concentration of Mn₂O₃ > 7.5 mol% induce phase separation in the glass matrix. The highest activation energy for crystallization is observed in the composition without B₂O₃ (INM4) (355 kJ/mol). The values of thermal expansion coefficient (TEC) and viscosity of this glass is 8 × 10⁻⁶ K⁻¹ and 10^4.2dPa s (850 °C), respectively. After long heat treatment (800 °C for 100 h), thermodynamically stable hexacelsian and monoclinic phases are formed. These phases are not detrimental to SOFC application.     

Crystallization behavior of Bi1.25Y1.75Fe5O12 prepared by coprecipitation process

A non-isothermal study of the crystallization kinetic of coprecipitation of Bi_1.25Y_1.75Fe₅O₁₂ was carried out by differential scanning calorimetry (DSC). The Avrami exponent n suggesting the dimensionality of crystal growth was determined using the Ozawa equation. From non-isothermal DSC data presented values in range of 775–1023 kJ/mol and 3.28–2.10 for the activation energy of crystallization and the Avrami exponent, respectively. These Avrami exponent values were consistent with surface and internal crystallizations growth simultaneously.     

Evaluation of novel composition (SiO2–CaO–Na2O–P2O5, SrO–CuO) degradable amorphous silicate glasses properties and comprehensive characterization of the thermal features

The current work presents and discusses the findings of a comprehensive study on the structural, chemical and thermal properties of SrO and CuO incorporated SiO₂–CaO–Na₂O–P₂O₅ amorphous silicate glass with a novel composition. Here, fundamental features (experimental density, oxygen density, and hardness) of all glasses were determined and chemical as well as phase composition of the glasses was verified with XRF and XRD, respectively. Moreover, the thermal behavior (viscos flow and crystallization kinetics) of amorphous silicate glass was investigated by non-isothermal methods using DTA analysis. The activation energies of glass transition (E_g) were calculated in the range of 546–1115 kJ/mol by Kissinger method, whereas the activation energies of crystallization (E_c) were calculated in the range of 164–270 kJ/mol by three different methods (Kissinger, Ozawa, Yinnon and Uhlmann). Avrami exponent (n) values ranged from 1.17 to 3.28 demonstrated that amorphous silicate glasses have different crystallization mechanism. Working temperature, which is one of the parameters indicating glass stability, increased with the incorporation of Sr and Cu from 187 °C to 245 °C. The initial dissolution measurement has been applied to study the degradability behavior of Sr and Cu incorporated amorphous glasses in vitro. Quantitative evaluation of Si⁴⁺ (0.156–0.373 kV), Ca²⁺ (0.043–0.332 kV), Na⁺ (0.044–0.329 kV), P⁵⁺ (0.057–0.289 kV), Sr²⁺ (0.134–0.385 kV), and Cu²⁺ (0.090–0.203 kV) depending on the ion activation energy (E_a-ion) and ion concentration at different temperature values (24, 37 and 55 °C) was performed in contact with Tris-HCl solution by ICP-OES analysis. The results revealed that investigated glasses were degradable and incorporation of Sr and Cu affected the glass initial dissolution. Overall, investigated glasses are suitable for various application such as hot-working production, glass-ceramic manufacturing, and glass or glass-ceramic scaffolds fabrication, due to wide working temperature ranges and high crystallization tendencies of the developed glasses.     

Crystallization of LiNbO3 and NaNbO3 in niobiosilicate glass–ceramics

Although glass–ceramics have been widely explored for their thermal stability and mechanical properties, they also offer unique symmetry-dependent properties such as piezoelectricity and pyroelectricity through controlled crystallization of a polar phase. This work examines crystallization of LiNbO₃ in a 35SiO₂–30Nb₂O₅–35Li₂O mol% composition and crystallization of LiNbO₃ and NaNbO₃ in a 35SiO₂–30Nb₂O₅–25Li₂O–10Na₂O mol% composition. Crystallization kinetics are examined using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory where the Avrami exponent, n, is calculated to be 1.0–1.5. Microscopical analysis shows dendritic morphology, which when combined with the JMAK analysis, suggests diffusion-controlled one-dimensional growth. Adding Na₂O to the glass composition increases the inter-diffusivity of ions which causes LiNbO₃ to crystallize faster and lowers the activation energy of transformation from 1054 ± 217 kJ/mol in the ternary composition to 882 ± 212 kJ/mol. Time-temperature-transformation diagrams are presented which show that the temperature for maximum rate of transformation for LiNbO₃ is ∼650°C and for NaNbO₃ is ∼715°C.     

Criterion for estimating the number of phases in phase-separated glass of the Na2O-K2O-B2O3-SiO2 system by dilatometric analysis

The data of dilatometry and electron microscopy of four series of xNa₂O-(8 ? x)K₂O-32B₂O₃-60SiO₂, xNa₂O-(8 ? x)K₂O-22B₂O₃-70SiO₂, xNa₂O-(6 ? x)K₂O-34B₂O₃-60SiO₂, and xNa₂O-xK₂O-(40 ? 2x)B₂O₃-60SiO₂ phase-separated glass heat-treated at 550°C for 144 h (for glass containing 70 mol % SiO₂) and 24 h (for glass containing 60 mol % SiO₂) for separation on phases are summarized. The comparison of dilatometric data and electron microscopy allow one to conclude that glass with a difference between the onset deformation temperature and a glass transition temperature of more than 100°C is phase-separated; and glass with a difference of less than 65°C is single-phase. Curves for the glass transition temperature as a function of the K₂O content reveal a mixed alkali effect, namely, minimums for glass containing 60% SiO₂, and maximums for glass containing 70% SiO₂.     

Study on non-isothermal crystallization kinetics of the BaO-CaO-Al2O3-B2O3-SiO2 glass for IT-SOFCs sealing

The crystallization ability plays a key role in effecting thermal ability of sealing glass for intermediate temperature-solid oxide fuel cells (IT-SOFCs) to prevent fuel leakage during operation and insulate the cell stack from the external atmosphere. Herein, using differential thermal analysis (DTA) techniques, the growth mode of crystals precipitated in BaO-CaO-Al₂O₃-B₂O₃-SiO₂ (BCABS) sealing glass through the heat treatment was calculated in terms of non-isothermal crystallization kinetics for the first time. The calculated results showed that the average kinetic exponent n of the glass was approximatively 1, indicating that the crystal nucleuses became to form and further grew with one-dimensional mode from the surface inwards. Scanning electron microscope (SEM) observations clearly revealed that a large number of one-dimensional filamentous crystals have been formed on the interface between the sealing glass and the electrolyte after the heat treatment at 973?K for 100?h, which perfectly coincided with the theoretical calculations, and the glass was well combined with the electrolyte without any visible cracks or peeling at the interface. The one-dimensional growth of hexagonal BaAl₂Si₂O₈ crystals verified by X-ray diffraction (XRD) could effectively decelerate the decrease of thermal expansion coefficient of glass to ensure enhance the thermo-stability of the BCABS sealing glass for IT-SOFC.     

Crystallization Kinetics and Dielectric Properties of a Low‐Fire CaO–Al2O3–SiO2 Glass + Alumina System

The crystallization kinetics and dielectric properties of a low‐dielectric, low‐temperature, cofirable ceramic system comprised of CaO–Al₂O₃–SiO₂ (CAS) glass and alumina have been investigated. Crystalline phases including pseudowollastonite (CaSiO₃), anorthite (CaAl₂Si₂O₈) and cristobalite (SiO₂) are formed during firing the pure CAS glass. The crystallization kinetics of both pseudowollastonite and cristobalite exhibit Avrami‐like behavior, and the results show apparent activation energies close to that of diffusion of alkali ions in the glass. With added alumina content greater than a critical value, the above crystalline phases are completely suppressed but more anorthite is formed. This result is attributed to the rapid dissolution kinetics of alumina into the CAS glass. As the degree of crystallization increases with firing time, the dielectric loss of the composite decreases significantly, however, with dielectric constant remaining relatively unchanged.     

Eu3+ doped ferroelectric CaBi2Ta2O9 based glass-ceramic nanocomposites: Crystallization kinetics,optical and dielectric properties

We report Eu³⁺ doped transparent glass-ceramics (GCs) containing bismuth layer-structured ferroelectric (BLSF) CaBi₂Ta₂O₉ (CBT) as the major crystal phase. The CBT crystal phase was generated in a silica rich glass matrix of SiO₂-K₂O-CaO-Bi₂O₃-Ta₂O₅ glass system synthesized by melt quenching technique followed by controlled crystallization through ceramming heat-treatment. Non-isothermal DSC study was conducted to analyze crystallization kinetics of the glass in order to understand the crystallization mechanism. The optimum heat-treatment protocol for ceramization of precursor glass that has been determined through crystallization kinetics analysis was employed to fabricate transparent GCs containing CBT nanocrystals, which was otherwise difficult. Structural analysis of the GCs was carried out using XRD, TEM, FESEM and Raman spectroscopy and results confirmed the existence of CBT nanocrystals. The transmittance and optical band gap energies of the GCs were found to be less when compared to the precursor glass. The refractive indices of the GCs were increased monotonically with increase in heat-treatment time, signaling densification of samples upon heat-treatment. The dielectric constants (ε_r) of the GCs were progressively increased with increase in heat-treatment duration indicating evolution of ferroelectric CBT crystals phase upon heat-treatment.     

The effects of La2O3 doping on the photosensitivity,crystallization behavior and dielectric properties of Li2O-Al2O3-SiO2 photostructurable glass

Photostructurable Li₂O-Al₂O₃-SiO₂ glass is a promising material to fabricate complex three-dimensional structure with a high aspect ratio. However, its high dielectric loss at high frequencies has restrained its application in the field of integrated circuits packaging. In this research, La₂O₃, which has a large ionic radius, as well as strong polarization and bonding strength, was used to obstruct mobile ion migration to reduce the dielectric loss. The results indicated that moderate doping with La₂O₃ could effectively reduce the dielectric loss. When the dopant amount was 3%, the dielectric loss was successfully reduced to a minimum of 4?×?10^?3 with a dielectric constant of 6.6 at 1?GHz, and this sample also possessed the optimal dielectric-temperature stability. Additionally, the effects of doping on the photosensitivity and crystallization behavior were also analysed. The results suggested that La₂O₃ doping did not affect the photosensitivity and selective crystallization characteristics. However, La₂O₃ restrained the precipitation of silicate from the [SiO₄] tetrahedron, resulting in a decrease of nucleation rate and a delay of crystallization.     

Nonisothermal crystallization of PP/nano‐SiO2 composites

The kinetics of nonisothermal crystallization of polypropylene (PP) containing nanoparticles of silicon dioxide (SiO₂) were investigated by differential scanning calorimetry (DSC) at various cooling rates. Several different analysis methods were used to describe the process of nonisothermal crystallization. The results showed that the Ozawa equation and Mo's treatment could describe the nonisothermal crystallization of the composites very well. The nano‐SiO₂ particles have a remarkable heterogeneous nucleation effect in the PP matrix. The rate of crystallization of PP/nano‐SiO₂ is higher than that of pure PP. By using a method proposed by Kissinger, activation energies have been evaluated to be 262.1, 226.5, 249.5, and 250.1 kJ/mol for nonisothermal crystallization of pure PP and PP/nano‐SiO₂ composites with various SiO₂ loadings of 1, 3, and 5%, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1013–1019, 2004     

Effect of Cr2O3 on the crystallization behavior of synthetic diopside and characterization of Cr-doped diopside glass ceramics

Diopside is the main crystalline phase in silicate materials such as ceramics and glass-ceramics. Herein, the effect of Cr₂O₃ on the microstructure and crystallization behavior of synthetic diopside, as well as the solubility of Cr₂O₃ in diopside is discussed. Samples were prepared by the melting method and characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, and confocal laser scanning microscopy. Results show that the maximum achievable solubility of Cr₂O₃ in diopside is between 1% and 3% by weight, and that the magnesiachrome spinel formed by Cr₂O₃ can act as a nucleating agent for the diopside phase. Glass ceramics was prepared by synthesis slag which simulates the chromium-containing waste. The activation energy of crystallization is 274 KJ/mol and Avrami parameter is 3.23. The leaching behavior of glass ceramics was studied. Additionally, the effect of Cr₂O₃ on the mechanisms of phase change were discussed. The study provides a theoretical basis for the preparation of chromium containing waste-based silicate materials with diopside as the main crystalline phase.     

Crystallization Kinetics of the LiBO2–Nb2O5 Glass Using Differential Thermal Analysis

The crystallization kinetics in the glass system (100− x )LiBO₂− x Nb₂O₅ (5≤ x ≤20, in molar ratio) prepared via the conventional metal-plate quenching technique have been studied by isothermal and non-isothermal methods using differential thermal analyses. X-ray powder diffraction studies carried out on heat-treated (500°C) glasses reveal the evolution of lithium niobate crystalline phase along with a minor phase of LiBO₂. The exponent n in the Jhonson–Mehl–Avrami (JMA) equation applied to the isothermal process is 2.62, which is in excellent agreement with that obtained under the non-isothermal process (2.67). The activation energies for crystal growth obtained from JMA equation under isothermal condition, modified Ozawa and Kissinger equations under non-isothermal conditions, are 293, 311, and 306 kJ/mol, respectively.     

Effect of A2O3 (A = La,Y, Cr,Al) on thermal and crystallization kinetics of borosilicate glass sealants for solid oxide fuel cells

Influence of various intermediate oxides on thermal, structural and crystallization kinetics of 30BaO–40SiO₂–20B₂O₃–10A₂O₃ (A = Y, La, Al, Cr) glasses has been studied. The highest glass transition temperature (T_g) with high thermal stability is observed in Y₂O₃ containing glasses as compared to other glasses. The thermal expansion coefficient (TEC) increases with increasing heat treatment duration in all the glasses. The maximum increase in TEC is observed in Cr₂O₃ containing glass ceramics. FTIR study showed that transmission bands due to silicate and borate chains become sharper with splitting after heat treatment. A selected glass sample (BaCr) has been tested for interaction and adhesion with Crofer 22 APU interconnect material for its application as a sealant in solid oxide fuel cell.     

Formation of alkoxy-derived 3Al2O3 · 2GeO2

Germanium-mullite (3Al₂O₃·2GeO₂) is formed directly as a single phase at lower temperatures from amorphous material with 50–66.7 mole% Al₂O₃ prepared by the alkoxy-method. The kinetic data of the 3Al₂O₃·GeO₂ crystallization with 50 and 60 mole% Al₂O₃ are represented by different solid-state equations. The difference of the crystallization mechanism is possibly explained in terms of the morphology of the 3Al₂O₃·GeO₂ particles.     

Effect of the Al2O3/SiO2 mass ratio on the crystallization behavior of CaO-SiO2-MgO-Al2O3 slags using confocal laser scanning microscopy

The crystallization behavior of a CaO-SiO₂-MgO-Al₂O₃ slag system with varying Al₂O₃/SiO₂ mass ratios from 0.03 to 1.10 has been investigated using a confocal laser scanning microscopy (CLSM). The resulting continuous cooling transformation (CCT) and time-temperature-transformation (TTT) curves showed that the initial crystallization temperature increased and the incubation time for crystallization slightly decreased with increasing Al₂O₃/SiO₂ ratio. The crystal growth rate first increased and then decreased with decreasing isothermal temperature. X-ray diffraction (XRD) analysis suggested that Ca₂MgSi₂O₇ or Ca₃MgSi₂O₈ precipitated as the primary phase at lower Al₂O₃/SiO₂ ratios, while the Ca₂Al₂SiO₇ phase was preferred at higher Al₂O₃/SiO₂ ratios. The observed crystalline phases correlated well with the expected thermodynamic predictions from FactSage. In addition, structural analysis using ²⁷Al magic angle spinning nuclear magnetic resonance (²⁷Al MAS-NMR) microscopy of the as-quenched slags indicated the presence of a higher ratio of tetrahedral [AlO₄]^5-structural units with increasing Al₂O₃/SiO₂ ratio, which enhanced the polymerization of tetrahedral [AlO₄]^5- and [SiO₄]^4- structural units to form Ca₂Al₂SiO₇.     

Crystallization kinetics of La2O3–Al2O3–B2O3 glass–ceramic composites

One glass formulation (L2 glass) with the composition of La₂O₃, Al₂O₃ and B₂O₃ in a molar ratio of 10:10:80 was selected to cofire with Al₂O₃ filler. The composites underwent a two-stage crystalline evolution in the temperature range of 800 to 975 °C. The crystallization kinetics of LaBO₃ grains and the transformation to LaAl₂B₃O₉ phase were investigated by DTA, XRD, SEM/EDS, and TEM. The results showed that the Al₂O₃ filler plays an important role as the heterogeneous sites of LaBO₃ nuclei, and as reactant for the formation of flaky LaAl₂B₃O₉ crystals. The apparent activation energy of LaBO₃-phase formation in L2 glass was 534 kJ/mol and reduced to 466 kJ/mol by the addition of Al₂O₃. The detail transformation reactions, kinetics, and the crystalline orientation relationship between those phases are reported.     

Utilization of DTA in determination of crystallization mechanism in SiO2–Al2O3–CaO–MgO(R2O) glasses in presence of various nuclei

The effect of various nuclei on crystallization mechanism of SiO₂–Al₂O₃–CaO–MgO(R₂O) glasses were investigated by differential thermal analysis (DTA) through Matusita, Marotta and modified Kissinger methods. The Avrami constant, n, and the activation energy for crystallization of the most promising specimens containing Cr₂O₃, Fe₂O₃ and TiO₂ in the single, double and triple nuclei series were determined. According to the results the Avrami constants derived from the Marotta method were more consistent with the other experimental observation. While glasses containing TiO₂ as the single nucleant represents surface crystallization and those containing Cr₂O₃ or Fe₂O₃ one-dimensional bulk crystallization, the crystallization mechanism of specimens containing both Cr₂O₃ and Fe₂O₃ and also the glasses containing the triple nuclei, are bulk and two dimensional.     

Formation of Bi2ZnB2O7 Nanocrystals in ZnO–Bi2O3–B2O3 Glass Induced by Femtosecond Laser

We report on the formation of Bi₂ZnB₂O₇ crystal structures with designated patterns in ZnO–Bi₂O₃–B₂O₃ glass by femtosecond laser direct writing. The crystallization mechanism in glass is investigated by crystallization kinetics analysis and simulation of the three‐dimensional temperature field distribution. The crystallized regions show larger third‐order optical nonlinearity than the unirradiated region in glass by Z‐scan technique. This finding is of great potential in application of nonlinear optical integrated devices and development of new nonlinear materials.