Crystallization Kinetics Of Glass Research Articles

Revealing bulk metallic glass crystallization kinetics during laser powder bed fusion by a combination of experimental and numerical methods

Laser powder bed fusion (PBF-LB/M) has been used to fabricate bulk metallic glass (BMG) parts. However, there is still a lack of understanding about the crystallization behavior of BMGs during PBF-LB/M. This article aims to combine experimental and numerical methods to gain a more comprehensive understanding of the BMG crystallization kinetics during PBF-LB/M. The material used in this work is an industrial-grade BMG commercially known as AMZ4 (Zr59.3Cu28.8Al10.4Nb1.5, at.%). The samples prepared by PBF-LB/M were characterized by optical microscopy, scanning electron microscopy, and nanoindentation. Simulations were performed using our in-house developed software with setups mimicking the PBF-LB/M experiment. The experimental and numerical results are compared and discussed in detail. The most important finding is that BMG crystallization in PBF-LB/M is a very localized phenomenon, mainly caused by short-range in situ heat treatment. Here, short-range in-situ heat treatment refers to concomitant heat treatment that occurs during the processing of the current melt line, very few subsequent melt lines, and very few subsequent layers. This work provides insight into the BMG crystallization phenomenon that occurs during PBF-LB/M processing, especially its underlying crystallization kinetics. Furthermore, this work demonstrates the usefulness of our in-house developed simulation software in guiding PBF-LB/M process development for BMGs and BMG composites.

Unusual crystallization pathways revealed in six barium disilicate (BaSi2O5) glasses

Due to the unusual crystallization of (nominally) stoichiometric BaSi2O5 (BS2) glass, which shows unexpected and diverse crystal phases, a series of six glasses with different chemicals and melting procedures were prepared in three laboratories and characterized before and after crystallization by differential scanning calorimetry, density measurements, X-ray diffraction, FTIR, and Raman spectroscopy. The aim of this study was to assess whether there is systematic behavior in the crystallization pathways in relation to precursor chemicals, impurities, and hydroxyl content of this glass. Small glass monoliths were treated at the first DSC crystallization peak and quenched to determine which phases formed in the early-stages of crystallization. The glass transition temperatures (Tg) divide these six glasses between those with a Tg near 690 °C versus those near 700 °C. The DSC peak crystallization temperatures varied even more; from 855 to 917 °C. In these six glasses, our results are best explained by a combination of metastable high-BaSi2O5 and Ba6Si10O26. Monotonic trends in crystallization show that the DSC signal from the Ba-rich phases increases as the Tg and the crystallization temperatures increase. The BS2 glasses with both the lowest Tg and lowest DSC crystallization temperatures show the most barium disilicate crystal. This leads to the conclusion that the metastable monoclinic high-BaSi2O5 is favored in these conditions. The small differences in glass synthesis conditions and chemicals used strongly influence the relative proportions of phases which crystallize and their kinetics. In-situ and ex-situ diffraction measurements confirm the conclusions above. The structural distinctions between the barium silicate crystals and the BS2 supercooled liquid, and the implications for the role of structural polymerization are discussed. We conclude that high-BaSi2O5 or Ba6Si10O26 are the predominant phases in the earliest stages of crystallization. This study highlights the extreme sensitivity of BS2 glass crystallization kinetics and pathways to minor differences in composition and synthesis conditions and explains the different conclusions reached by distinct authors that worked on the crystallization of BS2 glasses.

Effect of different nucleating agent ratios on the crystallization and properties of MAS glass ceramics

The effects of different kinds of nucleating agents on crystallization, microstructure and performances of Magnesium Aluminosilicate (MgO-Al2O3-SiO2, MAS) glass-ceramics which were fabricated by melting method in this study. Also, this paper systematically investigated the mechanism of glass stability, crystallization kinetics and element distribution of MAS glass-ceramics. Herein, we used three kinds of nucleating agents, which was TiO2, ZrO2 and composite nucleating agent (TiO2/ZrO2). The results showed after the doping of nucleating agent, the content of α-cordierite was increased, the stability and crystallization kinetics of glass was changed, the precipitated crystal phase was finer and more compact. Wherein, the sample with composite nucleating agents (TiO2, ZrO2) has the best performance due to the highest contents of α - cordierite, uniform distribution of elements without agglomeration in the crystal phase and the most compact structure, whose Vickers hardness and bending strength can reach 9.70 GPa and 312 MPa, respectively.

Modeling the relaxation and crystallization kinetics of glass without fictive temperature: Toy landscape approach

AbstractRelaxation and crystallization are key kinetic processes that must be understood to build a comprehensive understanding of the supercooled liquid and glassy states. Traditional approaches have been unable to capture the underlying physics accurately due to assumptions about phenomenological order parameters such as fictive temperature. In this work, we show that glass relaxation can be accurately modeled through a simplified “toy” enthalpy landscape approach, bypassing the use of fictive temperature. Moreover, the same simplified enthalpy landscape provides insights into the thermodynamics and kinetics of crystallization. The toy landscape approach recovers key predictions from the traditional fictive temperature description, but it is based on a more accurate physical framework, giving fundamental knowledge of the glass relaxation and crystallization processes.

Crystallization kinetics of glass prepared with foundry slag

Iron foundry slag and hydrated lime were used in glass preparation by the melt-quenching method. The glass obtained was heat-treated using the thermal analysis technique. A crystallization kinetics study was carried out with glass powder samples using a non-isothermal method at five different heating rates by differential scanning calorimetry (DSC). Considering that few studies compare kinetic results obtained by different methods, in this work, the activation energy (Ea) of the crystallization process was obtained using the Kissinger and Augis-Bennett models for comparison purposes. The Ea results showed negligible variation in comparing the methods used, nevertheless, linear fitting of crystallization peaks was slightly better by the Augis-Bennett than the Kissinger model. The Avrami index values showed an increasing nucleation rate for two stable phases and decreasing for the metastable phase present in the glass-ceramic. Avrami indexes obtained also indicated an interface-controlled particle growth, whose scanning electron microscopy images showed different morphologies of crystalline particles in the bulk of the glass matrix.

Glasses for Nuclear Waste Immobilization. Effect of Lutetium Addition on Yttrium Aluminosilicate Glass Crystallization Kinetics

Glasses have emerged as alternative materials that can be used for long-term treatment and management of radioactive waste. Specifically, glasses can be used as a matrix to immobilize the radioactive material. Within the glass industry, silicate glasses are the most widely used due to their properties and to the large knowledge existent about them. Alkaline free silicate glasses are particularly corrosion resistant. Due to the latter, rare earth aluminosilicate glasses are good candidates for actinides immobilization, especially, yttrium aluminosilicate (YAS) glasses. The crystallization kinetics of YAS glasses on heating has been already studied, and this work is focused on the effect of lutetium addition on the YAS glass crystallization kinetics. The presence of a small amount of lutetium in a YAS glass decreases the surface density of nucleation sites (Ns) by about 1 order of magnitude and significantly decreases the crystal growth rate (U). In this work, it was observed that lutetium additions on the order of 0.2 (wt %) to a YAS glass dramatically decreased Ns, for example, at 1000 °C from 1011 to 109 nuclei/m2. Additionally, U for yttrium disilicate phase decreased from (8.21 ± 0.28) μm/h to (0.54 ± 0.04) μm/h at the same temperature.

Glass transition and crystallization of ZnO-B2O3-SiO2 glass doped with Y2O3

The effect of Y2O3 on the glass transition kinetics, crystallization kinetics, phase separation and crystallization behavior of 60ZnO–30B2O3–10SiO2 glass has been investigated by non-isothermal differential thermal analysis, scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). The glass transition activation energies Eg calculated by using both Kissinger and Moynihan model decrease from 668 kJ/mol to 573 kJ/mol for Kissinger model, and 682 kJ/mol to 587 kJ/mol for Moynihan model with the increase of yttrium oxide doping content from 0 to 6 mol%. And the glass crystallization kinetics parameters, crystallization activation energy Ec and Avrami exponent n stands for crystal growth, are also obtained on the basis of several well developed equations. Increase of about 58 kJ/mol in Ec values obtained by different theoretical equations is caused by addition of 6 mol% yttrium oxide into 60ZnO–30B2O3–10SiO2 glass, and the Avrami exponent (n close to 2) suggests that crystal growth in 60ZnO–30B2O3–10SiO2 glass doped with or without yttrium is mainly one-dimensional growth of crystals. The results on the phase separation and crystallization behavior occurred at 893 K and 993 K respectively for base and doped glass, are well consistent with the glass transition and crystallization kinetics results. Hence, addition of yttrium oxide into 60ZnO–30B2O3–10SiO2 glass decrease the glass transition activation energy while increase the crystallization activation energy of glass, thereby the stability of glass structure is improved. Phase separation phenomenon and crystallization behavior occurred at glass surface provide some useful information for preparing glass ceramics with micro- or nano-crystals in surface.

Crystallization pathways and some properties of lithium disilicate oxynitride glasses

Abstract Lithium silicates have been used as model glasses for scientific and technological studies of glass-ceramics because they easily crystallize in the interiors, even without the addition of any nucleating agent. On the other hand, partial replacement of oxygens with nitrogens affects most properties of oxide glasses, but its effect on the crystallization kinetics of the glasses has been poorly documented. In this work, we report, for the first time, on the crystallization kinetics of nitrited lithium silicate glasses. The oxynitride glasses were prepared by partial substitution of oxygen by nitrogen, up to 6 at% N/(N+O), by melt-quenching the liquid under N 2 atmosphere inside a glove box. As expected, the density, microhardness, and Young's modulus of the glasses improved with increasing nitrogen content. Higher values of glass transition and crystallization peak temperatures were also obtained with an increase in the nitrogen content. Rietveld refinement analysis after adequate thermal treatment revealed that addition of nitrogen led to increasingly higher contents of lithium metasilicate at the expense of the (expected) lithium disilicate crystal phase. Crystallization kinetic parameters such as the activation energy and Avrami index were calculated using Ozawa's equations. These two parameters also increased with increasing nitrogen content, whereas the crystal growth rates decreased with increasing nitrogen content. The above-described changes in the properties of the oxynitride glasses are straightforwardly explained by the increase in the connectivity of the glass network, which results in enhancement of the atomic packing density owing to partial substitution of two-coordinated oxygens by three-coordinated nitrogens.

Crystallization kinetics of glass–ceramics prepared from high-carbon ferrochromium slag

Glass-ceramics were successfully prepared from high-carbon ferrochromium slag (HCFS), and the optimum heat-treatment conditions were determined by analysis of the crystallization kinetics. The parent glass is first prepared in five different ratios of HCFS to waste glass (R(H/W)), then heat-treated separately at five heating rates (α) and monitored by DSC. As the value of R(H/W) increases from 0.60 to 1.67, the crystallization activation energy (Ec) decreases from 253.41 to 183.52kJ/mol. The nucleation and crystallization temperatures decrease from 641.7 to 612.2°C, and 822.8–814.7°C, respectively, and both are lower than that of ordinary metallurgy slag. These results indicate that using HCFS to produce glass-ceramics both facilitates its production and saves energy. The crystallization index (n) increases with increasing R(H/W), and when n exceeds 2.32, all of the parent glass samples with different R(H/W) crystallize as bulk crystallization. The crystallization index (n) increases as the heating rate α decreases from 25 to 5°C/min, with a maximum value of n (5.94) observed when α is 5°C/min. These conditions produce the largest aspect ratio and highest density of the crystal grain in the glass-ceramics. Our results show the optimal HCFS-based glass-ceramics were obtained with a R(H/W) of 1.29 and a 5°C/min heating rate; under those conditions, the parent glass nucleates and crystalizes at 627.1 and 820.9°C, respectively.

Crystallization kinetics analysis of BaF2 and BaGdF5 nanocrystals precipitated from oxyfluoride glass systems: A comparative study

Analysis of crystallization kinetics in glasses is an essential tool to gain control over ceramization to achieve desired functionalities. Here, the non-isothermal kinetics of crystallization in two different oxyfluoride glasses have been analyzed using various well-established kinetic models. Activation energies (Ea) have been estimated using Kissinger, Augis–Bennett and Ozawa methods while both Ea and Avrami index (n) were predicted from the Matusita and Avrami–Erofeev models. The values of Ea and n as predicted using Avrami–Erofeev model are 285kJ/mol and 1.18, respectively for the oxyfluoride glass yielding BaF2 nanocrystals whereas 269kJ/mol and 1.33 for the glass yielding BaGdF5 nanocrystals. The Avrami indices predict three dimensional diffusion controlled crystallization through bulk nucleation. Moreover, isothermal prediction facilitated to optimize the ceramization temperature and time for obtaining transparent oxyfluoride glass-ceramics. Furthermore, Model-free kinetics analysis demonstrates initial decrease followed by a subsequent rise in activation energy during crystallisation in both the glass systems.

INVESTIGATION AND MODELING OF ZR-BASED BULK METALLIC GLASS CRYSTALLIZATION PROCESSES

The article describes the investigation and simulation of Zr-based bulk metallic glass crystallization kinetics using DSC and DIC techniques. The investigation of the kinetics of crystallization processes may eventually provide deeper understanding of the bulk metallic glass crystallization mechanism and promote the evidence-based selection of heat treatment to form desired structure and properties of bulk metallic glasses based composites.

Influence of TiO2 on thermal stability and crystallization kinetics of tellurite glasses within TeO2–Bi2O3–Nb2O5 pseudo-ternary system

Abstract Titanium dioxide (TiO 2 ) incorporated tellurite glasses (in composition of TeO 2 –Bi 2 O 3 –Nb 2 O 5 ) were prepared by melt-quenching method. Thermal properties and crystallization kinetics of glasses as a function of TiO 2 content were investigated by employing differential thermal analysis (DTA) method. Reinforcement of the tellurite glass network as well as reduction of glass thermal stability was observed as the TiO 2 content increased. The kinetic parameters of the glasses including crystallization activation energy ( E ) and Avrami parameter ( n ) were calculated. The result showed that TiO 2 as an effective nucleating agent would promote the three-dimensional crystallization in the TeO 2 –Bi 2 O 3 –Nb 2 O 5 glasses by thermal treatment. XRD study demonstrated that the formed crystals in glass matrix belong to Bi 4 TeO 8 phase.

Glass transition and crystallization kinetics of a barium borosilicate glass by a non-isothermal method

The glass transition and crystallization kinetics of a glass with a molar composition 60BaO-30B2O3-10SiO2 were investigated by differential scanning calorimetry (DSC) under non-isothermal conditions. DSC curves exhibited an endothermic peak associated with the glass transition and two partially overlapped exothermic peaks associated with the crystallization of the glass. The dependence of the glass transition temperature (Tg) and of the maximum crystallization temperature (Tp) on the heating rate was used to determine the activation energy associated with the glass transition (Eg), the activation energy for crystallization (Ec), and the Avrami exponent (n). X-ray diffraction (XRD) revealed that barium borate (β-BaB2O4) was the first crystalline phase to be formed followed by the formation of barium silicate (Ba5Si8O21). The variations of activation energy for crystallization and of Avrami exponent with the fraction of crystallization (χ) were also examined. When the crystallization fraction (χ) increased from 0.1 to 0.9, the value of local activation energy (Ec(χ)) decreased from 554 to 458 kJ/mol for the first exothermic peak and from 1104 to 831 kJ/mol for the second exothermic peak. The value determined for the Avrami exponent was near 2 indicating a similar one-dimensional crystallization mechanism for both crystalline phases. This was confirmed by the morphological studies performed by scanning electron microscopy (SEM) on glass samples heat-treated at the first and at the second crystallization temperatures.

Crystallization of an Yttrium Aluminosilicate Glass for Nuclear Waste Immobilization

ABSTRACTSiO2-Al2O3-Y2O3 glasses exhibit high glass transition temperatures, water corrosion resistance and good mechanical properties. These properties suggest that yttrium aluminosilicate glasses could potentially replace the borosilicate glasses usually used for immobilization of nuclear wastes. At the same time, yttrium can be used to simulate actinides.During waste immobilization, crystallization of the glassy matrix must be avoided or at least controlled, thus, the understanding of glass crystallization kinetics is essential.We found by XRD that the crystalline phases present on heat treatments are yttrium disilicate and sillimanite/mullite. By optical microscopy on polished cross-sections we could only identify highly yttrium enriched crystals which we associate with yttrium disilicate crystals.In this paper we measure the surface density of nucleation sites Ns in as obtained splat cooled pieces obtaining values of about 1.5 · 1011 nucleus · m-2. Crystal growth rate U in the temperature range 1000-1040 oC varies in the range 8-13 μm · h-1. These data are useful for designing sintering or melting thermal paths of YAS glasses in order to control their microstructure. We show the effect of glass particle size on DTA results: crystallization peaks moves towards lower temperatures for smaller particle size, which confirms that mainly surface nucleation is taking place on heating.

Crystallization and flexural strength optimization of fine-grained leucite glass-ceramics for dentistry

Objectives Leucite glass-ceramics with fine-grained leucite crystals promote improved mechanical strength and increased translucency. The objectives of the study were to optimize the microstructure of a fine-grained leucite glass-ceramic in order to increase its flexural strength and reliability as measured by its Weibull modulus. Methods Glass was prepared by a melt-derived method and ground into a powder (M1A). The glass crystallization kinetics were investigated using high temperature XRD and DSC. A series of two-step heat treatments with different nucleation/crystal growth temperatures and holds were carried out to establish the optimized crystallization heat treatment. Glass-ceramics were characterized using XRD, SEM and dilatometry. The glass-ceramic heat treated at the optimized crystallization parameters (M1A opt) was both sintered (SM1A opt) and heat extruded (EM1A opt) into discs and tested using the biaxial flexural strength (BFS) test. Results High temperature XRD suggested leucite and sanidine crystallization at different temperatures. Optimized crystallization resulted in an even distribution of fine leucite crystals (0.15 (0.09) μm 2) in the glassy matrix, with no signs of microcracking. Glass-ceramic M1A opt showed BFS values of [mean (SD), MPa]: SM1A opt = 252.4 (38.7); and EM1A opt = 245.0 (24.3). Weibull results were: SM1A opt; m = 8.7 (C.I. = 7.5–10.1) and EM1A opt; m = 11.9 (C.I. = 9.3–15.1). Both experimental groups had a significantly higher BFS and characteristic strength than the IPS Empress Esthetic glass-ceramic, with a higher m value for the EM1A opt material ( p < 0.05). Significance A processable fine-grained leucite glass-ceramic with high flexural strength and improved reliability was the outcome of this study.

Alkali-free bioactive glasses for bone tissue engineering: A preliminary investigation

An alkali-free series of bioactive glasses has been designed and developed in the glass system CaO–MgO–SiO2–P2O5–CaF2 along the diopside (CaMgSi2O6)–fluorapatite (Ca5(PO4)3F)–tricalcium phosphate (3CaO·P2O5) join. The silicate network in all the investigated glasses is predominantly coordinated in Q2 (Si) units, while phosphorus tends to remain in an orthophosphate (Q0) environment. The in vitro bioactivity analysis of glasses has been made by immersion of glass powders in simulated body fluid (SBF) while chemical degradation has been studied in Tris–HCl in accordance with ISO-10993-14. Some of the investigated glasses exhibit hydroxyapatite formation on their surface within 1–12h of their immersion in SBF solution. The sintering and crystallization kinetics of glasses has been investigated by differential thermal analysis and hot-stage microscopy, respectively while the crystalline phase evolution in resultant glass–ceramics has been studied in the temperature range of 800–900°C using powder X-ray diffraction and scanning electron microscopy. The alkaline phosphatase activity and osteogenic differentiation for glasses have been studied in vitro on sintered glass powder compacts using rat bone marrow mesenchymal stem cells. The as-designed glasses are ideal candidates for their potential applications in bone tissue engineering in the form of bioactive glasses as well as glass/glass–ceramic scaffolds.

Influence of barium oxide on the crystallization, microstructure and mechanical properties of potassium fluorophlogopite glass–ceramics

The influence of barium oxide, heat treatment time and temperature on the crystallization, microstructure and mechanical behavior of the system Ba x ·K 1−2 x ·Mg 3·Al·Si 3O 10·F 2 (where x = 0.0, 0.3 and 0.5) was investigated in order to develop novel, high strength and machinable glass–ceramics. Three glasses were prepared and characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscope (SEM) techniques and some mechanical testing methods. The crystallization kinetics of glass–ceramics was also studied. Activation energy and Avrami exponent calculated for the crystallization peak temperature ( T p) of three different glass batches. The Vickers hardness decreased slightly on formation of the potassium fluorophlogopite and barium fluorophlogopite phases, but decreased significantly on formation of an interconnected ‘house of cards’ microstructure.

Thermal stability and crystallization kinetics of Pb and Bi borate-based glasses

Glasses with compositions 60B2O3–40PbO, 60B2O3–40Bi2O3, and 60B2O3–30Bi2O3–10PbO have been prepared and studied by differential thermal analysis. The crystallization kinetics of the glasses was investigated under non-isothermal conditions. From dependence of the glass transition temperature (T g) on the heating rate, the activation energy for the glass transition was derived. Similarly the activation energy of the crystallization process was determined. Thermal stability of these glasses were achieved in terms of the characteristic temperatures, such as the glass transition temperature, T g, the onset temperature of crystallization, T in , the temperature corresponding to the maximum crystallization rate, T p, beside the kinetic parameters, K(T g) and K(T p). The results revealed that the 60B2O3–40PbO is more stable than the others. The crystallization mechanism is characterized for glasses. The phases at which the glass crystallizes after the thermal process have been identified by X-ray diffraction.

Influence of particle size on the crystallization kinetics of glasses produced from waste materials

The crystallization behavior and kinetics of glasses produced from coal fly ashes, red mud and silica fume were investigated by using differential thermal analysis, X-ray diffraction and scanning electron microscopy techniques. The kinetic parameters of the glass-crystallization transformation were estimated under non-isothermal conditions applying three different equations, namely, Kissinger, Matusuta-Sakka and Ozawa. Non-isothermal differential thermal analysis curves were obtained using both coarse and fine glass samples. The crystallization activation energies of coarse glasses are in the range of 233–439 kJ/mol while the activation energies of fine glasses change in the range of 369–450 kJ/mol. Avrami exponent, n, values of coarse glasses indicated the three-dimensional bulk crystallization. This result is in well agreement with the cross-sectional scanning electron microscopy investigations. The values of the n obtained experimentally are in the range of 1.24–1.36 for fine glasses which show the one-dimensional surface crystallization. The crystallized phase of the glass-ceramic samples produced from waste glasses by applying the controlled heat treatment process was identified as diopside by X-ray diffraction analysis.

The application of differential thermal analysis to the study of isothermal and non-isothermal crystallization kinetics of coal fly ash based glasses

The crystallization kinetics of glasses obtained from coal fly ash was investigated by both isothermal and non-isothermal methods using differential thermal analysis (DTA) data. In DTA experiments, glass samples having coarse (800–1000 μm) and fine (<180 μm) particle sizes were used and the results were compared. The Avrami exponent (n) was calculated by means of Johnson–Mehl–Avrami (JMA) and Ozawa equations. Calculated kinetic parameters indicated that the appropriate crystallization mechanisms were bulk and surface crystallization for coarse and fine particles, respectively. Isothermal and non-isothermal DTA experiments showed that the crystallization activation energies of coarse glasses are changed in the range of 444–578 kJ/mol, while the crystallization activation energies of fine glasses are changed in the range of 610–662 kJ/mol. It was found that crystallization activation energies of fine glasses are higher than those of the coarse glasses. Results showed that isothermal and non-isothermal crystallization kinetics of glasses produced from coal fly ash is in agreement within the experimental error.