Devitrification Process Research Articles

Commercial alkaline earth boroaluminosilicate glasses for sealing solid oxide cell stacks. Part II: Characterization of devitrification and glass‐ceramic phase assemblages

AbstractThe devitrification process and formation of crystalline phases from commercial alkaline earth boroaluminosilicate glasses containing 48‐61 mol% SiO2, 18‐28 mol% CaO, 1‐7 mol% MgO, 7‐10 mol% Al2O3, 1‐11 mol% B2O3 plus minor amounts of Na2O, K2O, FeO, and TiO2 were quantified through analysis of phase assemblages as function of heat treatments above the glass transition temperatures, using the electron microprobe and powder X‐ray diffraction. Treatments at 800 and 850°C lasted up to 6 weeks. Results indicate that devitrification was strongly activated through presence of heterogeneous nucleation, and that the growth mechanism gradually changed from three‐dimensional growth at the onset of devitrification toward one‐dimensional growth in later stages, when heterogeneous nucleation was absent or less dominating. Most glasses developed entangled and fibrous microstructures with little or no residual glass phase, which are adequate for rigid sealants, and only one of the laboratory analogue glasses, MCAS, developed microstructures with both more equiaxed grains and a considerable amount of residual glass phase, which may be adequate for more compliant and self‐healing sealants as often required in SOC‐applications. Even though the glasses lie within a relatively narrow compositional range, resulting phase assemblages differed significantly. Anorthite (plagioclase) developed as the main crystalline phase in all samples together with pyroxene (or pyroxenoide) and cristobalite. Calcium‐magnesium‐silicate pyroxene (diopside) was in a large part replaced by the calcium‐silicate pyroxenoid (wollastonite) in the samples where the mol‐proportion MgO:CaO was 1:5 or lower. In samples with a very low MgO proportion and consequently a high CaO proportion, calcium metaborate and calcium aluminum borosilicate (okayamalite) crystallized among the main phases and these glasses crystallized completely within the period of heat treatment. Although cristobalite is metastable at the annealing temperatures, both α and β forms were rapidly formed in most of the samples, likely due to kinetic reasons. The presence of the latter is explained by the stabilization effect of Al and B substitution for Si compensated by Ca stuffing in the structure. The stuffed cristobalite transformed with time to quartz (at 800°C) or quartz plus tridymite (at 850°C). Boron was incorporated in the first crystallizing phases, especially diopside, substituting for Al and Si, but the so established substitution partly disappeared with time during the heat treatment.

Commercial alkaline earth boroaluminosilicate glasses for sealing solid oxide cell stacks. Part I: Development of glass‐ceramic microstructure and thermomechanical properties

AbstractSealing performance in solid oxide cell (SOC) stacks and the devitrification process of commercially available alkaline earth boroaluminosilicate glasses containing 48‐61 mol% SiO2, 18‐28 mol% CaO, 1‐7 mol% MgO, 7‐10 mol% Al2O3, 1‐11 mol% B2O3 plus minor amounts of Na2O, K2O, FeO, and TiO2 were investigated and quantified through analysis of phase assemblages as function of heat treatments above the glass transition temperatures using the electron microprobe and powder X‐ray diffraction. For two of these glasses devitrification behavior was compared to the devitrification behavior of similar glasses produced in the laboratory. Glasses were characterized after annealing in air at 800°C and 850°C for up to 6 weeks. Even though the glasses lie within a relatively narrow compositional range, sealing performance and the resulting microstructures differed significantly. Best thermomechanical properties was developed in one of the laboratory‐produced glasses, MCAS, which may be applied in SOC‐stacks by allowing for a slow solidification in the range 750‐800°C followed by crystallization at or slightly above 800°C. The relatively high thermal expansion coefficient (CTE) from RT‐800°C, 11 × 10−6 K−1, which was developed over ~1000 hours at 800°C, depends mainly on the formation of cristobalite and quartz as well as the presence of a residual glass phase. The glass ceramic sealant appears relatively stable over time, except for a slow transition of cristobalite to quartz, and can possibly show self‐healing behavior if later brought close to 850°C. Devitrification led to increases of the thermal expansion coefficients in all other glasses tested, but did not reach levels interesting for SOC‐stack sealing.

Thermodynamic properties of (TeO2) n (MoO3)1–n glasses

The thermal behavior of (TeO2) n (MoO3)1–n (n = 0.75, 0.85, 0.90) tellurite glasses has been studied by differential scanning calorimetry in the range from T = 300 to T = 850 K and heat capacity has been measured in the temperature range. The thermodynamic characteristics of the devitrification process and glassy state have been determined. The experimental data obtained have been used to evaluate the standard thermodynamic functions of the system in glassy and supercooled liquid states: heat capacity C p °(T), enthalpy H°(T)–H°(320), entropy S°(T)–S°(320), and Gibbs function G°(T)–G°(320) in the temperature range 320–630 K. The composition dependences of the glass transition temperature and thermodynamic functions for the glasses have been obtained. The thermal and thermodynamic properties of the tellurite glasses have been compared to those of previously studied (TeO2) n (WO3)1–n and (TeO2) n (ZnO)1–n glasses.

Devitrification and hydrogen storage capacity of the eutectic Ca72Mg28 metallic glass

Very low density eutectic Ca72Mg28 at.% metallic glass was produced by a rapid solidification melt-spinning process. The glass is considered as being a precursor of more complex ternary Ca-Mg-Zn alloys consisting solely of biocompatible elements with the view to its potential use as bioresorbable alloy for orthopaedic applications. Density, elastic modulus, hydrogen storage capacity, thermal properties of the metallic glass, such as the glass transition, crystallization and melting temperatures, as well as heats of crystallization and melting are reported. The devitrification process of the amorphous alloy up to its melt is fully described.

Liquidus Tracking: Large scale preservation of encapsulated 3-D cell cultures using a vitrification machine

Currently, cryo-banking of multicellular structures such as organoids, especially in large volumes at clinical scale >1 L, remains elusive for reasons such as insufficient dehydration and cryoprotectant additive (CPA1) penetration, slow cooling and warming rates and devitrification processes. Here we introduce the concept of Liquidus Tracking (LT) using a semi-automated process for liquid volumes of up to 450 ml including 130 ml of alginate encapsulated liver cells (AELC) that archived controlled and reversible vitrification with minimized toxicity.First a CPA solution with optimal properties for LT was developed by employing different small scale test systems. Combining sugars such as glucose and raffinose with Me2SO improved post-exposure (at +0.5 °C) viabilities from 6% ±3.6 for Me2SO alone up to 58% ±6.1 and 65% ±14.2 respectively (p < 0.01). Other permeating CPAs (e.g. ethylene glycol, propylene glycol, methanol) were investigated as partial replacements for Me2SO. A mixture of Me2SO, ethylene glycol and glucose (ratio 4:2:1– termed LTdeg) supported glass-forming tendencies with appropriate low viscosities and toxicities required for LT. When running the full LT process, using Me2SO alone, no viable cells were recovered; using LTdeg, viable recoveries were improved to 40% ±8 (p<0.001%). Further refinements of improved mixing technique further improved recovery after LT. Recoveries of specific liver cell functions such as synthesis of albumin and alpha-fetoprotein (AFP) were retained in post thaw cultures.In summary: By developing a low-toxicity CPA solution of low viscosity (LTdeg) suitable for LT and by improving the stirring system, post-warming viability of AELC of up to 90% and a AFP secretion of 89% were reached. Results show that it may be possible to develop LT as a suitable cryogenic preservation process for different cell therapy products at large scale.

Retraction Note to: All-Atom Molecular-Level Analysis of the Ballistic-Impact-Induced Densification and Devitrification of Fused Silica

All-atom molecular-level computations are carried out to infer the dynamic response and material microstructure/topology changes of fused silica subjected to ballistic impact by a hard projectile. The analysis was focused on the investigation of specific aspects of the dynamic response and of the microstructural changes such as the deformation of highly sheared and densified regions and the conversion of amorphous fused silica to SiO2 crystalline allotropic modifications (in particular, α-quartz and stishovite). The microstructural changes in question were determined by carrying out a post-processing atom-coordination procedure. This procedure suggested the formation of stishovite (and perhaps α-quartz) within fused silica during ballistic impact. To rationalize the findings obtained, the all-atom molecular-level computational analysis is complemented by a series of quantum-mechanics density functional theory (DFT) computations. The latter computations enable determination of the relative potential energies of the fused silica, α-quartz, and stishovite under ambient pressure (i.e., under their natural densities) as well as under imposed (as high as 50 GPa) pressures (i.e., under higher densities) and shear strains. In addition, the transition states associated with various fused-silica devitrification processes were identified. The results obtained are found to be in good agreement with their respective experimental counterparts.

Complex remanent magnetization in the Kızılkaya ignimbrite (central Anatolia): Implication for paleomagnetic directions

Pyroclastic flow deposits, known as ash-flow tuffs or ignimbrites, are invaluable materials for paleomagnetic studies, with many applications for geological and tectonic purposes. However, little attention has been paid to evaluating the consistency and reliability of the paleomagnetic data when results are obtained on a single volcanic unit with uneven magnetic mineralogy. In this work we investigate this issue by concentrating on the Kızılkaya ignimbrite, the youngest large-volume unit of the Neogene ignimbrite sequence of the Central Anatolian Volcanic Province in Turkey, bringing evidence of significant magnetic heterogeneities in ignimbrite deposits (magnetic mineralogy, susceptibility, magnetic remanence, coercivity, etc.) and emphasizing the importance of a stratigraphic sampling strategy for this type of volcanic rocks in order to obtain reliable paleomagnetic data. Six sections were sampled at different stratigraphic heights within the devitrified portion of the ignimbrite. Isothermal remanence measurements point to low-Ti titanomagnetite as the main magnetic carrier at all sites; at some sites, the occurrence of oxidized Ti-magnetite and hematite is disclosed. The bulk susceptibility (km) decreases vertically at two out of six sections: its value for the topmost samples is commonly one order of magnitude lower than that of the samples at the base. In most cases, low km values relate to high coercivity of remanence (BCR) values, which range from 25 to >400mT, and to low S-ratios (measured at 0.3T) between 0.28 and 0.99. These data point to the occurrence of oxidized magnetic phases. We therefore consider the km parameter as a reliable proxy to check the ignimbrite oxidation stage and to detect the presence of oxidized Ti-magnetite and hematite within the deposit. The characteristic remanent magnetization is determined after stepwise thermal and AF demagnetization and clearly isolated by principal component analysis at most sites. For these sites, the site-mean paleomagnetic direction is consistent with data from the literature. At a few other sites, the remanence is more complex: the direction moves along a great circle during demagnetization and no stable end-point is reached. The occurrence of oxidized Ti-magnetite or hematite as well as two remanence components with overlapping coercivity and blocking temperature spectra suggest that the Kızılkaya ignimbrite acquired first a thermal remanent magnetization and then, during the final cooling or a short time later, a secondary remanent magnetization component which is interpreted as a CRM acquired during post-emplacement devitrification processes. Notwithstanding the Kızılkaya ignimbrite is a single cooling unit, its magnetic properties suffered substantial variations laterally and vertically within the deposit. The Kızılkaya case shows that thick pyroclastic deposits should be sampled using a stratigraphic approach, at different sites and different stratigraphic heights at each individual sampling location, otherwise, under-sampling may significantly affect the paleomagnetic results. When sampling is performed on a short duration or on very poorly preserved deposits we recommend drilling the lower-central portion in the most strongly welded and devitrified facies. Such sampling strategy avoids complications arising from the potential presence of a pervasive secondary CRM masking the original ChRM.

Kinetics and crystallization path of a Fe-based metallic glass alloy

The thermal stability and the quantification of the different transformation processes involved in the overall crystallization of the Fe50Cr15Mo14C15B6 amorphous alloy were investigated by several characterization techniques. Formation of various metastable and stable phases during the devitrification process in the sequence α-Fe, χ-Cr6Fe18Mo5, M23(C,B)6, M7C3, η-Fe3Mo3C and FeMo2B2 (with M = Fe, Cr, Mo), was observed by in-situ synchrotron high energy X-ray diffraction and in-situ transmission electron microscopy. By combining these techniques with differential scanning calorimetry data, the crystallization states and their temperature range of stability under continuous heating were related with the evolution of the crystallized fraction and the phase sequence as a function of temperature, revealing structural and chemical details of the different transformation mechanisms.

Devitrification of ultrafast laser plasma produced metastable glass layer

Erbium-doped tellurite modified silica (EDTS) is a newly formulated silicate glass that has the potential to realize on-chip optical amplifiers. The devitrification process of EDTS layer on host silica glass has been studied in the temperature range 300°C–1000°C. In-situ high-temperature X-ray diffraction, selective area electron diffraction and high-resolution transmission electron microscopy revealed the amorphous phase of EDTS as-fabricated up to 600°C and rapid irreversible crystalline phase developments above 600°C, contrasting the host silica. Distinct structural evolutions of EDTS with the variation in temperature were observed, including a complete evaporation of TeO2 at 800°C from the matrix.

Amorphous phase separation in an Fe-based bulk metallic glass

Although lanthanide elements play a critical role in increasing the glass forming ability and mechanical property alternation of Fe based bulk metallic glass (Fe-BMG), the atomic scale configuration of lanthanide in Fe-BMG remained unexplored. Here we have studied atomic configuration in the amorphous state of as-cast 4mm FeCoCrMoCBY bulk metallic glass sheet and its mechanical properties by nanoindentation, transmission electron microscopy, and atom probe tomography. The current results showed that yttrium rich clusters are enriched with carbon atoms in the amorphous state, and the three dimensional densities of these clusters can influence the hardness at the localized region. The finding of Y-C rich clusters also suggests that the amorphous phase separation can precede the devitrification process.

Synthesis and In Vitro Activity Assessment of Novel Silicon Oxycarbide-Based Bioactive Glasses.

Novel bioactive glasses based on a Ca- and Mg-modified silicon oxycarbide (SiCaMgOC) were prepared from a polymeric single-source precursor, and their in vitro activity towards hydroxyapatite mineralization was investigated upon incubating the samples in simulated body fluid (SBF) at 37 °C. The as-prepared materials exhibit an outstanding resistance against devitrification processes and maintain their amorphous nature even after exposure to 1300 °C. The X-ray diffraction (XRD) analysis of the SiCaMgOC samples after the SBF test showed characteristic reflections of apatite after only three days, indicating a promising bioactivity. The release kinetics of the Ca2+ and Mg2+ and the adsorption of H+ after immersion of SiCaMgOC in simulated body fluid for different soaking times were analyzed via optical emission spectroscopy. The results show that the mechanism of formation of apatite on the surface of the SiCaMgOC powders is similar to that observed for standard (silicate) bioactive glasses. A preliminary cytotoxicity investigation of the SiOC-based bioactive glasses was performed in the presence of mouse embryonic fibroblasts (MEF) as well as human embryonic kidney cells (HEK-293). Due to their excellent high-temperature crystallization resistance in addition to bioactivity, the Ca- and Mg-modified SiOC glasses presented here might have high potential in applications related to bone repair and regeneration.

Devitrification in SiO&lt;sub&gt;2&lt;/sub&gt;-B&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-La&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-TiO&lt;sub&gt;2&lt;/sub&gt; Glass during the Infiltration of Ceramic Composite

Dental prostheses made of ceramic composites infiltrated with glasses have been used due to their biocompatibility and possibility to mimic the natural teeth. In this study, the devitrification behavior of 20SiO2-25B2O3-25Al2O3-15La2O3-15TiO2 glass during the infiltration process in a porous alumina preform was investigated. Glass frits were prepared by melting the raw materials at 1500 °C for 60 min. The glass was infiltrated into the alumina preform at 1,150 or 1,200 °C for 60 min. The specimens were characterized by X-ray diffraction analysis and scanning electron microscopy. After the infiltration, it was possible to note that the devitrification process occurred in the remaining glass (excess glass that did not infiltrate in the preform), forming mostly aluminum borate and mullite crystalline phases. However, within the infiltrated composite no devitrification was noticed in the infiltrated glass. Possible explanations for this behavior are discussed.

In situ HEXRD study of a Ca61Al39 metallic glass

High energy X-ray diffraction (HEXRD) was used to characterize the amorphous structure of the as-prepared binary Ca61Al39 (at.%) metallic glass and its evolution during thermal loading. The investigation was performed in both reciprocal and real space by means of the first diffuse peak (FDP) analysis and the reduced atomic pair distribution function (PDF) analysis, respectively. It was found that bond lengths of the atomic CaCa and CaAl pairs of the as-prepared structure were 3.70 Å and 3.24 Å, respectively. The coordination number of the first coordination shell was estimated to be 11.9. The analysis of the FDP behaviour during thermal treatment proposed the existence of the relaxation temperature Tr at 150 °C. Analysis of summations of all absolute differences between two consecutive intensity curves in the region of the FDP as a function of temperature revealed two crystallization temperatures at 280 °C and 305 °C. Products of a devitrification process were identified to be alike a triclinic Ca8Al13 and monoclinic Ca13Al14 phase.

The Effect of High-Pressure Devitrification and Densification on Ballistic-Penetration Resistance of Fused Silica

Recent experimental and molecular-level computational analyses have indicated that fused silica, when subjected to pressures of several tens of GPa, can experience irreversible devitrification and densification. Such changes in the fused-silica molecular-level structure are associated with absorption and/or dissipation of the strain energy acquired by fused silica during high-pressure compression. This finding may have important practical consequences in applications for fused silica such as windshields and windows of military vehicles, portholes in ships, ground vehicles, spacecraft, etc. In the present work, our prior molecular-level computational results pertaining to the response of fused silica to high pressures (and shear stresses) are used to enrich a continuum-type constitutive model (that is, the so-called Johnson-Holmquist-2, JH2, model) for this material. Since the aforementioned devitrification and permanent densification processes modify the response of fused silica to the pressure as well as to the deviatoric part of the stress, changes had to be made in both the JH2 equation of state and the strength model. To assess the potential improvements in respect to the ballistic-penetration resistance of this material brought about by the fused-silica devitrification and permanent densification processes, a series of transient non-linear dynamics finite-element analyses of the transverse impact of a fused-silica test plate with a solid right-circular cylindrical steel projectile were conducted. The results obtained revealed that, provided the projectile incident velocity and, hence, the attendant pressure, is sufficiently high, fused silica can undergo impact-induced devitrification, which improves its ballistic-penetration resistance.

Crystal Growth of F‐Phlogopite from Glasses of the SiO2–Al2O3–MgO–K2O–F System

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 toward 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.

Spark plasma sintering of gas atomized AlNiYLaCo amorphous powders

Highly dense bulk samples were fabricated by spark plasma sintering (SPS) through a combined devitrification and consolidation process of partially amorphous AlNiYLaCo gas-atomized powders. The microstructure and mechanical properties were investigated in detail. The microstructure of the consolidated samples is mainly nanocrystalline. Moreover, the sintered sample exhibits a compressive fracture strength of approximately 1058.6MPa and a 4.8% compressive plastic strain prior to fracture. Our results indicate that bulk nanocrystalline alloy samples can be fabricated via devitrification for amorphous precursors and powder metallurgy.

Cathodoluminescence as a tool to discriminate impact melt, shocked and unshocked volcanics: A case study of samples from the El'gygytgyn impact structure

AbstractEl'gygytgyn (Chukotka, Arctic Russia) is a well‐preserved impact structure, mostly excavated in siliceous volcanic rocks. For this reason, the El'gygytgyn structure has been investigated in recent years and drilled in 2009 in the framework of an ICDP (International Continental Scientific Drilling Program) project. The target rocks mostly consist of rhyodacitic ignimbrites and tuffs, which make it difficult to distinguish impact melt clasts from fragments of unshocked target rock within the impact breccia. Several chemical and petrologic attempts, other than dating individual clasts, have been considered to distinguish impact melt from unshocked volcanic rock of the targets, but none has proven reliable. Here, we propose to use cathodoluminescence (imaging and spectrometry), whose intensity is inversely correlated with the degree of shock metamorphism experienced by the investigated lithology, to aid in such a distinction. Specifically, impact melt rocks display low cathodoluminescence intensity, whereas unshocked volcanic rocks from the area typically show high luminescence. This high luminescence decreases with the degree of shock experienced by the individual clasts in the impact breccia, down to almost undetectable when the groundmass is completely molten. This might apply only to El'gygytgyn, because the luminescence in volcanic rocks might be due to devitrification and recrystallization processes of the relatively old (Cretaceous) target rock with respect to the young impactites (3.58 Ma). The alteration that affects most samples from the drill core does not have a significant effect on the cathodoluminescence response. In conclusion, cathodoluminescence imaging and spectra, supported by Raman spectroscopy, potentially provide a useful tool for in situ characterization of siliceous impactites formed in volcanic target.

Devitrification behavior and preferred crystallization mechanism of glasses based on fluorrichterite (Na2CaMg5Si8O22F2) composition

This paper reports on the effect of different contents of fluorine on the thermal stability of glasses in the SiO2–MgO–CaO–Na2O–F system. Four glass compositions, with experimental fluorine contents varying from 2.12 to 4.39wt.%, were studied using differential scanning calorimetry (DSC). The devitrification behavior was assessed through the evaluation of both the glass stability (GS) and glass-forming ability (GFA) using different parameters calculated from the characteristic temperatures in non-isothermal DSC curves. The predominant crystallization mechanism was determined by the difference in the crystallization temperature (ΔTp) between fine and coarse glass samples. The results indicate that the studied melts exhibit a low tendency to devitrify during cooling, although this trend is increased with the fluorine content. The glass thermal stability is affected by the particle size, with it being easier to crystallize a glass powder sample than a coarse glass sample. The surface crystallization mechanism is predominant at the beginning of the devitrification process; however, the volume crystallization acquires importance with an increase in the fluorine content.

RETRACTED ARTICLE: All-Atom Molecular-Level Analysis of the Ballistic-Impact-Induced Densification and Devitrification of Fused Silica

All-atom molecular-level computations are carried out to infer the dynamic response and material microstructure/topology changes of fused silica subjected to ballistic impact by a hard projectile. The analysis was focused on the investigation of specific aspects of the dynamic response and of the microstructural changes such as the deformation of highly sheared and densified regions and the conversion of amorphous fused silica to SiO2 crystalline allotropic modifications (in particular, α-quartz and stishovite). The microstructural changes in question were determined by carrying out a post-processing atom-coordination procedure. This procedure suggested the formation of stishovite (and perhaps α-quartz) within fused silica during ballistic impact. To rationalize the findings obtained, the all-atom molecular-level computational analysis is complemented by a series of quantum-mechanics density functional theory (DFT) computations. The latter computations enable determination of the relative potential energies of the fused silica, α-quartz, and stishovite under ambient pressure (i.e., under their natural densities) as well as under imposed (as high as 50 GPa) pressures (i.e., under higher densities) and shear strains. In addition, the transition states associated with various fused-silica devitrification processes were identified. The results obtained are found to be in good agreement with their respective experimental counterparts.

Devitrification-induced an Ultrahigh Strength Al-based Composite Maintaining Ductility

A new Al-based composite consisting of submicron-sized α-Al matrix embedded with precipitated intermetallic phases was developed by controlling the devitrification process of an Al–Ni–Y–Co–La amorphous alloy. Such a homogeneous composite structure presented an ultrahigh strength of about 1.34 GPa and a large compressive plastic strain up to 22%. The unique mechanical properties during compression are mainly attributed to the dislocation slip deformation of ductile α-Al matrix and the shear-induced refinement of strengthening intermetallic phases.