Showing papers on "Devitrification published in 2022"

Glass formation and devitrification behavior of alkali (Li, Na) aluminosilicate melts containing TiO2

Abstract: The impact of TiO2 additions on the quenchability of melts derived from the stoichiometry of spodumene (LiAlSi2O6), eucryptite (LiAlSiO4) and nepheline (NaAlSiO4) was investigated by containerless melting. The results reveal a compositional dependence (Al2O3/SiO2 and M2O/Al2O3 ratios, M = Na or Li) of the role of TiO2 during devitrification. Amorphous samples incorporating up to 10 mol% TiO2 could be produced, above which devitrification invariably took place. Interaction of TiO2 with other glass components (such as Al2O3 and Na2O in nepheline glass) perceivably reduced glass stability, while eucryptite and spodumene glasses appeared only affected to the extent to which nanosized TiO2 polymorphs (TiO2(B), anatase and rutile) served as heterogeneous nucleation sites for quartz solid solutions, in which we inferred a substantial incorporation of Ti4+. A reduction in SiO2 content and a preference for peraluminous compositions stand out as viable compositional strategies to foster the glass-forming ability of TiO2-rich aluminosilicate melts.

Physicochemical Properties and Fiber-Drawing Ability of Tellurite Glasses in the TeO2-ZnO-Y2O3 Ternary System

Abstract: Glasses in the TeO2-ZnO-Y2O3 (TZY) ternary system are examined in the present work. The vitrification domain of the chosen oxide matrix is determined and differential scanning calorimetry as well as X-ray diffraction measurements are carried out. The material characterizations reveal that Y2O3 incorporation cannot exceed 5 mol.% without causing detrimental crystallization within the glass. Optical transmission and refractive index investigations are conducted on compositions yielding fully amorphous samples. Next, the fiber drawing ability of selected yttrium-containing zinc-tellurite glasses is assessed and fiber-attenuation measurements in the mid-infrared are presented. Finally, a multimode step-index fiber is fabricated by combining a TZY cladding glass with a La2O3-based tellurite core glass. It is believed that yttrium-containing glasses could prove useful in association with other high glass transition temperature (>300 °C) TeO2-based materials for the design of robust optical fibers with precisely engineered refractive index profiles.

Glass-forming ability and structural features of melt-quenched and gel-derived SiO2-TiO2 glasses

Abstract: SiO2-TiO2 glasses produced by aerodynamic levitation coupled to laser heating or by sol-gel spray-drying were compared to highlight their structural differences. Glass formation was possible by melt-quenching up to 10 mol% TiO2, while higher contents led to devitrification. Raman spectroscopy and solid-state 17O and 29Si magic-angle-spinning nuclear magnetic resonance confirmed the clear emergence of Ti-O-Si bonds and a tetrahedral oxygen coordination of Ti4+ leading to full network connectivity, as also substantiated by the synthesis of TiO2-doped cristobalite. In gel-derived glasses, water content induced partial network depolymerization, thereby enhancing the solubility of TiO2 in the hydrous silicate matrix. However, full dehydration during heating proved challenging due to a competing tendency towards devitrification: the glass-forming range in the anhydrous binary SiO2-TiO2 system does not therefore appear to be significantly enlarged by the sol-gel synthesis route.

Two-step devitrification of ultrastable glasses.

Abstract: The discovery of ultrastable glasses raises novel challenges about glassy systems. Recent experiments studied the macroscopic devitrification of ultrastable glasses into liquids upon heating but lacked microscopic resolution. We use molecular dynamics simulations to analyze the kinetics of this transformation. In the most stable systems, devitrification occurs after a very large time, but the liquid emerges in two steps. At short times, we observe the rare nucleation and slow growth of isolated droplets containing a liquid maintained under pressure by the rigidity of the surrounding glass. At large times, pressure is released after the droplets coalesce into large domains, which accelerates devitrification. This two-step process produces pronounced deviations from the classical Avrami kinetics and explains the emergence of a giant lengthscale characterizing the devitrification of bulk ultrastable glasses. Our study elucidates the nonequilibrium kinetics of glasses following a large temperature jump, which differs from both equilibrium relaxation and aging dynamics, and will guide future experimental studies.

Evolution of the structure and chemical composition of the interface between multi-component silicate glasses and yttria-stabilized zirconia after 40,000 h exposure in air at 800 °C

Abstract: The chemical and structural stability of two commercial multicomponent silicate glasses (SCN and G6) in contact with yttria-stabilized zirconia (YSZ) was investigated after exposure times of up to 40,000 h in air at 800 °C. With exposure time, interfacial layers develop at the SCN-YSZ and G6-YSZ interfaces, which were characterized in detail using both quantitative chemical analysis and atomic-resolution imaging. At the SCN-YSZ interface, a Ca-Ba-Si-O reaction phase was found to grow by diffusion control. In G6-YSZ, Raman spectroscopy and electron microscopy revealed a disorganized interfacial reaction later between G6 and YSZ, and the occurrence of cubic to tetragonal to monoclinic phase transformations in YSZ. This microstructural evolution is discussed in terms of devitrification resistance of glass and diffusion processes at interfaces.

Influence of CaO and Dy2O3 on the structural, chemical and optical properties of thermally stable luminescent silicate nanoglass-ceramics

Abstract: In this work, nano-glass ceramics constituted by SiO2–Na2O–CaO–Dy2O3 are synthesized with different contents of CaO (0–30 mol%) and Dy2O3 (0.1–4 mol%) through the melt-quenching technique at 1500 °C. The precipitation of nanocrystals occurs during the cooling stage of molten glass precursors. Depending on CaO content, nanocrystals of cristobalite (0 mol%) or combeite (30 mol%) are grown inside the amorphous silicate phase. FTIR and XPS studies indicate that non-bridging oxygens increase with CaO due to [SiO]4 tetrahedral rupture. However, if CaO is higher than 20 mol%, the non-bridging oxygens slightly decrease due to the prevalence of combeite nanocrystals. Moreover, the addition of CaO decreases the optical bandgap (4.18–3.91 eV) and increases the Urbach energy (0.54–0.75 eV). Although PL spectra acquired at λex of 348 and 386 nm show four peaks whose intensities augment with CaO, the most prominent peaks appear at 490 (4F9/2 → 6H15/2, blue) and 577 nm (4F9/2 → 6H13/2, yellow). The decrease in the yellow to blue ratio, with an increment in CaO content, is attributed to the devitrification of glass phase. The most intense PL intensity is obtained in the nano-glass ceramic constituted of 30 mol% CaO and 1 mol% Dy2O3. This sample demonstrates excellent thermal PL stability up to 400 °C, retaining 95.2% of the initial PL value. The results indicate that these nano-glass ceramics are good candidates for their use as yellow phosphors in high-power consuming and high-temperature applications, such as LED chips and luminescent solar concentrators.

Fluoride glass and optical fiber fabrication

Abstract: Fluoride glasses have emerged as a class of special glasses with unique properties and applications. It includes several families according to the main glass former. Major groups are fluorozirconates, fluoroaluminates, and fluoroindates. They are oxygen free and they must be processed in a very dry environment. Chemical composition is adjusted to minimize devitrification. Their softening temperature lies between 250 °C and 400 °C and their viscosity at liquidus temperature is very low. They are continuously transparent from the UV to the mid infrared spectrum. Their phonon energy is small by comparison to oxide glasses, which makes them attractive host for active rare earths. The major interest of fluoride glasses is based on optical fibers. They are currently drawn from preforms. Depending on applications, they are multimode, singlemode or polarization maintaining. Astronomy programs use them for coupling telescopes. Optical losses are lower than 20 dB/km in the 1–3.5 μm spectral range with a minimum attenuation of 1 dB/km at 2.55 μm. They may be used over tens of meters. While the development of ultra-low optical losses (< 0.1 dB/km) is still a matter of technology, various applications take place for optical transmission, remote spectroscopy, laser power handling and infrared imaging. Rare earth doped fibers are used in mid-IR fiber lasers and also for visible lasers. Reliable supercontinuum sources are available up to 4–5 μm. UV supercontinuum has been demonstrated with photonic crystal fibers.

Hybridization Engineering of Oxyfluoride Aluminosilicate Glass for Construction of Dual‐Phase Optical Ceramics

Abstract: The construction of transparent ceramics under mild conditionsand standard atmospheric pressure has great scientific and technological potential; however, it remains difficult to achieve when conventional ceramic sintering techniques are used. Herein, a mild strategy for constructing dual‐phase optical ceramics with high crystallinity (>90%) based on the stepped dual‐phase crystallization of hybridized aluminosilicate glass is presented. Theoretical and experimental studies reveal that the hybridization of the glass system enables a new balance between the glass‐forming ability and crystallization and can overcome the uncontrolled devitrification phenomenon during the dense crystallization of glass. Transparent hybridized oxide‐fluoride ceramics with fiber geometry and dual‐phase microstructures are also successfully fabricated. The generality of the strategy is confirmed, and transparent ceramics with various chemical compositions and phase combinations are prepared. Additionally, the cross‐section of the ceramic fibers can be easily tuned into a circle, square, trapezoid, or even a triangle. Furthermore, the practical applications of optical ceramics for lighting and X‐ray imaging are demonstrated. The findings described here suggest a major step toward expanding the scope of optical ceramics.

Temperature-Dependent Rotational Dipole Mobility and Devitrification of the Rigid Amorphous Fraction in Unpoled and Poled Biaxially Oriented Poly(vinylidene fluoride)

Abstract: In addition to the pronounced ferroelectric property from polar crystalline phases, poly(vinylidene fluoride) (PVDF) and its random copolymers also exhibit high dielectric permittivities as a result of highly mobile dipoles in the amorphous phase. In this study, we developed a new theoretical approach to determine the dipole concentration, dipole moment, dipole–dipole interaction, and rotational dipole mobility for PVDF by means of broadband dielectric spectroscopy. From the permittivity of molten PVDF, the Kirkwood–Fröhlich g-factor and its temperature dependence were determined and used as global parameters for the simulation of unpoled and highly poled biaxially oriented PVDF (BOPVDF). It was found that the concentration of active dipoles substantially increased as the temperature was increased from −30 to 40 °C, indicative of the devitrification of the rigid amorphous fraction (RAF). Both the calculated dipole moment and the g-factor of poled BOPVDF were higher than those of unpoled BOPVDF, resulting in a higher permittivity and piezoelectric performance. In addition, the dipole–dipole interaction was found to increase substantially upon increasing the temperature from −30 to 40 °C, leading to an increase of over 4 orders of magnitude in the rotational dipole mobility. This was direct evidence for the devitrification of the RAF in both unpoled and poled BOPVDF.

Single-Mode Electromagnetic Resonance Rewarming for the Cryopreservation of Samples with Large Volumes: A Numerical and Experimental Study.

Abstract: Rapid and uniform rewarming has been proved to be beneficial, and sometimes indispensable for the survival of cryopreserved biomaterials, inhibiting ice-recrystallization-devitrification and thermal stress-induced fracture (especially in large samples). To date, the convective water bath remains the gold standard rewarming method for small samples in the clinical settings, but it failed in the large samples (e.g., cryopreserved tissues and organs) due to damage caused by the slow and nonuniform heating. A single-mode electromagnetic resonance (SMER) system was developed to achieve ultrafast and uniform rewarming for large samples. In this study, we investigated the heating effects of the SMER system and compared the heating performance with water bath and air warming. A numerical model was established to further analyze the temperature change and distribution at different time points during the rewarming process. Overall, the SMER system achieved rapid heating at 331.63 ± 8.59°C min-1 while limiting the maximum thermal gradient to <9°C min-1, significantly better than the other two warming methods. The experimental results were highly consistent, indicating SMER is a promising rewarming technology for the successful cryopreservation of large biosamples.

Significance of tridymite distribution during cooling and vapor-phase alteration of ignimbrites

Abstract: Abstract Thick sequences of silicic ignimbrites contain complex emplacement and cooling histories, often masking contacts between ignimbrite flow packages. Mineralogical and textural variations in these sequences are primarily a function of emplacement temperature and cooling time. Here, we focus on the use of the silica polymorph tridymite to understand the association of vapor-phase crystallization and devitrification within ignimbrite flow packages. As opposed to the common occurrence of cristobalite, the restricted domains in which we observe tridymite may provide more relevant constraints for interpreting post-emplacement devitrification and vapor-phase alteration. This study examines sections through the Whakamaru (New Zealand), Bishop (U.S.A.), and Grey’s Landing (U.S.A.) ignimbrites by combining textural observations with measurements of density, groundmass crystallinity, and the distribution and proportion of tridymite to cristobalite. The rheomorphic Grey’s Landing ignimbrite represents a high-temperature end-member scenario, with widely distributed tridymite (up to 20%) resulting from a high-magmatic temperature and rapid devitrification in a low-porosity deposit. In the welded Whakamaru and Bishop ignimbrites, metastable tridymite (up to 13%) is concentrated along boundaries between flow packages. Here tridymite is interpreted to crystallize in transient permeable zones, forming during vapor-phase alteration prior to compaction, where upper denser-welded flow materials serve as vapor seals. Our results suggest that tridymite may link the initial cooling and welding history of ignimbrites to vapor-phase alteration and devitrification, and may serve as a potential mineralogical fingerprint of depositional contacts, important for consideration of lateral transport of fluids in geothermal reservoirs.

Thermoplastic embossing device to probe rheological changes of supercooled metallic liquids during rapid heating.

Abstract: The setup and working principle of a device designed for thermoplastic embossing and investigating rheological changes during fast-resistive heating of bulk metallic glasses (BMGs) is presented. The device was developed and custom-built at the Leibniz Institute for Solid State and Materials Research Dresden (Leibniz IFW Dresden) and is integrated into a universal testing machine. By varying the electrical-current pulse signal, the rate at which BMGs are resistively heated is controlled. Next to temperature and electrical resistance, the displacement of the punch, which penetrates the sample during rapid heating, is monitored. Additional pre-heating controlled by thermocouples allows for stable heating conditions to minimize heat extraction from the resistively heated specimen, which could eventually lead to damage of the device. The main focus of this device is to study fundamental phenomena under kinetic constraints evoked by fast heating conditions and to structure the surface of BMGs by thermoplastic embossing. A case study, which is carried out with Zr52.5Cu17.9Ni14.6Al10Ti5 BMG, demonstrates the device's performance covering heating rate ranges of three magnitudes and the access to rheological changes during the devitrification and subsequent crystallization of the BMG during rapid heating. Furthermore, the present device was successfully used to nanostructure the surface of the BMG at elevated heating rates.

Laser patterning assisted devitrification and domain engineering of amorphous and nanocrystalline alloys

Abstract: We have investigated laser-patterning and devitrification as a novel method to realize emergent properties in modified regions at the ribbon surface consisting of periodic localized laser spots thermally treated under rapid heating and cooling conditions. Fe-based amorphous ribbons were annealed for systematically varied laser power. Extremely high heating and cooling rates on the order of 108-1010K/s have been estimated by finite element analysis simulations. Observations suggest surface melting followed by rapid solidification fast enough to quench and form an amorphous structure upon cooling. Diffusion of heat occurs from the laser irradiated surface region so that a finite volume of material surrounding this region rises in temperature above the crystallization temperature relevant for conventional isothermal annealing experiments. The underlying mechanism of laser annealing and consequences of heat transients involved are discussed in terms of impacts upon micro/nanostructure, residual stresses, and magnetic domain structure surrounding the laser irradiated region. The study illustrates the potential to exploit spatially optimized phase transformations in a scalable manufacturing process of amorphous and nanocrystalline alloys to locally access otherwise inaccessible extreme heating and cooling rates.

On The Stability of Passive Film for Al-Rich Multicomponent Bulk Metallic Glass Under Long-Term Immersion in Chloride Containing Solution

Abstract: The electrochemical characteristics and passive film stability of an Al86Ni6Y4.5Co2La1.5 bulk metallic glass were systematically investigated in a chloride containing solution by the combination of electrochemical impedance spectroscopy and high-resolution transmission electron microscopy observations. The results demonstrated that the evolution of corrosion could be divided into five distinct zones: film growth in the initial immersion, a complete passive film with a dynamic and stable process, the occurrence of pitting on the passive film, accumulation of corrosion products, and the formation of continuous channels to failure. Note that in the second zone, the passive film achieved the highest stability at the middle of immersion due to the synergistic effect of film doping and thickening induced by the alloying of Y/La and Ni/Co. Afterwards, a gradual degradation of the passive film was observed, which was associated with the partial devitrification of the Y2O3 and La2O3 amorphous passive film. Correspondingly, the film/metal matrix interface underwent a transition from a flat interface to a curved one during the immersion, inducing the failure of the passive film. Our findings provide guidance for the design of Al-based amorphous alloys with high corrosion resistance.

Connections between structural characteristics and crystal nucleation of Al–Sm glasses near glass transition temperature

Abstract: A systematic investigation on connections between structural characteristics and crystal nucleation during isothermal devitrification of Al–Sm glasses has been carried out by utilizing molecular dynamics simulations combined with an effective data-driven approach named principal component analysis. The results suggest that icosahedral order dominants the local orders in Al–Sm liquids and glasses, whereas the development of crystal-like clusters has been greatly suppressed. Doping of Sm not only increases the population of icosahedral order in Al–Sm alloys, but also promotes the tendency of formation of icosahedral medium range order. Based on the calculation of local density and bond-orientational order parameters, a distinct decoupling in spatial distributions of fluctuations in local density and bond-orientational order is observed, and an obvious lagging of densification behind structural ordering is unveiled. These facts unambiguously evidence that the bond-orientational order instead of local density is the determinant factor for the origin of crystal nucleation in Al–Sm glass.

Controlling devitrification in the FeSiB system without alloying additions

Abstract: Efficient electric machines require soft magnetic materials with superior properties, motivating research on the processing-structure-response correlation in Fe-based metallic glass systems. Here, significant differences in the primary devitrification process and the resulting microstructure of amorphous metallic Fe79Si11B10 alloys synthesized into two different forms by different rapid solidification methods are confirmed. Melt-spun ribbons and water-quenched microwires were investigated with calorimetric, structural, and magnetic probes. It is found that the primary devitrification process of the ribbons occurs at a higher temperature (by 80 K) with a faster exothermic heat release relative to that of the quenched microwires, despite their common chemical composition and fully devitrified structural state. Analysis of the primary devitrification reveals that the ribbons exhibit a ∼70% higher effective activation energy and a ∼110% larger value of Avrami exponent relative to those characterizing the microwires, indicating different devitrification routes taken by these two types of material. In specific, the ribbons crystallize via a continuous nucleation process that partly relies on pre-existing surface nuclei, with an interface-controlled growth mechanism. In contrast, the quenched microwires devitrify solely from pre-existing nuclei, with diffusion-controlled growth. These differences are attributed to unique quenched-in structures that are created by the specific rapid solidification conditions. These results suggest approaches to control the microstructure in FeSiB compositions without the need for non-magnetic alloying additions.

Influence of Ceria Addition on Crystallization Behavior and Properties of Mesoporous Bioactive Glasses in the SiO2–CaO–P2O5–CeO2 System

Abstract: Knowledge of the crystallization stability of bioactive glasses (BGs) is a key factor in developing porous scaffolds for hard tissue engineering. Thus, the crystallization behavior of three mesoporous bioactive glasses (MBGs) in the 70SiO2-(26-x)CaO-4P2O5-xCeO2 system (x stands for 0, 1 and 5 mol. %, namely MBG(0/1/5)Ce), prepared using the sol–gel method coupled with the evaporation-induced self-assembly method (EISA), was studied. A thermal analysis of the multiple-component crystallization exotherms from the DSC scans was performed using the Kissinger method. The main crystalline phases of Ca5(PO4)2.823(CO3)0.22O, CaSiO3 and CeO2 were confirmed to be generated by the devitrification of the MBG with 5% CeO2, MBG5Ce. Increasing the ceria content triggered a reduction in the first crystallization temperature while ceria segregation took place. The amount of segregated ceria of the annealed MBG5Ce decreased as the annealing temperature increased. The optimum processing temperature range to avoid the crystallization of the MBG(0/1/5)Ce powders was established.

Spectroscopic properties of erbium doped germanate glasses and glass-ceramics

Abstract: In this paper structural, thermal and optical properties of Er 3+ doped germanate glasses with the composition of 63.0GeO 2 -9.8Ga 2 O 3 -11.1BaO-4.9X-8.8Na 2 O-2.5Er 2 O 3 (in mol%), where X = ZnO, TiO 2 , Al 2 O 3 and Y 2 O 3 are reported. The investigated glasses exhibit low phonon energies (<1000 cm -1 ) and high glass transition temperature varying between 588 and 642 °C. The Raman spectra evidence about different polymerization degree of the glasses. The thermal treatment leads to the precipitation of various crystals, the composition of which depends on the glass composition. According to the spectroscopic properties Er 3+ ions are suspected to have similar local environment in the as-prepared glasses. However, Er-doped crystals are expected to precipitate upon devitrification, which leads to significant change of the spectroscopic properties, in particular increase in the intensity of upconversion and MIR emissions is observed. It is demonstrated that the glasses with Y 2 O 3 , ZnO and TiO 2 are promising glasses especially for MIR applications.