Devitrification Process Research Articles

Crystallization path and non-isothermal kinetics of the Zr59.5Cu14.4Ni11.6Al9.7Nb4.8 metallic glass under different heating rates

In this work, the crystallization path and non-isothermal kinetics upon heating of the Zr59.5Cu14.4Ni11.6Al9.7Nb4.8 metallic glass were investigated. The devitrification process consists the formation of phases in the sequence of icosahedral quasicrystal (IQ) phase, Ni-containing phases, and Cu-containing phases. Avrami exponents were calculated at various heating rates, providing insights into the non-isothermal crystallization kinetics. The IQ phase and Ni-containing phases are interface-controlled growth, while the Cu-containing phases are diffusion-controlled growth. In addition, a continuous heating transition (CHT) diagram with a heating rate range exceeding six orders of magnitude was constructed, and the crystallization mechanism under different heating rates was revealed. These findings enrich the understanding of crystallization path and kinetics of metallic glass.

Petrogenesis of Paleozoic trachyte and rhyolite in the Haidewula area, East Kunlun Orogenic Belt, and their implications for uranium mineralization

Zircon U–Pb-Hf isotopic compositions, mineralogical chemistry, and whole-rock geochemistry analyses were performed on rhyolite and trachyte from the Haidewula deposit in the East Kunlun Orogen Belt (EKOB). These analyses aimed to elucidate the genetic relationship between trachyte and rhyolite and to investigate the role of these volcanic rocks in uranium mineralization. Zircon U–Pb isotope dating indicates that the Haidewula rhyolite and trachyte were contemporaneous with emplacement ages of 421 Ma to 428 Ma, respectively. The trachyte samples exhibit high K2O/Na2O and Fe# [FeO/(FeO + MgO)] ratios, and belong to metaluminous, ferroan volcanic rock; the rhyolite samples display high A/CNK and Fe# ratios, elevated high field strength element contents, and can be classified as strongly peraluminous A2-type magma. Trace and major elemental geochemical signatures demonstrate that the Haidewula trachyte originated from the high-temperature partial melting of a mafic lower crust, followed by fractional crystallization of plagioclase, pyroxene, magnetite, and/or K-feldspar. On the other hand, the rhyolite was likely generated by high-temperature melting of granodiorite in a low water and mid-crust pressure environment, followed by fractional crystallization of feldspar and ilmenite. The occurrence of A-type volcanic rocks at Haidewula suggests that the initial timing of crustal extension in the EKOB was not later than 428 Ma. Overall, Paleozoic igneous rocks in the EKOB revealed that a post-collisional extensional regime, resulting from the rewelding of the microcontinents in eastern Gondwana, was responsible for intensive magmatism during the Late Silurian period. In comparison to other volcanic complexes hosting uranium deposits in eastern China, the relatively U-rich rhyolite and trachyte had the potential to contribute to the formation of U mineralization. In particular, the rhyolitic tuffaceous U-rich glassy volcanic rocks in the Haidewula deposit may represent favorable U-source rocks for mineralization, with uranium released through volcanic glass devitrification processes and leaching by oxidizing hydrothermal fluids.

Dynamics of Cu–Zr metallic glass devitrification under ultrafast laser excitation revealed by atomistic modeling

The physics of metallic glass local devitrification employing ultrafast laser irradiation is the cradle of complex phenomena that are still not understood despite its applicative potential in material processing for nanotechnology. This paper reports a theoretical simulation combining the two temperature model and classical molecular dynamics simulations to unravel the mechanisms that lead to the localized phase transition in Cu–Zr metallic glass. According to observations, the initial composition of amorphous samples plays an essential role, in addition to nonequilibrium thermodynamic processes caused by the laser energy deposition that alters the atomic environment. We further demonstrate that specific compositions devitrify despite its high glass-forming ability. The thermodynamic conditions fostering the emergence of a stable nanocrystalline phase are clearly established. The compressive pressure wave and the rapid heating process caused by ultrafast laser energy deposition synergistically contribute to disrupt the microstructure of the glass significantly, thereby initiating the devitrification process. Results are discussed using additional classical MD simulations that provide valuable insights for interpreting the distinct contributions of temperature and pressure to the phase transformation. Finally, the impact of the formed nanocrystals on the phononic thermal conductivity of the alloy is presented confirming the potential application of the laser-induced devitrification process for the development of a new generation of nanoarchitectured materials.

Understanding the paradigm of vitrification-devitrification transitions in oxide network forming compounds using a revised positron lifetime analysis

Vitrification and devitrification transitions in network oxide compounds such as silicates and borates keeping the same composition of crystalline and non-crystalline polymorphs are examined in terms of volumetric nanostructurization using a revised positron annihilation lifetime analysis. Assuming simple conversion between Ps-decay and positron-trapping channels responsible for three-component lifetime spectra, probability of polymorphous crystalline-vitreous transformations is estimated by κ parameter defined as relative changes in average lifetimes for direct (Ps-to-positron) and inverse (positron-to-Ps) trapping conversion. Both volume-expanded vitrification and volume-contracted devitrification processes are realized in SiO2-based network systems where disordered counterparts are fused quartz, amorphous films or cylindrical-porous glass (κ < ∼6%), while they are questionable in grown silica films (κ ∼ 8%). Polymorphous transformations are unfavorable in B2O3-based systems because of entropy gain rearranging superstructural grouping in their networks (κ∼28%). But in modified borates like lithium tetraborate Li2B4O7 where Ps- and positron-related traps are composed of Li vacancies, these transitions become possible (κ∼3.2 %).

Glass softening in the limit of high heating rates: Heterogeneous devitrification kinetics on nano, meso, and micrometer scale.

When heated rapidly, glasses often devitrify heterogeneously, i.e., by a softening front that originates at the surface of an amorphous film. Yet the fundamentals of this devitrification regime are not completely understood; depending on experimental conditions, the reported front propagation distances differ by an order of magnitude. Using a high-resolution fast scanning calorimetry technique, we have investigated the softening of glassy methylbenzene films with thicknesses between 30 and 1400nm. We confirm first that, in all films, the devitrification process begins with the formation of a softening front that propagates through the films over distances of ∼50nm and that the front propagation kinetics at this stage follow an Arrhenius law. However, we also show that, in films with thicknesses above 165nm, the front propagation does not terminate with the onset of bulk softening. Specifically, increasing the films' thicknesses above 165nm yields sharp, clearly discernible endotherms that precede the bulk softening endotherms and that are consistent with a two-fold increase in the enthalpic barrier to front propagation at a well-defined critical temperature. We term this phenomenon "Arrhenius discontinuity" and use reaction rate and continuum front dynamics theories to explain its origins and the physical nature of the resulting distinct heterogeneous devitrification processes. Finally, we discuss the findings in the context of recent theoretical, computational, and experimental studies of heterogeneous devitrification by other research groups.

Characterization of Hydrothermal Alteration in Palagonitized Deposits Using Short-Wave Infrared Spectroscopy and X-Ray Diffraction Methods

Abstract In this contribution, we evaluate the applicability of short-wave infrared spectroscopy to characterizing mineral assemblages in palagonitized glaciovolcanic edifices at Cracked Mountain, a basaltic volcano within the Garibaldi Volcanic Belt, and Kima Kho, a basaltic tuya within the Northern Cordilleran Volcanic Province. Second-order evaluation of the approach was established through comparison with data obtained by semi-empirical X-ray diffraction methods. Reflectance spectra show an increase in the depth of water and hydroxyl bands in samples with increasing amounts of hydrated minerals and decreasing amounts of amorphous materials (as determined through X-ray diffraction), indicating that the relative strengths of H2O- and OH-related absorption features may be used as a proxy for the degree of palagonite alteration (hydrated minerals crystallized from basaltic glass). In addition, the full width at half maximum of the OH- and H2O-related absorption bands decreased with the formation of zeolites, indicating that the full width at half maximum of OH- and H2O-related features may be used to estimate the degree of crystallinity across the progressive palagonitization process. Finally, short-wave infrared spectroscopy revealed a decrease in band depth of water-related absorption features with no change in the full width at half maximum along the devitrification or alteration process that converts analcime to chabazite to wairakite, indicating that spectroscopy may be used to identify the final dehydration and cementation stages of palagonitization. Results show that the short-wave infrared spectroscopy method is more robust in identifying poorly crystalline hydrated samples, while X-ray diffraction methods are better suited to understanding the crystalline components of palagonite. Short-wave infrared spectroscopy is a remote sensing technique that has proven to successfully characterize the state of H2O in hydrated clay-rich material and thus may serve as an invaluable tool in identifying stages of palagonitization not only on subglacial edifices on Earth but also on off-planet environs, including the Martian surface.

Evolution of local atomic structure accompanying devitrification of amorphous Ni-Zr alloy thin films

Thin film metallic glasses undergoing devitrification can form partially crystallized or fully crystallized materials with novel structural and magnetic properties. The development of desired and tunable properties of such systems drives the need to understand the mechanism of their thermal evolution at the atomic level. Co-sputtered amorphous Ni-Zr alloy thin films which were thermally annealed in steps of 200°C from room temperature up to 800°C, were observed to undergo an amorphous-to-crystalline transformation. Evolutions in local atomic structure, including oxide formation and depletion during this devitrification process, were determined using a combination of X-ray reflectivity (XRR), grazing incidence X-ray diffraction (GIXRD) and Extended X-ray Absorption Fine Structure (EXAFS) techniques. The most probable phase of the alloy was determined as Ni7Zr2; undergoing a polymorphous transformation. The slight oxide content in the films was also noted to decrease rapidly as annealing proceeded; leaving the crystallization pathway unhindered. modeling and analyses of XRR and GIXRD data showed that film thickness decreased with annealing while long range order increased. Pair distribution function peak widths were observed to decrease with annealing, indicating a control over structural disorder in the system as it transitioned from the amorphous to crystalline state. Partial atomic distribution in the environment of each constituent was examined at every stage of annealing through EXAFS measurements, which gave proper insight into atomic scale changes to the order present. Detailed analyses through these techniques gave coherent results, thus providing a true picture of the thermal evolution process of devitrification in this technologically useful material.

Thermally induced microstructure evolution and effects on the corrosion behaviors of AlFeSi metallic glass coatings

The effects of the devitrification process on the microstructure evolution and corrosion resistance of arc-sprayed AlFeSi metallic glass coatings were explored. Detailed characterizations revealed that the structural relaxation coating (annealing at 300 °C) retains the phase structures of the as-sprayed coating. Annealing at 350 °C (above the onset crystallization temperature) facilitates nanoscale Al9Fe2Si2 and Al9FeSi3 new phase precipitation. Annealing at over 400 °C (above the full crystallization temperature) induces completely crystallized structures of α-Al, Al9Fe2Si2, and Al9FeSi3 in the coatings. The crystalline size response of the coatings depends on the annealing temperatures. Electrochemical tests indicated that devitrification increases the current density and reduces the impedance of the coatings. The best corrosion resistance is discernible for the as-sprayed AlFeSi metallic glass coating. The decreased amorphous fraction, larger nanocrystals, and crystal structure heterogeneity in the as-annealed coatings are responsible for the degradation of corrosion resistance. Additionally, the variations in the compositions and natures of the passive films with thermally induced microstructure evolution were elucidated in detail.

Controlling devitrification in the FeSiB system without alloying additions

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.

Study of beryllium hardening obtained by powder metallurgy

In the first part of the article the results of the study of powder hardening processes occurring during beryl powders consolidation by the hot pressing method are shown. The dependences of the content and morphology of the hardening phase depending on the content of low-melting impurities on the sintered Beryllium powder grains surface have been studied. A hypothesis is proposed that explains the transition of an oxide film from an amorphous to a crystalline state – devitrification, and the effect of low-melting impurities on the mechanism of the devitrification process and, as a consequence, on the effect of "dispersion-grain boundary" hardening. This hypothesis is based on theoretical confirmation with the provision of graphic material demonstrating the process of devitrification, accompanied by a dispersed-grain-boundary hardening mechanism. The final results of statistical processing carried out on industrial batches showing the dependence of the impurities content influence on the properties of hot-pressed beryllium are presented. In the second part of the article the results of studying the effect of hardening of beryllium obtained in the process of sintering by the method of hot isostatic pressing (HIP) are shown depending on the temperature of powders consolidation. Based on the results of electron microscopic studies, the dynamics of the reinforcing phase formation at the grain boundaries of sintered beryllium is shown. The quantitative dependence of the precision elastic limit and the conditional yield stress of gas-statically compressed beryllium on the size of the strengthening beryllium oxide particles and the consolidation temperature of the powders have been established. The resulting equation gives a description of the "dispersed-grain-boundary" hardening mechanism of isostatically pressed beryllium. All dependencies are also represented by graphic material reflecting the essence of the research.

A new criterion for glass-forming ability based on both devitrification and solidification processes

Based on the time-temperature-transformation interpretation, a new criterion for glass forming ability, Z = [(Tx-Tg)/(Tl-Tg)][(Tl–Tl(c))/(Tl-Tg)]0.556, is proposed, where Tg, Tx, Tl and Tl(c) respectively denote the glass transition temperature, the onset crystallization temperature upon heating, the liquidus temperature and the onset solidification temperature of the liquid upon cooling. The Z parameter jointly considers the stability of the liquid and the devitrification of glassy phases. A non-linear relationship between the parameter Z and the critical glassy size dc has been found to be log (dc)cal = 0.1392 + 17.0616Z - 41.985(Z)2, showing stronger correlation than other earlier reported parameters. The advantage of using Z as a GFA parameter is that it roughly reflects the relative influences of the thermodynamics and kinetics of the systems on glass formation. In addition, the parameter describes the stability of liquid in the course of being quenched from above liquidus temperature.

Eggshells as agro‐industrial waste substitute for CaCO3 in glass foams: A study on obtaining lower thermal conductivity

AbstractIn this work, discarded glass bottles (GB) and eggshells (ES) were used to produce foam glass designed for thermal insulation. The literature on the thermal conductivity of foam glasses produced with eggshells is sparse. This material was used as pore‐forming agent at 3% and 5% weight fractions to obtain a foam glass with low thermal conductivity. Homogenized powders were uniaxially pressed, and the compacts were fired at three temperatures (800, 850, and 900°C). Raw materials were characterized by chemical analysis and particle size distribution. The foam glasses were characterized by their porosity, phases, compressive strength, and thermal conductivity. The best insulating properties were obtained for the composition containing 5 wt% ES fired at 800°C. This sample displayed a porosity of 91.4% while its thermal conductivity was of 0.037 W/m.K, with a compressive strength of 1.12 ± 0.38 MPa. Crystalline phases were observed in samples fired at 850 and 900°C as a result of the devitrification process. The final properties of the materials are comparable to those of commercial foam glasses obtained from non‐renewable, more expensive raw materials, a great indicator that the studied compositions could be used as an environmentally friendly substitute.

Analysis of elemental distributions and phase separation in rare-earth-doped silica-based fiber preforms and optical fibers

The elemental distribution, phase separation and nanocrystallization process in rare-earth-doped silica-based fiber preforms and optical fibers were studied by using analytical electron microscopy. The particular properties of devitrification processes depending on the fiber core compositions and concentration of rare earth elements was systematically studied in aluminophosphosilicate fibers. It was investigated that the record high (for Modified Chemical Vapour Deposition manufactured samples) concentrations of rare-earth ions (up to 3 at% Yb3+) can be achieved alongside with a reasonably low background optical losses using aluminosilicate glass matrix. Two types of phase separation were revealed in the investigated samples of different composition: the droplet separation and the formation of two interpenetrated glass phases. It was concluded that the second type phase separation can be accompanied by the formation of nanocrystalline inclusions. Possible applications of the obtained glasses in practice for creation of highly-absorbing layers in optical fibers were discussed in the paper.

Specific trends in phosphate glass crystallization

This paper focusses on investigating and comparing the congruent crystallization of phosphate glasses with different degrees of polymerization. The study was performed both on powders, with different size fractions, and coarse particles which can be assimilated to bulk. From DSC experiments, corroborated by SEM analysis, it was demonstrated that LiPO3 crystallizes from surface whereas LiGe2(PO4)3 crystallizes in the whole volume. Sn2P2O7 presented both phenomena, the nucleation time lag being short enough to observe internal crystallization at the laboratory time scale. Using the non-isothermal Ozawa method, the kinetic parameters of the overall devitrification process were determined in terms of the Avrami exponent and of the activation energy for crystallization. The temperature of the maximum nucleation rate was calculated by using the nucleation adiabatic theory. For the achievement of this calculation, the heat capacity temperature dependence up to melting was determined from DSC experiments. The results were found in a good agreement with the SEM observation and the results of the non-isothermal crystallization study.

Microstructure Investigation of Oil-Bearing Rhyolites: A Case Study from the Hailar Basin, NE China

Understanding the microstructure of rhyolites may greatly promote exploration efforts on rhyolitic hydrocarbon reservoirs; however, related studies are sparse. In this contribution, the microstructure and related porosity of oil-bearing rhyolitic lavas from the Hailar Basin (NE China) were investigated using a combination of optical microscopy, fluorescence image analysis, and scanning electron microscopy. The direct visual and quantitative analyses show that the rhyolites are heterogeneous and porous rocks and have complex microstructures. Phenocryst-rich rhyolitic lava, perlitic lava, and spherulitic rhyolite may be favorable targets for rhyolitic hydrocarbon exploration. For the phenocryst-rich rhyolitic lavas, embayment pores, cleavages, cavitational and shear fractures, and intracrystalline sieve pores are commonly observed in the phenocrysts; while flow-parallel laminar and micropores are ubiquitous in the groundmass. Perlitic lavas are characterized by the occurrence of numerous perlitic fractures which can also be produced in the glassy groundmass of other lavas. Spherulitic rhyolites mainly consist of small-sized (&lt;1 mm) clustered or large-sized (&gt;1 mm) isolated spherulites. Clustered spherulites are characterized by the development of interspherulite pores. Isolated spherulites contain numerous radiating micropores. Both types of spherulites may have water expulsion pores formed in the spherulite–glass border. The formation of the microstructure and related porosity of rhyolites is controlled by pre-, syn- (e.g., deuteric crystal dissolution, cavitation, ductile–brittle deformation, and high-T devitrification), and post-volcanic (e.g., hydration and low-T devitrification) processes. Although pores with diameters &gt; 50 μm are often observed, small pores dominate in pore-size distribution. Small (&lt;15 μm) and large (&gt;300 μm) pores give the most volumetric contribution in most cases. Medium-sized pores with diameters ranging from ~150–300 μm are the least developed and contribute the least to the total volume. The results of this paper can be beneficial to further the understanding of the microstructure and pore system of rhyolites and may be applied to rhyolitic lava hydrocarbon reservoirs elsewhere.

Calorimetric distinction between the inter- and intra-molecular rearrangement processes in alkylcyclohexane liquids by means of spatial confinement

We report an investigation, by means of adiabatic calorimetry, on the thermal properties of ethylcyclohexane (ECH) confined to within silica-gel mesoscopic pores with an average pore size of 6 nm. As a result of confinement, crystallization was circumvented within the entire temperature range. The devitrification behavior of the confined glass was observed to mainly proceed in a two-step manner and these steps were attributed to the existence of distinct relaxation processes involving molecules in the inner-pore and pore-wall-interface regions. Additionally, two secondary relaxations, of smaller magnitudes, were identified: (1) one occurring within the glassy state, below the primary devitrification process; and (2) another occurring within the supercooled liquid state. Revisit of the data of similar investigations on crystallization-circumvented methylcyclohexane (MCH) indicated the existence of a relaxation process analogous to this latter one (2). The characteristic temperatures for the latter process in both ECH and MCH were found to be independent of the degree of confinement. On the other hand, the former secondary relaxation (1) occurring within the glassy state of ECH displayed pore-size dependent behavior. We interpreted the behavioral difference, between the two processes, as associated with the distinct origins of either intermolecular or intramolecular processes; namely, the relaxation (1) as ascribed to the so-called β-relaxation commonly observed in glasses and the relaxation (2) to the molecular rearrangement modes involving the positional conversion, of the substituted alkyl-group, between the axial and equatorial configurations. The energy difference between the axial and equatorial states inferred from the magnitude of heat-capacity jump at the glass transition temperature was rationalized to be (7.7 ± 0.3) kJ mol−1.

Study of the kinetics and products of the devitrification process of mechanically amorphized Fe70Zr30 alloy

Devitrification of mechanically alloyed amorphous Fe70Zr30 at. % compound consists on a two-step process: amorphous → amorphous + bcc Fe + Fe2Zr → Fe2Zr + Fe23Zr6. This sequence is inferred from the evolution of the Mössbauer spectra, the thermomagnetic experiments and the X-ray diffraction (XRD) patterns. Hyperfine parameters for both intermetallics have been obtained from Mössbauer spectroscopy in correlation with the phase identification from XRD results. The broadening of the stable compositional range of Fe2Zr intermetallic above 1000 K is responsible for a strong dependence of the phase fractions on heating and cooling rates. Despite the overlapping of the two processes involved in the devitrification, the individual Avrami exponents of each one have been estimated.

Correlation between glass transition temperature and the width of the glass transition interval

AbstractThe glass transition is a kinetic phenomenon. Its basic characteristics—the glass transition temperature, Tg, and the width, δTg, of the glass transition interval—depend significantly on cooling and heating rates as it is observed experimentally by standard DSC and fast scanning calorimetry. The knowledge of these and related correlations is of outstanding importance both for a theoretical understanding of vitrification and devitrification processes and their control in a variety of technological applications. By these reasons, general kinetic criteria of vitrification and, based on them, theoretical expressions for the glass transition temperature and the width of the glass transition range in dependence on rates of change of temperature have been derived in previous papers. These results are advanced here by establishing a direct correlation between these two quantities, Tg and δTg. The ratio δTg/Tg is shown, for arbitrary cooling and heating rates, to be a function of an appropriately defined index being a straightforward generalization of the definition introduced by Angell. The theoretical results are tested and confirmed by experiment. The methods employed here can be utilized generally for the description of vitrification caused also by a variation of other external control parameters like pressure.

Optical and structural properties of BCBS glass system with and without alumina

BaOCaOAl2O3SiO2 (BCAS) glass and their derivatives have gained extreme importance for their high endurance to elevated temperatures and being suitable for various electrochemical applications. Two glass systems, one being 50mol% [SiO2B2O3]-xBaO-(45-x)CaO5Al2O3 called as BCBSA and another without Al2O3 termed as BCBS were synthesized using melt quenching technique in the present work. Addition of ZnO and MgO as flux helped in melting them at 1300 °C which is much lower than the usual melting temperature of these glasses [1–4]. Density of the quenched glasses was measured by Archimedes method and structural bond vibrations were confirmed through FTIR. UV Visible spectroscopy was used to determine band gap energy and confirm the insulating nature of the synthesized glasses. The samples were isothermally heated at 700 °C, 800 °C for 50 h and at 900 °C for 50 and 100 h duration in air to allow the devitrification process to take place. The heat treated samples were analyzed by X-ray diffraction to identify the developed phases. Five Al2O3 free samples synthesized at 1300 °C by regular melt quenching technique were found to be devoid of the monocelsian phase. This is a detrimental phase for high temperature sealant applications as it has a very low coefficient of thermal expansion (CTE). Al2O3 free BCBS glasses, properties of which are being reported for the first time and glasses with low BaO concentrations are found to meet the requirements for high temperature applications as sealants in Solid Oxide Fuel Cell (SOFC).

Thermally Induced Bend Loss of Silica Optical Fiber

Multimode and single-mode silica fibers have been tested in a high-temperature setting, while simultaneously experiencing a bend. The range of temperature tested was 500 °C–1000 °C and the bend radii considered were 1.27, 2.54, and 3.81 cm (0.5, 1.0, and 1.5 in). Multimode fiber (MMF) was analyzed for transmission, while single-mode fiber (SMF) was both analyzed for transmission and interpreted by optical backscatter reflectometry. Attenuation was observed to increase in MMF with increasingly high temperatures and tighter bend radii. SMF was far more resilient to transmission loss than MMF, under similar conditions of temperature and curvature. Optical backscatter reflectometry was performed for bent SMF up to 1100 °C and revealed evidence that, at high temperatures, bends in fiber can enhance devitrification that can inhibit light transmission through the fiber. This paper suggests that the devitrification process begins at the surface of the fiber and moves inward. Moreover, this paper suggests that bend stress applied to surface flaws of the fiber leads to significantly higher crystallization rates at temperatures at which silica does not typically devitrify so rapidly.