Critical Heating Rate Research Articles

Shaped Laser Pulses for Microsecond Time-Resolved Cryo-EM: Outrunning Crystallization during Flash Melting.

Water vitrifies if cooled at rates above 3 × 105 K/s. In contrast, when the resulting amorphous ice is flash heated, crystallization occurs even at a more than 10 times higher heating rate, as we have recently shown. This may present an issue for microsecond time-resolved cryo-electron microscopy experiments, in which vitreous ice samples are briefly melted with a laser pulse because transient crystallization could potentially alter the dynamics of the embedded proteins. Here, we demonstrate how shaped microsecond laser pulses can be used to increase the heating rate and outrun crystallization. Time-resolved electron diffraction experiments reveal that the critical heating rate for amorphous solid water (ASW) is about 108 K/s. Our experiments add to the toolbox of the emerging field of microsecond time-resolved cryo-electron microscopy by demonstrating a straightforward approach for avoiding crystallization during laser melting and for achieving significantly higher heating rates, which paves the way for nanosecond time-resolved experiments.

Detecting reorganization in semicrystalline polymers during heating: Insights from Fast Scanning Chip Calorimetry coupled with real-time optical microscopy

Thermal behavior of semicrystalline polymers is notoriously complex due to the metastable nature of polymer crystals. This complexity is evidenced in the multiple melting endotherms frequently observed in the heating traces of various plastics, a phenomenon known as ‘multiple melting behavior’. Extensive research indicates that calorimetric analysis alone may not suffice to fully elucidate the processes occurring during thermal experiments. In this study, we introduce an experimental setup that integrates Fast Scanning Chip Calorimetry, or nanocalorimetry, with real-time polarized optical microscopy. This combination enables in-situ morphological observations during rapid heating/cooling experiments. The setup not only complements thermal analysis but also rivals the capabilities of fast in situ X-ray scattering experiments conducted at synchrotron sources. Our findings show that the obtained data help in identifying melting/recrystallization processes and, therefore, enable the determination of the critical heating rate above which reorganization processes during heating are kinetically bypassed. This ensures that the thermal events detected in calorimetric curves are exclusively due to the initial sample structure, without being influenced by any reorganization that may occur during the heating process.

Nanocrystal evolution during ultra-fast heating in an amorphous Fe85B15 alloy

During the crystallization of Fe-based metallic glasses the precipitation of the BCC-Fe nanocrystals smaller than the exchange length (30–40 nm) has been reported as an effective strategy for a reduced coercivity and an increased saturation magnetization. In binary Fe-B alloys it has been shown that nanocrystals well below the exchange length can be obtained by rapid heating above 100 K/s. In order to determine if the fast heating process can yield a further refinement in nanocrystal size, the influence of different heating rates (0.17–5000 K/s) on the crystallization behavior of an amorphous Fe85B15 alloy was investigated using Flash DSC and TEM. Above a critical heating rate (500 K/s), the number density and diameters of BCC-Fe nanocrystals become saturated due to diffusion-field impingement that enriches the amorphous matrix with B that leads to the precipitation of Fe3B nanocrystals that deteriorate the magnetic properties.

Effect of P addition on soft magnetic properties of Fe–Si–B–P–Cu–C nano-crystalline alloys

The effect of P addition on the nano-crystallization of Fe81.5Si0.5B15.5-xPxCu0.5C2 (x = 0, 4.5, 7.5, 11 at.%) amorphous alloys under various heating rates has been studied. Appropriate P addition enhanced the thermal stability of Fe–Si–B–P–Cu–C amorphous alloys. The results also revealed that P addition could decrease the required critical heating rate for the low coercivity and improve the magnetic softness of annealed samples. Although as commonly found in most Fe-based nano-crystalline alloys, a small amount of P addition (4.5 at.%) could effectively help reduce the coercivity when a high heating rate was applied during nano-crystallization, the high heating rate failed to decrease the coercivity in 7.5 at.% P-added alloys and even reversely caused the deterioration of magnetic softness for excessive P addition (11 at.%). The unusual phenomenon in the alloy with 11 at.% P addition lies in the fast increase of diffusion rate with rising temperature and delayed nucleation, which are caused by the weakened bond energy and increased segregation energy, respectively. The results suggest that the improvement of magnetic softness for Fe-based nano-crystalline alloys through simply increasing the P addition would meet its ceiling, due to the limited decrease in coercivity and even increase through applying high heating rate with excessive P concentration. The understanding of P role on the nano-crystallization mechanism could contribute to the compositional design of high-performance soft magnetic Fe-based alloys with an acceptable heating rate in industry.

Effect of Residual Deformation Energy and Critical Heating Rate on Cubic Texture and Grain Growth Behavior of Severely Deformed Aluminum Foil.

To clarify the microstructure, grain size, and recrystallization behavior during different annealing processes with controlled heating rates, the aim of this study was to investigate the effect of residual deformation energy after cold rolling and critical heating rate on cubic texture components, and grain growth behavior of aluminum plate, which was subjected to severe deformation. The experimental results revealed that the stored energy can be inferred from a calculation that fast annealing (FA) for 30 s was 2.2 times as large as slow annealing (SA) at 320 °C, which provided the driving force for grain growth during subsequent heating and resulted in a significant coarsening of grains in the FA process. In contrast, the intensity of cubic texture in SA was significantly higher than that in the FA process. A critical heating rate of 50 °C/min had been obtained to produce a homogeneous microstructure and strong cubic texture during the annealing processes with controlled heating rates and was verified by experiment. The relationship of Δηsur > 0.02ηb was as a criterion used to determine whether abnormal grain growth happened in aluminum foil, while the grain size exceeded the thickness of aluminum foil by examined calculation.

Glass transition of the phase change material AIST and its impact on crystallization

Engineering phase change materials (PCM) to realize superior data storage devices requires a detailed understanding of crystallization kinetics and its temperature dependence. The temperature dependence of crystallization differs distinctly between crystallizing from the glassy phase and the undercooled liquid (UCL). Hence, knowing the phase from which crystallization occurs is necessary for predicting the switching ability. Here, we measure the glassy dynamics and crystallization kinetics using calorimetry for heating rates spanning over six orders of magnitude. Our results show that the prominent PCM (Ag,In)-doped Sb2Te (AIST) exhibits a change from crystallizing from the glassy phase to crystallizing from the UCL at a critical heating rate of 5000 K/s. Above the glass transition, the activation energy of crystallization changes drastically enabling rapid crystallization at elevated temperatures.

The effect of chemical patterning induced by cyclic plasticity on the formation of precipitates during aging of an Al–Mg–Si alloy

Room temperature cyclic deformation of solution treated AA6061 led to the development of a high number density of Mg/Si clusters. The fine dispersion of clusters resulted in a strength comparable to that obtained using the T6 condition. Subsequent heat-treatment has the potential to further increase the strength of the alloy. Slow heating from room temperature to 177 °C allowed the clusters to catalyse the creation of a very high number density of precipitates. Isothermal aging for 2 h at this temperature produced a tensile strength which is 10% greater than that obtained using the T6 heat-treatment. The uniform and total elongation of cyclically deformed and heat-treated material were both greater than those obtained through the standard T6 treatment. In addition, the aging time needed to achieve the above properties in the cyclically deformed material (2 h) is significantly lower than the time needed to achieve peak strength in the traditional T6 treatment (25.5 h). Detailed observations of the microstructure using Transmission Electron Microscopy and Atom Probe Tomography suggest that the increased strength is due to the presence of a larger number density of fine precipitates in the cyclically hardened and aged material compared to the material that underwent traditional aging. The clusters formed during cyclic deformation can therefore play an important role in the nucleation of precipitates during subsequent aging. A simple model that captures the size evolution of clusters is presented to rationalize the experimental results and demonstrate the existence of a critical heating rate, above which, the clusters dissolve and are ineffective at promoting a high number density of precipitates.

Critical crystallization properties of an industrial-grade Zr-based metallic glass used in additive manufacturing

The major challenge to overcome when processing metallic glasses (MGs) is to avoid crystallization. Therefore, time-temperature-transformation (TTT) diagrams are used, but they are often derived from experiments in which heating or cooling rates are limited and do not cover the full range of processing conditions, especially those encountered in additive manufacturing (AM) where the rates are very high. Here, an industrial-grade Zr-based MG (AMZ4) is investigated via fast differential scanning calorimetry (FDSC). The critical cooling and heating rates of AMZ4 are experimentally measured and TTT diagrams are determined upon heating and cooling. The critical heating rate of 45,000 K/s is 18 times the critical cooling rate, which indicates the presence of a self-doped glass (SDG) that includes quenched-in nuclei. The results illustrate that AMZ4 is very sensitive to crystallization, even in laser-based AM conditions, where heating and cooling steps need to be distinguished.

Pathway-Dependent Co-Assembly of Elastin-Like Polypeptides.

In natural systems, temperature-induced assembly of biomolecules can lead to the formation of distinct assembly states, created out of the same set of starting compounds, based on the heating trajectory followed. Until now it has been difficult to achieve similar behavior in synthetic polymer mixtures. Here, a novel pathway-dependent assembly based on stimulus-responsive polymers is shown. When a mixture of mono- and diblock copolymers, based on elastin-like polypeptides, is heated with a critical heating rate co-assembled particles are created that are monodisperse, stable, and have tunable hydrodynamic radii between 20 and 120nm. Below this critical heating rate, the constituents separately form polymer assemblies. This process is kinetically driven and reversible in thermodynamically closed systems. Using the co-assembly pathway, fluorescent proteins and bioluminescent enzymes are encapsulated with high efficiency. Encapsulated cargo shows unperturbed function even after delivery into cells. The pathway-dependent co-assembly of elastin-like polypeptides is not only of fundamental interest from a materials science perspective, allowing the formation of multiple distinct assemblies from the same starting compounds, which can be interconverted by going back to the molecularly dissolved states. It also enables a versatile way for constructing highly effective vehicles for the cellular delivery of biomolecular cargo.

A novel strategy to design Zr–Co–Al BMG composites containing only B2–ZrCo phase

The B2 phase-containing Bulk Metallic Glass (BMG) composites, as a promising remedy to tackle the strain-softening and brittleness of BMGs, has been widely applied to enhance the work-hardening and plastic deformability. A novel strategy was proposed to select the composition of an alloy which effectively promotes the formation of B2–ZrCo phase. We designed and prepared six compositions and seven rod samples, and then analysed the precipitation of crystalline phase together with the mechanical properties. We found that the primary phases administrate the mechanical properties and the composition of an alloy determines the formation of crystalline phases. Also, the cooling rate cannot enhance the B2–ZrCo phase formation in as-cast Zr–Co–Al BMG composites. As a result, we found that the formation of a large quantity of glass matrix and only B2–ZrCo phase cannot be achieved simultaneously in as-cast Zr–Co–Al alloys. In order to resolve this issue, flash annealing has been introduced to solve this problem. Different compositions correspond to different critical heating rates and high heating rate usually aggravates the difficulty to achieve this aim. In order to reduce critical heating rate, the conventional annealing, which can be well controlled, was used to select the alloy composition and compare formation of the B2–ZrCo phase. And thus, an optimal composition of Zr–Co–Al alloy can be selected to produce the BMG composites incorporating the only B2–ZrCo phase via flash annealing. Therefore, we believe that this work provides a novel recipe to design the Zr–Co–Al BMG composites incorporating the only B2–ZrCo phase.

Growth and dissolution of crystal nuclei in poly(l-lactic acid) (PLLA) in Tammann's development method

By fast scanning calorimetry (FSC), the influence of the transfer of nuclei from the nucleation stage at low temperature to the growth stage at higher temperature was systematically studied. Heating rates above 1000 K s−1 are sufficient to prevent growth of crystal nuclei at the transfer from 60 °C to 125 °C in Poly(l-lactic acid) (PLLA). The critical heating rate for preventing nuclei growth is about 1000 times higher than the critical heating rate to prevent crystal growth in a nucleated sample on heating. In a second experiment, the cluster size distribution after isothermal nucleation of PLLA at 60 °C for 1000 s was estimated. In the temperature interval from 125 °C to 145 °C, the density of critical nuclei decreases from the initial value ∼4 × 1024 m−3 to zero, as nuclei with R > 2 nm, the critical radius for 145 °C, were not formed at the nucleation temperature.

Heating-Induced DMPC/Glycyrrhizin Bicelle-to-Vesicle Transition: A X-Ray Contrast Variation Study

In this study, we investigated the conversion of lipid bicelles into vesicles in the case of a system composed of the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and the saponin glycyrrhizin in the presence of sucrose. Glycyrrhizin is a biosurfactant present in the licorice root and possesses a triterpenic hydrophobic backbone and a hydrophilic headgroup built from two sugar molecules. The aim of this study is to determine the initial bicelle size at temperatures below the lipid’s main phase transition temperature Tm and, based on these results, characteristics of the temperature-induced bicelle-to-vesicle transition. Moreover, the influence of the heating rate on this transition is followed. The general picture concluded from photon correlation spectroscopy and small angle X-ray scattering was confirmed by additional imaging with cryogenic transmission electron microscopy. Small angle X-ray scattering was especially used to determine size parameters of the existing structures. To enhance the contrast for X-rays, a buffer containing 25 wt% sucrose was used. It was found that larger vesicles were formed from smaller precursor particles and that monodisperse precursors are required for formation of very monodisperse vesicles upon temperature increase. At high glycyrrhizin contents and above a critical heating rate of ∼5°C min−1, the polydispersity of these vesicles is decoupled from both parameters, glycyrrhizin content and heating rate. However, the vesicle size stays tunable by the glycyrrhizin content and increases upon increasing the glycyrrhizin concentration. Therefore, vesicles of defined size and with a rather low polydispersity of ∼12–14% can be formed.

Phase transformations in a Cu–Zr–Al metallic glass

A combination of conventional calorimetry, ultra-fast scanning calorimetry and resistive heating gives access to heating rates exceeding 6 orders of magnitude allowing to probe crystallization kinetics and mechanisms in a Cu-Zr-Al metallic glass. Continuous-heating-transformation and double-peak time-temperature-transformation diagrams are constructed and related to the formation of glass–crystal composites with enhanced ductility. The metastable B2-CuZr phase becomes dominantly formed at a heating rate of ~102 K s−1 and higher. A critical heating rate to bypass crystallization is ~10,000 K s−1. For isothermal annealing at >850 K, only one crystallization event is detected; for lower temperatures, a complex two-step transformation occurs.

Separating β relaxation from α relaxation in fragile metallic glasses based on ultrafast flash differential scanning calorimetry

Despite numerous studies on the glass transition and the related relaxation dynamics, the physical mechanism of activation of multiscale relaxation events under various external stimuli in amorphous materials is still unclear. In this study, by combining traditional differential scanning calorimetry (DSC) and Flash DSC with heating rates spanning over five orders of magnitude, the thermodynamic responses have been systematically studied for several fragile and strong metallic glasses (MGs). A common endothermic event, before the glass transition, is detected when the heating rate increases above a critical value for fragile MGs. This endothermic event is verified to represent the activation of secondary $\ensuremath{\beta}$ relaxation (Johari-Goldstein relaxation), which is commonly found in amorphous materials. For fragile MGs, with an increase in fragility, the critical heating rate to separate $\ensuremath{\beta}$ relaxation from $\ensuremath{\alpha}$ relaxation decreases. In contrast, the $\ensuremath{\beta}$ relaxation does not appear within the current experimental heating rate limit for strong glass systems. Finally, based on the potential energy landscape model and the flow unit model of the heterogeneous structure for MGs, a pathway is proposed for the fragile and strong MGs to understand the physical mechanism for the separation of $\ensuremath{\beta}$ relaxation from $\ensuremath{\alpha}$ relaxation via ultrafast heating. This study clearly demonstrates that the Flash DSC with a wide heating rate range is an effective tool to study the relaxation dynamics in amorphous materials.

Cooling control of thermally-induced thermal runaway in 18,650 lithium ion battery with water mist

Lithium ion battery (LIB) thermal runaway (TR) has always been a potential risk that could result in serious damage. This likelihood has increased owing to the widespread application of LIBs, particularly in the electric-vehicle industry. Therefore, an effective method must be determined to prevent or mitigate this hazardous process. As a clean and efficient cooling technique, the effect of water mist (WM) on TR has been investigated through a series of tests in this study. Batteries with various states of charge (SOC) were heated with an electric heater to induce TR, and the surface temperatures were measured throughout the tests. The results show that TR can be controlled when the WM is released before the critical temperature is reached; the threshold temperature is at least 20 °C lower than the temperature of the TR onset. The determined conservative temperature for the WM application is 186.5 °C. At 25% SOC, the critical WM cooling rate is 1.87 times that of the critical heating rate. The value increases to 4.98 at 100% SOC, thereby indicating the increasing suppression difficulty with increasing SOC. Above the critical temperature, the TR is unstoppable. However, the maximal surface temperature can be controlled at values approximately 300 °C lower than those of the cases without WM. This is beneficial for the prevention of the TR propagation. TR can still be a potential risk for suppressed batteries. Nevertheless, the thermal hazard is mitigated with increasing onset temperature and a longer heating process. This study can contribute significant results for the control of TR in practice.

What Thermal Analysis Can Tell Us About Melting of Semicrystalline Polymers: Exploring the General Validity of the Technique.

Thermal characterization of semicrystalline polymers can constitute a difficult task due to the metastable nature of polymer crystals. It is well documented that polymer structure can reorganize during the thermoanalytical experiment. It has become also clear that thermal analysis alone cannot discriminate the reorganization processes from multiple melting events. Therefore, instead of studying the initial sample state the measurements may simply reflect the structural evolution uncontrollably occurring during the experiment. Here an original setup combining in situ ultrafast chip calorimetry with millisecond time-resolved X-ray scattering is used to find the structural signature of the reorganization processes. The information is further used to construct the heating-rate versus crystallization-temperature reorganization (HR-CT-R) diagram. The diagram allows rationally designing thermoanalytical experiments in which one can completely exclude uncontrolled evolution of the semicrystalline structure. For a typical aromatic polyester, poly(trimethylene terephthalate), the critical heating rate above which all reorganization processes cease to exist can reach 1000 K/s and more.

Al2O3-MgO refractory castables with enhanced explosion resistance due to in situ formation of phases with lamellar structure

This work evaluated an alternative route (formic acid addition and in situ generation of hydrotalcite phases) to reduce the explosion trend of dense MgO-bonded refractory castables during their drying step. Aqueous suspensions containing different magnesia sources (caustic or dead-burnt) and hydratable alumina were firstly analyzed in order to identify the likelihood of generating these in situ compounds with a lamellar structure in mixtures prepared with and without formic acid (hydrating agent). After that, high-alumina vibratable castables containing MgO and this carboxylic acid were evaluated and the following experimental tests were carried out: thermogravimetry, mechanical strength evaluation, apparent porosity and hot elastic modulus measurements. According to the obtained results, the thermal decomposition of the formed hydrotalcite-like phases led to samples’ mass loss over a broader temperature range, preventing their explosion even when a critical heating rate (20 °C min−1) was applied during the tests. Besides that, no deleterious effect to the refractories’ mechanical properties were observed during firing (i.e. softening at high temperatures). Thus, the addition of formic acid and the in situ formation of hydrotalcite-like phases is suggested as an alternative route to the conventional incorporation of amorphous silica or polymeric fibers into the castable dry-mixes to prevent the explosion of MgO-bonded refractories.

Glass transition kinetics aspects of amorphous Se60Ge15As25 and Se60Ge15Sn25 compositions

This work aims to research the glass transition kinetics aspects for Se60Ge15As25 and Se60Ge15Sn25 compositions, utilized differential thermal analysis technique under the non-isothermal condition at various heating rates. Glass transition temperature (T g) has been discovered heating rate and composition dependence. Composition reliance of T g can be comprehended with the correlation between T g and coordination number and mean bond energy also for the investigated compositions. Heating rate dependence of T g reveals the activation energy of glass transition (E g) values according to various methods for T g with various definitions. The estimated E g values have been discovered enlarging with temperature throughout the glass transition region. The relative error (e %) for Kissinger’s activation energy and its related parameters have been resolved and discussed. The correlation between glass transition and crystallization temperatures reveals that the crystallization process is more sensitive to heating rate than glass transition process. The critical heating rate value reflects that the Se60Ge15As25 composition is the most thermal stable composition. Fragility index values have been assessed by various relations and categorized the compositions under review as strong glasses.

Reorganization of semicrystalline polymers on heating: Analyzing common misconceptions in the interpretation of calorimetric data. Response on the “Comment on “Re-exploring the double-melting behavior of semirigid-chain polymers with an in-situ combination of synchrotron nanofocus X-ray scattering and nanocalorimetry” by Dimitri A. Ivanov et al. [Euro. Polym. J. 81 (2016) 598–606.

In our recent article entitled “re-exploring the double-melting behavior of semirigid-chain polymers with an in-situ combination of synchrotron nanofocus X-ray scattering and nanocalorimetry” (European Polymer Journal 81 (2016) 598–606), we investigated complex thermal behavior of a typical semirigid-chain polymer, poly(trimethylene terephthalate), PTT. In the comment on our paper published by Furushima and colleagues (EUROPOL_2017_495), our interpretation of the multiple melting phenomenon was seriously questioned. In particular, it was argued that the main drawback in our paper was due to the fact that the critical heating rate above which the PTT structure does not reorganize after isothermal melt crystallization at 180°C should be 2000°C·s−1, i.e. higher than the rate of 1000°C·s−1 used in our experiments. It is noteworthy that the authors of the Comment performed all their experiments on a different grade of PTT, which makes quantitative comparison with the recrystallization rates in our experiments problematic. In the present paper, we employ a combination of X-ray scattering with fast single-photon-counting X-ray detection and custom-built ultrafast chip calorimeter to show that the claims of Furushima and colleagues are not relevant to our case and, therefore, cannot be generalized. Indeed, even for a PTT sample melt-crystallized at 150°C, which recrystallizes on heating much faster than the sample crystallized at 180°C, the critical heating rate is safely below 500°C·s−1. To further clarify the issue, we discuss on a general misconception in the literature concerning the interpretation of double melting peaks in DSC traces as being indicative of a melting/recrystallization process. Since many works in the field including the discussed one are based entirely on calorimetric data, the direct information on the structure is simply missing. Therefore, such interpretations of the thermal behavior evoking the so-called “single crystal population” are clearly inadequate. By contrast, on the basis of on-time X-ray scattering recorded simultaneously with ultrafast chip calorimetry we unambiguously show that even in the absence of reorganization processes a uniform population of PTT crystals formed at isothermal conditions exhibits double melting. In agreement with our earlier publications (e.g., Macromolecules 41 (2008) 9224–9231) this is explained by strong interactions between amorphous and metastable crystalline regions, which are very characteristic for the semirigid-chain polymer family.

Characterization and Thermal Decomposition of Nanometer 2,2′, 4,4′, 6,6′-Hexanitro-Stilbene and 1,3,5-Triamino-2,4,6-Trinitrobenzene Fabricated by a Mechanical Milling Method

ABSTRACTNanometer 2,2ʹ, 4,4ʹ, 6,6ʹ-hexanitro-stilbene (HNS) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) were fabricated on a high-energy ball mill. The particle sizes of nano-HNS and nano-TATB were 98.4 and 57.8 nm, respectively. An SEM analysis was employed to image the micron morphology of nano-explosives. The particle size distribution was calculated by measuring the size of 300 particles in SEM images. XRD, IR, and XPS analyses were used to confirm whether the crystal phase, molecule structure, and surface elements were changed by the milling process. Thermal decomposition of nano-HNS and nano-TATB was investigated by differential scanning calorimetry (DSC) and thermal-infrared spectrometry online (DSC-IR) analyses. Using DSC traces collected from different heating rates, the kinetic and thermodynamic parameters of thermolysis of raw and nano-explosives were calculated (activation energy (EK), pre-exponential factor (lnAK), rate constant (k), activation heat (ΔH≠), activation free energy (ΔG≠), activation entropy (ΔS≠), critical temperature of thermal explosion (Tb), and critical heating rate of thermal explosion (dT/dt)Tb). The results indicated that nano-explosives were of different kinetic and thermodynamic properties from starting explosives. In addition, the gas products for thermal decomposition of nano-HNS and nano-TATB were detected. Although HNS and TATB are both nitro explosives, the decomposition products of the two were different. A mechanism to explain the difference is proposed.