Ultrafast Scanning Calorimetry Research Articles

Dynamic heterogeneity in Pd40Ni40P20 glass-forming metallic melt and crystallization behavior probed by quasi-elastic neutron scattering and ultrafast scanning calorimetry

The intrinsic heterogeneity of metallic glasses is hidden in long-range disordered structures. Due to the lack of a long-range ordered structure, it is difficult to construct the structure-property relationship in metallic glasses. However, relaxation dynamics provides a powerful approach to understanding metallic glasses. State-of-the-art quasi-elastic neutron scattering (QENS) and ultrafast scanning calorimetry are used to study the atomic relaxation dynamics, dynamic heterogeneity, diffusion coefficient and crystallization behavior of the Pd40Ni40P20 metallic glass. The presence of dynamic heterogeneity in the Pd40Ni40P20 glass-forming metallic melt is evaluated from the dynamic susceptibility, which is derived from the QENS self-intermediate scattering function. The dynamic heterogeneity increases gradually with decreasing temperature, and a dynamic crossover arises at approximately 1235 K, which is related to the cooperative motion of atoms. Ultrafast scanning calorimetry combined with conventional calorimetry provides heating and cooling rates over seven orders of magnitude, allowing us to study how the liquid thermal history affects glass formation, glass transition, and crystallization. The critical cooling rate required for glass formation is directly determined. A continuous-heating-transformation diagram for crystallization is constructed. This study will improve our understanding of the atomic relaxation dynamics mechanism and intrinsic heterogeneity in metallic glasses.

Arrhenius behavior of crystallization at up to 184 000 K/s in Ge2Sb2Te5 thin films

We investigate the glass transition and crystallization of Ge2Sb2Te5 by nanocalorimetry on 32–57 nm layers at temperature scanning rates ranging from 23 to 184 kK/s. Crystallization follows the Arrhenius behavior observed at low heating rates, with an activation energy of 2.7 ± 0.1 eV. The crystal-growth velocity (>500 µm/s at 500 K) confirms fast values found in earlier work and by ab initio molecular dynamics simulations. These experiments also outline the importance of carrying out ultra-fast scanning calorimetry studies with samples in excellent thermal contact with the heating device.

An effective nucleating agent for isotactic polypropylene (iPP): Zinc bis- (nadic anhydride) double-decker silsesquioxanes

The zinc bicyclo [2.2.1]-heptane-2, 3-dicarboxylate-double-decker silsesquioxanes (Zn2(DDSQ-ND)) was firstly synthesized and the crystallization behavior of isotactic polypropylene (iPP) filled with different amount of Zn2(DDSQ-ND) (0–1 wt %) was investigated in detail. With the addition of Zn2(DDSQ-ND), the crystallization temperature enhanced significantly, indicating that it acted novel and effective nucleating agent in the iPP system. The morphology of spherulites, nucleation density, and the crystal structure of the samples were characterized using POM and WAXD. Besides, ultra-fast scanning calorimetry (FSC) was employed to study the effects of Zn2(DDSQ-ND) on the non-isothermal and isothermal crystallization behaviors of the sample iPP/Zn2(DDSQ-ND) under the high cooling rates and wide crystallization temperature ranges, as well as the cold crystallization and recrystallization behavior during the heating process. The data suggested that Zn2(DDSQ-ND) accelerated the formation of α-phase iPP and acted as a novel α-nucleating agent in the iPP system.

Thermal contact conductance at melting and crystallization of metal micro-droplets

To measure interfacial thermal contact conductance in fast thermal processes, ultrafast scanning calorimetry combined with high-resolution high-speed infrared thermography is applied. The dynamics of temperature distribution on the sample surface is measured by thermography during melting and crystallization of a tin particle of about 580 ng and 70 μm in diameter. The temperature difference on the sample/sensor interface is measured and used to determine the interfacial thermal contact conductance with acceptable accuracy on a millisecond time scale. It is shown that the temperature difference can be of the order of 100 K at melting and crystallization. This is very essential for applications with fast temperature changes like additive manufacturing and for calorimeter calibration. The method can be applied to different materials in fast thermal processes on a micro-scale. During crystallization, the effect of reheating (about 100 K) is observed.

Ultrafast scanning calorimetry of newly developed Au-Ga bulk metallic glasses

The isothermal crystallization times and critical cooling rates of the liquid phase are determined for the two bulk metallic glass forming alloys Au49Ag5.5Pd2.3Cu26.9Si16.3 and Au51.6Ag5.8Pd2.4Cu20.2Ga6.7Si13.3 by using fast differential scanning calorimetry, covering the whole timescale of the crystallization event of the metallic melt. In the case of Au49Ag5.5Pd2.3Cu26.9Si16.3, a typical crystallization nose was observed, whereas for the Au51.6Ag5.8Pd2.4Cu20.2Ga6.7Si13.3, a more complex crystallization behavior with two distinct crystallization noses was found. Even for the complex crystallization behavior of the Au51.6Ag5.8Pd2.4Cu20.2Ga6.7Si13.3 alloy it is shown that the minimal isothermal nose time does allow for a quantification of the macroscopic critical thickness. It is discussed in contrast to the critical cooling rate, which is found to allow less exact calculations of the critical thickness and thus does not correlate well with the critical cooling rate from macroscopic experiments. Additionally the crystallization data of Au49Ag5.5Pd2.3Cu26.9Si16.3 was modeled using classical nucleation theory with the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation, enabling a determination of the interfacial energy.

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.

Revealing hidden supercooled liquid states in Al-based metallic glasses by ultrafast scanning calorimetry: Approaching theoretical ceiling of liquid fragility

铝基非晶合金具有密度低、强度高、耐腐蚀等诸多优异性能; 然而, 铝基非晶合金形成能力差, 一般需要非常高的冷却速率, 这限制了铝基非晶合金的应用. 玻璃形成理论认为形成能力与过冷液体密切相关. 但在一般升温测量时, 铝基非晶合金不显示玻璃转变或过冷液体, 而是直接变成晶态. 目前为止, 关于铝基非晶合金的玻璃转变和过冷液体属性仍然是未知的. 本文采用超快速差热分析方法(Flash DSC)使得升温速度达到 10000 K s−1, 测量了20余种常见铝基非晶合金的玻璃转变行为和过冷液体特征. 发现铝基非晶合金普遍具有很高的液体脆度系数( m ), 其中某些成分 m >160, 已经接近理论上预测的脆度系数上限 m ~175. 通过系统研究这些成分的形成能力, 发现铝基非晶合金的玻璃形成能力与脆度系数成反相关, 而且这种相关不是线性的. 只有 m m 才会对玻璃形成能力有明显影响; 相反, m >100的玻璃形成力普遍较弱, 而且随 m 变化不显著. 因此, 过高的液体脆度系数可能是铝基非晶合金形成能力差的一个重要原因.

High-speed dynamics of temperature distribution in ultrafast (up to 108 K/s) chip-nanocalorimeters, measured by infrared thermography of high resolution

To study the kinetics of phase transitions and to obtain artificial materials with improved physical properties, a set of thin-film high-sensitivity sensors for ultra-fast scanning nanocalorimetry has been constructed. To investigate the dynamics of the temperature distribution in thin-film calorimetric sensors, high-resolution high-speed infrared thermography has been applied as a tool of non-contact thermal imaging in combination with ultra-fast scanning calorimetry. The dynamic heat-transfer problem, causing the temperature distribution in a thin-film sensor at ultrafast scanning of temperature, has been solved analytically. Analytical solutions for square and circular geometry have been obtained and compared with the temperature profiles obtained by infrared thermographic measurements. A theoretical background for ultra-fast-cooling experiments has been formulated. The origin of the restrictions imposed on the maximum attainable controlled cooling rate has been investigated. It is shown that thin-film sensors can be applied for controlled ultra-fast cooling, as well as heating, at 108 K/s and even 109 K/s.

Relaxation dynamics of glasses along a wide stability and temperature range.

While lots of measurements describe the relaxation dynamics of the liquid state, experimental data of the glass dynamics at high temperatures are much scarcer. We use ultrafast scanning calorimetry to expand the timescales of the glass to much shorter values than previously achieved. Our data show that the relaxation time of glasses follows a super-Arrhenius behaviour in the high-temperature regime above the conventional devitrification temperature heating at 10 K/min. The liquid and glass states can be described by a common VFT-like expression that solely depends on temperature and limiting fictive temperature. We apply this common description to nearly-isotropic glasses of indomethacin, toluene and to recent data on metallic glasses. We also show that the dynamics of indomethacin glasses obey density scaling laws originally derived for the liquid. This work provides a strong connection between the dynamics of the equilibrium supercooled liquid and non-equilibrium glassy states.

Crystallization of Polyethylene at Large Undercooling.

Extremely fast crystallization of high-density polyethylene and random copolymers of ethylene with up to 16 mol % 1-octene was observed for the first time by ultrafast scanning calorimetry. In order to account for the inherently high crystallization rate of polyethylenes, in nonisothermal and isothermal crystallization experiments cooling rates up to 1 000 000 K/s and crystallization times as short as 10 μs, respectively, were employed. It was possible to supercool the melt of high-density polyethylene down to 57 °C and the melt of a random ethylene/1-octene copolymer with 16 mol % 1-octene down to -33 °C, without prior crystallization. At these temperatures, the characteristic time of the primary crystallization process is of the order of magnitude of 100 μs. Complete vitrification of the liquid would require cooling even faster than 1 000 000 K/s. Compared to the homopolymer, the cooling-rate dependence of the crystallization temperatures and the temperature dependence of the characteristic time of primary crystallization of random ethylene/1-octene copolymers both are nearly parallel shifted to lower temperatures. Fast crystallization under conditions of reduced linear crystal growth rate is possibly caused by boosting homogeneous nuclei density up to 1027 m-3 and urgently requires further investigation.

Integration of ultrafast scanning calorimetry with micro-Raman spectroscopy for investigation of metastable materials.

A stage-type ultrafast scanning calorimetry (ST-UFSC) with controlled heating and cooling rates up to 10(5) K s(-1) was designed to integrate with microstructural characterization. This enables us to precisely control the evolution of fast transitional states of metastable samples provided by the UFSC platform, and to follow subtle structural changes between intermediate stages. As an example, we collected the Raman spectra of poly(ethylene terephthalate) quenched at different crystallization states obtained by programed rapid cooling and heating processes. Because of the very small sample mass for UFSC measurements, from minimum few nanograms to sub-micrograms, the sample's temperature is very sensitive to the perturbation from the laser illumination of the Raman spectrometer. Real time temperature monitoring and compensation was accompanied during the whole process of in situ spectroscopy. The results showed a good agreement of crystallization kinetics obtained from the Raman spectroscopy and from the calorimetric melting enthalpy, given that the sample temperature is well controlled during spectroscopic measurements and that the heating rate for calorimetry is fast enough to suppress structural reorganization during heating scans. We expect that the ST-UFSC is suitable to be integrated with other micro-analysis techniques to investigate the structure and dynamics of metastable states obtained by fast thermal treatments.

Determination of volatility of ionic liquids at the nanoscale by means of ultra-fast scanning calorimetry

The determination of vaporization enthalpies of extremely low volatility ionic liquids is challenging and time consuming due to the low values of vapor pressure. In addition, these liquids tend to decompose even at temperatures where the vapor pressure is still low. Conventional methods for determination of vaporization enthalpies are thus limited to temperatures below the decomposition temperature. Here we present a new method for the determination of vaporization enthalpies of such liquids using differential fast scanning calorimetry. We have developed and proven this method using [EMIm][NTf2] at temperatures of up to 750 K and in different atmospheres. It was demonstrated that evaporation is still the dominating process of mass loss even at such highly elevated temperatures. In addition, since the method allows very high heating rates (up to 10(5) K s(-1)), much higher temperatures can be reached in the measurement of the mass loss rate as compared to common devices without significant decomposition of the ionic liquid. We discuss the advantages and limits of this new method of vaporization enthalpy determination and compare the results with data obtained from established methods.

Crystallization Behaviour of Polytetrafluoroethylene over very Large Cooling Rate Domains

Polytetrafluoroethylene (PTFE) is a semi-crystalline polymer that demonstrates a very fast crystallization process on cooling. This study investigates the nonisothermal PTFE ultra-fast crystallization over a wide range of cooling rates via conventional Differential Scanning Calorimetry (DSC), Fast Scanning Calorimetry (FSC) and Ultra-Fast Scanning Calorimetry (UFSC). A new knowledge about crystallization kinetics of PTFE is obtained from the data obtained under very fast cooling rates. The shift of the melting peak to lower temperature shows that the crystals formed under fast cooling rates are slightly less stable than those produced under slower cooling rates. SEM analysis allows to observe these differences in crystal morphologies. According to the results, the crystallization is still present even for the fastest cooling rate employed and in consequences it is impossible to reach a metastable glassy state. The effective activation energy (Eα) displays a variation with the relative extent of crystallization (α) that is characteristic of a transition of PTFE crystallization from regime II to regime III around 312°C. Following the Hoffman-Lauritzen theory the Eα dependency obtained from the crystallizations under the different cooling rates was fitted in order to study the theoretical dependence of the growth rate.

Nonisothermal Crystallization of Polytetrafluoroethylene in a Wide Range of Cooling Rates

Compared to other semicrystalline polymers, PTFE demonstrates a very fast crystallization process on cooling. This study explores for the first time the nonisothermal PTFE ultrafast crystallization under tremendously fast cooling rates (up to 800,000 K·s(-1)) achieved by using fast scanning calorimetry (FSC) and ultra-fast scanning calorimetry (UFSC). Regular DSC was also used to get crystallization at slower rates. The data obtained on a wide range of cooling rates (over 8 orders of magnitudes) help to get new knowledge about crystallization kinetics of PTFE. Both FSC and UFSC data show that it is impossible to bypass the crystallization and thus to reach a metastable glassy state even for the fastest cooling rate employed (800,000 K·s(-1)). The crystals formed under such conditions are slightly less stable than those produced under slower cooling rates, as reflected by a shift of the melting peak to lower temperature. The difference in crystal morphologies was confirmed by SEM observations. The variation of the effective activation energy (Eα) with the relative extent of crystallization reveals that PTFE crystallization follows a transition from regime II to regime III around 315-312 °C. Corroborated temperature dependences of Eα obtained respectively for crystallizations under slow and fast cooling rates were combined and fitted to the theoretical dependence of the growth rate derived from the Hoffman-Lauritzen theory.

Atypical gelation in gelatin solutions probed by ultra-fast calorimetry

This paper describes the first application of ultrafast scanning calorimetry to the process of gelation in concentrated (40 wt%) aqueous gelatin solutions. It demonstrates that the regular gelation that occurs on cooling can be outrun at sufficiently fast cooling rates (≥500 K s−1) so that the solution reaches a metastable supercooled liquid state. Successive heating of the supercooled solution reveals an atypical process of gelation that takes place while continuously raising the temperature. Isoconversional kinetic analysis is applied to treat the atypical gelation process and to compare it with regular gelation on cooling. Although atypical and regular gelation occur on significantly different time scales they appear to have common dynamics.

Response to “Comment on ‘Glass transition in pure and doped amorphous solid: An ultrafast microcalorimetry study’ [J. Chem. Phys. 125, 094501 (2006)

We report results of ultrafast scanning calorimetry (USC) measurements of enthalpy relaxation time for propanol, toluene, pentanol, decalin, and 2-ethyl-1-hexanol in a temperature range from 120to180K. These new data show that the enthalpy relaxation times measured in USC experiments are within one order of magnitude of those derived from dielectric spectroscopy studies. Thus, we demonstrate that Johari’s critique of the USC study of pure and doped amorphous solid water is without merit, and that USC experiments do provide evidence against assignment of the glass transition temperature of amorphous solid water to 136K.

Fast isothermal calorimetry of modified polypropylene clay nanocomposites

Calorimetric experiments at cooling rates comparable to those during injection molding, as an example, are needed to study phase transitions under conditions relevant for processing. Ultra fast scanning calorimetry is a technique which provides a means to analyze the materials of interest under rapid cooling conditions and it is a promising technique by which the crystallization behavior of composite systems based on fast crystallizing polymers like isotactic polypropylene (iPP) can be studied. By combining conventional DSC and ultra fast chip calorimetry isothermal crystallization experiments were performed in the whole temperature range between glass transition and melting temperature of iPP. Because of the very small time constant of the calorimeter, isothermal crystallization processes with peak times down to 100ms were investigated after cooling the sample from the melt at 2000K/s. iPP grafted with maleic anhydride (PPgMA) – montmorillonite clay nanocomposites were studied. The influence of various clay loadings on the crystallization behavior of PPgMA at different temperatures was followed by ultra fast isothermal calorimetry. PPgMA clay nanocomposites showed a variation in crystallization peak times with different clay loadings at crystallization temperatures between 70°C and 100°C. No influence of clay loading was observed at lower crystallization temperatures. At these temperatures, where the mesophase is formed and homogeneous nucleation is expected, the contribution of the clay as a nucleating agent is negligible. For crystallization at about 80°C, where the α-phase is formed, the nucleating effect of the clay is observed yielding complex crystallization kinetics. In the temperature range 75–85°C in some nanocomposites a double peak during isothermal crystallization was observed corresponding to a fast and a slow crystallization processes occurring simultaneously. At higher temperatures, above 120°C, the clay slightly retards the crystallization process.