Via fast differential scanning calorimetry using an Au-based glass as an example, we show that metallic glasses should be classified into two types of amorphous/monolithic glass. The first type, ...termed self-doped glass (SDG), forms quenched-in nuclei or nucleation precursors upon cooling, whereas in the so-called chemically homogeneous glass (CHG) no quenched-in structures are found. For the Au-based glass investigated, the critical cooling and heating rates for the SDG are 500 K s
and 20,000 K s
, respectively; for the CHG they are 4000 K s
and 6000 K s
. The similarity in the critical rates for CHG, so far not reported in literature, and CHG's tendency towards stochastic nucleation underline the novelty of this glass state. Identifying different types of metallic glass, as is possible by advanced chip calorimetry, and comparing them with molecular and polymeric systems may help to elaborate a more generalized glass theory and improve metallic glass processing.
The kinetics of the glass transition and the characteristic size of the fluctuating spatio-temporal domains in supercooled glass-forming liquids, i.e., the Cooperatively Rearranging Regions (CRR), ...were measured upon cooling over a broad range of cooling rates using Differential Scanning Calorimetry (DSC) and chip-based Fast Scanning Calorimetry (FSC). The investigations were conducted on a selection of fragile glass formers (fragility indices between 80 and 140), with a large variance in the atomic or molecular structure but comparable thermal glass transition temperatures T g, with the aim of evaluating the influence of chemical composition and structure on the CRR size and the associated temperature fluctuation. The selected materials are two polymers (poly(vinyl acetate) (PVAc), poly(lactic acid) (PLA)) as well as the simplest chalcogenide glass-former (selenium). It turned out that the CRR size plotted against the reduced temperature T/T g follows the same trend, irrespective of the considered glass-former.
Crystallization of isotactic polypropylene was analyzed by fast scanning calorimetry (Flash DSC) at cooling rates between 1 and 4000 K s
−1
. By quantitative analysis of the glass transition ...intensity and the specific transformation enthalpy, the amount of mobile amorphous (MAF), rigid amorphous (RAF) and crystalline fractions (CFs) and its dependency on the cooling rate were determined. During cooling, two different crystalline phases are formed. At slow cooling rates (below 90 K s
−1
), the α-phase is crystallized. At faster cooling rates mesophase aggregates are formed. The crystalline phase reduces the relaxation time in the MAF independently from the kind of the crystalline phase. The RAF is formed during the crystallization process. In the case of mesophase crystallization, the ratio between CF and RAF is independent of the crystallinity. For α-phase crystals, this ratio depends on the crystallinity. A model for the CF-RAF structure is derived from the reported results.
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•Empirical model for the behavior of melting peaks during polymer reorganization.•Study of cold crystallization, melting and reorganization of the mesophase of iPP.•Study of the ...cooling rate dependence of the glass transition of iPP.•Relation between mobile amorphous, rigid amorphous and the crystalline fractions.
Crystallization, reorganization and melting of isotactic polypropylene (iPP) were analyzed by DSC and fast scanning DSC. The cooling and subsequent heating DSC curves are measured at scanning rates between 0.1K/min and 30,000K/s. We study the formation of the mesophase and the α-phase during cooling. Using subsequent heating measurements the formation of the mesophase during cold crystallization and the kinetics of the reorganization are analyzed. From the cooling rate dependence of the glass transition and the melting behavior we discuss relations between the crystalline fraction (CF), the mobile amorphous fraction (MAF), the rigid amorphous fraction (RAF) and the influence of these fractions on the reorganization processes. Furthermore, we use the heating rate dependence of the melting behavior for stability analyses of the related crystals and propose the Illers-plot as a simple analysis tool. Using this technique the melting temperature of the mesophase is determined to about 86°C.
Eutectic AlSi12, commonly used in casting and in additive manufacturing, is investigated with Fast Differential Scanning Calorimetry to determine the impact of different cooling rates from the liquid ...state upon the apparent specific heat capacity on subsequent heating. A heat flow correction strategy is developed and refined for the reliable and precise measurement of sample heat flow using chip sensors and assessed by the evaluation of results on pure (99.999%) aluminium. That strategy is then applied to the study of the AlSi12 eutectic alloy, and rate-dependent perturbations in the measured apparent specific heat capacity are discussed in terms of Si supersaturation and precipitation. Several cooling rates were implemented from − 100 to − 30,000 K s
−1
, and subsequent heating ranged from + 1000 to + 30,000 K s
−1
. After rapid cooling, a drop in AlSi12 apparent specific heat capacity is found on heating above ~ 400 °C; even at rates of + 10,000 K s
−1
, a result which has high relevance in metal additive manufacturing where similarly fast temperature cycles are involved. The Literature data, temperature modulated DSC and CALPHAD simulations on the heat capacity of AlSi12 are used to provide comparative context to the results from Fast Differential Scanning Calorimetry.
Structural relaxation in polymers occurs at temperatures in the glass transition range and below. At these temperatures, crystallization is controlled by diffusion and nucleation. A sequential ...occurrence of structural relaxation, nucleation, and crystallization was observed for several homopolymers during annealing in the range of the glass transition. It is known from the literature that all of these processes are strongly influenced by geometrical confinements. The focus of our work is copolymers, in which the confinements are caused by the random sequence of monomer units in the polymer chain. We characterize the influence of these confinements on structure formation and relaxation in the vicinity of the glass transition. The measurements were performed with a hydrogenated nitrile-butadiene copolymer (HNBR). The kinetics of the structural relaxation and the crystallization was measured using fast differential scanning calorimetry (FDSC). This technique was selected because of the high sensitivity, the fast cooling rates, and the high time resolution. Crystallization in HNBR causes a segregation of non-crystallizable segments in the macromolecule. This yields a reduction in mobility in the vicinity of the formed crystals and as a consequence an increased amount of so-called “rigid amorphous fraction” (RAF). The RAF can be interpreted as self-assembled confinements, which limit and control the crystallization. An analysis of the crystallization and the relaxation shows that the kinetic of both is identical. This means that the Kohlrausch exponent of relaxation and the Avrami exponent of crystallization are identical. Therefore, the crystallization is not controlled by nucleation but by diffusion and is terminated by the formation of RAF.
In this study, we combine in situ fast differential scanning calorimetry (FDSC) with synchrotron X-ray measurements to study simultaneously the structure and thermophysical properties of materials. ...Using the example of the organic compound BCH-52, we show that the X-ray beam can heat the sample and induce a shift of the heat-flow signal. The aim of this paper is to investigate the influence of radiation on sample behavior. The calorimetric data is used to quantify the absorbed beam energy and, together with the diffraction data, reveal an irreversible damage of the sample. The results are especially important for materials with high absorption coefficients and for high-energy X-ray and electron beams. Our findings illustrate that FDSC combined with X-ray diffraction is a suitable characterization method when beam damage must be minimized.
The glass transition is relevant for performance definition in rubber products. For extrapolation to high‐frequency behavior, time–temperature superposition is usually assumed, although most complex ...rubber compounds might be outside of its area of validity. Fast differential scanning calorimetry (FDSC) with cooling rates up to 1500 K/s and broadband dielectric spectroscopy (BDS) with frequencies up to 20 MHz are applied here to directly access both kinetics and dynamics of glass formation in a wide frequency range. For the first‐time, the relation between the thermal vitrification and the dielectric relaxation is studied on vulcanized styrene‐butadiene rubber, showing that both cooling rate and frequency dependence of its glass transition can be described by one single Vogel‐Fulcher‐Tammann‐Hesse equation. The results indicate the validity of the Frenkel‐Kobeko‐Reiner equation. Another focus is the sample preparation of vulcanized elastomers for FDSC and BDS as well as the temperature calibration below 0°C.
The influence of multi-walled carbon nanotubes (0–5 wt%) on the crystallization process in isotactic polypropylene has been investigated by DSC and fast scanning calorimetry. In the non-isothermal ...experiments the crystallization temperature shifts to higher temperatures with increasing nanotube content, αCNT, whereas the polymer crystallinity was not significantly influenced. The critical cooling rate, βc, at which the PP does not crystallize, increases with increasing of αCNT. From βc and αCNT a nucleation efficiency parameter was derived, which is independent of crystallization temperature and filler content. Isothermal crystallization experiments allow differentiating between α-phase and mesophase crystallization. Nanotubes accelerate only the α-phase formation. To describe the efficiency of a nucleation agent an acceleration factor, ε, was introduced, which is the ratio of the characteristic crystallization time of unfilled and filled polymer. For the α-phase formation the acceleration factor ε is related to the number of nuclei per nanotube and the specific effect of the filler on the growth rate.
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•Study of PP-MWCNT crystallization versus temperature, cooling rate and composition.•MWCNT accelerates the α-phase formation, but has no impact on mesophase formation.•Models are derived for the acceleration of crystallization due to nucleating agent.•The model parameters characterize the efficiency of a nucleating agent.
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