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  1. The high density of aluminum nanocrystals (>10 21  m −3 ) that develop during the primary crystallization in Al-based metallic glasses indicates a high nucleation rate (∼10 18  m −3  s −1 ). Several studies have been advanced to account for the primary crystallization behavior, but none have been developed to completely describe the reaction kinetics. Recently, structural analysis by fluctuation electron microscopy has demonstrated the presence of the Al-like medium range order (MRO) regions as a spatial heterogeneity in as-spun Al 88 Y 7 Fe 5 metallic glass that is representative for the class of Al-based amorphous alloys that develop Al nanocrystals during primary crystallization. From the structural characterization, an MRO seeded nucleation configuration is established, whereby the Al nanocrystals are catalyzed by the MRO core to decrease the nucleation barrier. The MRO seeded nucleation model and the kinetic data from the delay time ( τ) measurement provide a full accounting of the evolution of the Al nanocrystal density (N v ) during the primary crystallization under isothermal annealing treatments. Moreover, the calculated values of the steady state nucleation rates ( J ss ) predicted by the nucleation model agree with the experimental results. Moreover, the model satisfies constraints on the structural, thermodynamic, and kinetic parameters, such as the critical nucleus size, the interface energy, and the volume-free energy driving force that are essential for a fully self-consistent nucleation kinetics analysis. The nucleation kinetics model can be applied more broadly to materials that are characterized by the presence of spatial heterogeneities. 
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    Free, publicly-accessible full text available February 14, 2024
  2. The kinetics of the first order liquid–liquid transition (LLT) in a single-component liquid D-mannitol have been examined in detail by the high rate of flash differential scanning calorimetry measurements. By controlling the annealing temperature, the phase X formation from the supercooled liquid is distinguished by either a nucleation-growth or a spinodal-decomposition type of LLT. In the measured time–temperature-transformation curve the portion covering the nucleation-growth type of LLT can be well fitted with a classical nucleation theory analysis. 
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  3. The advent of chip calorimetry has enabled an unprecedented extension of the capability of differential scanning calorimetry to explore new domains of materials behavior. In this paper, we highlight some of our recent work: the application of heating and cooling rates above 104 K/s allows for the clear determination of the glass transition temperature, Tg, in systems where Tg and the onset temperature for crystallization, Tx, overlap; the evaluation of the delay time for crystal nucleation; the discovery of new polyamorphous materials; and the in-situ formation of glass in liquid crystals. From these application examples, it is evident that chip calorimetry has the potential to reveal new reaction and transformation behavior and to develop a new understanding. 
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  4. null (Ed.)