On the free energy change accompanying crystallisation of undercooled melts

Dubey, K. S.; Ramachandrarao, P.

doi:10.1016/0001-6160(84)90205-0

Cited by 144 publications

(55 citation statements)

References 14 publications

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“…The temperature dependence of C p for the solid phases was been described with C = F = 0, according to, 18) whereas a function with C = E = 0 has been used for the C p of undercooled liquid. A good description of the free energy difference between the undercooled liquid and the solid phases, proposed by Dubay and Ramachandrarao (DR) 19) following an hole theory for liquids, gives an enthalpy difference expressed as:…”

Section: Resultsmentioning

confidence: 99%

Kinetics and Thermodynamics of Bulk Glass Formation in a Zr52.5Cu17.9Ni14.6Al10Ti5 Alloy

et al. 2002

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Ti 5 bulk metallic glasses have been prepared by copper moulding. In order to obtain a fully amorphous sample, a careful control of the atmosphere conditions in the casting chamber was necessary. In particular, the presence of oxygen contamination promotes the nucleation of a fcc "big cube" phase, reducing glass formation. The crystallisation of bulk amorphous samples has been followed by DSC and values of about 4 kJ·mol −1 have been obtained for the heat release at about 740 K. By high temperature DSC, a metastable-to-stable phase transformation has been evidenced at 938 K, which gives a heat evolution of 1.12 kJ·mol −1 . Melting and solidification of the alloy have been observed at 1070 K, giving an average value for the enthalpy change of about 8.2 kJ·mol −1 . The temperature dependence of the enthalpy difference between undercooled liquid and equilibrium crystal phases has been described on the basis of different models for the specific heat difference (∆C p ) between the two phases. A best fitting of experimental data gives values of ∆C p of about 21 J·mol −1 · K −1 at the glass transition temperature (690 K), in good agreement with experimental values obtained from DSC measurements.

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Section: Resultsmentioning

confidence: 99%

Kinetics and Thermodynamics of Bulk Glass Formation in a Zr52.5Cu17.9Ni14.6Al10Ti5 Alloy

et al. 2002

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“…It also turns out to be sufficient for making an ordered Cr40Ti60 liquid more stable than the disordered fl-phase at the amorphization temperature close to 600°C: A calculation of the free energy difference between the two disordered phases shows that an ordering energy of at least 3.8 kJ/mol is required. For this calculation we used a Dubey-Ramachandrarao expression [21], thermodynamic data from Murry [22], and a value of 5.45 J/(molK) (0.8 times the entropy of fusion [23]) for the average excess specific heat of the liquid.…”

Section: Discussionmentioning

confidence: 99%

Scattering study of vitrifying Cr-Ti solutions

et al. 1992

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Abstract. The configurations involved in the spontaneous vitrification of quenched Cr-Ti fl-phase alloys were investigated by X-ray diffraction and elastic neutron scattering. The two methods yield complementary information: X-rays are sensitive to the topology whereas neutrons emphasize the chemical fluctuations. The results show the presence of two simultaneous but opposing processes, the formation of CsCl-type chemical short range order on one hand and progressive structural disordering on the other. The latter ultimately leads to amorphization. The probable reason for this behavior is that at the temperature in question only the chromium atoms are mobile. 81.30.Hd, 61.12.Dw, 61.55.Hg The low temperature spontaneous vitrification of homogeneous crystal phases driven to non-equilibrium conditions by temperature or pressure quenching has been a topic of current research [1][2][3]. Spontaneous vitrification was first observed in Cr-Ti thin films [4]. In this system, the high temperature bcc solid solution (fl-phase) is metastably frozen by temperature quenching. Only a moderate cooling rate is required, which allows the preparation of bulk fl-phase material [5]. A series of polymorphous transformations has been found to precede and accompany amorphization [6]: At a temperature TH between 370 and 450 ° C (depending on composition), alloys with 30M0 at.% Cr undergo an exothermic transition. A reversible step in the specific heat, followed by progressive amorphization, is observed in these alloys when heated to higher temperatures. The step in specific heat appears to originate from a kinetic transition associated with the unfreezing of diffusive mobility, a prerequisite of amorphization. Kim and Lee [7] recently found the activation energy for amorphization to be lower than that for equilibrium phase formation, namely 2 eV instead of 2.7 eV. They concluded that amorphization proceeds via Cr diffusion while the Ti atoms are still immobile. While the events preceding amorphization are easily reproduced, the amorphization step is difficult to control and seems to depend on intrinsic parameters like the defect concentration [8,9]. PACS:In order to understand the vitrified state as an extension of the liquid, stabilization by the formation of chemical short range order (CSRO) must be assumed to make spontaneous vitrification plausible on thermodynamic grounds [10]. In the present work we have studied the topological and chemical structures of the various transition states by X-ray diffraction and neutron scattering with the aim to investigate the occurrence of CSRO.The starting point of our investigation is the following consideration. The coherent scattering intensity per average atom of a binary alloy can be subdivided into the Bhatia-Thornton partial structure factors [11], The corresponding value for X-rays depends on the scattering vector. At the (110) Bragg position it is 0.0156 [13]. Neutron scattering is thus dominated by Scc(K) whereas X-ray diffraction provides SNN(K) [14].

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“…During solidification, the atomic aggregation varies from short-distance ordered structures to long distance. Solidification occurs due to nucleation (the formation of a solid form with particular characteristics) and to the accretion (entities of liquid binding themselves to the solid part while giving away vibrational energy) [39,40,41,42]. The priming mixes generally consist of Pb, Ba and Sb inorganic salts, as shall later discuss, when activated develop molten metal liquid → solid phase transition.…”

Section: Interpretation In the Context Of The Classical Nucleation Thmentioning

confidence: 99%

On the Formation and On the Surface of Inorganic Lead, Barium and Antimony Based Gunshot Residues: A Thermodynamic Approach

Nunziata¹,

Morin²

2017

Journal of Forensic Science & Criminology

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In their first full report on the analysis of GSR by SEM-EDS, Wolten and colleagues stated that the great majority of the gunshot residue particles (GSR), between 70 to 100%, have a characteristic morphology thus providing a detection criterion holding significance equal to that provided by the elemental composition. In fact, the particles must have a spherical or spheroidal shape and their surface should appear amorphous, devoid of any crystalline characteristic.

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On the free energy change accompanying crystallisation of undercooled melts

Cited by 144 publications

References 14 publications

Kinetics and Thermodynamics of Bulk Glass Formation in a Zr<SUB>52.5</SUB>Cu<SUB>17.9</SUB>Ni<SUB>14.6</SUB>Al<SUB>10</SUB>Ti<SUB>5</SUB> Alloy

Kinetics and Thermodynamics of Bulk Glass Formation in a Zr<SUB>52.5</SUB>Cu<SUB>17.9</SUB>Ni<SUB>14.6</SUB>Al<SUB>10</SUB>Ti<SUB>5</SUB> Alloy

Scattering study of vitrifying Cr-Ti solutions

On the Formation and On the Surface of Inorganic Lead, Barium and Antimony Based Gunshot Residues: A Thermodynamic Approach

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