573. Hysteresis in transitions in solids

Thomas, D. G.; Staveley, L. A. K.

doi:10.1039/jr9510002572

Cited by 27 publications

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“…An expansion of the baseline heat capacity of the specimen shows a reversible 0.2 J g -1°C-1 change in heat capacity between the crystalline forms in agreement with earlier studies [4]. Hysteresis in the transition between crystal structures is not unusual and has been observed in other systems [13,14]. One approach to establishing the absolute limit of this discrepancy between the transition point on cooling and that seen on heating is to observe the transition at progressively slower rates of temperature change and extrapolating the measurements to zero heating and cooling rates [15].…”

Section: Methodssupporting

confidence: 76%

Hysteresis in the β–α phase transition in silver iodide

Binner

Dimitrakis

Price

et al. 2006

J Therm Anal Calorim

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IntroductionSilver iodide can exist in three crystal polymorphs at atmospheric pressure [1]. Below 147°C the b-phase is stable; this has a wurtzite structure with the iodide ions arranged in a hexagonal close packed structure and with the silver ions occupying a sublattice of interstitial tetrahedral sites. Above 147°C silver iodide undergoes a crystalline transition to the high temperature a-phase, which has a body centred cubic arrangement of iodine ions with the silver ions distributed over a sublattice of interstitial sites whose number exceeds the occupancy of silver ions. This phase is stable up to the melting temperature of 555°C. Also present below 147°C is the metastable g-phase which differs from the b-phase in that it has a zinc blende structure with the iodide ions occupying a cubic close packed lattice. This can be viewed as a defect b-phase structure in which the iodide ions are layered ABABAB rather than ABCABC. Migration of Ag + though the disordered cationic lattice gives rise to exceptionally high ionic conductivity of the a-AgI phase [2]. The ordering of Ag + has been studied using computer simulations and it is the tendency of the cations to condense into a locally monoclinic arrangement which is unstable relative to the hexagonal (wurtzite) structure which is proposed as the driving force for the a-b phase transition [3].Previous investigators have reported the heat capacity of silver iodide using conventional and AC calorimetry [4,5]. These measurements have been carried out in heating only whereas Hanaya et al. have reported DSC studies on heating and cooling of the stabilisation of a-AgI by incorporating AgI inside porous silica [6]. In this work the nucleation of the low temperature phase is claimed to be inhibited by the reduction in AgI particle size. For bulk AgI claims have been made that the b-a phase transition can be made to occur around 100°C when the specimen is heated by microwave radiation rather than be conventional heating [7]. In this particular case, multi-phonon coupling between the electromagnetic field and vibrational motions within the AgI crystal are conjectured to stabilise the high temperature form in the same way that mechanical stress by reduction in particle size might also achieve the same effect. An alternative mechanism is the so-called 'ponderomotive effect' whereby microwave-excited ionic currents become locally rectified at interfaces (such as grain boundaries) so as to promote mass transport [8]. In the case of AgI there is no bulk diffusion of material during its structural transformation but it is not unreasonable to propose that this process might promote the formation of a-AgI.This work reports studies on the silver iodide a-b phase transition by conventional and modulated-temperature calorimetry. We also report dielectric property measurements under conventional and microwave heating. ExperimentalThe silver iodide powder (99.999%, Acros Organics) used for these studies was made into pellets with a density of 4.9±0.3 g cm -3 , i.e. 83% of theoretical d...

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Section: Methodssupporting

confidence: 76%

Hysteresis in the β–α phase transition in silver iodide

Binner

Dimitrakis

Price

et al. 2006

J Therm Anal Calorim

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“…1.696 £ 10 27 erg/cm. Using the Thomas-Staveley approximation [34] together with (020) plane growth, the derived value of s=DH o f is ca. 1.127 £ 10 28 cm.…”

Section: Dpls Studies On the Melt Crystallization Of Neat Spsmentioning

confidence: 99%

Miscible blends of syndiotactic polystyrene and atactic polystyrene. Part 2. Depolarized light scattering studies and crystal growth rates

Wang

Liao

Wang

et al. 2004

Polymer

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“…In this study, it was assumed that the growth front was the (110) plane as for PBS ( b 0 = 0.45 nm) and the mode of spherulite growth was regime II growth 24, 25, 27, 42, 43. For the lateral surface energy of linear polymer crystals, the following relation holds:44 …”

Section: Resultsmentioning

confidence: 99%

Crystallization behaviour of cellulose acetate butylate/poly(butylene succinate)‐co‐(butylene carbonate) blends

Lee

Wang

2006

Polymer International

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The kinetics of the isothermal crystallization process from the melt of pure poly(butylene succinate)‐co‐(butylene carbonate) (PBS‐co‐BC) and its blends with cellulose acetate butylate (CAB) (10–30 wt%) was studied by differential scanning calorimetry (DSC) and the well‐known Avrami equation. In the blends, the overall crystallization rate of PBS‐co‐BC became slower with increasing CAB content. The equilibrium melting temperature ($T_{\rm {m}}^{\rm {eq}}$) of PBS‐co‐BC decreased with increasing CAB content, which was similar to that with other miscible crystalline/amorphous polymer blends. The slower crystallization kinetics of PBS‐co‐BC in the blends was explicable in terms of a diluent effect of the CAB component. By application of Turnbull–Fisher kinetic theory for polymer–diluent blend systems, the surface free energy (σe) of pure PBS‐co‐BC and of the blends was obtained, indicating that the blend with CAB resulted in a decrease in the surface free energy of folding of PBS‐co‐BC lamellar crystals. Copyright © 2006 Society of Chemical Industry

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573. Hysteresis in transitions in solids

Cited by 27 publications

References 0 publications

Hysteresis in the β–α phase transition in silver iodide

Hysteresis in the β–α phase transition in silver iodide

Miscible blends of syndiotactic polystyrene and atactic polystyrene. Part 2. Depolarized light scattering studies and crystal growth rates

Crystallization behaviour of cellulose acetate butylate/poly(butylene succinate)‐co‐(butylene carbonate) blends

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