摘要:

AbstractIn recent years there has been much progress in the coupling of thermodynamics and phase diagrams. The development of solution models, of analytical and numerical techniques, and of computer software has now advanced sufficiently that it is possible to express the Gibbs energies of a wide variety of phases as functions of the state variables and to calculate multicomponent phase diagrams therefrom with good precision for many systems. This approach presents several advantages. Thermodynamic data and phase diagram measurements for a system can be critically assessed simultaneously. Once a set of thermodynamic functions has been compiled for a system, these can be extrapolated to calculate phase diagrams outside the ranges ofT, P, composition, partial pressures, etc. of the measurements, or to compute metastable phase boundaries.N‐component phase diagrams can be estimated from the properties of their (N– 1)‐component sub‐systems. Solution models can be tested or, conversely, used to predict or extrapolate phase d

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870302

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractPrecision calorimetry can provide detailed information about the phase transitions in solids which is utilized to give insight into the nature of transitions and to check the model theories for their validity. Examples of studies are reviewed in this vein on the soft librational mode transition in p‐chloranil, the orientational glass transition in carbon monoxide, and the order‐disorder transition in hydrogen hali

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870303

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractThe polymorphism and the phase transitions of the silica family are explained in terms of a quasi‐one dimensional lattice model. The origin of the different SiO2‐structures is found in two microscopic potentials. The first potential describes the covalent bonding due to the tetrahedral (sp3) silicon coordination and the twofold (pσ) oxygen coordination. The second potential is a local double‐well potential due to the non‐linear polarizability of the non‐bonding (p π) electrons at the oxygen site. This potential is equivalent to a fourth‐order electron‐lattice interaction which may be responsible for the low‐symmetry modifications of the SiO2‐crystals. It turns out that the different crystals with 1,2,3,4 and 6‐fold screw axes correspond to possible commensurate static solutions of the potential. The model also includes incommensurate states which may be interpreted as the vitreous str

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870304

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractA method of extrapolating configurational entropies from high pressure DSC data will be described. The method allows the separation of configurational entropies from entropy changes due to the volume changes of the transitions. The results on the solid‐solid transitions in the plastic crystals cyclohexane (with the use of literature data) and diamantane (using own experimental DSC measurements up to 5 kbar) are discussed with respect to the number of possible molecular orientations. Contrary to literature data rather small numbers are found that can be more easily discussed with consideration of the geometrical parameters of the molecule and the crystal lattic

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870305

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractField ion microscopy combined with mass spectroscopy, the atom probe, is applied to the analysis of nuclei in the decomposition of alloys. The interface of the particles shows the sharp concentration profile expected from Becker's theory. The time evolution of particle size, density and matrix supersaturation is measured for the first time during the nucleation stage of alloy decomposition. It is shown that Ostwald ripening must be taken into account already during this stage in agreement with a recent theory of Langer and Schwartz. The alternative spinodal decomposition mode can also be clearly recognized in the atom probe but a satisfactory non‐linear theory for this mode is still missin

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870306

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractA review and short discussion has been given of a particular type of phase transition called a diffuse phase transition and of microstructures which may give rise to it. Special attention has been paid to microdomains and hybrid crystal formation. Experimental evidence from literature has been reviewed. Results on some ferroelectric and ion conductive materials from the authors laboratory are summarised and discussed into more detail.

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870307

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractThe coupling of the concentration field to the strain field may lead to the occurrence of stable modulated structures near to the top of the miscibility gap. This has been demonstrated through a Landau type theory and verified experimentally in some alkaliborate glass melts.

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870308

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractA new way of treating kinetic problems in crystalline systems, applied earlier to homogeneous systems, here is applied to the Hillert model of an alloy i.e. to a model in which it is assumed that inhomogeneities in composition only exist in one crystal direction. For this model the diffusion equations are derived and shown to lead to equilibrium. The equations are solved in linear approximation. The solutions are unstable inside the spinodal and have characteristics that are in very good agreement with the Cahn‐Hilliard theory of spinodal decompositio

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870309

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractA martensitic transformation may be induced in confined tetragonal zirconia particles by the stress field in front of a crack tip, resulting in an increase in toughness. The microstructure, transformation mechanisms, elastic strain distribution, and in‐situ studies of the interaction of the confined particles with the stress field of the crack tip have been studied by means of high voltage transmission electron microscopy techniques. Facetted particles below a critical sizedcare retained metastably down to room temperature. — The transformation is predominantly controlled by a nucleation barrier. A model of nucleation by inhomogeneity of internal strains is postulated, in which the total resolved strain must exceed 0.25 of the unconstrained transformation strain over the volume of the nucleus for initiation of the martensitic transformation. The “critical size effect” may then be explained in terms of irregular‐shaped particles inducing an inhomogeneous internal strain field which scales with particle size and has a well‐defineddc. In contrast, regular‐shaped spherical particles have a homogeneous strain field with no well‐define

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870310

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractEnergetic particle irradiation produces supersaturation of vacancies and interstitials. The migrating defects annihilate at internal sinks and surfaces forming fluxes to the annihilation sites. Such defect fluxes may cause atomic redistribution in alloys due to an inverse Kirkendall effect. Local instability of the solid solution and precipitation may result. This mechanism is not confined to defect annihilation at sinks but might operate also for vacancy interstitial recombination. — An entirely different mechanism of phase transformation is induced by the atomic mixing effect occurring within the irradiation produced atomic collision cascades. Long range ordered precipitations can be dissolved that wa

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870311

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY