A Simple Dislocation Theory of Melting

1977 ◽  
Vol 30 (6) ◽  
pp. 641 ◽  
Author(s):  
FD Stacey ◽  
RD Irvine
Keyword(s):  
Melting Point ◽  
Phase Boundary ◽  
Pressure Dependence ◽  
Equilibrium Phase ◽  
Perfect Crystal ◽  
Dislocation Theory ◽  
Free Energies ◽  
Clapeyron Equation ◽  
Volume Increment ◽  
Theory Of Melting

The ratio of volume increment to energy for the introduction of a simple dislocation to a crystal is used in the Clausius-Clapeyron equation to determine the pressure dependence of the equilibrium phase boundary between a perfect crystal and a completely dislocated crystal. It yields the Lindemann melting formula, which is thermodynamically valid for materials with central atomic forces in which melting involves no gross changes in coordination. It is concluded that melting is properly described as the free proliferation of dislocations and that melting point is the temperature at which the free energies of dislocations vanish.

scholarly journals Nonequilibrium air clathrate hydrates in Antarctic ice: a paleopiezomdter for polar ice caps

1993 ◽  
Vol 90 (23) ◽  
pp. 11416-11418 ◽  
Author(s):  
H Craig ◽  
H Shoji ◽  
C C Langway
Keyword(s):  
Phase Boundary ◽  
Numerical Models ◽  
Equilibrium Phase ◽  
Vertical Displacement ◽  
Polar Ice ◽  
Ice Flow ◽  
Air Bubble ◽  
Ice Caps ◽  
General Parameter ◽  
Approximate Composition

"Craigite," the mixed-air clathrate hydrate found in polar ice caps below the depth of air-bubble stability, is a clathrate mixed crystal of approximate composition (N2O2).6H2O. Recent observations on the Byrd Station Antarctic core show that the air hydrate is present at a depth of 727 m, well above the predicted depth for the onset of hydrate stability. We propose that the air hydrate occurs some 100 m above the equilibrium phase boundary at Byrd Station because of "piezometry"--i.e., that the anomalous depth of hydrate occurrence is a relic of a previous greater equilibrium depth along the flow trajectory, followed by vertical advection of ice through the local phase-boundary depth. Flowline trajectories in the ice based on numerical models show that the required vertical displacement does indeed occur just upstream of Byrd Station. Air-hydrate piezometry can thus be used as a general parameter to study the details of ice flow in polar ice caps and the metastable persistence of the clathrate phase in regions of upwelling blue ice.

scholarly journals Atomistic study on the pressure dependence of the melting point of NdFe12

AIP Advances ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 025130
Author(s):  
C. Skelland ◽  
S. C. Westmoreland ◽  
T. Ostler ◽  
R. F. L. Evans ◽  
R. W. Chantrell ◽  
...  
Keyword(s):  
Melting Point ◽  
Pressure Dependence ◽  
Atomistic Study

scholarly journals Some crystal-boundary phenomena in metals

1949 ◽  
Vol 196 (1044) ◽  
pp. 64-73 ◽  
Keyword(s):  
Melting Process ◽  
Equilibrium Temperature ◽  
Freezing Process ◽  
Free Energies ◽  
Qualitative Explanation ◽  
Simultaneous Operation ◽  
Liquid Equilibrium ◽  
Theory Of Melting ◽  
Crystallographic Characteristics ◽  
Solid Liquid

Techniques are described for preparing specimens of tin and of lead consisting of two or three crystals with controlled orientations. The direction of formation of the boundary between two crystals is shown to be dependent on the relative orientations of the crystal axes, and to be a result of a Variation of the solid-liquid equilibrium temperature with the crystallographic characteristics of the solid surface in contact with the liquid. A qualitative explanation is advanced in term s of a theory of melting and freezing which envisages the simultaneous operation of a ‘melting’ process and a ‘freezing’ process which have equal rates at the equilibrium temperature. New observations of the ‘macro-mosaic’ effect are recorded, and it is shown that crystal boundaries can move at temperatures near the melting-point in the absence of plastic strain, if reduction of the area of the boundary is produced. It is also demonstrated that the specific free energies of all boundaries, except twin boundaries, in tin are equal, and do not depend on the relative orientations of the crystals.

Composition and Pressure Dependence of the Diffusion Coefficients in Binary Liquid Alloys

2010 ◽  
Vol 297-301 ◽  
pp. 1371-1376
Author(s):  
Dezső L. Beke
Keyword(s):  
Activation Energy ◽  
Melting Point ◽  
Pressure Dependence ◽  
Diffusion Coefficients ◽  
The Self ◽  
Interatomic Potentials ◽  
Liquid Alloys ◽  
Diffusion In Solids ◽  
Self Diffusion ◽  
Binary Liquid

There are a number of well-known empirical relations for diffusion in solids. For example the proportionality between the self-diffusion activation energy and melting point or between the entropy of the diffusion and the ratio of activation energy and the melting point (Zener rule) are perhaps the best known ‘rules of thumb’. We have shown earlier in our Laboratory, that these relations are direct consequences of the similarity of interatomic potentials seen by ions in solids. On the basis of this, similar relations were extended for impurity and self diffusion in binary solid alloys. In this paper, results for binary liquid mixtures will be reviewed. First a minimum derivation of the temperature dependence of the self-diffusion coefficient, D, is presented (minimum derivation in the sense that it states only that the reduced (dimensionless) D should be a universal function of the reduced temperature), using the similarity of interatomic potentials and dimensional analysis. Then the extension of this relation for determination of the pressure and composition dependence of the self-diffusion coefficients is described using pressure and composition dependent scaling parameters (melting point, atomic volume and mass). The obtained universal form (valid for binary liquid alloys) is very useful for the estimation of the temperature, composition and pressure dependence of the self-diffusion coefficients. Finally, the relation for the ratio of the impurity and self-diffusion coefficients is derived.

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