scholarly journals The Soft Core Model for the Self-Diffusion Constant in Simple Liquids

1975 ◽  
Vol 53 (1) ◽  
pp. 285-287
Author(s):  
Y. Hiwatari
Keyword(s):  
Diffusion Constant ◽  
The Self ◽  
Soft Core ◽  
Core Model ◽  
Simple Liquids ◽  
Self Diffusion

On The Melting of Amorphous Ge and Si

1981 ◽  
Vol 7 ◽  
Author(s):  
David Turnbull
Keyword(s):  
Glass Transition ◽  
External Surface ◽  
Rapid Heating ◽  
Diffusion Constant ◽  
Nucleation And Growth ◽  
The Self ◽  
Metallic State ◽  
Equilibrium Melting Temperature ◽  
Self Diffusion ◽  
Limiting Values

ABSTRACTThe amorphous semiconducting phase (a-sc) of Si or Ge is so resistant to crystallization that rapid heating may bring it into a temperature regime in which it melts. Such melting might occur in one or the other of two ways, either homogeneously, by the reverse of the glass transition, to a viscous semi-conducting melt (ℓ-sc) or by transition, probably by nucleation and growth, to the molten metallic state (ℓm). Using the self-diffusion constant of the crystalline elements in conjunction with the Stokes-Einstein equation, upper limiting values of the glass transition (a-sc→ℓ-sc) temperatures of Si and Ge were calculated. These were of the order 0.6 to 0.65 Tcℓ for slow and 1.1 Tcℓ for ultra rapid heating, where Tcℓ is the equilibrium melting temperature of the crystal. Arguments are given that superheating to a temperature 1.15 to 1.25 Taℓ (a-sc↔ℓm in equilibrium at temperature T = Taℓ< Tcℓ) may be required for copious internal nucleation of im in a-sc. At lesser superheating the transition must be initiated at internal flaws (e.g. voids) or at the external surface of the a-sc film. Therefore the superheating at perceptible onset of the transition during rapid heating can vary widely from specimen to specimen, depending on the flaw concentration and how the external surface of a-sc was treated.

scholarly journals Time-of-flight modulated intensity small-angle neutron scattering measurement of the self-diffusion constant of water

2021 ◽  
Vol 54 (3) ◽  
Author(s):  
Stephen J. Kuhn ◽  
Niels Geerits ◽  
Christian Franz ◽  
Jeroen Plomp ◽  
Robert M. Dalgliesh ◽  
...  
Keyword(s):  
Neutron Scattering ◽  
Small Angle ◽  
Small Angle Neutron Scattering ◽  
Spin Echo ◽  
Time Of Flight ◽  
Diffusion Constant ◽  
The Self ◽  
Neutron Resonance ◽  
High Energy Resolution ◽  
Self Diffusion

The modulated intensity by zero effort small-angle neutron scattering (MI-SANS) technique is used to measure scattering with a high energy resolution on samples normally ill-suited for neutron resonance spin echo. The self-diffusion constant of water is measured over a q–t range of 0.01–0.2 Å−1 and 70–500 ps. In addition to demonstrating the methodology of using time-of-flight MI-SANS instruments to observe diffusion in liquids, the results support previous measurements on water performed with different methods. This polarized neutron technique simultaneously measures the intermediate scattering function for a wide range of time and length scales. Two radio frequency flippers were used in a spin-echo setup with a 100 kHz frequency difference in order to create a high-resolution time measurement. The results are compared with self-diffusion measurements made by other techniques and the general applicability of MI-SANS at a pulsed source is assessed.

Permeability in Relation to Viscosity and Structure of Rubber

1942 ◽  
Vol 15 (3) ◽  
pp. 537-544 ◽  
Author(s):  
Richard M. Barrer
Keyword(s):  
Viscous Flow ◽  
Thermal Energy ◽  
Diffusion Constant ◽  
The Self ◽  
Self Diffusion ◽  
Functional Relations ◽  
Diffusion Media ◽  
Entropy Of Activation ◽  
Arrhenius Energy ◽  
And Diffusion

Abstract Some properties of flow of solutes in and through rubbers are outlined. These properties indicate that, due to fluctuations of thermal energy, activated zones exist in certain polymers, of which viscous flow and diffusion are a consequence. A simple statistics of activated zones has been given, and from it equations are obtained for ΣN, D, Ds, and η, denoting respectively the total number of activated zones in rubber, the diffusion constant of simple solutes in the polymer, the self-diffusion constant of rubber, and its viscosity. Functional relations are predicted between log Do, log ηo, or ΔS* (the entropy of activation) and the Arrhenius energy of activation for diffusion or viscous flow. The available data clearly demonstrate this relationship. They also indicate no discontinuity between rubbers and liquids as diffusion media.

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