Atomic Diffusion and its Relation to Thermodynamic Forces in Al-Ni Melts

2009 ◽  
Vol 289-292 ◽  
pp. 705-710 ◽  
Author(s):  
Axel Griesche ◽  
Bo Zhang ◽  
Jürgen Horbach ◽  
Andreas Meyer
Keyword(s):  
Chemical Diffusion ◽  
Atomic Diffusion ◽  
Dynamic Simulations ◽  
X Ray ◽  
Self Diffusion ◽  
Ni Alloys ◽  
Quasielastic Neutron ◽  
Cross Correlations ◽  
Quasielastic Neutron Scattering ◽  
Thermodynamic Forces

We make use of a novel X-ray radiography method to measure chemical diffusion in capillaries in binary Al-Ni melts. Data are compared to self diffusion coefficients of Ni obtained by quasielastic neutron scattering as well as diffusion and thermodynamic data obtained by molecular dynamic simulations. Interdiffusion compared to self diffusion is enhanced with a maximum at Al40Ni60. We show that this enhancement is caused by thermodynamic forces as described by the Darken-Manning equation. In liquid Al-Ni alloys the Manning factor that is smaller than one can be attributed to collective cross correlations.

Self Diffusion in Liquid Titanium: Quasielastic Neutron Scattering and Molecular Dynamics Simulation

2009 ◽  
Vol 289-292 ◽  
pp. 609-614 ◽  
Author(s):  
Andreas Meyer ◽  
Jürgen Horbach ◽  
O. Heinen ◽  
Dirk Holland-Moritz ◽  
T. Unruh
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Coefficient ◽  
Neutron Scattering ◽  
The Self ◽  
Dynamics Simulation ◽  
Self Diffusion ◽  
Quasielastic Neutron ◽  
Liquid Titanium ◽  
Quasielastic Neutron Scattering ◽  
Self Diffusion Coefficient

Self diffusion in liquid titanium was measured at 2000K by quasielastic neutron scattering (QNS) in combination with container less processing via electromagnetic levitation. At small wavenumbers q the quasielastic signal is dominated by incoherent scattering. Up to about 1.2 °A−1 the width of the quasielastic line exhibits a q2 dependence as expected for long range atomic transport, thus allowing to measure the self diffusion coefficient DTi. As a result the value DTi = (5.3± 0.2)× 10−9 m2s−1 was obtained.With a molecular dynamics (MD) computer simulation using an embedded atom model (EAM) for Ti, the self diffusion coefficient is determined from the mean square displacement as well as from the decay of the incoherent intermediate scattering function at different q. By comparing both methods, we show that the hydrodynamic prediction of a q2 dependence indeed extends up to about 1.2 °A−1. Since this result does not depend significantly on the details of the interatomic potential, our findings show that accurate values of self diffusion coefficients in liquid metals can be measured by QNS on an absolute scale.

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