**8. Hydrogen and electric field effect to Iron impurities diffusion in Ta-Fe melt**

Hydrogen and Iron atoms radial distribution functions and diffusion constants had been found by MD method in the Tantalum melt at 3400K in the presence and absence of outer electric field (fig. 16).

The model system was presented by 486 tantalum, 1 iron and 1hydrogen atoms in a cubic cell of 2.13572 nanometers cube edge length. Computer experiment data have found short order of Ta-Fe-H system at 3400K is close to Tantalum structure: first maximum at RTa-Ta ≈ 0.29 nm corresponds to Tantalum atom radius ≈ 0.292 nm. All RDF maxima diffusion is observed at electric field and Hydrogen in the Ta-Fe system. This fact may indicate liquid transition to more disordered structure.

Unusual kind of RDF curve for Ta-H atoms pairs obtained at electric field 1020v/m intensity (fig. 17): first maximum of the curve is bifurcated, besides first sub-peak at r1 = 0.22nm corresponds to one of most probable distance Ta-H and second sub-peak at r2 = 0.24nm corresponds to Ta-Fe without electric field.

Dynamics and local structure of the close to Hydrogen surrounding for the ternary interstitial alloy should depend on Hydrogen concentration, temperature and solvent structure short order. There is no conventional opinion about Hydrogen location in such systems. Since the Hydrogen atom radius is 0.032 nm, it can occupy octahedron (0.0606 nm), as well as tetrahedron (0.0328нм) (Geld et.al, 1985) location. System Ta – H particularity is

Molecular Dynamic Simulation of Short Order and

agreement with Ta-H and Ta-Fe bonds strength.

and Ni-Zr structure had been obtained.

Ta-Fe 3400 0.29

1.5·10-4cm2 s-1.

**9. Conclusion** 

Hydrogen Diffusion in the Disordered Metal Systems 303

Fig. 17. Partial distribution function of the atomic Ta-H pair in electric field 1020 v/m (dashed curve) and Ta-Fe without electric field (solid curve), obtained by MD model.

After Hydrogen induction into MD cell, Tantalum diffusion constant increases from 1.7·10-4 до 7.·10-4 cm2 s-1, which some less, than Iron diffusion constant increase: from 1.3·10-5 to

Thus, Hydrogen increases Iron atoms mobility more than electric field. This fact is in god

Ta-Fe-H 3400 0.26 0.24 0.22 Ta-Fe-H 3400 85 0.26 0.24 0.235 Ta-Fe-H 3400 1020 0.26 0.24 0.22/0.24

Amorphous and liquid systems structure for Fe, Pd, Zr, Ta, Si with presence and absence of Hydrogen atoms had been researched by means of x-rays diffraction and molecular dynamic methods. Strong affect of H atoms to amorphous matrixes Fe-Ni-Si-b-C-P, Pd-Si

Observed RDF changing at Hydrogen presence had been revealed in better resolution of the close and distant maxima could indicate to stable hydride bonds like Pd-H, Si-H, Zr-H formation. Calculated by MD model Hydrogen diffusion constants increase on H concentration and hydride forming element presence in alloy (system Ni-Zr-H). Not only amorphous alloy

rTa-Ta rFe-Fe rTa-H

System T, K E,V/m PRDF (nm)

Ta-Fe-H 3400 85 0.26 0.25

Table 4. Partial inter-atomic distances in the Ta-Fe by MD calculation.

that starting from the concepts of geometry, distance between Tantalum atom and octahedron interstice centre in Tantalum cell more, than Ta (0.146nm) and Н (0.032nm) radii sum. Distance Ta – H remains less than equilibrium distance, and Hydrogen not always occupies interstice centre.

Fig. 16. Radial distribution function g (r) for Ta-Fe melt at 3400 K temperature, obtained in MD model at 15.4 g/sm3 liquid Ta density. 1. No electric field, no hydrogen, 2. Electric field 85 [V/m], no hydrogen, 3. Hydrogen, no electric field, 4. Electric field 85 [V/m], Hydrogen, 5. Electric field 1020 [V/m], Hydrogen.

At the same time, distance from the octahedron interstice centre to the second neighbors, R2=a/√2=0.234nm is more than Tantalum plus Hydrogen distance. That leads to Hydrogen atoms shift from octahedron centre to whatever neighbor of Tantalum atom.

Dynamics and local structure of the close to Hydrogen surrounding for the ternary interstitial alloy should depend on Hydrogen concentration, temperature and solvent structure short order. There is no conventional opinion about Hydrogen location in such systems. Since the Hydrogen atom radius is 0.032 nm, it can occupy octahedron (0.0606 nm), as well as tetrahedron (0.0328нм) (Geld et.al, 1985) location. System Ta – H particularity is that starting from the concepts of geometry, distance between Tantalum atom and octahedron interstice centre in Tantalum cell more, than Ta (0.146nm) and Н (0.032nm) radii sum. Distance Ta – H remains less than equilibrium distance, and Hydrogen not always occupies interstice centre.

At the same time, distance from the octahedron interstice centre to the second neighbors, R2=a/√2=0.234nm is more than Tantalum plus Hydrogen distance. That leads to Hydrogen atoms shift from octahedron centre to whatever neighbor of Tantalum atom.

Hydrogen shift from geometric centre of octahedron position during heating of researched system is possible. According to computer experiment data, distance between nearest Tantalum and Hydrogen atoms changes at electric field and Hydrogen presence, but Ta-Fe remains constant (table 4).

that starting from the concepts of geometry, distance between Tantalum atom and octahedron interstice centre in Tantalum cell more, than Ta (0.146nm) and Н (0.032nm) radii sum. Distance Ta – H remains less than equilibrium distance, and Hydrogen not always

Fig. 16. Radial distribution function g (r) for Ta-Fe melt at 3400 K temperature, obtained in MD model at 15.4 g/sm3 liquid Ta density. 1. No electric field, no hydrogen, 2. Electric field 85 [V/m], no hydrogen, 3. Hydrogen, no electric field, 4. Electric field 85 [V/m], Hydrogen,

At the same time, distance from the octahedron interstice centre to the second neighbors, R2=a/√2=0.234nm is more than Tantalum plus Hydrogen distance. That leads to Hydrogen

Dynamics and local structure of the close to Hydrogen surrounding for the ternary interstitial alloy should depend on Hydrogen concentration, temperature and solvent structure short order. There is no conventional opinion about Hydrogen location in such systems. Since the Hydrogen atom radius is 0.032 nm, it can occupy octahedron (0.0606 nm), as well as tetrahedron (0.0328нм) (Geld et.al, 1985) location. System Ta – H particularity is that starting from the concepts of geometry, distance between Tantalum atom and octahedron interstice centre in Tantalum cell more, than Ta (0.146nm) and Н (0.032nm) radii sum. Distance Ta – H remains less than equilibrium distance, and Hydrogen not

At the same time, distance from the octahedron interstice centre to the second neighbors, R2=a/√2=0.234nm is more than Tantalum plus Hydrogen distance. That leads to Hydrogen

Hydrogen shift from geometric centre of octahedron position during heating of researched system is possible. According to computer experiment data, distance between nearest Tantalum and Hydrogen atoms changes at electric field and Hydrogen presence, but Ta-Fe

atoms shift from octahedron centre to whatever neighbor of Tantalum atom.

atoms shift from octahedron centre to whatever neighbor of Tantalum atom.

occupies interstice centre.

5. Electric field 1020 [V/m], Hydrogen.

always occupies interstice centre.

remains constant (table 4).

Fig. 17. Partial distribution function of the atomic Ta-H pair in electric field 1020 v/m (dashed curve) and Ta-Fe without electric field (solid curve), obtained by MD model.

After Hydrogen induction into MD cell, Tantalum diffusion constant increases from 1.7·10-4 до 7.·10-4 cm2 s-1, which some less, than Iron diffusion constant increase: from 1.3·10-5 to 1.5·10-4cm2 s-1.

Thus, Hydrogen increases Iron atoms mobility more than electric field. This fact is in god agreement with Ta-H and Ta-Fe bonds strength.


Table 4. Partial inter-atomic distances in the Ta-Fe by MD calculation.
