Nb and Ta diffusion in titanite

First-principles calculation of phase equilibrium of V-Nb, V-Ta, and Nb-Ta alloys

In this paper, we report the calculated phase diagrams of V-Nb, V-Ta, and Nb-Ta alloys computed by combining the total energies of 40–50 configurations for each system (obtained using density functional theory) with the cluster expansion and Monte Carlo techniques. For V-Nb alloys, the phase diagram computed with conventional cluster expansion shows a miscibility gap with consolute temperature ...

Oxygen diffusion in titanite: Lattice diffusion and fast-path diffusion in single crystals

Oxygen diffusion in natural and synthetic single-crystal titanite was characterized under both dry and water-present conditions. For the dry experiments, pre-polished titanite samples were packed in O-enriched quartz powder inside Ag–Pd capsules, along with a fayalite–magnetite–quartz (FMQ) buffer assemblagemaintained physically separate by Ag–Pd strips. The sealed Ag–Pd capsules were themselve...

Helium diffusion and (U–Th)/He thermochronometry of titanite

We have explored the diffusivity characteristics of radiogenic He in titanite (sphene) and have developed analytical techniques for (U–Th)/He dating of this mineral. Results of incremental He outgassing experiments performed on titanites from a variety of geological environments suggest a thermally activated volume diffusion mechanism with an activation energy of 44.6 6 3.4 (2s) kcal/mol and a ...

Contrasting ion-association behaviour of Ta and Nb polyoxometalates.

Small-angle X-ray scattering (SAXS) studies of aqueous [Ta6O19](8-) compared to prior studies of aqueous [Nb6O19](8-) reveals key differences in behaviour, which is likely at the root of the difficultly in developing polyoxotantalate chemistry. Specifically, where contact ion-pairing dominates between [Nb6O19](8-) and its counterions, solvent-separated ion-pairing between [Ta6O19](8-) and its c...

BEHAVIOUR OF Nb-Ti-Ta WIRE IN NON-STATIONARY CONDITIONS