Фазовая диаграмма системы Pt-V
К оглавлению: Другие диаграммы (Others phase diargams)
Pt-V (Platinum-Vanadium)
J.F. Smith
The assessed Pt-V phase diagram is based on [73Wat] with review of the data of
[74Sta]. Temperatures in the assessed diagram for the invariant
transformations have precisions on the order of с10 C.
A superlattice near Pt8V, analogous to Ni8V in the Ni-V system [82Smi], has
been reported by [86Sch] as part of an extensive investigation of ordering in
the Pt-V system. This Pt8V phase may or may not be an equilibrium feature of
the system; extensive anneals such as the 3-week or more periods found by [
85Aok] to be necessary for the establishment of equilibrium in the Co-rich
region of the Co-V system have not been made for the Pt-V system. Even if Pt8V
proves to be an equilibrium feature, there is at present no basis for deciding
whether it forms by first- or second-order transformation nor for associating
temperatures and compositions with boundaries defining its range of existence.
Therefore, the phase has not been included in the assessed diagram.
[73Wat] showed a single congruent transformation near 1015 C from the
terminal solution to a lower-temperature phase with the Al3Ti structure. [
73Wat] was unable to form the ordered AuCu3 structure at ideal stoichiometry
but was able to form the phase at Pt-rich compositions. However, the manner of
its formation was such that [73Wat] suggested that the phase might be
metastable rather than an equilibrium phase in the binary diagram. Recent work
on the Co-V system [79Aok, 85Aok] supports the view that the AuCu3-type phase
is likely to be metastable rather than stable.
[86Sch] confirmed that the AuCu3 structure is metastable in Pt-V and that it
does not occur at a stoichiometry of Pt3V. Instead, at ideal stoichiometry,
the (Pt) terminal solution was found to transform to the Al3Ti structure via
metastable intermediate structures that are associated with long-range
antiphase boundaries. The observation [86Sch] of a superstructure with
stoichiometry of Pt8V and related to the AuCu3 structure is unequivocal, and,
in the composition region between Pt8V, there were found only substitutionally
disordered derivatives of Pt8V and the AuCu3 structure without long-range
periodicity.
PtV3 becomes superconducting at low temperatures [61Mat, 63Mat]. Annealing [
73Cox] tends to raise the superconducting transition temperature, but only
slightly. At elevated temperatures, the phase exists from 66 to 82 at.% V [
73Wat] and decomposes peritectically near 1800 C. It is in eutectic
equilibrium with liquid and the Pt-rich terminal solution near 1720 C and in
eutectoidal equilibrium with the Pt-rich terminal solution and PtV near 1410
C. AuCu3-type ordering has been observed in coexistence with the Cr3Si-type
structure at compositions in the vicinity of 75 at.% V, but there is agreement
[64Mal, 64Phi] that this results from contamination by interstitial elements,
definitely oxygen and probably nitrogen and/or carbon.
[56Gre] found that terminal solutions up to ~40 at.% V in (Pt) could be
retained by rapid cooling and concluded that the terminal solubility at
elevated temperatures exceeded 40 at.% V. [73Wat] and [74Sta] agree that the
solubility limit at the ~1720 C eutectic reaction is near 60 at.% V. Both
also agree that the ordered structures of the three Pt-rich phases all form
from this terminal solution by congruent reactions during cooling.
[73Wat] and [74Sta] show extensive terminal solubility of Pt in (V). According
to [73Wat], this terminal solubility increases from a composition near 5 at.%
Pt at 700 C to near 12 at.% Pt at the 1800 C peritectic temperature. The
report by [55Gel] of more than 8 at.% Pt solubility in (V) at elevated
temperature corroborates the general range of the assessed solvus.
55Gel: S. Geller, B.T. Matthias, and R. Goldstein, J. Am. Chem. Soc., 77, 1502-
1504 (1955).
56Gre: P. Greenfield and P.A. Beck, Trans. AIME, 206, 265-276 (1956).
61Mat: B.T. Matthias, V.B. Compton, and E. Corenzwit, J. Phys. Chem. Solids,
19, 130-133 (1961).
63Mat: B.T. Matthias, T.H. Geballe, and V.B. Compton, Rev. Mod. Phys., 35, 1-
22 (1963).
64Mal: A. Maldonado and K. Schubert, Z. Metallkd., 55, 619-626 (1964).
64Phi: H. von Philipsborn and F. Laves, Acta Crystallogr., 17, 213-214 (1964).
73Cox: J.E. Cox and R.M. Waterstrat, Phys. Lett. 46, 21-22 (1973).
73Wat: R.M. Waterstrat, Metall. Trans., 4, 455-466 (1973).
74Sta: E.A. Statnova and V.V. Kuprina, Vestn. Mosk. Univ., (2), 243-245 (1974)
in Russian; TR: Moscow Univ. Chem. Bull., 29(2), 88-89 (1974).
79Aok: Y. Aoki, Y. Obi, and H. Komatsu, Z. Metallkd., 70, 436-440 (1979).
82Smi: J.F. Smith, O.N. Carlson, and P.G. Nash, Bull. Alloy Phase Diagrams, 3,
342-348 (1982).
85Aok: Y. Aoki and J. Echigoya, Scr. Metall., 19, 639-642 (1985).
86Sch: D. Schryvers and S. Amelinckx, Acta Metall., 34, 43-54 (1986).
Published in Phase Diagrams of Binary Vanadium Alloys, 1989. Complete
evaluation contains 1 figure, 2 tables, and 36 references.
Special Points of the Pt-V System