Interaction of platinum with antimony-bearing compounds in NaF fluids at 800 °C and 200 MPA

Studies conducted in NaF-containing hydrothermal fluids have shown that the oxide compounds Sb⁵⁺ are unstable at 800 °C, Р_total = 200 MPa and fO₂ (fH₂) specified by Co–CoO and Ni–NiO buffers interact with the Pt material of the ampoule, forming antimony intermetallics with platinum on the inner surface of the ampoule. The formation of the following intermetallics was established through the analysis of data obtained from studies conducted on an electronic microscope: Pt_90.3±0.8Sb_9.7 (~ Pt₁₀Sb), Pt_82.8±1.3Sb_17.2 (~ Pt₅Sb) and Pt_69.2±4.4Sb_30.8. Pt₁₀Sb compound which was obtained on the inner surface of the Pt ampoule is the limiting solid solution of antimony in platinum at 800 °C. It exhibits a cubic crystal system \(Fm\overline{3}m\) with a lattice constant of a = 3.943(3) Å and forms an underdeveloped surface < 111>. Pt₅Sb compound, presumably hexagonal P6/mmm crystal system with unit cell parameters a = b = 4.56(4), c = 4.229(2) Å, α = β = 90°, γ = 120°, forms a thin film (≤ 10 μm) on the Pt surface and appears to be a metastable phase. The intermetallic compound of Pt₆₉Sb₃₁ is a rapidly cooled melt of appropriate composition.

A mechanism for deep penetration of Sb into the walls of the Pt ampoule is proposed.