Thermal Stability of $$\beta $$ β -PtO $$_2$$ 2 Investigated by Simultaneous Thermal Analysis and Its Influence on Platinum Resistance Thermometry

Abstract

We present thermogravimetric and differential scanning calorimetric studies of PtO 2 powders measured in different atmospheres. In synthetic air a mass loss of 11.4 % is found at the decomposition temperature T D = 595 • C which can be attributed to the reduction of PtO 2 . In a helium atmosphere the mass loss is 12.0 % and is found at 490 • C. Subsequent heating in air leads to another oxidation process above T D and a reduction at 800 • C. The second oxidation and reduction process is strongly suppressed when the powder is heated in He. The remaining mass above T D does not comply with a reduction path PtO 2 → PtO → Pt. Differential scanning calorimetry shows an endothermic reaction at T D in synthetic air as well as in helium which corresponds with the mass loss. These measurements imply that the powder can be assigned to be β-PtO 2 . Furthermore, catalytic activity of the PtO 2 powder is evidenced by mass spectrometry to be present below 460 • C. Finally, the impact of these findings on the stability of platinum resistance thermometers is discussed.

Interplay of valence states and magnetic interactions in the perovskite system LaNi1Rh O3

“…PtO2 exists in two polymorphs, 𝛼and 𝛽-PtO2 (Figure 16b-c), where both structures have Pt in octahedral coordination with the stable 𝑑 6 low spin electron configuration. 𝛽 -PtO2 forms at high temperature and high pO2 (Figure 17a), crystallising in the CaCl2 structure (Pnnm), and decomposes above ~595 °C in air [89]. The 𝛽-PtO2 structure is similar to the rutile structure (P42/mnm), consisting of chains of edge-sharing PtO6-octahedra along the 𝑐-axis (Figure 16c).…”