Thermal Stability of \beta -PtO_2 Investigated by Simultaneous Thermal Analysis and Its Influence on Platinum Resistance Thermometry

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 \(T_\mathrm {D}\)  = 595  \(^{\circ }\hbox {C}\) 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  \(^{\circ }\hbox {C}\) . Subsequent heating in air leads to another oxidation process above \(T_\mathrm {D}\) and a reduction at 800  \(^{\circ }\hbox {C}\) . The second oxidation and reduction process is strongly suppressed when the powder is heated in He. The remaining mass above \(T_\mathrm {D}\) does not comply with a reduction path PtO \(_2 \rightarrow \) PtO \(\rightarrow \) Pt. Differential scanning calorimetry shows an endothermic reaction at \(T_\mathrm {D}\) 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 \(\beta \) -PtO \(_2\) . Furthermore, catalytic activity of the PtO \(_2\) powder is evidenced by mass spectrometry to be present below 460  \(^{\circ }\hbox {C}\) . Finally, the impact of these findings on the stability of platinum resistance thermometers is discussed.