Netsu Sokutei

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The thermal decomposition of praseodymium oxalate decahydrate, Pr₂(C₂O₄)₃·10H₂O, was studied in atmospheres of He+O₂, He and CO₂ by a multiple technique of simultaneous thermogravimetry (TG) and differential thermal analysis (DTA) coupled with evolved gas analysis (EGA). The decomposition proceeded basically by the following steps in all the atmospheres:
Pr₂(C₂O₄)₃·10H₂O→Pr₂(C₂O₄)₃→Pr₂O(CO₃)₂→Pr₂O₂CO₃→Pr oxide,
yielding Pr₇O₁₂ in (4:1) He+O₂ mixture, and Pr₂O₃ in He and in CO₂ as end products. In CO₂ atmosphere, the decomposition of anhydrous oxalate took place at higher temperatures than in other atmospheres owing to the stabilization of intermediate carbonates. All the DTA peaks were endothermic in He and in CO₂, whereas exothermic peaks were also detected in He+O₂ probably due to the oxidation of CO and deposited carbon, and the disproportionation of CO. In inert atmospheres, finely divided carbon particles were markedly deposited, and then reacted with CO₂ which was evolved during the decomposition of Pr₂O₂CO₃. Instead of the disproportionation of CO, the direct formation of carbon and CO₂ from Pr₂O(CO₃)₂ was proposed as a possible mechanism for the deposition of carbon particles.

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The definition and realization of a new temperature scale, The 1976 Provisional 0.5K to 30K Temperature Scale (EPT-76), are reviewed. The scale is intended to correct deviations of the IPTS-68 from the thermodynamic scale below 30K and to set an international temperature scale down to 0.5K. The realization of superconductive transition points as reference temperatures, the interpolation by gas thermometer and magnetic one, and the calibration of a germanium thermometer and a Rh-0.5% Fe alloy thermometer are illustrated.

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