An improved analyzer for measuring in-situ gas pressure in sealed quartz tube, and absolute and differential temperatures in heat treatments up to high temperatures

Abstract

The measurement of in-situ pressure in synthesis and decomposition experiments, carried out in sealed quartz tubes or ampoules, provides important information about the reactions that occur during the heat treatment processes. In this work, a thermobarometric differential-thermal analyzer (TBDTA) is detailed to perform measurements of in-situ pressure in sealed quartz ampoules, and absolute and differential temperatures in heat treatments up to 800°C. The system can also operate, with certain precautions, above 800°C to approximately 1100°C, but in this temperature range the pressure sensor is not so perfectly linear elastic. The uncertainties in the in-situ pressure measurements of the developed analyzer are ± 0.01 bar, and the data acquisition was performed with a sampling rate of 2 readings per second. The analyzer can be used in synthesis and decomposition processes, and in isochoric thermodynamic studies of pure substances. The developed TBDTA was applied to study the vaporization of pure water, and the measurements of pressure and temperature between 200 and 300°C allowed to determine precise experimental values of the enthalpy of vaporization of the water at 220°C (the temperature of 220°C was chosen just as an example). In another application, it was possible to follow, during the heating and vaporization up to about 1000°C, the in-situ pressure of the element selenium, indicating the formation of different gas species (selenium allotropes in the gaseous phase) as a function of temperature. The results obtained can be considered compatible with mass spectroscopy technique results.