Thermobarometric analysis applied to the hydrated calcium oxalate decomposition.

Name: Messias Bicalho Cevolani
Type: MSc dissertation
Publication date: 10/04/2017

Namesort ascending Role
Alfredo Gonçalves Cunha Advisor *

Examining board:

Namesort ascending Role
Thiago Eduardo Pedreira Bueno External Examiner *
José Roberto de Oliveira External Examiner *
Jorge Luis Gonzalez Alfonso Internal Examiner *
Alfredo Gonçalves Cunha Advisor *

Summary: This work is concerned with the characterization of the Thermobarometric Analysis technique applied to the decomposition of Calcium Oxalate Monohydrate (CaC2O4.H2O). This decomposition occurs in three steps with three different gaseous products. This is a technique that makes it possible to obtain direct measurements of temperature and pressure simultaneously during the heat treatment process, this was done in constant volume inside a quartz bulb. Consequently, it was possible to identify thermodynamic parameters of the phase transition and verify the energy conservation quantity such as enthalpy, entropy and Gibbs free energy through the pressure and temperature measurements. The samples were decomposed by varying systematically the initial experimental conditions such as mass, heating rate, heat treatment final temperature and initial pressure. The present results allowed the identification and description of several physical phenomena related to the compound decomposition process. It was possible to identify that an increase in pressure displaced the of the first and third steps transition temperature to higher levels. In the second transition step, the increase in pressure caused the transition temperature to move to lower levels. It has been observed a proportional relationship between mass and the pressure for each transition steps. Therefore, the mass variation also displaces the transition temperatures of the three decomposition steps. Analyzing the initial pressures of each experiment, it was possible to identify a small amounts of H2O, such as humidity, in many samples and in the quartz bulb dedicated to the process. The amount of H2O relative to this humidity is exponential in relation to the initial pressure used to close the ampoules. In this work, it also discovered some limitations of the Thermobarometric Analysis technique when applied to the decomposition of CaC2O4.H2O. By this way, the temperature range limited to 800°C was identified as the most adequate for the experiments of this work.

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