About a first order transformation of magnetite at 1 160 {\deg}C

TL;DR

This paper investigates a first-order phase transformation of magnetite at 1,160°C, providing thermodynamic data and demonstrating the transformation through experimental enthalpy and entropy measurements.

Contribution

It presents the first experimental demonstration of a first-order transformation of magnetite at 1,160°C and provides thermodynamic parameters for this transition.

Findings

Transformation occurs at 1,160°C with specific enthalpy and entropy changes.

Thermodynamic properties of magnetite are characterized near the transition.

Approximate enthalpy versus temperature curves are established.

Abstract

In the literature on the w{\"u}stite/magnetite transformation, there are two distinct values of the enthalpy and entropy terms of the equilibrium between these two oxides. The formalism established previously for the calculation of thermodynamic properties of w{\"u}stite is taken as well as the adjustment of the boundary between the respective domains. A first-order transformation of the magnetite is demonstrated at 1 433 K or 1 160{\textdegree}C where the change in the reference enthalpy is -9 990 J.mole-1 at heating, with the corresponding entropy change being-6.89 J.K-1. . mole-1. The approximate determination of enthalpy vs temperature is made for both varieties of magnetite. Two values of the molar heat content are deduced, with which a direct experimental value can be compared.