Thermodynamic Principle of Metallurgy

Having seen (Section 1.3.2) that several different reducing agents -- carbon, carbon monoxide, hydrogen, aluminium, or a reactive metal -- can in principle be used to reduce a given metal oxide, the natural question is: which one should actually be chosen, and under what conditions? This section develops the THERMODYNAMIC framework for answering that question.

Consider the general reduction of a metal oxide MxOy: MxOy(s) → xM(s) + (y/2)O2(g) ...... (1). This reduction can, in turn, be coupled to the OXIDATION of a chosen reducing agent -- if that reducing agent is carbon, it may itself be oxidised either fully to CO2, C + O2 → CO2(g) ...... (2), or partially to CO, 2C + O2 → 2CO(g) ...... (3); if the reducing agent is carbon monoxide itself, it is oxidised to CO2, 2CO + O2 → 2CO2(g) ...... (4). …