Effect of Pore Formation on Redox-Driven Phase Transformation

TL;DR

This study investigates how pore formation during redox-driven phase transformations affects reaction kinetics, using iron oxide reduction as a model, revealing pore-related effects on local equilibrium and sluggish reduction.

Contribution

It provides a combined experimental-theoretical analysis of pore effects on phase transformation mechanisms in solid-state redox reactions.

Findings

Pores influence local chemical equilibrium during reduction.

Water accumulation inside pores affects re-oxidation.

Pore effects contribute to sluggish reduction kinetics.

Abstract

When solid-state redox-driven phase transformations are associated with mass loss, vacancies are produced that develop into pores. These pores can influence the kinetics of certain redox and phase transformation steps. We investigated the structural and chemical mechanisms in and at pores in a combined experimental-theoretical study, using the reduction of iron oxide by hydrogen as a model system. The redox product (water) accumulates inside the pores and shifts the local equilibrium at the already reduced material back towards re-oxidation into cubic-Fe1-xO (where x refers to Fe deficiency, space group Fm3-m). This effect helps to understand the sluggish reduction of cubic-Fe1-xO by hydrogen, a key process for future sustainable steelmaking.