Figure 124.

Some of the transport and redox processes involved during hydrogen-based direct reduction, where after the first surface reduction step a thin iron layer forms so that the oxygen must diffuse either through this solid material or through cracks and other defects that form due to the volume mismatch between the two phases (iron and oxide).²⁴¹ See also Figure 84, Figure 85, and Figure 123. The figure is reproduced in modified form with permission from ref (241). Copyright 2021, Elsevier.