In recent years, metal fuels were discussed as a contribution to meeting the challenges of the energy transition to a climate-friendly, sustainable energy economy. One material system with high potential to store and release a large amount of energy is iron powder and its reducible solid product iron oxide powder. In this study, the evolution of the particle morphology during single particle combustion in a laminar flow reactor is analyzed. Partially oxidized iron particles are sampled at different heights above the burner and their internal morphological structure is revealed qualitatively and quantitatively by tomography and microscopy methods (μCT, SEM, EDX, EBSD). The findings show that interfacial phenomena might play a major role when describing single particle combustion as the existence of two liquid phases with emulsification phenomena can be detected. Based on the results, a morphological description of the oxidation progress is proposed within the frame of this work.