Abstract
The thermal expansion of α-Fe (ferrite) and γ -Fe (austenite) nanocrystals confined inside multiwalled carbon nanotubes (MWCNTs) is studied in situ, using synchrotron x-ray diffraction, as a function of temperature. While the thermal expansion of ferrite is similar to that of bulk material, a peculiar behavior is evidenced for austenite: The thermal expansion becomes abnormally high above 500 ◦C. A scenario involving progressive carbon uptake in γ -Fe nanocrystals gives a satisfactory understanding of the phenomenon, and allows one to propose a value of the carbon solubilization rate in γ -Fe particles confined inside MWCNTs.