Transition in the nanoporous structure of iron oxides during the oxidation of iron nanoparticles and nanowires

Stress development during reaction of metallic nanospheres with gas

“…It was studied to a large extent experimentally in binary stoichiometric systems [1][2][3][4][5][6] and also theoretically [7][8][9][10][11]. From the experimental studies, it is evident that the formation of a hollow nanosphere of stoichiometric phase M p X q must be preceded by the formation of a sufficiently thick M p X q nanoshell on the metallic core of phase M. Moreover, it is also demonstrated experimentally that no M p X q hollow nanospheres are formed from larger M nanospheres, and the nanospheres with M core and M p X q shell represent stable objects.…”

Application of the Kirkendall Effect to Morphology Control of Nanowires: Morphology Change from Metal Nanowires to Oxide Nanotubes

“…8(b)). In our previous paper, we found out the experimental result supporting that the formation of the additional spherical nanovoids is closely correlated with the shrinkage of the cylindrical nanopore; the additional nanovoids appeared at 673 K, where the diameter of nanotubes started to decrease (Nakamura et al, 2009a). Furthermore, from the line profile of Fig There is a definite difference in morphology change during shirking between CuO and NiO, and Fe 3 O 4 ; additional nanovoids are introduced along the inner wall of the nanotubes only in the shrinking process of Fe 3 O 4 n a n o t u b e s .…”

“…Furthermore, from the line profile of Fig There is a definite difference in morphology change during shirking between CuO and NiO, and Fe 3 O 4 ; additional nanovoids are introduced along the inner wall of the nanotubes only in the shrinking process of Fe 3 O 4 n a n o t u b e s . I t w a s r e p o r t e d i n o u r p r e v i o u s p a p e r s (Nakamura et al, 2008b) that a similar tendency can be seen in the shrinking process of hollow oxide nanoparticles; hollow CuO and NiO nanoparticles become solid particles without the formation of additional voids, whereas hollow Fe 3 O 4 nanoparticles turn into solid γ-Fe 2 O 3 via a porous structure (Nakamura et al, 2009a). It should be pointed out, as mentioned above, that the phase transformation from Fe 3 O 4 to γ-Fe 2 O 3 proceeds when the formation of additional voids and the shrinkage of a cylindrical nanopore occur simultaneously while the crystal structure of CuO and NiO nanotubes remains unchanged in the process of shrinking.…”

“…Therefore, our focus has been on the fabrication of oxide nanotubes via the oxidation of metal nanowires such as Cu, Ni and Fe, taking vacancy clustering inside metal nanowires due to the Kirkendall effect into consideration. In this chapter, we will overview our recent results on the morphology changes of metal nanowires via oxidation reactions (Nakamura et al, 2009a(Nakamura et al, , 2009b. The formation mechanisms of oxide nanotubes and porous nanowires will be discussed in terms of diffusion in metals and oxides.…”

Synthesis and Characterization of Nontoxic Hollow Iron Oxide (α-Fe2O

“…Removal of core in the core shell NPs is an important parameter to make them hollow structures [15,16]. The formation of metal oxide hollow NPs is due to the coalescence of cation vacancies formed due to the difference in diffusion rates ( metal > oxygen ) of metal and oxygen after oxidation of metals while having noncoalesced vacancies after oxidation.…”