Relationship Between Iron Whisker Growth and Doping Amount of Oxide During Fe₂O₃ Reduction

Iron whisker growth during Fe₂O₃ doped with oxide reduced by CO was investigated by using in situ observation and scanning electron microscopy. The results indicated that the minimum doping amount (MDA) of various oxides, hindering the iron whisker growth, was different. The MDA of Al₂O₃, Li₂O, Na₂O, and K₂O was 0.5, 0.4, 4, and 12 pct, respectively. From the reduction rate, it was found that Li₂O, MgO, and Al₂O₃ had some suppressive effects on the Fe₂O₃ reduction process, thus, confining the growth of iron whisker. However, other oxides had some catalytic effects on the Fe₂O₃ reduction process (Fe₂O₃-Fe₃O₄-FeO-Fe), such as CaO, SrO, BaO, Na₂O, and K₂O. As long as their doping amount was enough, these oxides could inhibit the diffusion of the Fe atom. When the metal ionic radius in doped oxide was bigger than that of Fe³⁺, such as Ca²⁺, Sr²⁺, Ba²⁺, Na⁺, and K⁺, there were lots of spaces left in Fe₂O₃ doped with oxide after reduction, improving Fe atom diffusion. Consequently, their MDA was more than that of small radius to restrain the growth of iron whisker. Finally, the relationship between corresponding metal ionic radius, electron layer number, valence electron number, and MDA of oxide was expressed by using data fitting as follows: