Micrometer-Scale Kirkendall Effect in the Formation of High-Temperature-Resistant Cr₂O₃/Al₂O₃ Solid Solution Hollow Fibers

The Kirkendall effect in the formation of hollow structures mainly focuses on nanoscaled metal-metal reactions; few have been performed to fabricate micrometer-scale ceramic hollow structures due to the diffusion difficulty. Here, through introduction of the liquid mesophase to accelerate the diffusion rates, we identify that a micrometer-scale ceramic hollowing process could be achieved via the Kirkendall effect. The formation mechanism of the Cr₂O₃/Al₂O₃ solid solution hollow fibers is analyzed. The small Kirkendall voids appear at the interface between Cr₂O₃ and Al₂O₃ via a bulk diffusion process. Then, the core material diffuses along the pore surface through the liquid mesophase, which leads to the depletion of the center matter and forms the hollow structures. The introduction of the liquid mesophase is the key factor in the formation of Cr₂O₃/Al₂O₃ hollow fibers. The as-fabricated Cr₂O₃/Al₂O₃ hollow fibers have a pore size of 8 μm and a shell thickness of 2 μm. The hollow structure remains well after being heat-treated at 1400 °C for 100 h in air, which indicates that the hollow fibers have excellent high temperature resistance. This method confirms that micrometer-scale ceramic hollow fibers can be fabricated in a simple and low-cost method using commercial raw materials without pollutant emissions. We expect that our findings could offer new perspectives in fabricating micrometer-scale ceramic hollow structures, such as hollow sphere, tube, and heterotypic structures.