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.