Effect of calcination temperatures on HfO₂ fibers via electrospinning

Hafnium oxide (HfO2) fibers can be widely used in ultra-high temperature ceramics (UHTCs) as reinforced material in order to achieve better antioxidant performance and less cracks and flaking on surface of UHTCs in field of ultra-high temperature thermal protectors. Calcination temperature is one of essential parameters for forming HfO2 fiber. In this work, one-dimensional (HfO2) fibers were prepared through the electrospinning method and further post-calcination treatment. During the calcination treatment, the monoclinic-HfO2 (m-HfO2) was formed from as-spun HfO2 fibers at 432 degrees C, and only a small amount of m-HfO2 was converted into the tetragonal HfO2 at 1013 degrees C, which can increase the fiber density and decrease the grain size. However, the remaining m-HfO2 was directly converted into the cubic HfO2 at 1351 degrees C. The unique temperatures of forming monoclinic, tetragonal, cubic phase were much lower than the phase-transition temperature. The prepared HfO2 fiber could still maintain fibrous morphology after 10 times cyclic thermal shock in air. Moreover, the fibers calcined at 900 degrees C and 1200 degrees C have better thermal shock resistance for their stable phase and fibrous morphology with uniform grain growth after the thermal shock test.