Effect of in situ formed acicular mullite whiskers on thermal shock resistance of alumina-mullite refractories

Abstract

Acicular mullite whisker has been broadly applied in refractory materials, and its aspect ratio is crucial to the properties of refractories. Few studies have focused on the in situ generation of acicular mullite whiskers possessing large length-to-diameter ratio in refractories and its influence on properties (especially the thermal shock resistance) of alumina-mullite refractories. Thus, this work involves in the relationship between properties (especially the thermal shock resistance) of as-prepared alumina-mullite materials and mullite morphology (in situ formed in refractories). Different additives are introduced into alumina-mullite materials to explore the effect of growth mechanism on the aspect ratio of in situ generated mullite whisker. Moreover, the properties of alumina-mullite materials containing mullite with different morphologies are also investigated in terms of thermal shock resistance, bulk density, apparent porosity, and cold and hot mechanical strength, respectively. Results from experiments show that the acicular mullite whiskers with the length-to-diameter ratio of 30-50 present in the sample with addition of 3 wt.% AlF₃·3H₂O and 5 wt.% Al(OH)₃ powders; those as-synthesized mullite whiskers with 3-dimentional structure are conductive to relieve the stress concentration at the microcracks and then hinder crack propagation. Thereby, the thermal shock resistance of alumina-mullite material containing 3 wt.% AlF₃·3H₂O and 5 wt.% Al(OH)₃ powders is significantly enhanced and the corresponding residual CMOR ratio is raised to ~ 83.47%.