Achieving high strength and low thermal conductivity: Additive manufacturing of mullite lightweight refractory

Abstract

Complex geometries of mullite lightweight refractory materials with high strength and low thermal conductivity were successfully achieved through additive manufacturing using the direct ink writing technique and fly ash beads coated with alumina sol. In the refractory preparation process, printing ability of the ink was enhanced by adding additives (dispersant and binder). The adjustment of printing parameters, such as pressure, nozzle size, and printing speed, resulted in an enhancement of the refractory structure's accuracy. Compared to the ink with uncoated fly ash beads, the inks with coated fly ash beads show better stability and shear thinning behavior. The compressive strength of the refractories improved significantly. Meanwhile, the thermal conductivity of the refractories kept in a low level. The use of fly ash beads coated with alumina sol in the preparation of porous refractory resulted in the formation of mullite wishers within the pore walls. This created micron-size pores between the whiskers, greatly enhancing the thermal insulation and strength of the porous refractories. The Ashby-Glicksman model was particularly advantageous in predicting the thermal conductivity of the insulation refractories, especially when dealing with a complex pore structure. Therefore, utilizing the direct ink writing technique to produce lightweight refractory materials shows promise in addressing the challenge of creating intricate lightweight refractory parts.