The properties of alumina bubble ball castables with different amounts of alumina bubble balls treated at 110°C for 24h, 1100°C for 3h and 1350°C for 3h are different.
 
(1) With the increase of alumina bubble ball content, the volumetric density of the sample decreases. This is because alumina bubble balls, as a lightweight aggregate, have a smaller bulk density than dense aggregates such as brown corundum and mullite. Aluminum bubble balls will introduce some pores into the refractory castable, which will reduce the bulk density of the refractory castable. Especially when the mass fraction of alumina bubble balls exceeds 18%, the bulk density will drop sharply. When the addition amount (w) of alumina bubble balls is 22%, the bulk density of the sample treated at 110℃ for 24h is 2.37g·cm-3.
(2) After treatment at 1100℃, the linear change rate of samples with different alumina bubble ball contents did not change much, and the shrinkage rate showed a decreasing trend as a whole. This is because the raw materials used do not undergo complete sintering reaction after treatment at this temperature, and alumina bubble balls are added as aggregates, which have better high-temperature performance and volume stability than other aggregates. After the sample was heat-treated at 1350℃, the shrinkage rate first increased and then decreased. At this temperature, two reaction processes of kyanite mullite expansion and liquid phase sintering occurred. When the content of alumina bubble balls is low, kyanite mulliteization dominates. With the increase of alumina bubble ball content, the porosity increases, which offsets the effect of kyanite mullite expansion to a certain extent. The liquid phase sintering reaction is dominant, resulting in an increase in shrinkage. The content of alumina bubble balls is further increased, and the function of bubble balls as skeleton support is strengthened, which reduces the shrinkage rate of alumina bubble ball castables. When the added amount (w) of alumina bubble balls is 22%, the heating line change rate of the sample treated at 1350℃ for 3h is -0.03%.
(3) With the increase of alumina bubble ball content, the flexural strength and compressive strength of alumina bubble ball castables decrease gradually. This is due to the point contact between the alumina bubble balls and the alumina bubble balls, the alumina bubble balls and the aggregates, the matrix fills the gaps between the spheres and the spheres and between the spheres and the aggregates, and the alumina bubble balls and the same particle size are in contact with each other. Compared with the dense aggregate, the strength is lower, and the failure occurs before the dense aggregate when subjected to force. And with the increase of the content of bubble balls, the failure mode changes from penetrating ball fracture to extending ball fracture.
(4) With the increase of alumina bubble ball content, the thermal conductivity of alumina bubble ball castable at 800 ℃ gradually decreased after being treated at 110 ℃ for 24 h. This is due to the closed pore structure of the alumina bubble ball itself, which prevents heat transfer.