Zhongxing Lei

A novel method based on ultrastable foam and improved gelcasting for fabricating porous mullite ceramics with thermal insulation–mechanical property trade-off

AbstractFoam instability and long drying cycle limits the widespread use of foaming method. In this paper, a kind of porous mullite ceramic with thermal insulation–mechanical property trade-off were fabricated via novel ultrastable foam and improved gelcasting procedure. The solidification process and stability of foam slurry, as well as the thermal, mechanical property and pore structure of the porous mullite ceramics were investigated. The results showed that porous mullite ceramics with different bulk densities could be prepared via varying volume of foam which was stable enough to be maintained in slurry for a long time. The accelerated gelation rate as well as the gelation degree resulted in the improved gelcasting method led to a shortened period of drying and demould. The obtained pores, which were small, smooth, and unimodal distributed in size in porous mullite ceramics, contributed to achieving the trade-off between thermal insulation and mechanical property.

Stability and shear thixotropy of multilayered film foam

Understanding of foam rheology is significant for the study of foam stabilization. In fact, the foam thixotropy is an important factor to foam stability, but the study about it has not attached great importance. Shear viscosity of different foam stabilizer solutions were investigated as well as microstructure, shear viscosity thixotropy, and stability of different foam systems prepared by the different foam stabilizers. The results show that high shear viscosity of foaming agent solution contributes to decreasing drainage of foam. Collapse of foam depends on the compact degree of molecular alignment. Reaction between the hydrophilic groups of foam stabilizer molecule and accessory ingredient molecule determines shear viscosity of foaming agent solution. Thixotropy of the foam can be used to evaluate the recoverability after sheared by high speed. Strong interaction forces and compact arrangement between the foam stabilizer molecule and accessory ingredient molecule contributes to improving stability and recoverability of foam. Foam stability increases with shear thixotropic recoverability of foam.