Effect of post-precipitation treatment on the pore-structure stability of sol-gel-derived lanthanum zirconate

The importance of post-precipitation treatments (pore-fluid exchange and its removal) on the evolution of the texture of coprecipitated lanthanum zirconate has been investigated. The nature of the pore fluid and the type of fluid-removal (drying) process have shown a profound effect on the aggregate structure (packing of primary particles within the aggregates of the gel). Exchanging the pore fluid with organic fluids such as ethanol or tetrahydrofuran resulted in higher specific surface area, larger pore volume, and, most frequently, larger pore radii. The effect has been attributed to the surface tension of the pore fluid rather than to the polycondensation effect. Freeze drying and microwave drying of ethanol-washed lanthanum zirconate gel also resulted in higher surface area, compared to the oven-dried gel. Freeze drying and microwave drying yielded a surface area of ∼30 m²/g, whereas oven drying yielded a surface area of 20 m²/g after heating at 800°C.