Wet forming and sintering behavior of nanometer-sized ceria powder

An aqueous suspension of 25 vol.% ceria powder of 14 nm diameter (powder A) was consolidated by filtration through a gypsum mold. However, many cracks were formed during drying of the ceria compact. Addition of larger ceria powder of 37 nm diameter (powder B) to the 14 nm-ceria powder was effective to prevent the formation of cracks. The densification of the dried powder compacts with 90 vol.% powder A, 10 vol.% powder B was divided into four ranges with sintering temperature: range I (500-800 °C), sintering of primary particles within a secondary particle cluster; range II (800-1200 °C), grain growth of primary particles in a dense secondary particle cluster; range III (1200-1500 °C), sintering of dense secondary particle clusters with grain growth, and range IV (1500-1600 °C), grain growth of dense secondary particle clusters. Increased fraction of powder B to 40-60 vol.% suppressed the decrease of specific surface area of powder compact in the ranges I and II, leading to a continuous densification in the rages I and II. In the ranges III and IV, the densification rate was enhanced by the addition of powder B of 60 vol.%, because the coordination number of ceria grains to a pore decreased with addition of 37 nm-powder.