Abstract
Nano-particles as particles in the size range of 1 to 100 nm, in which the characteristic length scale falls in between the microscopic and macroscopic worlds. Due to the unusual property falls in the nano-material as compared to the bulk material and that there is no simple theory that can describe the thermodynamic change of physical property well, we choose SiO2 as the system to study the size effect of nano-particles for sintering behavior.We have the particle sizes of 7-10nm, 10-13nm, 50nm and 80nm produced by factory using the method of water-glass and 30nm synthesized by the hydolysis of TEOS. Several characterizations including BET, SEM, DTA, gravimetry, light-scattering, XRD and ESCA are employed to analyze the sintering mechanism effected by the particle size and sintering temperatures at 800℃,900℃ and 1000℃.The 7-10nm was sintered faster than the 10-13nm at 800℃, however, there was no sintering for the 50nm and 80nm. The 7-10nm and 10-13nm may undergo the initial sintering stage with the phenomena of neck growing, disappearance of small pores, and large pores growing. For the 7-10nm and 10-13nm, the sintering was faster at 900℃than 800℃, however, the 50nm and 80nm still did not sinter at 900℃. The 7-10nm and 10-13nm would become the bulk material without pores when sintered above 900℃ and become the one with large pores below 800℃. Besides, the 7-10nm sintered at 850℃ would become the bulk material essentially with a lot of pinholes.As for the phase transition, the morphology would change from amorphous to tridymite when 7-10nm was sintered for 24 hours at 900℃. And the morphology would change to cristobalite when 7-10nm was sintered for 2 hours at 1000℃ and then change to tridymite when sintered for 16 hr. The cristobalite may be present when 10-13nm was sintered for 8 hours at 900℃.The 30nm would undergo the initial stage with the phenomena of neck growing, disappearance of small pores, large pores growing and then would enter the evolution of the intermediate stage with equilibrium shapes and continuous shrinkage. But up to now, we still can not explain the unreasonable phenomena for 30nm sintered at 800℃ compared with the same condition of 7-10nm and 10-13nm.