Summary
The driving force for sintering is reduction in surface energy
Hence begin with powder particles of high surface area. In other words, we need particles that are fine, porous and soft.
Compact the powder to get a shape and to provide inter-particle contact necessary for diffusion
Sintering depends on diffusion of atoms, which in turn, depends on concentration of structural imperfections such as vacancies
The concentration of structural imperfections is a function of temperature, atmosphere and dopant
Bring down the sintering temperature by utilizing atmosphere and dopant
For uranium dioxide, atmosphere has been used for lowering sintering temperature from 1700 to 1200 ºC.
In the case of thorium dioxide, dopant has been used for lowering sintering temperature from 1700 to 1150 ºC