Linear grain growth in sintering U O2 active powder pellets

The grain growth during sintering implies the diffusion by one of the well known processes of the atoms from one grain to another, reorganizing the crystal structure, atom by atom. The mean grain size (d) increases with time (t) according to the law: dn-don = K(T) x t, where n takes values from 2 to 5, depending on predominant diffusion process and K(T) is a growth constant depending on physical parameters of U O2 powders and sintering temperature. In order to obtain U O2 grains larger than 25 μm, we prepared an active powder by precipitation with ammonia donors and mixed ammonia donors and N H3 solutions from U O2(NO3)2 solutions and thermochemical treatment. Although the physical properties are closed to those of standard powders, their particularities are revealed during sintering first of all by different grain growth kinetics. The mean grain size diagrams as a function of time for this powders show a linear grain growth, the growing rates depending on uranium concentration in U O2(NO3)2 solution. (Author)