Evolution of a fractal system with conserved order parameter under thermal annealing.

Mesoscopic structural evolution under thermal annealing of yttrium aluminium garnet fractal aggregates has been investigated by small-angle neutron scattering. Fractal dimension remains invariant with sintering temperature but the extent of the fractal realm is narrowed down significantly. A Monte Carlo simulation, based on Ostwald-ripening type of relaxation of fractal aggregates for a mass conserved system, has been attempted in order to understand the aforementioned novel observation. A local group merge sintering model was adopted for the relaxation of the fractal aggregates. Diffusion driven mass transport over local branches of fractal clusters causes smoothening of branches but keeps the overall shape unaltered at lower resolution. Predictions of the model were found to be consistent, in terms of microstructural evolution, with experimental data. The present simulation was also successful in explaining the evolution of the particle size distribution of the aggregate. To the best of our knowledge this is the first reported experimental and theoretical investigation on the effect of annealing temperature on nano-ceramic fractal aggregates.