Too late but it might help others have same question:

> An aggregate is a discrete assemblage of primary particles strongly bonded together (i.e., fused, sintered, or metallically bonded), which are not easily broken apart. Aggregates have an overall specific surface area less than that of the constituent primary particles.

> An agglomerate is assemblages of particles (including primary particles and/or smaller aggregates) held together by relatively weak forces (e.g., Van der Waals, capillary, or electrostatic), that may break apart into smaller particles upon processing (e.g., using sonication or high intensity mixing). agglomerates exhibit the same overall specific surface area of the constituent particles

> Source: Article Ultrasonic dispersion of nanoparticles for environmental, he...