Powder rheology and compaction behavior of novel micro-granulates for ceramic tiles

Using spray-dried powders is widely consolidated in ceramic production, especially for porcelain stoneware tiles and slabs. However, a novel micro-granulation process can reduce the consumption of water and energy. It is based on wetting-agglomeration-drying operations that can be managed either as dry (dry-milled powders, micro-granulation) or hybrid route (wet-milled slurry and dry-milled powders, micro-granulation). The goal is to compare these new dry and hybrid micro-granulates with conventional spray-dried and dry-granulated powders by determining: grain size, shape and moisture distribution; static and dynamic angles of repose; poured and tap density, Hausner ratio; mass flow rate; compaction response; microstructure, pore size distribution and yield strength. The new micro-granulates exhibit improved rheological performances, approaching under some manufacturing conditions those of spray-dried powders, particularly in case of the hybrid route. Differences persist in compaction behavior: this is the consequence of distinct microstructure, porosity and stiffness of spray-dried agglomerates and dry/hybrid micro-granules.