Introduction
Spray granulation is the cornerstone technology for producing ceramic powders with superior flowability and high bulk density in advanced industrial ceramic manufacturing. During this dynamic heat and mass transfer process, the ceramic slurry functions not merely as a carrier of solid particles, but as a sophisticated physicochemical system. Achieving perfect, solid spherical granules requires atomic-level regulation of slurry rheology and droplet solidification kinetics through the scientific selection of chemical additives in the Formulation.
1. Dispersant Selection: From Steric Hindrance to High Solids Loading
The primary objective of a dispersant is to counteract the Van der Waals attractive forces between raw powder particles, lowering slurry viscosity and driving solids loading to its thermodynamic limit before atomization.
As demonstrated by rheological investigations published in the Journal of the European Ceramic Society, the implementation of composite dispersants based on ammonium polyacrylate (APA) or polyethylene glycol (PEG) enables alumina or zirconia slurries to achieve a solids loading exceeding 55 vol% while maintaining a shear viscosity under 200 mPa·s. This minimized water content significantly accelerates evaporation during spraying, directly suppressing the formation of hollow or cratered "apple-shaped" granules.
2. Binder-Plasticizer Synergy: Optimizing Green Strength and Debinding Performance
Binders act as the mechanical scaffolding during droplet desiccation, endowing the granulated powder with structural integrity, while plasticizers modulate deformability during subsequent compaction.
At Sunlets, we mitigate this by engineering a matrix using Polyvinyl Alcohol (PVA) with a tailored molecular weight distribution as the primary binder, coupled with low-molecular-weight PEG as the plasticizer. Guided by ISO 13320 particle characterization methodologies, we precisely calibrate the binder-to-plasticizer mass ratio between 3:1 and 4:1. This formulation optimizes granule sphericity to above 0.95, granting excellent packing flowability during dry pressing or High-Pressure Casting, and ensuring pristine debinding characteristics during Firing without leaving carbon residues at the grain boundaries.
3. Defoamers and Lubricants as Precision Auxiliaries
Trace additives exert disproportionate control over final product consistency, serving as vital fine-tuning agents.
Defoaming Dynamics: High-shear agitation and atomization inevitably introduce micro-bubbles. Sunlets utilizes modified silicone emulsions as defoamers to radically reduce liquid-gas interfacial tension, eliminating hidden internal porosity. we incorporate stearate-based lubricants during the final granulation stage. This minimizes inter-particle and die-wall friction during compaction, establishing the structural blueprint for flawless Vitrification.