Colloid mills reduce particle size predominantly by which mechanical action within the narrow rotor–stator gap?

Introduction / Context:
Colloid mills are widely used to produce emulsions, suspensions, and fine dispersions in food, pharmaceutical, and chemical processing. Knowing the dominant mechanism helps in selecting suitable equipment for rheology targets.

Given Data / Assumptions:

• High-speed rotor–stator device with narrow gap.
• Fluid feed containing droplets or soft particles.

Concept / Approach:
In a colloid mill, fluid accelerates through a small gap, generating very high shear rates. The intense shear and turbulence cause droplet breakup and solid deagglomeration primarily via attrition mechanisms. Impact and compression are minimal compared to shear; cutting applies to knife mills rather than rotor–stator dispersers.

Step-by-Step Solution:
Identify equipment geometry: rotor–stator with narrow gap.Relate to mechanism: high shear → attrition-based size reduction.Select “Attrition (intense shear)”.

Verification / Alternative check:
Process literature correlates droplet size with shear rate and residence time in colloid mills.

Why Other Options Are Wrong:
Impact/Compression: dominant in crushers/mills with media.Cutting: characteristic of knife/cutter mills.

Common Pitfalls:
Assuming “impact” because of high speed; in liquids, shear dominates.

Final Answer:
Attrition (intense shear)