Ultrafine grinding — dominant breakage mechanism In ultrafine grinders (e.g., fluid energy mills, stirred media mills), the main size-reduction mechanism is:

Introduction / Context:
Ultrafine grinding targets sub-10 μm (often sub-5 μm) sizes for pigments, fillers, and pharmaceuticals. Different mills rely on different breakage modes; matching mechanism to material saves energy and preserves product quality.

Given Data / Assumptions:

• Ultrafine grinders include jet mills and stirred media mills.
• Particles experience high-frequency, low-amplitude interactions.

Concept / Approach:
At ultrafine scales, attrition (surface abrasion and shear between particles or between particles and media) dominates, producing smooth, very fine particles. While impact contributes (e.g., in jets), attrition is the principal, especially in stirred media milling where shear fields are intense and continuous.

Step-by-Step Solution:
Identify the class of mills → ultrafine grinders.Recall primary mechanism → attrition (shear/abrasion).Select “attrition.”

Verification / Alternative check:
Process texts describe stirred media mills as attritors; the name itself highlights the attrition mechanism.

Why Other Options Are Wrong:

• Cutting: typical of knife mills for coarse sizing.
• Compression: primary in roll crushers.
• Impact: key for hammer mills but less dominant in ultrafine attritors.

Common Pitfalls:

• Assuming “jet mill” implies pure impact; interparticle attrition in high-velocity jets is substantial.

Final Answer:
attrition