Which of the following ultrafine grinders primarily employ attrition (particle–particle and particle–wall friction) as the main mechanism for achieving micron/submicron sizes?

Introduction / Context:
Ultrafine grinding targets d50 in microns or below. Fluid-energy devices accelerate particles in gas streams; size reduction occurs by high-velocity collisions and attrition rather than bulk compression.

Given Data / Assumptions:

• Devices listed are gas-entrained mills.
• Focus is on dominant breakage mode.

Concept / Approach:
Jet mills, fluid energy mills, and branded “micronizers” create intense particle–particle impacts and rubbing in turbulent jets. The absence of mechanical media avoids contamination, and attrition plus impact between like particles achieves very fine sizes.

Step-by-Step Solution:
Identify each device as a fluid-energy type.Note attrition/impact dominance without grinding media.Conclude that all three employ attrition significantly.

Verification / Alternative check:
Manufacturer data cite gas energy and inter-particle collisions as the core mechanism for these mills.

Why Other Options Are Wrong:
High-pressure rolls: compressive bed grinding, not attrition-dominant ultrafine gas milling.

Common Pitfalls:
Assuming mechanical media are required for ultrafines; fluid energy suffices.

Final Answer:
All (a), (b) and (c)