Role of the fluid energy (jet) mill:\nA fluid energy mill is chiefly used for which comminution duty?

Introduction / Context:
Fluid energy (jet) mills accelerate particles in high-velocity gas streams, causing interparticle collisions that fracture brittle materials. They are designed to achieve very fine sizes with narrow distributions, often without moving mechanical parts in the grinding zone—ideal for heat-sensitive or contamination-intolerant products.

Given Data / Assumptions:

• Gas jets generate supersonic velocities and strong turbulence.
• Classifying nozzles or internal classifiers may be present for cut control.

Concept / Approach:
Because breakage occurs via high-energy particle–particle impacts, fluid energy mills can reach micron and even submicron sizes (ultrafines) that are impractical in conventional tumbling mills without excessive residence times. They are not intended for coarse crushing or mere cutting; their forte is ultragrinding with tight control and low contamination when constructed of suitable materials.

Step-by-Step Solution:

Verification / Alternative check:
Pharma and specialty chemical datasheets list median sizes of 1–10 µm routinely achieved in jet mills.

Why Other Options Are Wrong:

• Cutting/crushing: different mechanisms and size ranges.
• “Grinding (general)” is too broad; jet mills specifically target ultrafine ranges.

Common Pitfalls:
Ignoring high energy and heat generation—cool, dry gas and controlled feed are essential for thermosensitive materials.

Final Answer:
Ultragrinding (very fine to micron/submicron)