A jet mill (fluid‑energy mill) uses high‑speed compressed air or inert gas jets to accelerate ATH particles. Size reduction is achieved by particle‑to‑particle collision, with no grinding media, rollers or hammers contacting the material. For heat‑sensitive, high‑purity ultrafine aluminum hydroxide (ATH), jet milling has unique strengths compared with mechanical mills such as ACM mills and ring‑roller mills, along with clear application boundaries.
Core Working Principle for ATH
High‑pressure gas nozzles generate supersonic gas flow, accelerating ATH particles. Particles collide violently with each other; comminution comes from inter‑particle impact rather than metal‑component impact. An integrated dynamic air classifier controls final particle‑size distribution. The whole grinding process relies on gas energy, with almost no mechanical friction heat generated inside the grinding chamber.
Key Advantages for Ultrafine ATH Grinding
1. Extremely low heat generation, excellent protection of ATH crystal water
This is the most prominent advantage for heat‑sensitive ATH.
- Grinding energy comes from compressed gas expansion; gas expansion produces adiabatic cooling effect. Chamber temperature does not rise sharply even during long‑run operation.
- Avoids frictional heat accumulation seen in roller‑type or high‑speed impact mechanical mills. Greatly reduces risk of local hot‑spots and thermal decomposition of ATH crystal water.
- Well suited for ultra‑fine ATH production where over‑heating must be strictly eliminated. Even for D97 2 μm or finer grades, LOI value can be well maintained at the theoretical 34.5 %.
2. Ultra‑low metal contamination, high‑purity powder output
Since there is no metal grinding roller, hammer or rotor directly striking ATH particles. Comminution depends on particle‑against‑particle collision.
- When equipped with ceramic‑lined grinding chamber and classifier wheel, iron impurity can be controlled to extremely low levels.
- Produces high‑whiteness, low‑iron ATH for premium LSZH cable, high‑voltage insulation and high‑end polymer composites. Mechanical mills always face wear‑risk of rotating metal components, even with ceramic liners.
3. Capable of producing extremely fine ATH powder
Jet mill reliably reaches D97 1‑3 μm ultrafine ATH, which is difficult for ring‑roller mills.
- Combined with high‑precision internal air classifier, it achieves narrow particle‑size distribution and strict over‑size control.
- Good at manufacturing special ultrafine ATH grades for high‑performance halogen‑free flame‑retardant formulations.
4. Less particle surface damage
Breakage occurs mainly at particle crystal boundaries. Jet‑milled ATH retains relatively complete crystal morphology. The particle surface has fewer fresh sharp broken edges compared with strong mechanical shear grinding. This brings benefits for subsequent silane surface modification: modifier coats particle surfaces more uniformly.
5. Can adopt inert‑gas atmosphere for special‑process requirements
When needed, nitrogen can replace compressed air as grinding medium. Closed inert‑gas operation prevents moisture absorption of ultrafine ATH powder and avoids oxidation risks for downstream modified products.
Limitations of Jet Mill for ATH Production
It is not a universal solution for all ATH projects, with obvious practical constraints:
- Low production capacity: Energy consumption is high. Typical output for D97 2‑3 μm ATH is only 50 ~ 300 kg/h. Not economical for large‑tonnage bulk ATH filler production. Most mass‑production cable‑grade ATH plants choose closed‑circuit ACM mechanical mill lines for higher throughput.
- High compressed‑air consumption, higher operating cost per ton of finished powder.
- Strict feed requirements: feed material must be pre‑ground, de‑agglomerated and dry. Large lumps or wet filter‑cake cannot directly feed into jet mill.
- Not suitable for coarser ATH grades (D97 > 6 μm); mechanical mills achieve far better cost‑performance at this fineness range.
Comparison Summary for ATH Applications
- Jet mill: Best for small‑batch, ultra‑fine, high‑purity ATH (D97 1‑3 μm), premium‑grade special filler; high cost, low capacity.
- ACM / ring‑roller closed‑circuit mill: For large‑volume industrial production, D97 3‑25 μm; higher throughput, lower energy cost, must rely on water‑jacket cooling and anti‑wear lining to avoid over‑heating and iron pollution.
The main advantages of jet mill for ultrafine ATH are: low‑temperature grinding with adiabatic gas cooling to preserve crystal water, minimal metal contamination, capability for extremely fine particle size, and favorable particle surface condition for subsequent surface modification. Due to low capacity and high energy cost, jet mill is mostly used for high‑end small‑batch special ATH products, rather than mainstream large‑scale mass‑production lines.
