Aluminum hydroxide (gibbsite ATH) is soft, heat‑sensitive, and prone to fine‑particle agglomeration. Even with jet‑mill adiabatic cooling, dry‑grinding has practical physical limits driven by particle surface‑energy‑driven re‑agglomeration. Data below refers to real stable industrial dry‑jet‑milling results, not one‑off lab test values.
Fluidized‑bed opposed jet mill (industrial preferred for ATH)
- Stable commercial fineness: D97 1.5‑2.0 μm, typical D50 0.7‑1.0 μm
- Absolute lab‑scale limit: D97 ≈ 1.0 μm (small‑lab equipment, extremely low throughput < 20 kg/h). At this level severe agglomeration occurs; capacity collapses, energy consumption surges sharply, and it is not viable for routine production.
- Real‑world high‑end small‑batch ATH products: most jet‑milled premium ATH settle at D97 2‑3 μm. This gives acceptable throughput (100‑300 kg/h), good PSD narrowness, low iron contamination, and well‑preserved crystal‑water LOI value.
Spiral (pancake) jet mill for ATH
Due to broader PSD and higher wall‑impact‑caused agglomeration:
- Reliable stable fineness: D97 2.5‑4 μm.
- Hard to stably push below D97 2 μm; excessive super‑fine fractions raise oil‑absorption and worsen powder agglomeration.
Why ATH cannot easily go to sub‑micron (D97 < 1 μm) by dry jet‑milling
- Agglomeration equilibrium: As particle size drops below ~1 μm, huge specific surface energy makes fine ATH particles stick together by van‑der‑Waals force. Grinding force and re‑agglomeration reach equilibrium; further increasing jet‑pressure / classifier speed yields little benefit.
- ATH is hygroscopic; trace moisture in compressed gas promotes soft agglomerates. Even perfectly dry feed, ultra‑fine ATH will re‑agglomerate inside the mill loop.
- Throughput penalty: chasing D97 < 1.5 μm makes capacity drop to tens of kg/h, with extreme compressed‑air consumption. For bulk filler it is economically unfeasible.
Note: Sub‑micron ATH is achievable by wet bead milling, not dry jet milling.
Key practical constraints to achieve jet‑mill ultrafine ATH
- Feed material must be pre‑ground, de‑agglomerated, free moisture ≤ 0.15 %. High moisture will cause wall‑sticking and block classification.
- Use high‑purity dry compressed air or nitrogen; avoid humid compressed gas.
- High‑precision ceramic‑lined turbine classifier wheel for sharp top‑cut.
- Accept low hourly output: the finer the target, the lower capacity.
Summary Table for reference
| Jet‑mill type | Stable production D97 for ATH | Typical capacity | Remarks |
|---|---|---|---|
| Fluidized‑bed opposed jet mill | 2‑3 μm (main‑stream)；1.5‑2.0 μm (special small‑batch) | 100‑300 kg/h (D97 2‑3 μm) | Preferred for high‑end ultrafine ATH |
| Fluidized‑bed opposed jet mill (lab‑limit) | ~1.0 μm | < 20 kg/h | Only lab‑test, not for commercial production |
| Spiral jet mill | 2.5‑4 μm | 20‑120 kg/h | Broader PSD, not for strict cable‑grade |
