Aluminum hydroxide (ATH) loses crystal water permanently above 150 °C, which destroys its flame-retardant and smoke-suppression properties. Therefore, temperature control is one of the most critical parameters during surface modification. The optimal operating temperature window for ATH surface modification in a JSGX vortex modification mill is 80 °C to 110 °C, with the target set point normally maintained at 90–100 °C.
Why this temperature range
- Below 80 °C: Insufficient thermal energy for the reaction.
For silane modification, the reaction between silane and ATH surface hydroxyl groups becomes slow. Low temperature leads to incomplete chemical bonding, low coating efficiency, and many partially unactivated ATH particles. For stearic acid, poor melting and spreading occur; the modifier cannot form a uniform thin layer on particle surfaces. - 80–110 °C: The ideal working zone.
Mild friction heat from particle collision and rotor shear provides enough energy to promote uniform spreading of atomized modifier and drive stable surface reaction. At this range, ATH retains all crystal water, whiteness stays consistent, and coating coverage can reach ≥95%. - Above 110 °C but below 150 °C: High-risk zone.
Even though massive dehydration does not happen immediately, local hot spots may trigger partial crystal water loss. The powder may turn slightly yellow, flame retardancy drops, and some modifiers start to degrade. If temperature spikes exceed 110 °C continuously, an interlock alarm should activate and reduce feed rate. - Over 150 °C: Permanent damage to ATH.
ATH decomposes and releases crystal water. The powder loses its core flame retardant function and cannot be used for LSZH cable or high-end composite applications.
Different modifier fine-tuning inside the window
- Silane coupling agent (cable-grade ATH): Preferred target 90–100 °C. This supports stable chemical bonding between silane and ATH hydroxyl groups without modifier degradation.
- Stearic acid / stearate: Preferred target 85–95 °C. Enough heat to fully melt and spread stearic acid. Higher temperature may increase blooming risk of free stearic acid.
Key operational notes
- Heat mainly comes from rotor shear and particle friction inside the JSGX mill. External heating is usually not required; cooling air is used to control temperature and avoid hot spots.
- Install multi-point temperature sensors in each modification chamber for real-time monitoring. Interlock protection automatically reduces feed rate when temperature exceeds 110 °C.
- Incoming ATH powder moisture must be controlled at 0.2–0.5%. High moisture requires more heat for evaporation, which may push chamber temperature up and disrupt coating uniformity.
- Avoid sharp temperature fluctuations. Stable temperature keeps consistent coating efficiency and batch-to-batch product quality.
The optimal temperature for ATH surface modification is 80 °C to 110 °C, with recommended operating temperature of 90–100 °C for silane treatment and 85–95 °C for stearic acid treatment. This window balances sufficient energy for modifier spreading and surface reaction while preventing ATH crystal water decomposition. Continuous temperature monitoring and interlock protection are essential for stable coating quality and preserved ATH flame-retardant performance.
