How to choose a depolymerization scheme for submicron high purity alumina micro powder that is prone to agglomeration

The core reason why surface treatment is necessary for submicron high-purity alumina micro powder (usually with a particle size between 100nm and 1 μ m) is that its huge specific surface area leads to extremely high surface energy. This physical property causes it to exhibit serious' side effects' in its untreated state. Submicron high-purity alumina micro powder is prone to agglomeration due to its small particle size, large specific surface area, and high surface energy, which is a common problem in its application. To solve this problem, it is necessary to comprehensively consider the three dimensions of physics, chemistry, and technology, and choose the most suitable depolymerization solution.

Surface modification: reducing agglomeration tendency from the root

This is the core means to solve the agglomeration problem, aimed at changing the surface properties of powders through chemical or physical methods, reducing their surface energy, or introducing repulsive forces between particles.

1. Choose the appropriate surface modifier

① Silane coupling agent, titanium ester coupling agent, aluminum ester coupling agent, etc. are commonly used choices. They can react with hydroxyl groups on the surface of alumina to form an organic molecular layer, improving their compatibility and dispersibility in organic systems. When selecting, attention should be paid to the hydrolysis activity and condensation rate of the coupling agent to avoid exacerbating agglomeration due to "bridging" between particles caused by too fast a reaction.

② Polymer dispersant aqueous system: Anionic dispersants such as sodium polyacrylate and sodium hexametaphosphate are preferred, which generate electrostatic repulsion (double-layer effect) through ionization to stabilize dispersion. Oil phase/organic solvent system: Choose dispersants with long-chain alkyl groups, such as phosphate esters, sodium oleate, or high molecular weight block copolymers, which mainly prevent particles from approaching through steric hindrance effects.

③ Inorganic coating uses the sol gel method to coat the surface of alumina particles with a layer of nano SiO ₂ and other oxides to form a physical barrier, effectively blocking the direct contact between particles.

2. Optimize the dosage of modifier

The amount of dispersant or coupling agent added is usually 0.5% -3% of the powder mass. Insufficient dosage cannot fully cover the surface of particles, while excessive dosage may lead to multi-layer adsorption or increase in system viscosity, which in turn affects performance. Suggest determining the optimal dosage through small-scale experiments.

Process optimization: using physical means to break agglomeration

On the basis of surface modification, combined with appropriate physical processes, the formed aggregates can be effectively dispersed.

1. Mechanical dispersion

① Ultrasonic dispersion utilizes the "cavitation effect" generated by ultrasonic waves in liquids to form strong local impact forces, which can effectively break down soft aggregates. Suitable for laboratory or small batch slurry dispersion, temperature control should be taken into account during processing to prevent overheating.

② High energy ball milling/sand milling forcefully opens up agglomerates through the collision, shear, and friction between the grinding medium (such as zirconia balls) and the powder. This method has high efficiency, but it requires optimization of speed, ball to material ratio, and time to avoid excessive grinding that introduces impurities or damages particle morphology.

2. Optimize drying process

Drying is a key step leading to secondary agglomeration. During traditional drying, the capillary force generated by the evaporation of moisture will tightly pull the particles together.

① Freeze drying first freezes the suspension containing powder into a solid state, and then directly sublimates the ice in a vacuum environment. This process completely avoids the generation of liquid bridges and capillary forces, and is one of the best drying methods to prevent hard agglomeration and obtain loose powders.

② Spray drying can obtain spherical particles with good fluidity by atomizing the slurry and drying it quickly. Accurate control of parameters such as inlet air temperature and atomization speed is required, and dispersants can be added to the slurry in advance to assist.

Choose equipment based on your process flow (dry or wet).

The following are the methods recommended by SAT NANO technician DANA based on the company's production methods and equipment.