In the fields of metal powder injection molding (MIM), 3D printing (such as SLM technology) and powder metallurgy, the fluidity of metal powder directly determines the density, dimensional accuracy and yield rate of the final product. However, metal powders usually have fine particles and large specific surface areas, and are easily agglomerated due to van der Waals forces and electrostatic interactions. In addition, they are sensitive to moisture and easily oxidized, resulting in poor fluidity. Hydrophobic vapor-phase silica, as an efficient nanoscale flow aid, plays a key role in improving the processing performance of metal powders.

Its core mechanism lies in the "bearing effect" and "isolation effect". The particle size of hydrophobic vapor phase silica is only 7-40 nanometers, which is much smaller than metal powder particles. When added in trace amounts and mixed evenly, these nanoparticles will be adsorbed on the surface of micron-sized metal particles, forming an extremely thin "ball layer". This layer of structure significantly increases the distance between metal particles and greatly reduces the friction coefficient between particles, making the powder as smooth as a fluid during the mold filling or powder spreading process.

More importantly, its hydrophobic properties protect metal powders. If there is trace amounts of moisture on the surface of metal powders (especially iron, copper, and aluminum-based powders), liquid bridges can easily form, leading to adhesion or even oxidation. Hydrophobic vapor phase silica has undergone surface silanization treatment and is extremely hydrophobic, which can effectively isolate environmental moisture and eliminate the possibility of liquid bridges. This not only ensures the long-term storage stability of the powder, but also prevents the degradation of rheological properties caused by moisture absorption.

In 3D printing applications, metal powders added with hydrophobic fumed silica exhibit lower angles of repose and bulk density, and the powder spread is more uniform and dense, reducing void defects during the printing process. In summary, hydrophobic vapor phase silica solves the pain points of easy agglomeration of metal powder and fear of moisture through the dual effects of physical friction reduction and chemical hydrophobicity, and is an indispensable modification additive in high-end powder metallurgy processes.