Dispersion and Surface Modification of Nanopowders​

Agglomeration Mechanism Analysis​​

​​Van der Waals Forces:​​
F=−C/r⁶
(C: material-dependent constant, r: interparticle distance)
​​Impact:​​ Dominates agglomeration when particle size ​​<100 nm​​, requiring surface modification or mechanical dispersion for mitigation.

​​Surface Chemical Effects:​​

• ​​Hydroxyl (-OH) Adsorption:​​ Metal oxides (e.g., TiO₂, SiO₂) form hydrogen-bonded networks on surfaces.
• ​​Electrostatic Attraction:​​ Agglomeration occurs when |​​Zeta potential| <30 mV​​ (per DLVO theory).

​​Process Factors:​​

• ​​Capillary forces​​ during drying induce particle clustering.
• ​​Incomplete solvent removal​​ post wet grinding causes secondary agglomeration.

​​Solutions to Nanopowder Agglomeration​​

Uniform dispersion requires ​​physical dispersion, chemical modification, and stability control​​.

Physical Dispersion Techniques​​

Mechanical activation (e.g., ultrafine grinding) modifies surface properties:

• Crystal structure (amorphization)
• Solubility
• Chemical reactivity

​​1. Ultrasonic Dispersion​​

• ​​Parameters:​​
  • Frequency: ​​20 kHz​​ (coarse clusters) → ​​1 MHz​​ (fine dispersion)
  • Power density: ​​0.5–2 W/mL​​; Duration: ​​10–60 min​​ (<50°C)
  • ​​Optimization:​​ Pulsed mode (5s on/2s off) + dispersants (e.g., 0.1% SDS).

​​2. Mechanical Ball Milling​​

• ​​Critical speed:​​ 65–80% of ​​Nc = 42.3/√D​​ (D: mill diameter in meters)
• ​​Ball-to-powder ratio:​​ 3:1–10:1 (material-dependent)
• ​​Duration:​​ 1–10 hr, with ​​size monitoring every 30 min​​ (prevent overgrinding)

​​3. Spray Drying​​

• ​​Conditions:​​
  • Inlet temp: ​​150–250°C​​ (solvent-dependent)
  • Atomization pressure: ​​0.2–0.5 MPa​​
  • Feed rate: ​​5–20 mL/min​​ (instant drying)
• ​​Defect Control:​​ Inert gas (N₂/Ar) shielding prevents sintering.

Chemical Surface Modification​​

​​1. Surface Chemical Modification​​

Reactions between modifiers and particle surfaces alter structure/properties via:

• Functional group coupling
• Free radical reactions
• Chelation
• Sol-gel adsorption
• Coupling agents

​​Key Factors:​​ Nanoparticle surface properties, modifier type/dosage, process parameters.

​​2. Polymer Coating​​

Surface encapsulation using surfactants, polymers (e.g., PEG), or fatty acid soaps via adsorption/chemical bonding.

​​3. Precipitation Modification​​

Wet-chemical deposition of modifier layers onto particle surfaces.

​​Dispersion Stability Control​​

​​1. Steric Stabilizers​​

• ​​Agents:​​ HPMC, PEG (​​0.1–1 wt%​​, MW >10 kDa)

​​2. Rheological Control​​

• ​​High-viscosity media​​ (e.g., glycerol) suppress Brownian motion.
• ​​Thixotropic fluids:​​ 0.5% fumed silica (Aerosil 200).

​​3. Storage Protocols​​

• ​​Temperature:​​ 4–25°C (no freezing)
• ​​Humidity:​​ Sealed, ​​RH <40%​​
• ​​Antistatic:​​ Grounded containers + 0.01% antistatics (e.g., carbon black)

Conclusion​​

Nanomaterial efficacy correlates directly with ​​dispersion quality​​. Surface modification—enhancing particle-matrix compatibility—is pivotal for overcoming agglomeration bottlenecks.

​​Yanbei Advanced Materials​​ specializes in:

• Nanoscale alloy powders
• High-performance ceramics
• Multi-component high-entropy alloys
  for aerospace, energy, electronics, and additive manufacturing.

​​Core Technologies:​​

• ​​Plasma Rotating Electrode Process (PREP)​​
• Precision gas atomization

​​Product Attributes:​​

• ​​Size control:​​ 50–500 nm
• High sphericity (≥95%)
• Low oxygen content (<100 ppm)
• Narrow size distribution (PDI<0.2)