Selection Guide for Dispersants of Photovoltaic Silicon Wafer Nano-Microsilicon Powder (Particle Size of Crystalline Silicon Nano-Microsilicon Powder 10-200nm)
⚠️Key Prerequisites: Nano-silicon powder has an extremely high specific surface area, making it highly susceptible to oxidation and soft agglomeration. In photovoltaic applications, two key operating conditions need to be distinguished:
① This aqueous-based wire cutting fluid is specifically designed for cyclic cutting systems. Its excellent dispersion stability ensures uniform suspension of silicon powder, effectively inhibiting particle agglomeration, thus preventing scratches on the silicon wafer surface and improving cutting yield.
② Silicon-based slurry (also known as silicon ink) is a functional conductive composite material with silicon as the core functional phase, dispersed in aqueous or alcohol-based solvent systems, specifically used for coating processes.
Note:
1. Due to the strict control of phosphorus impurities in battery manufacturing processes, traditional small-molecule phosphate dispersants that introduce additional phosphorus elements must be discarded.
2. The use of sulfur-containing and heavy metal ion-based additives must be strictly limited.
3. Silicon powder has a weak negative charge on its surface; using cationic dispersants can easily cause particle flocculation due to charge neutralization, therefore, careful selection is necessary.
I. Solvent/Alcohol Systems (Ethanol, Isopropanol, Terpineol systems, anhydrous, prevent silica powder oxidation)
Nano silica powder is prone to oxidation when exposed to water. To maintain its chemical stability, many nano silica slurries use alcohols as dispersion media:
Preferred: Modified polyether and polyester polyurethane superdispersants
Principle: In an anhydrous system, due to the lack of a medium for forming an electric double layer, system stability cannot rely on electrostatic repulsion. Therefore, stable dispersion must be achieved by constructing a steric hindrance layer through the adsorption of polymers on the particle surface.
Recommended Types:
1. Polyurethane superdispersants (RK-4035, RK-4036, RK-4029)
2. Modified polyether long-chain dispersants (alcohol-soluble)
Dosage: 2%–6% of powder (higher dosage for nano silica)
II. Aqueous Systems (Cutting Fluids, Aqueous Silicon Slurry Systems)
Option 1: Comb-shaped Ammonium Polycarboxylate / Modified Polyether Carboxylate Dispersant (Mainstream for Industrial Production)
✅Advantages: Achieves dual stability through the synergistic effect of electrostatic repulsion and steric hindrance, possessing low foaming, shear resistance, and low ionic contamination characteristics; specifically designed for silicon systems with pH 7–9;
Applications: Photovoltaic diamond wire cutting fluids, high-solids-content water-based nano-silicon suspensions
Recommended Dosage: 2.3%–5% of silicon powder mass (nano-silicon powder is higher than micron-sized silicon powder)
Representative Type: Low-foaming ammonium polycarboxylate dispersant (without APEO)
Option 2: Anionic Polyurethane Dispersant (High-end Silicon Ink, Slot Coating Slurry)
✅Advantages: Excellent anchoring properties and long-chain steric hindrance effect achieve good storage stability in high-solids-content nano-silicon systems, and is compatible with ethylene glycol and propylene glycol co-solvent environments.
Suitable for: Water-based conductive silicone slurries, silicon wafer coating inks
References: RK-4057, RK-4039AC water-based polyurethane dispersants
Alternative: Low-foaming block polyether nonionic dispersant (only suitable for simple suspension and temporary low-solids dispersion)
Disadvantages: Dispersants relying solely on steric hindrance have limited anti-settling ability in high-solids-content systems and are usually not used alone as the main dispersant, but rather tend to be compounded with other additives to achieve synergistic stabilizing effects.
❌Not Recommended: Sodium polyacrylate carries the risk of molecular chain breakage and degradation, and foam induction under long-term high-temperature cycling conditions.
III. Differentiating Between Two Easily Confused Scenarios [Key Point]
Scenario A: Silicon Wafer Diamond Wire Cutting Fluid (Water-based Circulating Fluid)
Ideal Combination: Low-foaming modified polycarboxylate dispersant + low-foaming wetting agent
Requirements: Achieve long-term uniform suspension of nano-silicon sawdust, effectively inhibit powder agglomeration and wire marks on the silicon wafer surface, possess good temperature resistance, low-foaming characteristics, and long-term cycling stability;
To avoid heat dissipation failure and workpiece edge chipping due to bubble accumulation during high-speed cutting, easily foaming dispersants should be discarded.
Scenario B: Preparation of Silicon Slurry/Conductive Coating (Coating, Printing) from Nano-Silicon Powder
Preferred: Polyurethane dispersant
Advantages: Good dispersion stability and rheological retention; no particle agglomeration or sedimentation stratification during long-term storage; and maintains good electrical performance consistency after film formation.
IV. Key Points of Practical Process
1. Ideal Feeding Sequence: First, completely dissolve the dispersant in solvent or water, then slowly add the nano-silica powder to achieve sufficient pre-wetting, and finally perform sand milling.
2. To inhibit the agglomeration of nano-silica powder, it is recommended to use a vacuum drying process to effectively remove surface adsorbed water.
3. Determining the Ideal Dosage: In viscosity curve testing, the dosage corresponding to the minimum viscosity value is the ideal dosage.
4. If dispersion is still difficult: It is recommended to pre-treat the powder surface with a silane coupling agent (alcohol-soluble systems are preferred) to improve its wetting properties.
