Fumed Silica Products: Technical Analysis, Applications, and Quality Control - Enhancing Performance Through Precision Surface Modification and Dispersion Stability - NetEase

创建于02.27

Technical Analysis of Fumed Silica Products

I. Basic Characteristics and Preparation Process

Fumed silica (CAS No.112945-52-5) is a nanoscale powder material generated by the high-temperature hydrolysis (at 1800℃) of silicon tetrachloride or methyltrichlorosilane in a hydrogen-oxygen flame. The typical physical parameters are as follows:

Primary particle size: 7-40nm (measured by laser particle size analyzer)
Specific surface area: 50-380m²/g (measured by the BET method)
Bulk density: 30-60g/L
Purity: SiO₂≥99.8% (detected by XRF)

Its three-dimensional dendritic structure is formed by the aggregates (Aggregates) of molten primary particles (Primary particles) through hydrogen bonding, and further forms a flocculent network through physical adsorption (Figure 1).

II. Technical Classification Standards

According to GB/T 32678-2016, it is classified into:

Hydrophilic type (Type A)

• Density of surface hydroxyl groups: 2.5-3.5 per nm² (measured by acid-base titration)

• pH value: 3.6-4.3 (10% aqueous dispersion)

• Oil absorption value: 2.5-3.5g/100g (ASTM D281)

Hydrophobic type (Type B)

• Surface treatment agent: Hexamethyldisilazane/Dimethyldichlorosilane

• Contact angle: ≥120° (dynamic wetting method)

• Carbon content: 0.5-5.0% (elemental analysis)

III. Key Functional Characteristics

Reinforcing Effect

In silicone rubber, adding 15phr of fumed silica can increase the tensile strength from 0.5MPa to 12MPa (GB/T 528). The reinforcing mechanism involves:

Physical entanglement: The three-dimensional network structure restricts the movement of chain segments.
Chemical adsorption: The surface silanol groups form hydrogen bonds with the polymer.

Thixotropic Property

In coatings, with an addition amount of 0.5-2.0%, it can achieve:

Thixotropic index (TI): 2.5-5.0 (measured by a rotational viscometer)
Anti-sag value: ≥250μm (ASTM D4402)

Adsorption Characteristics

There is a linear relationship between the specific surface area and the adsorption capacity:

When S = 380m²/g, the DBP absorption value reaches 320g/100g (ASTM D2414).

IV. Typical Application Technical Parameters

Reinforcement of Silicone Rubber

Addition amount: 8-20wt%
Reinforcement effect: Tear strength is increased by 5-8 times (ASTM D624)

Anti-sedimentation of Coatings

Recommended addition amount: 0.3-1.5%
Storage stability: ≥12 months (without hard sedimentation)

Anti-caking in Food

Permissible addition amount: ≤2% (GB 2760)
Angle of repose: ≤35° (to improve fluidity)

V. Surface Modification Technology

In-situ Modification

Introduce silane coupling agents (such as KH-550) at the synthesis stage:

Modification temperature: 800-1000℃
Grafting rate: 70-85% (measured by TGA)

Post-treatment Modification

Parameters of the wet process:

Solvent: Ethanol/water (volume ratio 7:3)
Reaction temperature: 60-80℃
Modification time: 4-6h

VI. Key Points of Quality Control

Ignition loss: ≤2.0% (105℃×2h)

Residue on sieve (45μm): ≤0.04% (wet sieving method)

Chloride content: ≤100ppm (potentiometric titration method)

Total heavy metal content: ≤50ppm (ICP-OES)

(Data sources: GB/T 20020-2013, ISO 18473-3:2018, Cabot product technical white paper)

This material can precisely meet the rheological requirements of different application scenarios by adjusting the specific surface area (Figure 2), the type of surface groups, and the degree of agglomeration. The current technological development focuses on precise surface modification and the improvement of dispersion stability, promoting its application expansion in emerging fields such as coating for new energy battery separators and 3D printing materials.

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