Performance Comparison and Application Selection Between Precipitated Silica and Fumed Silica
Performance Comparison and Application Selection Between Precipitated Silica and Fumed Silica
In business negotiations and communications, we often refer to the classification of silica gel as “American Standard,” “European Standard,” or describe it as “complying with FDA standards” or “meeting LFGB standards.” However, such statements are actually inaccurate. Below is a detailed breakdown I have compiled of the two main categories of silica gel raw materials: one is precipitated silica gel (precipitated silica), and the other is fumed silica gel (fumed silica). We can understand these two most commonly used silica gel raw materials from various dimensions. Then, based on our own needs and budget, we can select the appropriate material for product manufacturing to achieve our desired results and objectives.
Supplementary Notes:
- FDA: Short for the U.S. Food and Drug Administration. The standards it formulates are commonly used to regulate the safety of materials that come into contact with food and pharmaceuticals, and are widely recognized globally.
- LFGB: The full name is Lebensmittel-, Tabakwaren-, Kosmetik- und Bedarfsgegenständeverordnung (German Food, Tobacco Products, Cosmetics and Other Daily Necessities Regulation). It is an important regulation for the safety of daily necessities in Europe, especially with strict requirements for materials that come into contact with food.
- Precipitated Silica Gel vs. Fumed Silica Gel: Both are commonly used industrial silica gel raw materials. Their core difference lies in the production process (precipitation method vs. fuming method), which leads to variations in purity, specific surface area, mechanical properties, and other aspects. These differences further affect their application scenarios in different products (such as food-contact utensils, medical supplies, industrial seals, etc.).
Precipitated silica and fumed silica are the two most commonly used types of organosilicon materials. Their core differences stem from the preparation process, which further leads to significant distinctions in structure, performance, cost, and application scenarios. Below is a systematic analysis of the differences between the two from core dimensions, balancing professionalism and practicality:
1. Core Difference: Preparation Process and Raw Materials (Fundamental Distinction)
| Dimension | Precipitated Silica (Precipitated Silica Gel) | Fumed Silica (Fumed Silica Gel) |
| Preparation Principle | Wet process: Using water glass (sodium silicate) as raw material, silica gel precipitate is generated through neutralization reaction with acids (such as sulfuric acid, hydrochloric acid), followed by washing, drying, and crushing. | Dry process: Using halosilanes such as silicon tetrachloride (SiCl₄) as raw materials, nanoscale fumed silica is directly produced through hydrolysis and condensation in a high-temperature (above 1000℃) hydrogen-oxygen flame. |
| Raw Material Cost | Water glass is inexpensive, and the process is simple, resulting in low cost. | Halosilane raw materials are expensive, and the high-temperature reaction consumes high energy, leading to high cost (about 3-5 times that of precipitated silica). |
| Product Form | Larger particles, with aggregated state in “flocculent” or “lumpy” form, requiring crushing and classification. | Extremely small primary particles (nanoscale), with aggregated state in “chain-like” or “network-like” form, no need for crushing, directly in powder form. |
2. Structural Differences: Particle Size, Specific Surface Area, and Pores
1) Particle Size and Dispersibility
- Precipitated Silica: Larger primary particle size (10-100nm), particles tend to agglomerate into large clusters, resulting in poor dispersibility (dispersants are required for uniform dispersion in systems).
- Fumed Silica: Extremely small primary particle size (5-50nm), particles agglomerate in a chain-like structure. After dispersion, they can form a three-dimensional network structure, achieving excellent dispersibility (especially in organic systems).
2) Specific Surface Area and Pores
- Precipitated Silica: Smaller specific surface area (100-400 m²/g), low porosity, and larger, uneven pore size.
- Fumed Silica: Large specific surface area (100-400 m²/g, up to over 600 m²/g for high-grade products), high porosity, small and uniform pore size, and more surface active groups (-OH).
3) Structural Stability
- Precipitated Silica: Loose aggregated structure, low mechanical strength, and easy decomposition and agglomeration at high temperatures.
- Fumed Silica: Stable chain-like aggregated structure, which can maintain dispersibility at high temperatures (≤500℃) and is not prone to structural collapse.
3. Key Performance Differences (Directly Affecting Applications)
| Performance Dimension | Precipitated Silica | Fumed Silica |
| Reinforcement Performance | Moderate: When used in rubber and plastics, it can improve hardness and wear resistance, but the elastic retention is poor. | Excellent: The chain structure can form “physical cross-linking points”, significantly improving the tensile strength and tear strength of rubber/plastics without losing elasticity. |
| Thickening Thixotropy | Weak: Poor thickening effect on liquid systems (such as coatings and adhesives), and insignificant thixotropy (thickening at rest, thinning under stirring). | Strong: A small amount of addition (0.1%-5%) can significantly increase the viscosity of the system, with excellent thixotropy (preventing flow and improving workability). |
| Light Transmittance | Poor: Particle agglomeration causes light scattering, and products tend to turn white and have low light transmittance after addition. | Good: Nanoscale particles disperse uniformly, causing weak light scattering, which enables the preparation of high-light-transmittance products (such as transparent silica gel and optical coatings). |
| High and Low Temperature Resistance | Average: Long-term service temperature ranges from -50℃ to 200℃, and it is prone to aging at high temperatures. | Excellent: Long-term service temperature ranges from -60℃ to 300℃, with strong high-temperature stability, resistance to aging and yellowing. |
| Compatibility | Average: Poor compatibility with organic systems (such as oils and resins), requiring modification. | Good: Surface active groups are easy to combine with organic molecules, with excellent compatibility, and can be used in most organic systems without modification. |
4. Differences in Application Scenarios (Selection Based on Needs)
1) Precipitated Silica: Cost-Effective Choice, Focusing on Basic Functions
- Rubber Industry: Tires (tread, sidewall), seals, conveyor belts, etc. (improving wear resistance, reducing costs, no need for high elasticity);
- Plastic Modification: Filler for general plastics such as PVC and PP (improving hardness and heat resistance, reducing raw material costs);
- Coatings/Inks: Matting agent and filler for architectural coatings and industrial coatings (reducing costs, with low requirements on light transmittance and workability);
- Daily Necessities: Abrasive in toothpaste, filler in cosmetics (low cost, no need for high dispersibility);
- Others: Adsorbents (such as food desiccants), catalyst carriers (low requirements on structural stability).
2) Fumed Silica: High-End Scenarios, Focusing on High Performance
- Silica Gel Products: High-temperature vulcanized silica gel (HTV), liquid silica gel (LSR), such as baby pacifiers, medical catheters, high-temperature resistant seals (requiring high elasticity, high light transmittance, and resistance to high and low temperatures);
- High-End Coatings/Inks: Automotive original paint, optical coatings, UV-curable inks (requiring high thixotropy, high light transmittance, and aging resistance);
- Adhesives/Sealants: Silicone adhesives, epoxy adhesives (improving bonding strength and thixotropy, preventing flow, and adapting to high and low temperature environments);
- Electronic Materials: LED packaging adhesives, thermal conductive silica gel pads (requiring high insulation, high light transmittance, and high temperature resistance);
- Others: Thickening stabilizers in cosmetics (such as liquid foundation, sunscreen) (improving skin feel and preventing stratification), aerospace sealing materials (resistant to extreme environments).
5. Summary: How to Choose?
| Selection Criterion | Prefer Precipitated Silica | Prefer Fumed Silica |
| Cost Budget | Limited, pursuing cost-effectiveness | Sufficient, pursuing high performance |
| Core Requirement | Basic filling, wear resistance, low cost | High reinforcement, high thixotropy, high light transmittance, resistance to high and low temperatures |
| Product Requirement | Low requirements on elasticity, light transmittance, and stability | High elasticity, high light transmittance, aging resistance, and application in extreme environments |
| System Type | General rubber, plastics, ordinary coatings (low-cost systems) | Silicone rubber, transparent products, high-end coatings/adhesives (high-performance systems) |
Supplementary: Cross-Application of Modified Products
- Modified Precipitated Silica (e.g., silane modification): Can improve compatibility with organic systems, and is used in mid-end coatings and rubber, balancing cost and performance;
- Modified Fumed Silica (e.g., hydrophobic modification): Can be used in oil-based systems and flame-retardant materials, further expanding high-end scenarios (such as thickeners for high-end lubricating oils).
In short, precipitated silica focuses on “low cost and basic functions”, while fumed silica focuses on “high performance and high-end scenarios”. The selection should be accurately matched with the cost budget and the core performance requirements of the product.
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