The international standards and testing methods for precipitated silica are centered around the ISO and ASTM standard systems, focusing on the precise measurement of key performance indicators such as specific surface area, particle size distribution, and chemical composition, ensuring high consistency in product quality across applications in rubber, plastics, coatings, and other fields.
I. Main International Standard Systems
1. ISO International Standards
ISO 5794 series: A complete standard system for precipitated hydrated silica (precipitated silica), where ISO 5794-1 specifies the technical conditions, and ISO 5794-2 describes the identification method in styrene-butadiene rubber.
ISO 1138:2022: The latest revised standard for "Rubber compounding ingredients—Carbon black—Determination of sulfur content," using the combustion furnace method and automatic analyzer method to determine the sulfur content of carbon black.
ISO 19096-1:2016: "Plastics and rubber—Precipitated silica—Testing and analysis protocol," establishing general principles and experimental conditions for precipitated silica testing.

2. ASTM American Standards
ASTM D3765: The most commonly used standard for precipitated silica fineness testing, using the gas adsorption method (BET method) to determine the specific surface area.
ASTM D6602-13(2022)e: The latest version of the "Standard for Sampling and Testing of Carbon Black Emissions," providing scientific guidelines for distinguishing between carbon black and environmental particulate matter.
ASTM D4122: Used for the identification method of standard reference carbon black, which has been modified and adopted by the Chinese standard GB/T 9580-2009.

II. Core Testing Methods and Technical Indicators
1. Specific Surface Area Measurement
Nitrogen adsorption method (BET method): According to GB/T 10722-2014 and GB/T 19587-2017, this is the standard method for measuring the specific surface area of precipitated silica, applicable to conventional precipitated silica in the range of 100-400 m²/g.
CTAB method: Used to measure the specific surface area of precipitated hydrated silica in rubber compounding ingredients. The standard method is given in HG/T 23656-20167. Single-Point Nitrogen Adsorption Method:  The two methods specified in ISO 4652:2020 – automatic gas chromatography (Method A) and automatic volumetric method (Method B) – are used for determining the specific surface area of carbon black for rubber applications.
2. Particle Size and Fineness Analysis
Laser Particle Size Analysis:  Measures particle size distribution using laser scattering technology to ensure particle uniformity.
Sedimentation Method: Primarily used for determining the particle size of precipitated silica larger than 100 micrometers, calculating the average particle size by measuring the sedimentation rate of the material in a liquid.
45μm Sieve Residue Determination:  According to HG/T 3064-2008 standard, controls the particle size of precipitated silica.

3. Chemical Composition Testing
Silicon Dioxide Content Determination:  Using the HG/T 3062-2008 standard, the purity of silicon dioxide is determined by the calcination method.
Heavy Metal Content Detection:  Atomic absorption spectrometry is used to detect the total copper, total manganese, and total iron content to ensure product safety.
Sulfur Content Determination:  According to GB/T 3780.14-2019 (modified from ISO 1138:2007), determined by the combustion furnace method or automatic analyzer method.

4. Physical Properties Testing
Oil Absorption Value Determination: Evaluates the ability of precipitated silica to adsorb oil, an important indicator of rubber reinforcement performance.
pH Value Determination: Measures the pH value of the aqueous suspension using a pH meter, controlling it within the range of 5.0-8.0.
Thermal Stability Testing:  Determines the heating loss (4.0-8.0%) and ignition loss (≤7.0%) using thermogravimetric analysis.

5. Special Performance Evaluation
Nitrogen Adsorption Isotherm Analysis: Used to analyze the pore structure of precipitated silica and determine the pore size distribution.
Surface Hydroxyl Content Analysis:  Analyzes the types of surface hydroxyl groups (isolated hydroxyl groups, adjacent hydroxyl groups, siloxane groups) using infrared spectroscopy, which affects the material's hydrophilicity and adsorption performance.
Dispersibility Test: According to HG/T 2404-2008, evaluates the dispersibility of precipitated silica in rubber to ensure no significant agglomerates. III. Standard Application and Industry Practices
1. Differences in Industry Standards
Precipitated silica: Primarily follows the HG/T 3061-2020 standard, which specifies key indicators such as silicon dioxide content (≥90%), 45μm sieve residue (≤0.5%), and pH value (5.0-8.0).
Fumed silica: Adheres to stricter standards, with a specific surface area typically between 100 and 400 m²/g, and a pore size distribution mainly consisting of mesopores of 2-50 nm.
Bio-based silica for tires: Follows the T/CIEPXXXX—XXXX standard, adding special indicators such as total surface area (105-215 × 10³ m²/kg).
2. Trends in Testing Technology
Multi-method combination: Modern testing tends to combine multiple methods, such as the BET method combined with the CTAB method, to improve the accuracy of specific surface area measurement.
Automated testing: The automatic volumetric method (Method B) has better repeatability than the automatic gas chromatography method (Method A), with a repeatability of ±1.54 m²/g for the N100 series.
Standard updates: International standards are constantly being updated, such as ISO 1138 from the 2007 version to the 2022 version, and ASTM D4122 from the 2006 version to the 2017 version.
3. Key Points of Quality Control
Sample pretreatment: Silica needs to be heated under vacuum at 160℃±10℃ for 120 minutes to ensure complete degassing, avoiding the influence of moisture and impurities on the test results.
Standard reference material: Standard reference carbon black (SRB) is used for equipment verification. Calibration is required when the measured value deviates from the nominal value by more than ±1.2 m²/g.
Stability control: Studies show that silica can maintain its physicochemical properties stably for a long time by simply sealing it in a thick plastic bag and isolating it from air.
IV. Application Fields and Standard Selection Suggestions
1. Standard Focus in Different Application Fields
Rubber industry: Focuses on specific surface area, oil absorption value, dispersibility, and physical and mechanical properties (such as 300% modulus ≥5.5 MPa). Coatings Industry: Focuses on particle size distribution, whiteness, and matting performance; CTAB specific surface area needs to be controlled within 100–210 × 10³ m²/kg.
Food and Pharmaceutical Fields: Strict control of heavy metal content (total copper ≤ 10 mg/kg, total manganese ≤ 40 mg/kg) and microbial limits.
2. Recommendations for Choosing a Testing Agency
Professional Testing Agencies: Such as Beijing Qingxi Technology Research Institute and Shenzhen Huarui Testing Technology Co., Ltd., which provide comprehensive testing services for precipitated silica.
Testing Cycle: The conventional testing cycle is 7-10 working days; expedited services are available upon request.
Selection of Testing Items: Select core items based on product application, such as particle size distribution, specific surface area, pore volume, pore size distribution, and thermal stability.
With technological advancements and application expansion, the precipitated silica standard system will continue to improve. In the future, more emphasis will be placed on multi-performance synergistic evaluation and environmentally friendly indicators, promoting the application of precipitated silica in high-end fields such as new energy, electronics, and medicine. When choosing testing standards, enterprises should combine specific application requirements and prioritize the latest international standards or domestic standards that are aligned with international standards to ensure the international competitiveness of their products.