ISO 3262-20:2021

Overview

ISO 3262-20:2021 - “Extenders - Specifications and methods of test - Part 20: Fumed silica” specifies quality requirements and corresponding laboratory test methods for fumed (pyrogenic) silica used as an extender or raw material. The second edition updates classification, test methods and limits for critical parameters such as silica content, inorganic oxide impurities, carbon and chloride content, loss on ignition and pH. It also defines sampling and analytical procedures to ensure consistent product quality.

Key topics and technical requirements

• Scope: Requirements and test methods specifically for fumed silica (amorphous silica produced by high‑temperature flame hydrolysis).
• Quality grades: The standard distinguishes at least two grades (e.g., Grade A and Grade B) with different limits for certain properties.
• Principal characteristics and limits (examples from Table 1):
  • Silica content: minimum 99.8% (by mass).
  • Oxide impurities: maximums for Al2O3 (~0.05%), TiO2 (~0.03%) and Fe2O3 (~0.003%).
  • Carbon content: criteria differentiating grades (e.g., <0.3% vs ≥0.3%).
  • Chloride content: maximum 0.025%.
  • Residue on 45 µm sieve: max 0.05% (Grade-dependent).
  • Matter volatile at 105 °C: Grade-dependent limits (e.g., max 3% and 1%).
  • Loss on ignition: Grade-dependent limits (e.g., max 2.5% and 10%).
  • pH of aqueous suspension: specified ranges for grades (e.g., ~3.4–4.5).
• Analytical methods described:
  • Silica content by ignition and acid treatment (sulfuric + hydrofluoric acid - HF is hazardous; work in fume hood).
  • Al, Ti, Fe determined by spectrometry (sample preparation, calibration and expression of results).
  • Carbon and chloride determination procedures, loss on ignition and matter volatile at 105 °C.
  • Sampling according to ISO 15528; duplicate determinations recommended for key tests.
• Safety note: Use of hydrofluoric acid requires strict fume hood and safety controls (document includes a warning).

Applications and who uses this standard

• Manufacturers and suppliers of fumed silica for quality control and product specifications.
• Quality laboratories in paints, coatings, adhesives, sealants, rubber, plastics, cosmetics and specialty materials that need to verify raw‑material conformity.
• Procurement and regulatory teams specifying acceptance criteria in contracts and safety/data sheets.
• Ensures consistent performance where fumed silica is used for rheology control, reinforcement, matting or anti‑settling functions.

Related standards

• ISO 3262-1 (general test methods for extenders)
• ISO 15528 (sampling)
• ISO 787 series (general methods for pigments and extenders: volatile matter, pH, tamped volume, residue on sieve)
• ISO 3696 (water for analytical laboratory use)
• ISO 18451-1 (terminology)

Keywords: ISO 3262-20:2021, fumed silica, extenders, test methods, silica content, spectrometry, loss on ignition, chloride content, sampling, quality control.