ISO 3262-18:2023

Overview - ISO 3262-18:2023 (Precipitated sodium aluminium silicate)

ISO 3262-18:2023 is an international standard in the ISO 3262 series that defines specifications and test methods for precipitated sodium aluminium silicate, an amorphous silicate produced by reacting sodium silicate with mineral acid and/or an aluminium salt. The document sets essential quality criteria, sampling rules and laboratory procedures to assess chemical composition, physical properties and suitability as an extender in pigments, paints, coatings, rubber and related materials.

Key topics and requirements

The standard covers both requirements and validated test methods, including:

• Essential characteristics and limits (see Table 1)

  • Silica (SiO2) content: minimum 75% (determination by acid treatment, ignition and mass loss)
  • Oxide content: Na2O and Al2O3 ranges (Na2O ≈ 3–10% mass fraction; Al2O3 ≈ 5–15% mass fraction)
  • Residue on 45 µm sieve: maximum 2% mass fraction
  • Lightness: minimum 95% (test method in preparation)
  • Matter volatile at 105 °C: max 10% (ISO 787-2)
  • Loss on ignition: 3–12% (ISO 3262-1)
  • Oil absorption value: minimum 70 g/100 g (ISO 787-5)
  • pH of aqueous suspension: 7–12 (ISO 787-9)

• Analytical test methods

  • Silica determination: repeat acid digestion, drying at 140 °C, ignition at 1000 °C, HF treatment to volatilize silicon tetrafluoride - silica calculated from mass loss (includes repeatability/reproducibility guidance).
  • Composition by spectrometry: preparation of standard-matching solutions and spectrometric measurement for Si, Al, Na; conversion to oxide content.
  • Residue on sieve: standardized sieving procedure and expression of results.
  • Sampling: representative sampling per ISO 15528.

• Conditional requirements

  • Particle size distribution and specific surface area (to be agreed between parties; specific surface area referenced to ISO 5794-1:2022, Annex D).

Applications and users

ISO 3262-18:2023 is intended for:

• Manufacturers and suppliers of precipitated sodium aluminium silicate and extenders for paints, coatings, inks and rubber compounds.
• Quality control laboratories performing routine acceptance testing and batch release.
• Formulators and R&D teams who need consistent raw material specifications for pigment/extender performance (dispersion, opacity, rheology).
• Procurement and compliance teams requiring standardized product specifications for supplier contracts.

Practical uses include material specification, supplier qualification, comparative testing and ensuring consistent performance in coatings, adhesives and rubber compounding.

Related standards

• ISO 3262-1 (general test methods for extenders)
• ISO 787 series (ISO 787-2, -5, -9) - general test methods for pigments and extenders
• ISO 15528 (sampling)
• ISO 3696 (water for laboratory use)
• ISO 5794-1:2022 (precipitated silica tests)
• ISO 18451-1 (terminology)

Keywords: ISO 3262-18:2023, precipitated sodium aluminium silicate, extenders, silica content test, oxide content, sieve residue, oil absorption, spectrometry, pigment standards.