ISO 3262-8:2023

Overview

ISO 3262-8:2023 - Extenders: Specifications and methods of test - Part 8: Natural clay specifies requirements and corresponding test methods for naturally occurring hydrated aluminium silicates (primarily kaolinite) used as extenders. This second edition updates test references and presents the Andreasen method as the referee procedure for particle-size distribution. The standard covers composition limits, physical fractions, sampling and detailed laboratory procedures needed to demonstrate conformity.

Key topics and requirements

• Scope and definitions - Natural clay defined as hydrated aluminium silicates with lamellar crystal structure (predominantly kaolinite).
• Grades and essential requirements (Table 1) - Typical requirements by grade include:
  • Kaolinite content: Grade A ≥ 90%; Grade B ≥ 85%; Grade C ≥ 70%; Grade D ≥ 50% (by X‑ray diffraction or agreed method).
  • Residue on 45 µm sieve: max 0.02–0.5% depending on grade (ISO 787-7).
  • Particle-size distribution (Andreasen method) - percentage <2 µm: Grade A 90% min; B 70%; C 40%; D 20%.
  • Matter volatile at 105 °C, loss on ignition (specified ranges), matter soluble in water (hot extraction), and pH of aqueous suspension (ISO 787 series and ISO 3262-1 methods).
• Particle-size testing - Andreasen method (Stokes’ law, sedimentation) is the referee method; ISO 8130-13 (laser diffraction) is a conditional instrumental alternative by agreement.
• Sampling and test procedures - Sampling per ISO 15528; detailed apparatus, calibration, temperature control and duplicate determinations for reproducible results.
• Test reporting - Prescribed expression of results and acceptance criteria.

Applications and practical value

ISO 3262-8:2023 is essential for manufacturers, quality laboratories and specifiers who use natural clay extenders in formulations and raw materials for paint, coatings, ceramics, plastics, paper and other industrial products. The standard helps to:

• Ensure consistent particle-size distribution, chemical composition and purity of clay extenders.
• Verify suitability of clay for specific processing and performance requirements (dispersion, opacity, rheology).
• Provide traceable test methods for supplier certification and incoming quality control.

Who should use this standard

• Raw material suppliers and producers of natural clay.
• Quality control and R&D laboratories in coatings, ceramics and polymer industries.
• Procurement and specification engineers requiring standardized test evidence for extenders.

Related standards

• ISO 3262-1 (Introduction and general test methods)
• ISO 8130-13 (Particle size by laser diffraction)
• ISO 787 series (general test methods for pigments and extenders)
• ISO 15528 (Sampling)
• ISO 3696 (Water for analytical use)
• ISO 18451-1 (Terminology)

Keywords: ISO 3262-8:2023, natural clay, extenders, Andreasen method, particle-size distribution, kaolinite, test methods, specifications.