Overview
ISO 6745:1990 specifies requirements and test methods for zinc phosphate pigments intended for use in corrosion‑inhibiting paints. The standard defines classification by loss on ignition (LOI), required compositional and physical characteristics, and laboratory procedures for determining LOI, zinc content and phosphate content. For phosphate determination the gravimetric (quinoline phosphomolybdate) method is the referee (dispute) method.
Key topics and requirements
-
Classification by LOI (600 °C)
- Type 1: LOI > 8.5% and ≤ 10.0% (m/m)
- Type 2: LOI > 10.0% and ≤ 13.0% (m/m)
- Type 3: LOI > 13.0% and ≤ 16.0% (m/m)
-
Compositional limits (based on ignited test portion)
- Zinc content: approximately 50.5 – 52.0 % (m/m) (expressed for the ignited portion)
- Phosphate content (PO4): approximately 47.0 – 49.0 % (m/m)
-
Other specified characteristics
- pH of aqueous suspension: 6.0 – 8.0
- Minimum resistivity of aqueous extract and particle residue limits (refer to ISO 6745 tables for exact values)
- Conditional requirement: oil‑absorption value not to differ by more than 10% from an agreed reference pigment (when specified)
-
Test methods described
- LOI determined by ignition in a muffle furnace at 600 °C ±20 °C.
- Zinc determined by complexometric titration with EDTA (indicator and pH control).
- Phosphate: gravimetric precipitation of quinoline phosphomolybdate (referee) and an alternative titrimetric method using ion‑exchange resin and NaOH titration. Detailed apparatus, reagent and procedural requirements are provided.
Applications and users
ISO 6745:1990 is primarily useful for:
- Paint and coatings manufacturers specifying or qualifying zinc phosphate corrosion‑inhibiting pigments.
- Pigment producers and suppliers for product specification and batch quality control.
- Analytical and QC laboratories performing compositional and physical testing of pigments.
- Procurement specialists and standards officers requiring traceable test methods and acceptance criteria for anticorrosive coatings.
Keywords: ISO 6745:1990, zinc phosphate pigments, corrosion‑inhibiting paints, loss on ignition, zinc content, phosphate content, gravimetric method, pigment testing.
Related standards
ISO 6745 references several normative documents useful in implementation, including:
- ISO 842 - Sampling raw materials for paints and varnishes
- ISO 3696 - Water for analytical laboratory use
- ISO 787 series - General methods of test for pigments and extenders (pH, density, residue on sieve, oil absorption)
- ISO 4793 - Sintered glass filter crucibles
For procurement or laboratory use, consult the full ISO 6745:1990 text and the referenced ISO documents for complete test procedures and acceptance criteria.
