Overview
ISO 2177:2003 defines a coulometric method by anodic dissolution for measuring the thickness of metallic coatings. The method is applicable only to conductive coatings and can be used on single- and multi-layer systems (for example Cu–Ni–Cr), cylindrical parts and wires. Thickness is determined from the electrical charge (coulombs) required to dissolve the coating in a defined cell area; the end-point is detected by a change in cell potential. Annexes list typical electrolytes and instrument types.
Keywords: ISO 2177, coulometric method, anodic dissolution, coating thickness measurement, metallic coatings, electrolyte.
Key Topics
- Scope and applicability
- Conductive coatings only; multilayer systems and some diffusion/alloy layers can be measured.
- Typical coating/substrate combinations are listed; other combinations require validation of electrolyte and system suitability.
- Principle
- Dissolve a well-defined area anodically and calculate thickness from charge (constant-current/time or integrated current).
- Instrumentation
- Direct-reading and integrator-type instruments; proprietary devices often supplied with recommended electrolytes.
- Instruments must be checked against specimens of known thickness (agreement within ±5% recommended).
- Electrolyte
- Must be chemically stable, wet the test area, dissolve the coating efficiently and give a detectable potential change at penetration.
- Typical electrolytes provided in Annex A; manufacturers may recommend specific solutions.
- Factors affecting accuracy
- Coating thickness limits (accuracy reduced >50 µm and <0.2 µm unless special equipment used).
- Current variation, measuring-area accuracy (gasket wear), agitation, alloy/diffusion layers, coating purity, surface condition, density, and cleanliness of cell/electrical connections.
- Procedure and reporting
- Surface preparation, cell application, controlled electrolysis, post-test examination, expression of results, and uncertainty estimation are defined.
Applications
- Quality control and production inspection in electroplating, galvanizing and surface‑treatment industries.
- Thickness verification for multilayer coatings (e.g., decorative and functional finishes).
- Measurement on curved surfaces, cylindrical specimens and wires where destructive cross-sectioning is impractical.
- Process control, specification compliance, failure analysis and R&D for coating processes.
Who uses it: plating shops, materials engineers, QA/QC laboratories, corrosion specialists, calibration labs and standards bodies.
Related Standards
- ISO 2064:1996 - Definitions and conventions for coating thickness measurement
- ISO 2080 - Surface treatment vocabulary
ISO 2177 is the standard reference for coulometric/anodic dissolution thickness testing and should be used alongside instrument manufacturer guidance and the normative references above.