ISO 9689:1990

Overview

ISO 9689:1990 specifies a standardized test method and classification for the resistance of raw optical glass to attack by aqueous alkaline phosphate-containing detergent solutions at 50 °C. The procedure measures mass loss and calculates the time required to etch a surface layer to a depth of 0.1 µm, then assigns a phosphate resistance (PR) class. The method is intended for raw optical glasses and can be applied to other glass types.

Key topics and technical requirements

• Test solution: prepared from purified sodium tripolyphosphate to give approximately 0.01 mol/L phosphate; pH adjusted to 10 ± 0.1 (at 20 °C).
• Test temperature: 50.0 ± 0.2 °C with stirring (typical stirrer speed 100 r/min).
• Samples: annealed, polished specimens (nominally 30 × 30 × 2 mm); fine grinding and polishing procedures are specified to ensure reproducible surface finish.
• Cleaning and handling: ultrasonic cleaning sequence, use of isopropyl alcohol and nitric acid rinses, desiccation and weighing to ±0.1 mg accuracy. A minimum of two samples per test is required.
• Measurement principle: determine mean mass loss (m1 − m2), use the glass density and the total surface area to calculate the time needed to produce a 0.1 µm etched depth. This calculated time determines the phosphate resistance class (PR) using the classification table in the standard.
• Visual evaluation: post-test surface changes are reported qualitatively (no visible change; irregular/pitted; staining/interference colours; tenacious whitish layer; loose thick deposit).
• Apparatus: stainless-steel test vessel, thermostatically controlled heating bath, PTFE or stainless stirrer, analytical balance, ultrasonic cleaner, pH electrode.

Applications and who uses it

ISO 9689:1990 is practical for:

• Optical glass manufacturers - quality control and material selection for lenses, prisms and precision components.
• Materials testing laboratories - routine chemical durability testing and classification of raw optical glass batches.
• R&D teams - comparing formulations and processing effects on phosphate/detergent resistance.
• Purchasing and specification engineers - specifying glass materials with required resistance to alkaline phosphate detergents used in cleaning processes.
• Suppliers of cleaning agents and process engineers - evaluating interactions between detergent chemistries and optical glass surfaces.

Keywords: ISO 9689:1990, raw optical glass, phosphate resistance, tripolyphosphate, detergent solutions, test method, classification, chemical durability, 50 °C.

Related standards

• ISO 9802 (Raw optical glass - Vocabulary)
• ISO 3585 (Borosilicate glass properties)
• ISO 3696 (Water for analytical laboratory use)
• ISO 2768-1 (General tolerances)
• International Commission on Glass (ICG) test-method background and chemical durability work