Overview
ISO 695:1991 - Glass - Resistance to attack by a boiling aqueous solution of mixed alkali - Method of test and classification defines a standardized laboratory test to quantify the alkali (basic) resistance of glass. The standard specifies reagents, sample preparation, test apparatus and temperature control, the test procedure (immersion in a mixed sodium carbonate/sodium hydroxide boiling solution), calculation of mass loss per unit area, classification of results and required test report content. It is applicable to glass and, where indicated, to certain vitroceramics.
Key topics and technical requirements
- Reagents: equal volumes of sodium carbonate solution c(Na2CO3) = 0.5 mol/L and sodium hydroxide solution c(NaOH) = 1.0 mol/L; supporting reagents (acetone, HCl, HF) and distilled or equivalent laboratory water (ISO 3696 quality).
- Samples: two specimens per test, each with total surface area (including edges) between 10 cm² and 15 cm². Edges must be smoothed (no sharp corners); if cutting increases area by >20% a decap (acid etch) procedure is required.
- Apparatus: corrosion-resistant test vessels (silver, silver alloy or specified stainless steel), condenser (Allihn/Liebig), heated bath (glycerol or similar) to maintain bath 110–112 °C while holding test solution at 102.5 °C ± 0.5 °C inside the vessels.
- Procedure: immerse samples in the mixed-alkali boiling solution for 3 h ± 2 min; afterwards rinse, dry at 110 °C for 60 min, cool in desiccator and weigh.
- Result expression: calculate mass loss per unit area (PA) in mg per dm² using:
PA (mg/dm²) = 100 × (m1 − m2) / A
where m1 = initial mass (mg), m2 = final mass (mg), A = total area (cm²). Average the two sample results; repeat if results differ by >10%.
- Classification (after 3 h):
- A1 (low attack): PA ≤ 75 mg/dm²
- A2 (slight attack): 75 < PA ≤ 175 mg/dm²
- A3 (strong attack): PA > 175 mg/dm²
- Precision data: repeatability ≈ 16 mg/dm²; reproducibility ≈ 25 mg/dm².
- Report items: standard reference, sample ID, test condition (as-tested or “as material”), area, PA value (mean), class (A1/A2/A3), and any peculiarities.
Applications and users
ISO 695:1991 is used for:
- Quality control and acceptance testing of laboratory glassware, chemical process vessels and other glass products exposed to alkaline environments.
- Product classification and material specification in glass manufacturing and R&D.
- Comparative testing in materials laboratories and conformity assessments.
Primary users: glass manufacturers, laboratoryware producers, materials testing laboratories, research institutions, and standards/quality engineers concerned with alkali resistance, glass durability, and hydrolytic performance.
Related standards
- ISO 3696 - Water for laboratory use (quality specifications)
- ISO 720 / ISO 719 - Hydrolytic resistance tests for glass (related classifications)
- ISO 4799 - Laboratory condensers (refrigerants) and ISO 683-13 - stainless steel specification for test vessels
Keywords: ISO 695:1991, glass alkali resistance, mixed alkali boiling test, glass testing, test method, classification, mass loss per area, laboratory glassware quality.
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