Overview
ISO 8424:2023 - Raw optical glass - Resistance to attack by aqueous acidic solutions - Test method and classification specifies two standardized test methods and a classification system for the acid resistance of raw optical glass. The standard defines a surface method (SR‑S) for polished plate-shaped samples and a powder method (SR‑P) for crushed granular material. Results are used to classify optical glasses according to their susceptibility to aqueous acidic attack.
Key Topics and Requirements
- Two complementary test methods
- Surface method (SR‑S): Polished glass samples are exposed at 25 °C to test solutions (nitric acid, pH ~0.3 or a pH 4.6 buffer). Mass loss before/after immersion is measured to determine the time needed to remove a surface layer of 0.1 µm, yielding an SR‑S class.
- Powder method (SR‑P): Glass is ground to particles 425–600 µm, placed in a platinum basket and boiled >98 °C in a dilute nitric acid solution (c(HNO3)=0.01 mol/L, pH ~2.2) for 1 h. Acid resistance is expressed as percentage mass loss and categorized as SR‑P.
- Classification and designation: Separate notations - SR‑S and SR‑P - avoid ambiguity because results correlate but are not directly convertible.
- Test controls and apparatus: Requirements cover sample preparation (lapping, polishing, cleaning), specific reagents, temperature control, stirrers, baskets, balances and pH calibration. The surface method emphasizes polished-surface assessment; the powder method emphasizes speed and simplicity.
- Selection guidance: The document summarizes pros and cons of each method (e.g., surface method reflects real polished-product conditions; powder method is faster and uses less material).
Applications
- Quality control and acceptance testing of raw optical glass for lenses, prisms, windows and other optical components.
- Material selection and R&D for corrosion-resistant glass formulations used in optics, photonics and precision instrumentation.
- Failure analysis where acid attack or chemical durability is a concern (laboratory optics, medical optics, chemical sensors).
- Supplier specifications and contractual testing to ensure consistent acid resistance performance.
Who Would Use This Standard
- Glass manufacturers and optical component producers
- Quality assurance and testing laboratories
- Materials scientists and R&D teams in optics and photonics
- Procurement/specification engineers and standards committees
Related Standards
Normative references cited include ISO 2768‑1, ISO 3310‑1, ISO 3585, ISO 4797, ISO 4799, and ISO 10110‑8, which cover tolerances, sieves, borosilicate glass, laboratory glassware and optical drawing practices relevant to implementing ISO 8424:2023.
Keywords: ISO 8424:2023, raw optical glass, acid resistance, surface method SR‑S, powder method SR‑P, optical glass testing, aqueous acidic solutions, classification.
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