ISO 1690:1976

Overview

ISO 1690:1976 specifies a standardized gravimetric method for the determination of silica content in sodium and potassium silicates used in industrial applications. This international standard, developed by the International Organization for Standardization (ISO), defines a precise laboratory procedure involving acidification, evaporation, filtration, and calcination steps. The method measures silica by isolating the insoluble fraction and quantifying the difference in mass after treatment with hydrofluoric and sulfuric acids.

This gravimetric approach ensures accurate and reproducible silica analysis, essential for quality control and regulatory compliance in industries utilizing sodium and potassium silicates.

Key Topics

• Scope: Determination of silica content specifically in industrial-grade sodium and potassium silicates.
• Principle: Acidification of the test sample followed by evaporation to dryness, dissolution and washing of soluble salts, filtration of insoluble matter, and weight measurement after calcination and acid treatment.
• Apparatus:
  • Platinum crucibles
  • Electric ovens and furnaces with controlled temperature settings
  • Porcelain capsules and filtration equipment
• Reagents:
  • Hydrochloric acid (HCl)
  • Sulfuric acid (H2SO4)
  • Hydrofluoric acid (HF)
  • Nitric acid and silver nitrate for filtration clarity checks
• Procedure Steps:
  • Preparation of the test portion and acidification
  • Evaporation, filtration, and washing of insoluble silica fractions
  • Repetition of evaporation and filtration to ensure completeness
  • Calcination, acid treatment to volatilize silica, and final weighing
• Result Expression: Silica content expressed as mass percentage (% m/m SiO₂), calculated based on the difference in mass before and after acid treatment.
• Precision: Method offers high reproducibility with ±0.2% absolute accuracy in silica content measurement.
• Documentation: Requirements for detailed test reports including methods, results, unusual observations, and any deviations.

Applications

ISO 1690:1976 is critical for industries where sodium and potassium silicates play a vital role, such as:

• Glass manufacturing: Ensuring the correct silica content affects glass quality and properties.
• Detergents and cleaners: Accurate silica determination impacts formulation stability and performance.
• Adhesives and coatings: Silica content controls product durability and adhesion properties.
• Water treatment chemicals: Quality control in the production of silicate-based agents.
• Ceramics and refractory materials: Maintaining specific silica concentrations enhances material integrity.

Implementing this gravimetric standard assists laboratories and quality control units in maintaining consistent product specifications, optimizing industrial processes, and complying with international quality requirements.

Related Standards

ISO 1690:1976 is part of a comprehensive set of ISO standards concerning sodium and potassium silicates, including:

• ISO 1686: Sampling and general testing techniques for sodium and potassium silicates.
• ISO 1687: Determination of density of silicate solutions.
• ISO 1688: Gravimetric method for determining dry matter content.
• ISO 1689: Gravimetric method for calculating Na2O or K2O ratios.
• ISO 1691: Carbonate content determination.
• ISO 1692: Total alkalinity measurement by titrimetric method.
• ISO 2122: Dissolution methods and insoluble matter determination.
• ISO 2123 and 2124: Viscosity and titrimetric silica analysis methods.
• ISO 3200 and 3201: Sulfate and iron determination methods.

These interconnected standards provide a full framework to evaluate, analyze, and control the quality of industrial silicate products.

Adopting ISO 1690:1976 ensures accurate silica content measurement through a reproducible gravimetric process, supporting high-quality production and material consistency across diverse industries working with sodium and potassium silicates.