ISO 5939:1980

Overview

ISO 5939:1980 specifies a standardized method for determining the water content in pitch used for electrodes in aluminium production. This International Standard employs the azeotropic distillation technique, commonly known as the Dean and Stark method, which involves heating pitch under reflux with xylene. The distillate-a mixture of xylene and water-is collected and the volume of separated water is measured. This method is applicable for pitches with water content ranging from 0.1% to 2% by mass (m/m).

Developed by ISO Technical Committee ISO/TC 47 on Chemistry, ISO 5939:1980 ensures precise, repeatable, and reproducible chemical analysis of carbonaceous materials critical in aluminium electrode manufacture. It is essential for maintaining quality control and optimizing electrode performance by accurately measuring water contamination in pitch.

Key Topics

• Azeotropic Distillation (Dean and Stark) Method
  Utilizes heating under reflux with a solvent (xylene) to separate water from pitch. Water volume is then quantitatively measured in a calibrated receiver.

• Scope of Application
  Suitable for pitch samples containing between 0.1% and 2% water by mass. For higher water content, modifications such as using larger receivers are recommended.

• Apparatus Requirements

  • Dean and Stark apparatus with a 500 ml distillation flask
  • Graduated receiver calibrated to 0.05 ml with maximum error ±0.02 ml
  • Reflux condenser designed to minimize water carryover
  • Use of analytical-grade reagents, including xylene or its isomers

• Testing Procedure

  • Sample preparation ensuring representative and moisture-controlled portions
  • Controlled heating to dissolve pitch and maintain drop rate of condensate (2–5 drops per second)
  • Continuous monitoring until water volume stabilizes
  • Accurate volume measurement corrected for receiver calibration errors

• Safety Considerations
  Tests must be performed in well-ventilated areas to minimize operator exposure to toxic xylene vapors.

• Precision and Accuracy

  • Repeatability: ±0.1 g water
  • Reproducibility: ±0.2 g water
    These metrics guarantee trustworthy results in laboratory and industrial settings.

Applications

• Quality Control in Aluminium Production
  Monitoring water content in electrode pitch ensures improved conductivity, mechanical strength, and overall electrode performance.

• Industrial Material Testing
  Enables precise water determination that influences processing parameters and material specifications within carbonaceous electrode materials.

• Research and Development
  Supports formulation adjustments in pitch production to optimize water levels for desired electrode characteristics.

• Environmental and Safety Compliance
  Measuring moisture assists in preventing degradation and safety hazards during handling and processing of carbonaceous materials.

Related Standards

ISO 5939:1980 references and correlates with multiple ISO standards within the realm of carbonaceous materials and water content analysis, including:

• ISO 383 – Laboratory glassware - Interchangeable conical ground joints
• ISO 5940 – Carbonaceous materials - Determination of softening point by the ring and ball method
• ISO 6257 – Carbonaceous pitch - Sampling procedures
• ISO 3733 – Petroleum products and bituminous materials - Determination of water by distillation
• ISO 348, 589, 934, 939, 1015 – Various methods for moisture determination in coals, oils, spices, and other materials using volumetric or azeotropic distillation methods

These related standards provide complementary procedures and apparatus specifications to ensure robust and consistent moisture determination across diverse carbonaceous and industrial materials.

Keywords: ISO 5939:1980, water determination, electrode pitch, carbonaceous materials, aluminium production, azeotropic distillation, Dean and Stark method, xylene reflux, moisture analysis, electrode manufacturing standards, pitch water content testing.