CCQM-GAWG Task Group on Passivation Chemistry (CCQM-GAWG-TG-CPCHEM)

Terms of Reference

The task to establish the state of the art in gas cylinder passivation techniques for calibration gas mixtures

Goals of the Task Group

a) Knowledge Collation

• Objective: To document the current knowledge of adsorption, desorption, and reactive changes in low amount fraction gas mixtures in high-pressure gas cylinders, including greenhouse gases (GHGs), VOCs, NH₃, NO₂, and other reactive species.
• Approach: Collect and analyze published data, expert experience, and stakeholder feedback to establish a comprehensive overview of current practices and the state of the art.
• Output: Publish review papers in Metrologia and contribute a dedicated chapter to the Guidance Document on Cylinder Passivation.

b) Modeling and Theoretical Understanding

• Objective: To connect modeling and theoretical approaches that help explain and predict adsorption, desorption, and other processes affecting gas component stability in compressed gas cylinders.
• Approach: Review and summarize existing models, identify gaps and limitations, and provide recommendations for model validation and experimental needs.
• Output: Publish review papers related to modeling and theoretical understanding of gas component stability in Metrologia and contribute a dedicated chapter in the Guidance Document on Cylinder Passivation.

c) Optimization of Passivation Strategies for Gas-Specific Stability

• Objective: To identify and establish optimal passivation techniques, cylinder materials, and surface treatment methods that ensure the stability of low amount fraction gas mixtures for different gas species.
• Approach:
  • Based on the outcome of Goal a), review existing knowledge and data on passivation techniques, cylinder materials, and surface treatments applied to various gas species (e.g., CO₂, CO, NO₂, NH₃, VOCs, etc.).
  • Evaluate the effectiveness of different passivation and cylinder types (e.g., stainless steel, aluminum, nickel-treated, or glass-lined cylinders) and determine the most suitable combination for each gas species to achieve long-term stability at low amount fractions.
  • Where necessary, conduct collaborative experimental studies with NMIs and stakeholders (e.g., specialty gas producers, cylinder manufacturers, and reference material users) to validate and characterize passivation performance and cylinder compatibility.
• Output: A comprehensive summary of optimized passivation methods, cylinder materials, and surface treatments by gas species, including experimental findings and jointly developed recommendations with NMIs and stakeholders, to support long-term stability of gas mixtures for inclusion in the Guidance Document on Cylinder Passivation.