Determination of Oxygen and Nitrogen in Reactive/Refractory Metals and Their Alloys*

Significance of the Topic

Trace oxygen and nitrogen levels critically influence the mechanical properties, corrosion resistance, and structural integrity of reactive and refractory metals such as titanium, zirconium, tungsten, molybdenum, tantalum, niobium, and hafnium. Reliable quantification of these interstitial elements is essential for quality control in aerospace, nuclear, biomedical, and industrial applications.

Study Objectives and Overview

This application note describes a validated protocol using the LECO TC500 inert gas fusion analyzer for simultaneous determination of oxygen and nitrogen in reactive and refractory metals and their alloys. It outlines sample preparation, instrument set up according to ASTM standards E-1409, E-1569, and E-1937, calibration procedures, and method performance.

Methodology and Instrumentation

• Sample Preparation: Samples are cleaned by acid leaching or abrasion, rinsed with acetone, and dried with warm air to remove surface contaminants.
• Accessories: 782-720 graphite crucible, 782-721 electrode tip, 502-344 ultra high purity nickel baskets, 501-073 graphite powder, 503-032 glass accelerator scoop, and 501-059 tin capsules for powdered materials.
• Calibration Standards: LECO titanium and zirconium pins or NIST reactive and refractory metal standards.
• Instrument Parameters:
  • Outgas Cycles: 2
  • Analysis Delay: 20 seconds
  • Furnace Power: 6300 W outgas, 5300 W analysis
  • Timer Settings for Oxygen and Nitrogen detection
• Theory of Operation: Inert gas fusion in helium releases oxygen as carbon monoxide and nitrogen as molecular nitrogen. The carbon monoxide is oxidized to carbon dioxide for infrared detection, while nitrogen is measured by thermal conductivity after removal of carbon dioxide and water.

Key Results and Discussion

Typical analyses of titanium and zirconium reference materials demonstrate high precision. In ten replicate measurements of titanium pins, average oxygen was 0.1830% (plus/minus 0.0012% standard deviation) and nitrogen was 0.0190% (plus/minus 0.0004% standard deviation). Zirconium wire results showed 0.1251% oxygen (plus/minus 0.0018% standard deviation) and 0.0018% nitrogen (plus/minus 0.0002% standard deviation). These results confirm the reproducibility and sensitivity of the method at low part per million levels.

Benefits and Practical Applications

• Rapid and fully automated analyses reduce operator intervention and improve throughput.
• Low sample mass requirements preserve valuable materials.
• Compliance with ASTM standards ensures data acceptance in regulated industries.
• Applicable across a broad range of reactive and refractory metals for quality control, research and development, and production monitoring.

Future Trends and Opportunities

Advancements may include integration of multielement detection capabilities, enhanced sensitivity through improved gas purification, miniaturized fusion cells for field deployment, and connectivity to laboratory information management systems for streamlined data handling. Data analytics and machine learning could further optimize calibration and predict material performance.

Conclusion

The LECO TC500 inert gas fusion method provides a robust, accurate, and efficient solution for quantifying oxygen and nitrogen in reactive and refractory metals. This protocol meets rigorous ASTM requirements and offers excellent precision and reproducibility for critical material characterization.

References

• ASTM E 1409 Standard Test Method for Determination of Oxygen Content in Titanium and Titanium Alloys
• ASTM E 1569 Standard Test Method for Determination of Oxygen Content in Tantalum
• ASTM E 1937 Standard Test Method for Determination of Nitrogen Content in Titanium and Titanium Alloys