Oxygen and Nitrogen Determination in Refractory Metals and Their Alloys

Importance of the Topic

Titanium and related refractory metals rely on precise control of interstitial oxygen and nitrogen to balance strength, ductility, and corrosion resistance. Excess levels can embrittle surfaces, while controlled additions improve hardness and wear properties. Accurate, simultaneous measurement of these elements is essential for aerospace, medical, and military applications where material performance and safety are paramount.

Aims and Overview

This application note presents a validated procedure using the LECO ON736 inert gas fusion analyzer for simultaneous determination of oxygen and nitrogen in titanium and other refractory alloys. The method conforms to ASTM E1409 and E1569 standards and supports stringent quality requirements in advanced manufacturing and research laboratories.

Methodology

The inert gas fusion technique involves melting the sample in a graphite crucible under an inert helium atmosphere. Oxygen is detected by infrared absorption, and nitrogen by thermal conductivity. Key steps include:

• Sample preparation: chemical etching or mechanical abrasion, solvent rinsing, and drying to remove surface contaminants.
• Blank determination: repeated runs without sample to establish instrument baseline.
• Calibration: analysis of certified reference materials across three replicates to correct drift.
• Sample analysis: consistent weighing (0.10–0.15 g), addition of graphite powder flux, and automated or manual furnace cycles.

Instrumentation

• LECO ON736 simultaneous oxygen/nitrogen analyzer
• Graphite crucibles (782-720)
• Nickel baskets (502-344) or capsules (502-822) for powders and chips
• Graphite powder flux (501-073) and nibbled nickel flux (501-598)
• Optional autoloader, electrode tips, and cleaning accessories

Main Results and Discussion

Testing on standard reference materials and real-world samples (titanium pins, zirconium pins, molybdenum rods, tantalum sheets, tungsten chips, and alloy powders) demonstrated:

• Oxygen accuracy within ±0.005 % and nitrogen precision below ±0.0005 % N.
• Standard deviations typically below 0.002 % O and 0.0008 % N for powders.
• Optimized helium carrier gas parameters (power, integration times) ensuring rapid analysis; argon use requires longer integration and reduced power.

Benefits and Practical Applications

This method offers rapid, simultaneous O/N determinations with automated sequences, minimizing operator error. It supports:

• Quality control in alloy production and certification.
• Failure analysis where interstitial contamination may impact mechanical properties.
• Research and development of new refractory materials.

Future Trends and Potential Applications

Emerging developments may include deeper automation integration, enhanced calibration routines for novel alloys, and expansion of inert gas fusion to measure additional interstitials such as hydrogen and carbon. Coupling with digital laboratory management systems can streamline data handling and traceability.

Conclusion

The LECO ON736 inert gas fusion approach delivers a reliable, ASTM-compliant solution for simultaneous oxygen and nitrogen analysis in refractory metals and alloys. Its high precision, robust calibration, and flexibility across sample types make it an indispensable tool for industries demanding exacting material specifications.