Purge Gas Effectiveness for Oxygen Removal in Thermogravimetric Analyzers

Introduction

In thermogravimetric analysis (TGA), maintaining a truly inert environment is essential when studying materials prone to oxidation at elevated temperatures. While most commercial TGAs provide sufficient oxygen exclusion for polymer or hydrocarbon testing, more sensitive applications—such as metal oxidation or catalyst studies—require a higher level of oxygen control.

This application note demonstrates how simple, practical tests can verify purge gas effectiveness. It also highlights how AMI’s micro-furnace and dual-purge architecture achieve exceptional oxygen removal without relying on high flow rates or mass flow controllers (MFCs)—reducing both cost and system complexity.

How Much Oxygen Removal Is Enough?

The necessary level of oxygen exclusion depends on the sample. While trace O₂ is tolerable for routine polymer analysis, materials like finely divided metals or sensitive catalysts may oxidize even in low-oxygen environments. For these applications, it is essential that the TGA system:

• Rapidly displaces oxygen during purge
• Maintains a stable inert atmosphere throughout the experiment
• Prevents reintroduction of oxygen during sample loading or cooling

Micro-Furnace + Dual-Purge: A Smarter TGA Design

AMI TGA systems utilize a compact micro-furnace that reduces dead volume and shortens gas paths, paired with a dual-zone purge system:

• Sample zone purge: Directly surrounds the crucible to displace oxygen at the reaction site
• Balance zone purge: Isolates and protects the balance from reactive gases or vapor intrusion

This architecture ensures efficient oxygen exclusion without requiring high flow rates or expensive gas control hardware.

Experimental Validation: Carbon Black Oxidation Test

To validate purge effectiveness, carbon black was used as a sensitive test material:

• Method: A 10 mg sample was held isothermally at 700 °C under flowing inert gas
• Observation: Oxidation of carbon black causes mass loss; minimal loss indicates effective O₂ removal
• AMI Result: <1% mass loss over 30 minutes, confirming stable, oxygen-free conditions using only ~50 mL/min N₂

This test demonstrates the system's ability to maintain an inert environment under thermal stress.

Do You Really Need High Flow Rates or MFCs?

Many systems rely on purge rates of 300+ mL/min, controlled by MFCs, to sweep oxygen from the furnace. AMI’s results show that:

• High flow rates are unnecessary when furnace volume is minimized and purge paths are optimized
• Dual-zone purging is more effective than single-zone high-volume flushing
• Eliminating MFCs lowers cost and simplifies maintenance—without compromising oxygen exclusion

Conclusion

The AMI TGA-1000 proves that superior oxygen control can be achieved through smart system architecture rather than brute-force gas handling. With its micro-furnace and dual-purge design, it offers:

• Excellent purge performance
• Reliable data even for oxygen-sensitive materials
• Lower operational cost and complexity

For labs demanding precision and affordability, AMI provides a powerful and practical solution for high-quality thermal analysis.