LOI in Combustion Residues (TGA801)

Significance of the Topic

Thermogravimetric analysis (TGA) determination of Loss on Ignition (LOI) in combustion residues is essential for quality control in cement manufacture and other industries that reuse by-products of combustion. Accurate quantification of moisture and residual volatiles supports process consistency, material certification, and regulatory compliance.

Objectives and Study Overview

This application note demonstrates a robust macro-TGA method for sequentially measuring moisture content, LOI, and net LOI on combustion residues following ASTM D7348. The primary goals are to:

• Establish temperature ramps and holds for moisture removal (25–110 °C), initial LOI (110–500 °C), and final LOI (500–950 °C).
• Validate method repeatability across multiple sample replicates.
• Provide clear calculation steps for moisture, LOI, and LOI-dry values.

Methods and Instrumentation

Sample Preparation:

• Fine powder sieved to –60 mesh.
• Sample mass targeted at ~1.0 g (range 0.8–1.2 g).

Thermogravimetric Method Parameters:

• Instrument: LECO TGA801 macro balance with dual-furnace option.
• Atmospheres: Nitrogen for moisture step, oxygen for LOI steps.
• Gas flow: 10 L/min constant.
• Temperature program:
  
  • Moisture removal: 25→110 °C at 6 °C/min, hold 5 min.
  • First LOI: 110→500 °C at 6 °C/min, hold 5 min.
  • Final LOI: 500→950 °C at 8 °C/min, no hold.
• Data collection until constant weight (constancy window 9 min, level 0.0005 g).

Used Instrumentation

• LECO TGA801 Thermogravimetric Analyzer with dual furnaces.
• Large ceramic crucibles (621-331) and double-ended scoops (621-011-507).

Main Results and Discussion

Ten replicate analyses of fly ash samples yielded:

• Average moisture: 0.17 % (s = 0.02 %).
• Average LOI: 2.10 % (s = 0.03 %).
• Average LOI-dry: 1.93 % (s = 0.03 %).

The low standard deviations demonstrate high reproducibility. Dual-furnace operation reduced sample throughput time without compromising accuracy. Observed batch differences were within acceptable quality limits, confirming method robustness.

Benefits and Practical Applications

The described TGA-based LOI protocol offers:

• Rapid, automated determination of moisture and volatile content in heterogeneous residues.
• Enhanced precision from gram-scale sampling and controlled atmospheres.
• Compliance with international standards (ASTM D7348).
• Applicability to cement raw material characterization, waste valorization, and environmental monitoring.

Future Trends and Opportunities

Advancements likely to shape LOI analysis include:

• Integration of evolved gas analysis (EGA) for compositional insights.
• Automated sample handling and data processing for higher throughput.
• Miniaturized TGA platforms for field-deployable quality checks.
• Machine-learning algorithms to predict material behavior from TGA profiles.

Conclusion

The macro-TGA method on the LECO TGA801 provides a validated, reproducible approach for sequential moisture and LOI measurements in combustion residues. Its adherence to ASTM D7348 ensures reliable quality assessment for industrial and environmental applications.

References

• ASTM D7348 Standard Test Methods for Loss on Ignition (LOI) of Solid Combustion Residues.
• LECO Corporation. Application Note: LOI in Combustion Residues, Form No. 203-821-587, 2019.