Thermogravimetric analysis (TGA) has become an indispensable tool for determining the loss on ignition (LOI) in solid combustion residues such as biomass ash, coal ash, and cement residues.
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LOI is a key parameter for assessing the quality and usability of these residues. This parameter refers to the mass loss when the sample is heated to high temperatures, around 750–950 °C, in an air or oxygen atmosphere.
This article looks at the principles, methodologies, and benefits of using TGA for LOI determination.
Principles of Thermogravimetric Analysis for LOI
TGA involves continuously measuring a sample’s mass as it is heated under controlled conditions. The process begins by heating the sample in an inert atmosphere like nitrogen (N2) to remove moisture.
The sample is then switched to an oxidizing atmosphere, such as oxygen (O2), before being heated to the target temperature (750 °C or 950 °C). The mass loss measured during this phase indicates the LOI value, which results from the decomposition of minerals and the combustion of unburned carbon.
TGA Instruments and Their Operation
The current generation of TGA instruments enables the simultaneous automated analysis of multiple samples, reducing human error and considerably increasing throughput versus traditional manual methods. These instruments precisely control atmosphere and temperature, ensuring reproducible and consistent results.
The typical process of determining LOI via TGA involves:
- Initial heating in an inert atmosphere such as N2 to eliminate moisture content
- Transition to an oxidizing atmosphere by switching to an oxidizing environment like O2 to initiate the decomposition of minerals and combustion of residual carbon
- Heating to the target temperature of either 750 °C or 950 °C, depending on the sample being analyzed
- Measurement and recording of mass loss during the heating process, corresponding to the LOI value
Advantages of TGA for LOI Determination
TGA offers several benefits over conventional LOI methods, making it the preferred choice in a wide range of industries.
Accuracy
TGA provides accurate LOI values by accounting for carbonate decomposition and mineral dehydration. There is a risk of conventional methods overlooking these factors, potentially resulting in less precise measurements.
Efficiency
Automated TGA instruments have the capacity to simultaneously analyze multiple samples, significantly reducing the time and labor required for LOI determination.
Detailed Analysis
TGA enables differentiation between different components contributing to mass loss, for example, elemental carbon, organic carbon, and mineral decomposition.
Precision
TGA’s precise temperature regulation and controlled environment ensure high reproducibility of results by minimizing errors associated with manual methods.
Challenges and Considerations
TGA offers improved accuracy and efficiency, but it is important to recognize that mass loss in TGA cannot be attributed solely to carbon oxidation.
For instance, the dehydration of portlandite (Ca(OH)2) contributes to weight loss in the same temperature range (250 °C to 500 °C), meaning that interpreting TGA results necessitates careful consideration of all possible reactions taking place throughout the analysis.
Automated TGA instruments like XRF Scientific’s advanced xrTGA 1100 offer a pioneering solution for loss on ignition determination in solid combustion residues.
These instruments provide accurate, rapid, and efficient analyses, and underpin industries dependent on precise material assessments. The xrTGA 1100 supports a wide range of product improvements and industrial processes by providing detailed insight into the quality and composition of materials like biomass ash, coal ash, and cement residues.
The xrTGA 1100’s high precision and reliability make it an invaluable tool, reinforcing XRF Scientific’s commitment to driving innovation in the industry and improving material testing methodologies.
This information has been sourced, reviewed, and adapted from materials provided by XRF Scientific.
For more information on this source, please visit XRF Scientific.