Understanding Material Behavior: Thermogravimetric Analysis (TGA)

Introduction

Understanding material behavior is crucial in material science. Thermogravimetric Analysis (TGA)and differential thermogravimetric analysis(DTA) are essential tools in this endeavor. TGA is a thermal analysis technique that measures changes in the weight of a sample as it’s heated, cooled, or held at a constant temperature. The major three types of thermogravimetric analysis are isothermal/static, quasistatic, and dynamic thermogravimetry. It is a powerful tool for characterizing materials and their thermal properties.TGA can analyze various materials, from polymers to metals and ceramics to composites. It’s used in multiple industries, including pharmaceuticals, food, and electronics.

What is Thermogravimetric Analysis (TGA)?

TGA, also sometimes called Thermogravimetric Analysis, is a class of thermal analysis used to study the thermal behaviors of materials. In any one TGA experiment, a small quantity of a sample is usually heated or cooled. The weight of a sample, as a function of time, is recorded, enabling us to observe changes in a sample’s mass as it undergoes thermal transitions. 

Examples of such transitions include

• Evaporation or sublimation (phase transition from solid or liquid to gas).
• Oxidation or reduction (involving loss or gain of oxygen).
• Decomposition (breaking down of compounds into simpler substances).
• Desorption, absorption, or adsorption of gasses.

The Scope of TGA in Material Characterization

TGA plays a crucial role in material characterization. Differential Scanning Calorimetry and Thermogravimetric Analysis are both thermal analysis techniques that measure changes in a sample as its temperature is controlled. TGA provides valuable data on the thermal stability and composition of materials. By monitoring weight changes, TGA can identify different components in a sample. This includes volatile substances, which can evaporate during heating, and inorganic materials, which remain residues after all organic matter has decomposed.

Furthermore, TGA can provide insights into a material’s thermal stability. By observing at what temperatures weight changes occur, we can determine the temperatures at which a material starts to decompose or react. This is vital information for many applications, such as material selection for high-temperature environments.

Working Principle  of TGA

The principle of thermogravimetric analysis is very simple: it measures sample weight while heating, cooling, or keeping the temperature at a constant value. The sample is placed inside a small precision balance incorporated within the TGA. Subsequently, the temperature will be programmed to change with time in a previously set way. Upon heating, the sample might undergo several changes: evaporation, oxidation, reduction, decomposition, etc., where changes in weight for the sample may happen.

The TGA instrument continuously records the sample’s weight. Eventually, this data is plotted against time or temperature to give a TGA curve. In many ways, this can be instructive about the sample’s properties. For instance, temperatures at which significant weight changes occur may indicate the existence of different components or phases in the material.

TGA Instrumentation

The main components comprising a TGA are a high-precision balance that can detect minute changes in the weight of the sample while it undergoes thermal processes.

Another essential accessory is the furnace, which heats the sample at high temperatures, usually up to 1000°C. The temperature control system provides a consistent heating rate according to the pre-designed program.

The last is the sample holder or pan, where we place the sample. Further, we usually make the sample holder from inert material to ensure it does not react with the sample.

TGA vs Other Thermal Analysis Techniques

Every method has unique strengths and applications, which makes it particularly useful for studying decomposition, oxidation, and reduction reactions.

Data and Result

Interpretation of TGA data requires knowledge of the sample’s weight loss events. The TGA curve, a plot of weight loss against temperature, provides this information. Each step in the curve corresponds to a different weight loss event.

These can be events of evaporation, sublimation, chemical reactions, or decomposition. The temperature at which these events take place could provide information about the material’s thermal stability and composition. Along with this TGA curve, one more curve, the derivative thermogravimetric curve, is also common. The DTG curve, which shows the pace of weight reduction, makes finding overlapping weight loss events easier. 

Conclusion

The selection of the proper material for an application involves more than just selecting the strongest or most durable. It also requires an understanding of how various materials can react under different conditions and making the appropriate choice. TGA is a major part of such a process, providing the exact information needed to reach defensible conclusions.

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