TGA or Thermogravimetric analysis is an advanced analytical technique to characterize materials’ thermal stability and the fraction of volatile components by monitoring the weight change that occurs as a sample is heated at a definite temperature. TGA analysis is very much used in pharmaceutical, food, environmental, and petrochemical applications to determine the composition, purity, decomposition reactions, decomposition temperature, and absorbed moisture content of various samples.
A wide range of material characteristics can be received by a sample to be characterized and kept to a precise temperature under strict atmospheric controls in this instrument. Generally, a sample is heated from ambient to 10000C in atmospheres having controlled humidity and oxygen concentration. As a result, weight loss occurs to the presence of various semi-volatile compounds, polymer degradation, ash content, carbon black, and moisture.
TGA Principle and Procedure
The thermogravimetric analysis gives data for quantitative evaluation of any weight changes in material brought on by a thermally induced transition state. The sample analysis is completed by increasing the temperature in the furnace at a controlled rate in inert or reactive atmospheres as its weight is measured on an analytical balance that remains outside of the furnace. The weight changes at various time intervals are recorded as a function of temperature. The molecular level structure of the tested sample frequently affects the thermally induced reaction rates. The Thermogravimetric analysis analyzer operates in the definite to 1200oC for proper evolution.
The changes of weight in sample material are plotted against temperature or time to explain the thermal transitions in the material for loss of solvent and plasticizers in polymers, hydration of water in inorganic materials, and, finally, decomposition of the sample material. [1]
The result from this analysis can be presented in the following two ways:
TG curve: The weight change of sample material is represented as a function of temperature or time. This curve is very unique for representing the physical changes and the building and breaking of chemical bonds at definite high-temperature ranges, and mass changes result.
TG curve derivative (DTG): The TG curve’s first derivative is plotted against either temperature or time which is known as the pyrolysis curve. DTG analysis curve is generated after plotting the weight change over time (dW/dT) vs temperature. The value of the DTG curve shows zero when no weight loss has occurred. Inflection occurs on the unique TG curve when dW/dT is minimum but not zero value.
TGA Instrumentation
The TGA analyzer mainly consists of a precision balance with a furnace designed to linearly increase the temperature over time. It also contains a sample container, temperature sensor, furnace liner, thermocouple, recorder, computer, a purge system for providing an inert atmosphere, etc.
The sample container is made of platinum which is known as a crucible is used to hold the test sample and is connected to an automatic recording microbalance. The null point balances are the generally used form of the microbalance system because the balance beam can move away from its normal position whenever there is a change in sample weight. All of the weight change deviations can be detected by a sensor and creates a force that will restore the balance to the null position. This restoring force is directly proportional to the weight change in material. [2]
The following points should be remembered at the time of monitoring the test:
It should monitor carefully the weight change of the sample as a function of temperature.
The heating rate of the sample material should be linear.
The sample must be kept in a sample holder in the furnace’s hot zone where a constant temperature should be available.
The balance of this analyzer must be free from corrosive gases and the furnace.
Important information during analysis
Sample size: The weight of the sample should have 50 milligrams during analysis.
Timing: It should maintain an analysis time of about 1 hour for proper evolution.
Types of TGA
There are three types of thermographic analysis are used to apply heat to the sample, as weight change is measured over time which is given below:
Isothermal or static thermogravimetry: In this type of analyzer the temperature remains constant for evolution.
Dynamic thermogravimetry: In this type of analyzer the temperature is changed in a linear manner for evolution.
Quasi-Static thermogravimetry: In this type of analyzer the temperature is changed in a series of ways for evolution.
TGA Applications
Thermal characterization of various polymeric materials, primary and secondary standard substances can be measured by this technique. The purity, corrosion studies, and compositions of alloys and mixtures are identified easily through this analysis. The moisture contents of several inorganic and organic components, industrial raw materials, foods, medications, etc. can be evaluated by TGA analysis. The study of the kinetic of isothermal reactions can understand through this analysis. [3]
Advantages of TGA
TGA is a modern and rapid process for material characterization. It needs a short time for proper analysis through the TGA technique. It can be maintained a fast heating rate with good resolution in this analysis.
Limitations of TGA
The solid sample is only analyzed in the TGA technique. The change in temperature-related issues is a sensitive topic to evaluate the heating rate and sample masses for both qualitative and quantitative analysis.
References
1.Prime, R. B., Bair, H. E., Vyazovkin, S., Gallagher, P. K., & Riga, A. (2009). Thermogravimetric analysis (TGA). Thermal analysis of polymers: Fundamentals and applications, 241-317.
2.Saadatkhah, N., Carillo Garcia, A., Ackermann, S., Leclerc, P., Latifi, M., Samih, S., … & Chaouki, J. (2020). Experimental methods in chemical engineering: Thermogravimetric analysis—TGA. The Canadian Journal of Chemical Engineering, 98(1), 34-43.
