Difference Between TGA DTA and DSC

Main Difference – TGA vs DTA vs DSC

TGA, DTA, and DSC are three terms used to describe the analysis of compounds that take part in chemical reactions using changes in temperature of these compounds. TGA stands for Thermal Gravimetric Analysis, and DTA stands for Differential Thermal Analysis while DSC stands for Differential Scanning Calorimetry. All these three techniques are types of thermal analysis. The main difference between TGA DTA and DSC is the method of measuring the changes in samples that are caused by heat. In TGA, the change in mass of the sample is measured with the increasing temperature while, in DTA, the temperature difference that builds up between the sample and a reference is measured and in DSC, the heat released during a chemical process is measured.

Key Areas Covered

1. What is TGA
      – Definition, Method of Analysis, Applications
2. What is DTA
      – Definition, Method of Analysis, Applications
3. What is DSC
      – Definition, Method of Analysis, Applications
4. What is the Difference Between TGA DTA and DSC
      – Comparison of Key Differences

Key Terms: Differential Scanning Calorimetry, Differential Thermal Analysis, DSC, DTA, TGA, Thermal Analysis, Thermal Gravimetric Analysis

What is TGA

TGA is Thermal Gravimetric Analysis. It is a thermal analysis technique. Here, the change of the mass of a sample is observed and analyzed with the change of the temperature. This can also be measured as a function of time at a constant temperature. This method is commonly used for the analysis of sample purity, carbonate and organic matter content in the sample, etc.

The substances that can be analyzed using this technique include inorganic materials, metals, polymers, plastics, ceramics, glasses and composite materials. The device that is used for this purpose is called Thermogravimetric analyzer. It measures the mass of the sample continuously with the change of temperature. The basic parameters that are measured from TGA are mass, temperature and time.

Figure 1: A thermogram showing the change of mass of a substance at different temperatures.

In order to take accurate measurements, the temperature is gradually increased or decreased and the mass is measured continuously. The analysis can be done at different atmospheric conditions such as normal atmospheric conditions and at vacuum.

TGA can be used to evaluate the thermal stability of substances. Sometimes it is very helpful in determining the mass changes that take place in combustion reactions. For highly volatile compounds, TGA can be a good technique to determine the evaporation rate. This method also helps to determine the curie temperature of substances.

What is DTA

DTA or Differential Thermal Analysis is a thermal analysis technique. Here, the temperature difference that is developed between a sample and a reference compound is measured at identical heat treatments. The reference material should be inert. Both reference material and sample should be provided with the same conditions and the same treatments.

If there is a zero difference between temperatures of the sample and the reference, then the sample compound is thermally inert. This is because the reference material is also thermally inert and the sample is analyzed with respect to the reference material.

Figure 2: A differential thermal analyzer with an attached mass spectrometer.

The analyzer is composed of a sample holder, sensors, furnace, temperature controlling system and a recording system. This instrument can be used at very high temperatures. It is also highly sensitive. These are the advantages of the DTA method.

DTA technique can be used in analyzing the thermal properties of minerals, for the characterization of polymers; in pharmaceutical and food industry, it can be used as a method of analyzing biological materials.

What is DSC

DSC is Differential Scanning Calorimetry. In DSC, the heat flow is measured against the temperature change at a particular time. The instrument that measures DSC (calorimeter) uses two chambers to keep the sample and a reference material. The reference chamber is filled with a solvent. The sample chamber is filled with the sample substance dissolved in the same solvent (same amount) used as the reference. This technique can be used for both substances and chemical reactions.

Difference Between TGA DTA and DSC_Figure 3

Figure 3: A differential scanning calorimeter

At the end of the experiment, a thermogram is obtained. This thermogram provides the deviation of the heat energy released by the sample with respect to the reference. The curve for reference is called the base line. A deviation above the base line is called exothermic transition and a deviation below the base line is called an endothermic transition. The area under the peak is directly proportional to the amount of heat energy absorbed or released by the sample.

In this method, a small amount of the sample is enough for the analysis. This is because the sample is dissolved in the same solvent used in reference chamber before analysis. This technique is applicable for the determination of the heat of reaction of a particular chemical reaction. However, both sample and reference should be given the same conditions and the same heat treatments should be done for both in order to obtain accurate results.

Definition

TGA: TGA is Thermal Gravimetric Analysis.

DTA: DTA is Differential Thermal Analysis.

DSC: DSC is Differential Scanning Calorimetry.

Technique

TGA: In TGA, the change of the mass of a sample with the change of the temperature is observed and analyzed.

DTA: In DTA, the temperature difference that is developed between a sample and a reference compound is measured at identical heat treatments.

DSC: In DSC, the heat flow is measured against the temperature change at a particular time.

Compounds Analyzed

TGA: TGA can be used to analyze inorganic materials, metals, polymers, plastics, ceramics, glasses and composite materials.

DTA: DTA can be used to analyze thermal properties of minerals, for the characterization of polymers, and biological materials.

DSC: DSC can be used to analyze proteins, antibodies, etc.

Nature of Sample

TGA: The sample can be used as a solid substance in TGA as a powder or small pieces.

DTA: The sample can be used in its solid state for DTA.

DSC: The sample is always a liquid; the substance that is going to be analyzed is dissolved in the solvent used as the reference.

Conclusion

TGA, DTA and DSC are thermal analysis techniques. These techniques are used to analyse the behavior of a particular substance when the temperature is changed. These techniques are also applicable for certain chemical reactions in order to find the relationship between reactions and the temperature. The main difference between TGA, DTA and DSC is the method of measuring the changes in samples that are caused by heat.

References:

1. “Differential Scanning Calorimetry.” Chemistry LibreTexts, Libretexts, 7 Jan. 2017, Available here. Accessed 27 Sept. 2017.
2. Samira Mohammadpour. “Differential thermal analysis & Differential Scanning Calorimetry.” LinkedIn SlideShare, 6 Aug. 2014, Available here. Accessed 27 Sept. 2017.
3.“Thermogravimetry (TG) or Thermogravimetric Analysis (TGA) or Thermal Gravimetric Analysis.” Anderson Materials Evaluation, Inc., Available here. Accessed 27 Sept. 2017.

Image Courtesy:

1. “Whewellite tga” (CC BY-SA 3.0) via Commons Wikimedia
2. “210 014 001” by U.S. Department of Energy (United States government work) via Flickr
3. “Differential scanning calorimeter” (Public Domain) via Commons Wikimedia