Thermogravimetric Analysis (TGA)

Thermogravimetric analysis involves measuring a sample’s change in mass as it is heated and is a very useful technique for analyzing samples that either gain or lose mass during heating. It can be used to study decomposition, reaction equlibrium, pyrolysis, oxidation, filler mass, ash percent, metallic residue, and loss of solvents/water/plasticizer during heating or aging.

Typical Experimental Results

TGA measurement of Calcium Oxalate Monohydrate, CaC₂O₄•H₂O.

Applications

For more information please read our application notes:
Simultaneous Thermal Analysis of the Decomposition of Calcium Oxalate, PDF
Thermogravimetric Analysis of Calcium Oxalate, PDF

Instruments: STA 449 F3 Jupiter Thermal Analyzer

Instrument Key Specifications

Simultaneous Thermal Analysis of the Decomposition of Calcium Oxalate

Simultaneous thermal analysis (STA) performs thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) simultaneously on a sample. STA allows for precise correlation of changes in mass with changes in energy and vice versa. It provides not only results one can get from separate TGA or DSC analysis, but also better correlation between the two kinds of analyses because they are run under the exactly same conditions.

STA is invaluable in certain applications, such as differentiating between phase transformation and decomposition, or recognizing pyrolysis, oxidation and combustion reactions. The technique can also be used to determine reaction kinetics, physical transitions, residual mass or curing and evaporation rates. STA has applications in characterizing pharmaceutical materials, cements, minerals, resins, etc. Any material that undergoes changes in mass or internal energy when subjected to a controlled heating program can be analyzed using STA.

Calcium Oxalate Monohydrate, CaC₂O₄•H₂O, is a useful industrial compound used to make organic oxalates, and glazes. Understanding Calcium Oxalate’s thermal behavior when applied as part of a glaze is crucial to determining kiln temperature. If the kiln is not hot enough, the calcium oxalate won’t decompose properly. If it is overheated, the glaze’s viscosity will lower to the point that it runs off the surface of the pottery it was applied to. Thermal decomposition data for CaC₂O₄•H₂O was obtained using a Netzsch STA 449 F3 Jupiter Simultaneous TGA-DSC (Germany). Table 1 summarizes the three decomposition reactions that occurred during the test.

The DSC data shows that the first and third reactions are purely endothermic, as would be expected from a simple decomposition reaction. However, the second reaction step shows evidence of two overlapping reactions, one endothermic and the other exothermic. This can be explained by the Boudouard reaction, the equilibrium redox reaction of carbon monoxide into carbon dioxide and carbon. At elevated temperatures that are less than 700°C, carbon monoxide will react to form carbon and carbon dioxide, which is an exothermic reaction.

The measured mass losses during steps 1 to 3 closely match the predicted mass losses, which verify the theoretical predictions of the thermal decomposition for the calcium oxalate monohydrate. It is interesting to note the slight difference in the mass loss between theoretical calculation and actual measurement for decomposition in step 2. This can be explained by the Boudouard reaction depositing carbon residue on the sample, resulting in a mass loss that is significantly lower than expected.

If this experiment had been performed using only DSC or TGA, there would not have been
enough information to analyze and fully understand the reactions occurring.

Thermogravimetric Analysis of Calcium Oxalate

Thermogravimetric analysis (TGA) is a type of analysis that determines the mass change of a sample over time as it is heated. This analysis requires that the test instrument be able to accurately measure mass, temperature, and temperature change. Typically, samples are analyzed in an inert atmosphere although an oxidizing or reducing atmosphere can be used when necessary. TGA is widely employed in research and development, testing and characterization of all kinds of materials from metals and alloys to polymeric and ceramic composites. Typical applications of TGA may include determination of polymer degradation and decomposition temperatures, moisture content of materials, oxidation resistance and dynamics, volatile and nonvolatile components, thermal stability, etc.

Thermal decomposition is the process in which a substance decomposes due to the application of heat. The phenomenon is common to most organic substances and occurs in many inorganic substances as well. Certain substances can undergo multiple decomposition reactions, each at a different temperature. Using thermogravimetry, the decomposition temperature and mass loss of each reaction can be determined.

Calcium Oxalate Monohydrate, CaC₂O₄•H₂O, is a useful industrial compound used to make oxalic acid, organic oxalates, and glazes. Thermal decomposition data for CaC₂O₄•H₂O was obtained using a Simultaneous TG-DTA/DSC Apparatus STA 449 F3 Jupiter (Netszch, Germany).

Thermal decomposition of CaC₂O₄•H₂O occurs in three distinct steps, as can be seen in Figure 1. The theoretical mass loss during each step can be calculated using the molar masses of the individual components. Table 1 shows the decomposition reactions that occur at each step as well as the theoretical and measured mass loss for each step.

The measured mass losses during steps 1 to 3 closely match the predicted mass losses, which verify the theoretical predictions of the thermal decomposition for the calcium oxalate monohydrate. It is interesting to note the slight difference in the mass loss between theoretical calculation and actual measurement for decomposition in step 2. According to research, this is most likely due to disproportionation (a type of redox reaction during which a reactant is simultaneously oxidized and reduced, thus forming two different products) of CO into CO₂ and carbon. This disproportionation is highly dependent on the impurities within the sample as well as the cleanliness and material of the sample holder.