Analysis and interpretation of thermogravimetric analysis (TGA) results

Click here to see other posts about TGA/DTG

Only 10$ for interpretation of your TGA thermogram
Payment Upon Completion

 Send your thermograms...

TGA is a powerful and robust technique to explore the thermal stability of a material. By accurately monitoring the weight of a sample while heating at a constant rate, we can measure changes in a sample’s weight and attribute this to a specific material response to a thermal stress (Figure 1). This is perfect for exploring, in detail, decomposition temperatures and ensuring a material performs adequately in a given temperature range.

During a test, a carrier gas flows over the sample and the weighing mechanism.  This carrier gas serves two purposes: protecting the internals from corrosion/oxidation above 500 °C, and to interact with the sample through gas-solid or gas-liquid reactions. By providing an inert atmosphere, we can test the thermal stability of a material. Reducing environments can explore gas-solid phase reduction reactions or protect specific samples from being oxidized. By the nature of the sensitivity of the TGA balance, we also can observe the absorption of gas onto a porous material at various temperatures. This is an ideal technique for exploring metal organic frameworks, or catalytic porous materials. Owing to the sensitivity of the balance on our SETARAM Labsys Evo instrument, we have ideal sensitivity for running thermokinetic experiments. This experiment has applications towards thermal stability of a given material at elevated temperatures.

The SETARAM Labsys offers the ability to perform TGA analysis up to 1600 °C and additionally under a variety of gas mixtures due to our gas-mixing option.

Differential Scanning Calorimetry (DSC)

DSC is a flexible technique to explore thermal transitions within a given sample. By heating a sample and measuring the heat flow as compared to a reference standard, we can access thermoanalytical information on a given material. DSC curves are generated by plotting heat flow (mW) vs sample temperature (°C), and an example plot is found in Figure 2, and demonstrates the melting and fusion of Indium Corp. Indalloy 80Au/20Sn solder. In this case, we observe a phase change (solid-liquid followed by liquid-solid); however, we can also observe other thermal transitions within a material, such as evaporation, thermal transitions between polymorphs, and determination of key thermal constants. One of these key thermal constants is heat capacity (Cp), which an be difficult to acquire due to the demanding experiment required to gain access to this information. Heat capacity requires precise and very specific sensitivity of the DSC sensor, as it is a very small and difficult thermal effect to capture effectively. Owing to our 3D Calvet type sensor on our µDSC 7, we have the capability to measure such small thermal effects (0.02 µW) requiring the upmost sensitivity and precision from 0 – 120 °C. For higher temperatures, our SETARAM Labsys Evo instrument has a specifically designed 3D-psuedo-Calvet sensor, which allows TAL to perform Cp testing with better than 2% accuracy from ambient temperatures to 1600 °C. This very sensitive and difficult to determine thermal effects also include the glass transition point (Tg), water state in materials and other thermodynamic and thermokinetic effects.

Figure 2: (main) A thermogram demonstrating the melting point of a common solder at 280.782 °C as compared to its literature point of 280 °C. The melting point is determined using the ISO 11357-3 standard definition. (inset): A picture of the internals of our DSC 7, showing a sample and its reference during a DSC experiment.

Differential Thermal Analysis (DTA)

DTA is a similar technique to DSC, however instead of measuring the heat flow between the furnace temperature and the sample, you measure the temperature difference between a sample and a standard reference using thermocouples. This is particularly useful for phase-change materials and the study of organic and polymeric materials using analytical precision. Owing to the more sensitive detector within typical DTA sensors, DTA testing is particularly useful for running thermokinetic experiments due to the lower thermal inertial barrier. TAL offers DTA testing from ambient to 1200 °C, allowing us to explore thermal effects at elevated temperature, capabilities which we have newly acquired.

Figure 3: A thermogram showing two experimental curves of the decomposition of CuSO4•5H2O, a TGA standard. TGA (blue curve) thermogram shows the loss of 5 water (36 wt%). Each loss of water corresponds to an endotherm signal (DSC, orange), which would be expected for the loss of water from CuSO4•5H2O.

While each of these techniques may be used to probe into a single physical characteristic of a material, the real power we provide is simultaneous thermal analysis techniques for niche applications on a single sample. With TAL’s Labsys Evo 1600 and DSC 131, we offer capabilities to include high temperature ranges with mixtures of gases. For example, TAL offers TGA, DSC and DTA experiments from ambient temperatures up to 1600 °C. Figure 3 shows a TGA-DSC decomposition experiment captured on our Setaram Labsys Evo apparatus, where CuSO4•5H2O decomposition can be measured by TGA (water, SO2 and O2) and DSC. In addition to these coupled thermal experiments, we offer the capacity to provide gas mixtures for high precision control over the exact atmospheric exposure during thermal analysis runs. TAL also offers the capacity to run samples under vacuum (10-3 Bar) using our Labsys Evo system, which is useful for isolating gas-sample interactions. TAL also offers pressurized DSC experimentation, allowing for the study of various samples under 200 psi. This can provide insight into thermal transitions under pressure, such as those in the oil and fuel industry or in the case of high-pressure lubricants.