Master Thermal Analysis in Just 30 Minutes!

Webinar summary

Simultaneous Thermal Analysis, or STA, combines thermogravimetric analysis (TG) with either differential thermal analysis (DTA）or differential scanning calorimetry (DSC) so that mass changes and thermal events can be measured at the same time on the same sample under the same test conditions. TG tracks changes in sample mass as a function of temperature or time during a controlled temperature program such as heating or cooling. A stable, unchanging portion of the TG curve represents the baseline, a downward shift indicates mass loss, and an upward shift indicates mass gain. DTA or DSC measures the temperature difference or heat-flow difference between a sample and a reference. On these curves, endothermic events appear as downward peaks and exothermic events appear as upward peaks.

The advantage of STA comes from linking mass change directly with thermal behavior. A TG result alone can show that a sample gained or lost mass, but it does not fully explain why. A DTA or DSC result can show that a thermal event occurred, but not necessarily whether the sample decomposed, oxidized, volatilized, dehydrated, melted, crystallized, or underwent another physical or chemical change. By combining both measurements, STA provides a clearer picture of how a material behaves under thermal conditions.

A horizontal differential balance with triple-coil mechanism is described as offering high stability, low baseline noise and low drift under gas flow conditions, as well as compatibility with evolved gas analysis systems. In this type of TG system, sample-side and reference-side balance beams operate independently. A position detection unit uses a light source, shutter, and optical sensors to monitor beam position. When sample mass changes, the balance beam shifts, the shadow position changes, and the system records this movement. A drive coil returns the beam to its original position, and the current required to do so is proportional to the mass change. Because the response is very fast, the balance beams remain effectively horizontal throughout the measurement.

DTA and DSC measurements are based on comparing the changes in the sample and reference materials as both are heated or cooled in a furnace. If the sample does not undergo a change, its temperature follows the reference temperature. During an endothermic event, such as melting or dehydration, the sample absorbs heat and temporarily lags behind the reference, producing a negative temperature difference. During an exothermic event, such as crystallization or combustion, heat is released by the sample, producing a positive temperature difference. These differences generate peaks that help identify thermal reactions.

STA curves can indicate several kinds of thermal behavior, including crystal transitions, glass transitions, decomposition, combustion, melting, dehydration, crystallization, amorphization, and reactivity with atmospheric gases. For example, indium shows an endothermic DSC peak at about 156.67°C with no accompanying TG mass change, indicating melting rather than decomposition or volatilization. In more complex compounds, several thermal events can occur in sequence, and STA data alone may not be enough to identify every process confidently. Real-time sample observation can help by synchronizing visual images with TG, DTA, or DSC data.

One example involved trehalose dihydrate heated in air atmosphere from room temperature to 350°C. An endothermic event near 120°C was associated with dehydration and mass loss, with little visible change in color or shape. Additional thermal events occurred around 160°C, 180°C, and 210°C, corresponding to amorphization, crystallization, and melting, along with sample shrinkage and color change from white to light brown. Around 300°C, an exothermic combustion event accompanied with rapid mass loss, sample expansion, and blackening.

STA is useful across fields such as materials science, chemistry, pharmaceuticals, polymers, ceramics, food science, and related industries. In pharmaceuticals, it can help determine drug stability by showing how a material responds to temperature, which is important for safety, storage period and conditions, and performance. In polymer analysis, polyethylene terephthalate PET was used as an example. The DSC curve showed a glass transition around 70°C, crystallization around 160°C, and melting around 250°C, while the TG curve showed significant mass loss beginning around 300°C, indicating thermal decomposition. A more sensitive PET measurement showed a small mass loss between 30°C and 70°C from volatilization and a 0.03% mass loss between about 70°C and 85°C associated with trace gas release near the glass transition.

Accessories expand the information available from STA measurements. A sample observation capability can record visual changes during measurement up to 1000°C and synchronize those images with the thermal data. Copper sulfate pentahydrate was used as an example of staged dehydration. The substance lost water in three steps: two water molecules in the first stage, two more in the second stage, and one in the third stage. The first two dehydration steps each produced about 14% mass loss, and the third produced about 7% additional mass loss. The sample color changed from blue to a pale color as water molecules were removed.

Humidity-controlled STA can evaluate how materials absorb and release water. A humidity generation system can perform TG-DTA or TG-DSC measurements under high-humidity controlled atmospheres up to 80°C and 90% relative humidity. α-cyclodextrin was used as an example because water sorption and absorption affect its stability, storage conditions, and performance in pharmaceutical and food applications. At 25°C, increasing humidity from dry conditions to 90% relative humidity caused a 6.6% mass gain. Reducing humidity back to dry conditions caused a 6.5% mass loss. Heating the sample from 25°C to 150°C under dry conditions caused additional mass loss.

STA systems can also be adapted for controlled-atmosphere or hazardous-gas work. A separate controller design allows the control unit and the balance mechanism to be located separately, making it suitable for configurations where only the balance mechanism is installed inside the glove box. This arrangement helps prevent air-sensitive samples from being exposed to air and helps prevent hazardous gases from escaping. In one example, niobium metal was fluorinated with fluorine gas at a heating rate of 10°C/min. Mass loss began around 180°C and coincided with an exothermic reaction. The reaction led to nearly 100% mass loss, indicating that the niobium was volatilized through fluorination.

Overall, STA provides a combined understanding of mass change, heat flow or temperature-difference behavior, reaction enthalpy when using TG-DSC, and visual sample behavior when paired with an observation camera. This makes it valuable for identifying thermal transitions, decomposition, dehydration, combustion, volatilization, water sorption/desorption, and reactions under specialized atmospheres.