Simultaneous thermal analysis (STA) is a simultaneous measurement of different thermal properties in the same sample by combining DSC and TGA in a single instrument. Both DSC and TGA are the most commonly used thermal analysis techniques, and when combined as STA, more comprehensive information is provided. A DSC measures the fluctuation of heat flow in a sample as the temperature is gradually increased or decreased. Changes in the measured heat-flow indicate phase transitions, which are then compared to reference standards to provide insight into the stability, kinetics, water distribution and other material properties of the sample. Similarly, DTA is a technique that measures temperature changes while the heat flow is held constant. Both DSC and DTA functionalities are often found in a single instrument. TGA has the same principle as DSC, but instead of heat flow, the weight of the sample is monitored as a function of temperature. Gas, water, and other volatile compounds are released from the sample as the temperature is gradually increased, resulting in a change in the sample weight. The measured weight loss indicates transitions, decomposition, solvent loss and corrosion of the sample. In STA, the combination of TGA and DSC is possible due to the identical test conditions for both techniques. DSC and TGA both require the same atmosphere, flow rate, vapor pressure, heating rate, thermal contact to the sample and radiation effect. By running both techniques simultaneously, STA has an advantage of having a faster runtime and more reliable results compared to running each technique separately, since the STA system obtains two streams of complementary information from DSC and TGA in a single run. Furthermore, an STA instrument can be coupled with FTIR or MS to augment the information provided by STA analysis alone. The price of an STA instrument is generally more affordable than buying DSC and TGA instruments separately. However, as a downside, STA systems are generally more complicated, as various sensors for DSC and TGA have to be combined in a single device. The intricate design may lead to reduced sensitivity and less-clear signals, which may compromise measurement parameters. STA instruments have different specifications with an average maximum temperature of 1500°C, while some instruments go up to 2400°C. Other variations include the sensitivity of temperature/heat sensor and weight balance sensor, automation and instrument design. For instance, TA Instruments' SDT 650 provides a real-time measurement with modulated DSC and Hi-Res TGA equipped with a flexible autosampler. PerkinElmer offers the STA 6000 with a vertical-displacement balance sensor and SaTurnA sensor, which measures both sample and reference temperature directly. NETZSCH provides the STA 449 F3 Jupiter, which offers a wide temperature range (-150–2400°C) and an easily interchangeable sample holder and furnace. Typical applications of STA can be found in the polymer, pharmaceuticals and food industries. The combined DSC and TGA analyses are essential in measuring phase transitions in polymers, ensuring the stability of drugs in pharmaceutical preparations and monitoring textural changes in food during processing. While increasing oil prices might inhibit growth in the polymer industry, substantial investments by American and European pharmaceutical companies along with the surging demand for food testing in Asian countries are the main drivers of growth in demand for STA. The global STA market is estimated to be over $90 million in 2017, with a projected mid-single digit growth rate in 2018.
Simultaneous Thermal Analysis at a Glance:
- TA Instruments (Waters)
- Polymers and Plastics