Thermal analysis techniques measure the physical and chemical properties of materials as a function of temperature. Thermogravimetric Analysis (TGA) monitors mass changes, while Differential Scanning Calorimetry (DSC) measures heat flow associated with thermal transitions.
Thermogravimetric Analysis (TGA)
In TGA, a precision balance continuously measures the mass of a sample as it is heated or cooled at a controlled rate in a defined atmosphere such as N2, O2, air, or Ar. A TGA curve (thermogram) plots mass or mass percent versus temperature or time, where mass losses indicate decomposition, evaporation, desorption, or oxidation. The first derivative (DTG) highlights the temperature of maximum decomposition rate and helps resolve overlapping events.
TGA Instrumentation
The instrumentation includes a microbalance with a sensitivity of 0.1 µg, located above or below the furnace to protect it from heat; a furnace capable of heating from ambient to 1000-1600°C with programmable temperature ramps of 1-50°C/min; a purge gas system that controls the sample atmosphere, where inert gas like N2 prevents oxidation while air or O2 promotes combustion; and sample pans made of platinum, alumina, or aluminum, selected based on temperature range and sample reactivity.
TGA Applications
TGA is used for compositional analysis of polymers including determination of filler content, volatile content, and thermal stability; oxidation and decomposition studies of pharmaceuticals, lubricants, and catalysts; moisture and ash content determination in coal, food, and construction materials; and kinetic analysis of decomposition reactions using the Ozawa-Flynn-Wall or Kissinger methods.
Differential Scanning Calorimetry (DSC)
In DSC, the sample and an inert reference are heated at the same rate, and the difference in heat flow required to maintain temperature equality is recorded. Endothermic events such as melting, glass transition, and dehydration absorb heat, while exothermic events such as crystallization, oxidation, and curing release heat. A DSC curve plots heat flow in mW versus temperature, and the peak area is proportional to the enthalpy change (ΔH).
DSC Applications
DSC is used for melting point determination and purity analysis of crystalline pharmaceuticals; glass transition temperature (Tg) measurement for polymers and amorphous materials; crystallization kinetics and degree of crystallinity in semicrystalline polymers; polymorph identification in drug substances, as different crystal forms have distinct melting points; and oxidation stability of oils and fats by measuring the oxidation onset temperature.
Complementary Techniques
TGA and DSC are often combined in a single instrument, known as simultaneous TGA-DSC or STA, to correlate mass changes with thermal events. TGA-MS and TGA-FTIR couple TGA with mass spectrometry or infrared spectroscopy to identify evolved gases during decomposition. Dynamic mechanical analysis (DMA) measures viscoelastic properties and is complementary to DSC for polymer characterization.
