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Thermal Analysis
Differential Scanning Calorimetry (DSC) and
Thermogravimetric Analysis (TGA)
Differential
Scanning Calorimetry, DSC,
is a thermo analytical technique in which the difference in the amount of heat required to
increase the temperature of a sample and reference are measured as a function
of temperature. Both the sample and reference are maintained at nearly the same
temperature throughout the experiment. Generally, the temperature program for a
DSC analysis is designed such that the sample holder temperature increases
linearly as a function of time. Only a few milligrams of material are required
to run the analysis.
Principle of Operation
When a sample undergoes a physical transformation such as a phase transition, more or less heat will need to flow to it than to the reference (typically an empty sample pan) to maintain both at the same temperature. Whether more or less heat must flow to the sample depends on whether the process is exothermic or endothermic. For example, as a solid sample melts to a liquid it will require more heat flowing to the sample to increase its temperature at the same rate as the reference. This is due to the absorption of heat by the sample as it undergoes the endothermic phase transition from solid to liquid. Likewise, as the sample undergoes exothermic processes (such as crystallization) less heat is required to raise the sample temperature. By observing the difference in heat flow between the sample and reference, differential scanning calorimeters are able to measure the amount of heat absorbed or released during such transitions. DSC may also be used to observe more subtle phase changes, such as glass transitions.
Applications
DSC is commonly used to measure a variety of
properties in both organic and inorganic materials, from metals and simple
compounds to polymers and pharmaceuticals. The properties measured include:
- Glass transitions
- Phase changes
- Melting
- Crystallization
- Product stability
- Cure / cure kinetics
- Oxidative stability
- Heat capacity and heat of fusion
measurements
Thermogravimetric Analysis (TGA) measures weight changes in a material as a function of temperature (or time) under a controlled atmosphere. Its principle uses include measurement of a material’s thermal stability, filler content in polymers, moisture and solvent content and the percent composition of components in a compound.
Principle of Operation
The analysis is performed by gradually raising the temperature of a sample in a furnace as its weight is measured on an analytical balance that remains outside of the furnace. In TGA, mass loss is observed if a thermal event involves loss of a volatile component. Chemical reactions, such as combustion, involve mass losses, whereas physical changes, such as melting, do not. The weight of the sample is plotted against temperature or time to illustrate thermal transitions in the material such as loss of solvent and plasticizers in polymers, water of hydration in inorganic materials and finally decomposition of the material.
Applications
Typical TGA applications include:
- Filler content of polymer resins
- Residual solvent content
- Carbon black content
- Decomposition temperature
- Moisture content of organic and inorganic materials
- Plasticizer content of polymers
- Oxidative stability
- Performance of stabilizers
- Low molecular weight monomers in polymers
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