How Thermal Analysis Works & the Benefits of Leasing a Thermal Analyzer

Conducted by thermogravimetric analyzers, thermogravimetric analysis (TG) continuously measures the mass of a sample’s temperature changes over time. The result of such an analysis is a plot of mass as a function of either time or temperature. These devices consist of a lab balance with the desired sample on it contained within a temperature-controlled furnace. These analyzers are also known as thermobalances.

They are used in determining materials thermal stability, oxidation, and combustion mass losses, in addition to the thermal decomposition present in pyrolysis and computation of materials.

Identifying gases released directly from a sample during thermal treatment cannot happen without coupling a spectroscopic method like Fourier-Transform-Infrared (FT-IR) spectroscopy to a TG analyzer. This integration, referred to as TG-FTIR, pairs the quantification capabilities of TG with the identification abilities of FTIR spectroscopy.

Observing dimensional changes in materials as a function of temperature or time is done using a thermomechanical analyzer. Thermomechanical analysis is considered a sub-discipline of thermomechanometry.

The sample is placed inside a furnace and a force generator is attached to it. The generator is used to deform the sample either by compression, tension, flexure, or torsion, and those changes are measured and recorded. The constant application of force or non-oscillating stress deforms the sample over time.

Expansion/compression, penetration, or tension probes are used depending on what type of measurement is needed.

A dielectric thermal analyzer, or more simply put a dielectric analyzer (DEA), measures a material’s capacitance, conductance, and phase change by applying an oscillating electrical field to it and observing it as a function of time and temperature.

DETAs are also used to observe the curing behavior of thermosetting resin systems, composite materials, and other polymers. This is achieved by placing two electrodes on the material and applying a sinusoidal voltage to one of them. The response measured from the second electrode is recorded and is used to determine other material properties.

A thermoanalytical technique that measures the temperature of a substance as it is heated or cooled at a specific rate. Simultaneously, a known reference inert material undergoes an identical thermal cycle and its temperature is also recorded.

The difference between the two temperatures is plotted against either time or temperature and this plot then is used to determine other properties of the substance. This curve can then be used to plot exothermic and/or endothermic changes in the substance to identify transformation temperatures or when it melts, sublimates, and crystalizes.

Differential thermal analyzers’ ability to identify these transition points makes it extremely useful for material identification. DTA is found in pharmaceutical, mineralogical, and environmental fields.

Furthermore, it can be coupled with thermogravimetric analysis (TG-DTA) to characterize multiple thermal properties of a sample in a single experiment. Fundamentally, TG involved in TG-DTA is very similar to the standard thermogravimetric analysis in that it can provide measurements concerning temperatures changes as a result of decomposition, reduction, or oxidation.

Similar to thermomechanical analyzers, dynamic mechanical analyzers look at a material’s dimensional changes as a function of time, temperature, and frequency of stress. As the frequency of the strain that is applied varies, the resulting stress on the material is measured. This sinusoidal force is applied by a probe that deforms the material, and the relationship between the force applied and the deformation is then measured.

When testing polymer materials, different deformation techniques are used depending on the force that needs to be measured. Tension, compression, dual cantilever bending, three-point bending, and shear modes are examples of a few techniques.

Dilatometry is the technique used to measure dimensional changes in a sample’s volume as changes in temperature occur. A simple and well-known dilatometer is a mercury-in-glass thermometer. As the mercury heats up, its volume expands at a measurably consistent rate. DILs can be subdivided into several types:

• Capacitance: The sample is placed between two parallel plates, one stationary and one movable. As the sample’s temperature changes and its length changes, it will move one plate, changing the gap between them.
• Connecting Rod (Push Rod): The pushrod touches the sample which is placed inside a furnace, and the thermal expansion is then measured by a strain gauge which charts the change in shape.
• High Resolution (HR) Laser: Dimensional variations that are a result of temperature changes are quantified using light interference. The most accurate method of laser dilatometer is the Michelson Interferometer type Laser Dilatometer.
• Optical: Uses high-resolution cameras to capture images of the material as it undergoes dimensional changes, achieving non-contact measurements.

Known as both a calorimetric and thermal analysis technique, differential scanning calorimetry (DSC) is used to provide test data for a wide range of materials. This includes polymers, rubber, petroleum, chemicals, plastics, adhesives, composites, coatings, organic materials, pharmaceuticals, and much more.

DSC devices measure how change’s in a material’s temperature alter its heat capacity. It is used to evaluate material properties such as glass transition temperature, melting, crystallization, specific heat capacity, thermal stability, and oxidation behavior, among others.

Additionally, DSC can be coupled with TG (TGA-DSC) in order to perform microplastic characterization.

Simultaneous thermal analysis—or STA—is a combination of DSC and TG methods. By coupling thermogravimetric effects with the recording of a DSC heat flow signal, both measuring methods can be compared. This excludes the influence changed sample atmospheres can have on the reaction equilibrium, which can often occur with individual measurements.

Simultaneous thermal analyzers are able to make up for the uncertainties that TG or DSC measurements can create due to such inaccuracies as sample inhomogeneities, sample geometry, and temperature fluctuations.

Combining these two methods ultimately results in an almost complete sample characterization, especially for complex reactions. The complimentary pairing allows researchers to observe and understand differentiation between endothermic and exothermic events, which have no associated weight change and those that do involve weight change.

Thermal analysis’ use of equilibrium thermodynamics, irreversible thermodynamics, and kinetics concepts allow it to be an effective tool that is used in both academic and professional fields. Material science, geology, quality assurance, heat transfer, and the pharmaceutical industry are just some examples.

Though they are used as independent devices, thermal analyzers can also be combined with other measurement and testing devices to provide a more comprehensive testing system. Their base range of uses and ability to couple with other devices means that thermal analyzers are extremely prevalent in many applications. In fact, this analysis method is now being used in interstellar research.

Putting materials into space poses interesting problems due to the lack of an atmosphere. Additionally, reentry into the earth’s atmosphere poses unique issues when materials are exposed to extreme temperatures. NASA has had to perform extensive thermal analysis on its Earth Entry Vehicles (EEV) specifically to avoid any damage to the EEV for the Mars Sample Return mission. It would be an absolute tragedy if those samples returning to Earth ended up burning upon reentry.