How thermal analysis improves renewable energy systems

How is thermal analysis applied in the field of renewable energy and what techniques are used to ensure material quality control?

Renewable energy resources are now widely used as substitutes for fossil fuels. Developments are progressing rapidly and new materials used by renewable energy industries require proper testing and quality control. This is where thermal analysis comes in!

Methods based on thermal analysis techniques such as differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA) are essential for characterizing the materials and compounds used.

This analysis measures the physical properties and behavior of materials as a function of temperature, including melting, thermal stability, and hardening reactions.

What factors have driven the shift to renewable energy and how does thermal analysis contribute to the understanding of materials used in sustainable energy technologies?

In the last 20 or 30 years, there has been a significant shift towards renewable and sustainable energy sources.

This shift has been catalyzed by concerns about limited fossil fuel resources, increased awareness of environmental issues, and unresolved challenges associated with the operation and decommissioning of nuclear power plants. Several serious accidents in recent years have also undermined the widespread acceptance of nuclear power.

Renewable energy is derived from naturally powered resources over a short period of time, such as hydroelectric power, wind power, biomass, solar power, geothermal power, and biofuels. Related technologies, including fuel cells, batteries and energy storage systems, use specialized compounds that can also be analyzed by thermal analysis.

Typical questions that arise when evaluating materials for renewable energy applications include: what is the thermal stability of the compound, does the oxidative stability of biofuels meet the required standards, and how to evaluate the curing behavior of a material.

For example, in the wind energy industry, it is necessary to describe the degree of curing of epoxy resins used in the manufacture of laminated rotor blades for wind turbines. This analysis can be easily performed using DSC.

Image credit: bombermoon/Shutterstock.com

How can thermal analysis be defined and what techniques are used in thermal analysis for material characterization?

The ICTAC definition of thermal analysis is: “A group of techniques in which a physical property of a substance is measured as a function of temperature while the substance is subjected to a controlled temperature program.”

Thermal analysis includes techniques for investigating physical events and processes when a sample is heated. During heating, for example, a sample may melt, change from a solid to a liquid state, or undergo oxidation, where exposure to air or oxygen can lead to oxidation and eventual decomposition.

The five most important techniques used in thermal analysis to characterize renewable energy materials include DSC, thermo-optical analysis (TOA), TGA, TMA and DMA.

Each of these techniques measures different properties and provides insight into different applications.

What is DSC and how does it apply to materials analysis?

DSC is a thermal analysis technique that measures the energy absorbed or released by a sample as it is heated, cooled, or held at a constant temperature.

DSC instruments vary in temperature range, sensor type, and heating/cooling rates. The METTLER TOLEDO DSC 1 measures from -150 °C to 700 °C at heating rates up to 300 K/min, with sample sizes between 2 and 20 mg.

A typical DSC measurement curve of a semicrystalline polymer displays various thermal events: initial deformation at start-up, glass transition, cold crystallization, melting and oxidative decomposition.

Understanding behaviors such as glass transition, crystallization, melting, solid-solid transitions and chemical reactions are very important in materials used in renewable energy processes. Key applications include the determination of glass transition temperature, melting enthalpy, curing rates, oxidative stability and specific heat capacity.

For example, DSC is used in biodiesel testing, where oxidation of unsaturated fatty acids can lead to short chain formation and rancidity. Therefore, stabilizers are added to biodiesel to prevent oxidation. Stability tests can then be performed by DSC as part of materials development and for final product quality control.

Can you please explain TOA?

TOA, or thermo-optical analysis, is a group of techniques used to measure the optical properties of a sample, or those that can be observed visually, as it is heated or cooled. Some TOA instruments allow the simultaneous measurement of calorimetric effects such as enthalpy changes while allowing visual observation of the sample.

The primary applications of TOA for renewable materials include the determination of changes in morphology, shrinkage, and crystallization behavior. TOA can also measure thermochromism and oxidative stability.

What is TGA and how does it work?

TGA is a technique in which the mass of a sample is continuously measured as it is heated or cooled in a controlled atmosphere. A few milligrams of sample are placed in a crucible, weighed and heated, and the change in weight is recorded continuously as a function of temperature or time. This process provides information about the sample composition, such as polymer and filler content.

TGA is also used to analyze processes such as vaporization or decomposition. Further evolved gases can be examined online using hyphenated techniques such as TGA mass spectrometry (MS), TGA-Fourier transform infrared spectroscopy (FTIR), or TGA-GC/MS (chromatography/mass spectrometry).

The primary analytical applications of TGA for materials in the renewable energy sector include detailed information on composition, including filler content. It is also useful for evaluating the thermal or oxidative stability of products such as biodiesel and analyzing the moisture or volatile content of formulated products.

What is TMA and how is it used to analyze materials in renewable energy applications?

TMA is a technique that measures dimensional changes in a sample as it is heated or cooled.

TMA has several analytical applications for materials in the renewable energy sector. The main application is to determine the expansion behavior of materials and the coefficient of thermal expansion. TMA is also very effective for identifying the glass transition temperature and examining softening, creep or swelling behavior in a solvent.

Consider a practical example. During use, the separator membrane in lithium batteries can become too hot, which can cause the battery to shrink, tear, and eventually fail as the separator degrades. To prevent this, the thermal stability of the membrane material is evaluated using TMA, allowing a usable temperature range of the material to be determined. TMA is also very useful for assessing the quality of raw materials and detecting polymer blends.

How can we understand DMA?

DMA is a technique for measuring the mechanical and viscoelastic properties of a material as a function of time, temperature and frequency as the material is subjected to periodic oscillating stress over a controlled temperature schedule.

DMA has various analytical applications for materials in the renewable energy sector. In general, it provides information on mechanical modulus, compliance, damping and viscoelastic behavior.

Glass transition temperatures, softening temperatures or beta-relaxation processes are identified as peaks in the bronze delta or by modulus changes.

Where can readers find more information?

Resources can be downloaded from the Internet for more information on the use of thermal analysis in renewable energy. METTLER TOLEDO publishes articles on thermal analysis applications in various fields twice a year in UserCom, its biannual customer technical magazine. Previous titles are available online as PDFs. A compilation of applications can also be found in the “Thermal Analysis in Practice” manual.

This information was obtained, reviewed and adapted from materials provided by METTLER TOLEDO – Thermal Analysis.

For more information on this source, please visit METTLER TOLEDO – Thermal Analysis.