How is thermal analysis applied in the field of renewable energy, and what techniques are used to ensure quality control of materials?
Renewable energy resources are now widely used as a replacement for fossil fuels. Developments are progressing rapidly, and new materials employed by renewable energy industries require suitable testing and quality control. This is where thermal analysis comes into play!
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 materials’ physical properties and behavior as a function of temperature, including melting, thermal stability, and curing reactions.
What factors have driven the shift towards renewable energy, and how does thermal analysis contribute to understanding materials used in sustainable energy technologies?
There has been a significant shift towards renewable and sustainable energy sources over the last 20 or 30 years.
This shift has been catalyzed by concerns over limited fossil fuel resources, increased awareness of environmental issues, and unresolved challenges associated with operating and decommissioning nuclear power plants. Several serious accidents in recent years have also undermined the widespread acceptance of nuclear power.
Renewable energy is derived from resources naturally replenished on a short timescale, such as hydropower, wind power, biomass, solar energy, geothermal power, and biofuels. Related technologies, including fuel cells, batteries, and energy storage systems, utilize specialized compounds that can also be analyzed through 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 meets the required standards, and how to assess the curing behavior of a material.
For example, in the wind energy industry, it is necessary to describe the degree of cure of epoxy resins used to manufacture laminated rotor blades for wind turbines. This analysis can easily be performed using DSC.
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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 to investigate physical events and processes when a sample is heated. During heating, for instance, a sample may melt, transition from a solid to a liquid state, or experience 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 materials in renewable energy include DSC, thermo-optical analysis (TOA), TGA, TMA, and DMA.
Each of these techniques measures different properties and provides insight into various applications.
What is DSC, and how is it applied in analyzing materials?
DSC is a thermal analysis technique that measures a sample's absorbed or released energy as it is heated, cooled, or held at a constant temperature.
DSC instruments vary based on 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 semi-crystalline polymer displays various thermal events: initial start-up deflection, glass transition, cold crystallization, melting, and oxidative decomposition.
Understanding behaviors such as the glass transition, crystallization, melting, solid-solid transitions, and chemical reactions are very important in materials used in renewable energy processes. Key applications include determining the glass transition temperature, melting enthalpy, curing rates, oxidative stability, and specific heat capacity.
For example, DSC is used in biodiesel testing, where the oxidation of unsaturated fatty acids can lead to short-chain formation and rancidity. Stabilizers are therefore added to biodiesel to prevent oxidation. Stability tests can then be carried out by DSC as part of the material development, and for quality control of the final product.
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 visually observed, as it is heated or cooled. Some TOA instruments allow 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 determining 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 the sample are placed in a crucible, weighed, and heated, and the weight change is continuously recorded as a function of temperature or time. This process provides insights into the sample's composition, such as its polymer and filler content.
TGA is also used to analyze processes such as vaporization or decomposition. The subsequent evolved gases can be examined online using hyphenated techniques like TGA-mass spectrometry (MS), TGA-Fourier-transform infrared spectroscopy (FTIR), or TGA-GC/MS (chromatography/mass spectrometry).
TGA’s primary analytical applications for materials in the renewable energy sector include detailed composition information, including filler content. It is also useful for assessing the thermal or oxidative stability of products like biodiesel and analyzing moisture or volatile content in 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 primary application is to determine expansion behavior of materials and the coefficient of thermal expansion. TMA is also highly effective for identifying the glass transition temperature and examining softening behavior, creep, or swelling in a solvent.
Consider a practical example. During usage, the separator membrane in lithium batteries can become too warm, potentially causing shrinkage, rupture, and, ultimately, battery failure 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 raw material quality 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 a periodic oscillating stress, along a controlled temperature program.
DMA has various analytical applications for materials in the renewable energy sector. It generally provides insights into mechanical modulus, compliances, damping, and viscoelastic behavior.
Glass transition temperatures, softening temperatures, or beta-relaxation processes are identified as peaks in the tan delta or through changes in the modulus.
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 across various fields twice yearly in UserCom, its biannual technical customer magazine. Back issues are available as PDFs online. A compilation of applications can also be found in the “Thermal Analysis in Practice” handbook.
This information has been sourced, reviewed, and adapted from materials provided by METTLER TOLEDO - Thermal Analysis.
For more information on this source, please visit METTLER TOLEDO - Thermal Analysis.
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