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In this interview, AZoM and Jurgen Schawe of METTLER TOLEDO talked about fast scanning chip calorimetry and its various applications.
DSC technology measures the heat involved in a thermal event. This can be an endothermic or exothermic transition of the material. In addition to isothermal measurement, this technology can also be used in heating and cooling modes. For traditional DSC, the typical scan rate range is 0.1 to 100 °C per minute, and a milligram range sample enclosed in a small crucible is used.
Traditional DSC equipment contains a sensor with two independent measurement positions-one for the sample in the crucible and the other for reference, usually an empty crucible. The sensor is located in a furnace operating at a precisely controlled temperature. The diameter of the measuring system is a few centimeters.
The information that can be obtained from the DSC curve is the enthalpy and temperature of the phase transition, such as crystallization, melting, solid-solid transition, and liquid-liquid transition of liquid crystal materials. For amorphous and semi-crystalline materials, the glass transition can be analyzed. In addition, the enthalpy and temperature of chemical reactions such as cross-linking, decomposition, or dehydration can also be measured. The kinetics of these thermal events can be analyzed by measuring various heating or cooling rates.
There are limitations in the interpretation of measurement curves and the understanding of material behavior during processing.
Let's start with the explanation.
Modern materials such as polymers, metal alloys, or drugs often form metastable structures, which may transform into more stable variants during heating. This recombination process is not always visible in traditional DSC, because exothermic and endothermic events can occur simultaneously, and the total heat measured becomes very small.
Many thermal events are so fast that they cannot be fully studied using traditional DSC. For example, many polymers or the crystallization of glass-forming metal alloys. Due to the limitation of scan rate, it is impossible to study isothermal crystallization in a wide temperature range, because crystallization may have occurred during the cooling process from melting to crystallization temperature.
Another problem is related to the thermal stability of many organic materials. This material tends to decompose during the melting process. This makes it impossible to correctly determine the melting enthalpy and melting temperature using conventional calorimetric techniques.
Material processing is usually related to rapid cooling or heating. Typical rates are between 10 and several thousand °C per second. It is not possible to directly study the behavior of materials at this rate using traditional DSC. In addition to many traditional processing techniques, modern additive manufacturing techniques (also known as 3D printing) are also examples of the use of high heating and cooling rates.
In order to overcome the limitation caused by insufficient scan rate, METTLER TOLEDO developed Flash DSC. This is a new fast scanning DSC instrument using the latest technology.
Flash DSC is a non-insulated chip calorimeter that combines innovative measurement and control concepts with user-friendly ergonomics and functions.
The Flash DSC sensor is based on MEMS technology and includes a complete DSC with the sample and reference furnace embedded on the silicon nitrate film. This sensor design makes the heat capacity of the furnace small, which leads to a fast scanning speed.
In order to cool the sample at a faster cooling rate, the sample is surrounded by relatively cool gas. This allows the sample to cool quickly. In order to improve the thermal contact between the sample and the sensor, the sample is placed directly on the sensor without any crucible.
Currently, there are two types of sensors to choose from-the standard sensor UFS with a maximum temperature of approximately 500 °C and the high-temperature sensor UFH with a maximum temperature of 1000 °C. The lowest temperature is about -95°C. These sensors provide a wide range of scan rates, for UFS sensors, usually between 1 and 10,000 °C per second, and for UFH sensors, the scan rate is usually as high as 50,000 °C per second. This high dynamic range opens up new horizons for the dynamic analysis of thermal events.
It is important to realize that there is an overlap in scan rate between Flash DSC and traditional DSC.
In order to achieve ultra-high scan rates, Flash DSC can handle small samples—usually a few micrograms to a few nanograms in mass.
The preparation and insertion of these tiny samples can be performed by a user who can sit comfortably in front of the instrument. To ensure the best thermal contact, the sample is placed directly on the sensor with the help of a microscope. This also ensures simple and reliable sample handling. In addition, other preparation techniques are also possible. For example, spin coating or sputtering can be used to prepare thin films.
Thanks to the innovative sensor support, the sensor can be replaced quickly and easily in less than a minute. The cover can also be installed on the top of the sensor bracket and sealed with screws to protect oxygen-sensitive materials.
The core of Flash DSC is a chip sensor based on MEMS technology. The standard UFS sensor is mounted in a ceramic frame with electrical contacts and consists of two identical two-micron thick silicon nitride films. The sensor has sample and reference areas, which contain heaters and thermocouples, each with a diameter of 0.5 mm.
The sensor is actually a complete miniaturized DSC furnace for sample and reference analysis.
The high symmetry, high sensitivity and short time constant on both sides of the sensor make the measurement reproducibility of the Flash DSC extremely good, and the dynamic range is high, which is about two orders of magnitude larger than that of the traditional DSC. The nominal maximum temperature of the UFS sensor is 450 °C. However, it can also be used at higher temperatures up to 520 °C. Flash DSC can be operated with standard UFS sensors or high temperature UFH sensors.
The UFH sensor can measure temperatures up to 1000 °C, making it ideal for studying ceramics and metals, such as bulk metallic glass. The sample and reference areas are small. The diameter is 80 microns. Two heaters surround these areas. The smaller geometry reduces the time constant of the sensor and increases the maximum scan rate to more than 10,000 degrees Celsius per second. This makes the sensor also useful for many polymer applications.
When the kinetic process significantly affects the structure formation of the studied material, it is usually recommended to use multiple heating and cooling rates.
In these cases, the structure depends on the cooling conditions and is usually metastable. This means that the structure will change due to temperature changes or isothermal storage.
Polymers are an example of materials that form metastable structures. Due to their molecular structure, they only produce small crystallites when cooled from the melting point. The size of the crystallites depends on the crystallization temperature. A higher cooling rate will lower the crystallization temperature, and by further reducing the crystallization temperature, glass can be formed for many polymers.
Recombination occurs when heated, resulting in perfect crystals. One possible process might be to melt imperfect crystallites and recrystallize them to form a more stable structure. In this case, the exothermic and endothermic processes occur at the same time, and the DSC curve does not show obvious such processes.
It should be noted that in these cases, the DSC melting curve shows the result of recombination, not the melting of the original crystallites.
The degree of reorganization depends on the heating rate, and at high heating rates, reorganization can be inhibited. Metastable structures are formed in many other materials besides polymers, such as polymorphic substances.
In metal alloys, diffusion processes, phase separation, precipitation, and other time-related processes lead to the formation of metastable structures.
The different phases and their distribution depend on the crystallization conditions.
For example, physical stability at low temperatures, entropy delay, and crystallization kinetics are particularly important for glass molding materials.
Since the activation energy of physical processes and chemical reactions are different, chemical reactions (such as decomposition) can be separated from phase changes such as glass transition and melting by using a high heating rate. This is a great advantage for measuring chemically unstable materials.
The kinetics of structure formation can be studied by cooling measurements at different cooling rates.
An important advantage of Flash DSC is that the cooling rate corresponds to the cooling rate of a technical process, such as the cooling rate that occurs in injection molding or laser sintering. This allows us to closely track the formation of structures that occur during the process and obtain information about the function and effect of additives.
Other application areas of Flash DSC include process analysis involving complex and rapid structure formation, rapid reaction kinetic determination, or the study and comparison of the effects of additives at cooling rates directly related to the process.
Due to the high scan rate, a comprehensive thermal analysis of the material can be performed in the millisecond range. For example, the isothermal crystallization process can be directly measured in a wide temperature range.
These measurements are very sensitive to the effects of additives or small component modifications. Flash DSC allows the study of very small samples, as low as a few nanograms.
Since the data can be measured under actual process conditions, it can be used for simulation calculations, such as optimizing tool performance, material composition or processing parameters.
Potential applications have driven the need for higher heating and cooling rates than traditional DSCs.
Flash DSC is an ideal complement to traditional DSC. This is mainly because the instrument provides an extremely wide range of heating and cooling rates-which is a very important factor in characterizing modern materials.
The data obtained with Flash DSC optimizes the production process, especially because the materials can be measured at the cooling rate at which they were produced. By measuring structure formation at a cooling rate that is related to the cooling rate that occurs in production, materials or production conditions can be improved.
The rapid and variable measurement capabilities of the instrument also allow the material to be characterized in a short period of time.
The ultra-high cooling rate of Flash DSC can be used to measure the process involved in the formation of cooling structures. In contrast, the ultra-high heating rate reduces the measurement time and can be used to study the recombination process or prevent recombination from occurring.
Due to its high sensitivity, the heating and cooling rate of Flash DSC overlaps to a certain extent with traditional DSC. This allows direct comparison of experimental results.
The Flash DSC has a temperature range of -95 °C to 1000 °C. The application-oriented ergonomics and functions of the instrument are specially designed to prepare samples easily and quickly.
A large number of scientific publications show that Flash DSC has become an important method for material characterization, many previously unknown effects have been discovered, and its application range is also expanding.
Various Flash DSC applications can be downloaded via the Internet. METTLER TOLEDO publishes articles on thermal analysis and applications in different fields in the well-known METTLER TOLEDO Biennial Technical Customer Magazine. Past issues can also be downloaded as PDF.
To learn more about Flash DSC or other METTLER TOLEDO thermal analysis products, please visit our website or call your local METTLER TOLEDO sales specialist. Our website also includes information about our full range of manuals, manuals, webinars, videos, application notes, training courses, applications and other products.
Jürgen EK Schawe received his PhD. Received a PhD in solid-state physics in 1984. After that, Dr. Schawe worked in the Polymer Physics Group of the University of Rostock and from 1992 to 1998 in the Department of Calorimetry, University of Ulm. Since 1999, he has been working at Mettler-Toledo GmbH in Nänikon, Switzerland. Dr. Schawe is a senior applied scientist in material characterization. Since 2020, he has been a visiting scientist in the Department of Materials at ETH Zurich. Dr. Schawe was awarded the 2010 STK Award for Applied Chemical Thermodynamics by the Swiss Society of Thermal Analysis and Calorimetry. To date, Dr. Schawe has published 80 articles in pre-reviewed scientific journals, including highly-rated journals such as Nature Communications. Editor-in-chief of "Thermochimica Acta" special issue, wrote chapters of monographs, and obtained 5 patents.
This information is derived, reviewed and adapted from material provided by Mettler Toledo-Thermal Analysis.
For more information on this source, please visit METTLER TOLEDO-Thermal Analysis.
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