The Revolutionary Flash DSC 1: Optimum Performance for Metastable Materials

This article presents the new Flash DSC 1. This ultra-fast scanning DSC instrument is based on a sensor in the form of a chip which contains a complete miniaturized DSC.

The Flash DSC 1 provides heating and cooling rates of several thousand Kelvin per second, that is, more than 100 000 K/min).

The instrument can be used to analyze changes in the microstructure of metastable materials, to optimize the composition of materials, to simulate technological processes, and for the thermal analysis of very small samples.

Introduction

The commercialization of the DSC technique in the 1960s led to a rapid expansion of the use of this method for the thermal characterization of substances and materials. The great strength of DSC is that complex information can be quickly and easily obtained about physical transitions, the structure of materials, the kinetics and composition of chemical reactions, and other processes. Conventional DSC has therefore developed into a widely used standard method. Modern conventional DSC instruments have a signal time constant of about one second. Heating rates are between 0.1 K/min and 300 K/min, or about 3.5 decades.

Many materials such as semicrystalline polymers, polymorphic substances, composites or alloys are metastable. Their structure and hence their thermal, mechanical, electrical and magnetic properties depend on their thermal history. In particular, different cooling rates can lead to different metastable structures when the materials are cooled from the melt. The structures often change before melting when the materials are heated again. The reorganization processes involved are time dependent and the result of a DSC heating measurement depends on the heating rate. The reorganization often cannot be measured by DSC because it consists of exothermic and endothermic events that take place simultaneously. 

Cooling rates of up to several hundred Kelvin per second are often used in the production of materials. Unfortunately, the heating and cooling rates of conventional DSC instruments such as the DSC 1 are too low to investigate the behavior of materials under these technologically interesting conditions. DSC instruments are needed that can achieve cooling rates of about 1000 K/s (60 000 K/min). In fact, heating and cooling rate ranges must be as wide as possible (about 6 decades) to study many aspects of structure formation and reorganization. 

The main reason behind the development of the Flash DSC 1 was to make this heating and cooling rate range available for practical applications. The instrument is a commercial DSC based on new technology that allows heating and cooling rates of several thousand K/s.

This article presents the Flash DSC 1 and describes several interesting experiments

The Flash DSC 1 

The Flash DSC 1 (Figure 1) is a completely new type of commercial DSC with a signal time constant of less than 1 millisecond. This allows very high heating and cooling rates to be achieved. Although the time constant is so short, the sensitivity of the DSC is still excellent so that measurements can also be performed at relatively low heating rates. The heating rate range is 1 K/s to 40 000 K/s (60 K min to 2 400 000 K/min). 

There is therefore a region in which the lower heating and cooling rates of the Flash DSC 1 and the higher heating and cooling rates of a conventional DSC overlap. The Flash DSC 1 is therefore an ideal complement to a conventional DSC instrument. The combination of both instruments makes available a heating and cooling rate range of more than 7 decades and thereby enables new information to be obtained on structure formation and reorganization of metastable materials.

The Flash DSC 1 can be equipped with an IntraCooler. This allows a temperature of about –100 °C to be reached. The maximum temperature is determined by the sensor. The UFS 1 sensor is specified up to 450 °C. The optional microscope facilitates convenient sample preparation near the sensor. The sensor can easily be exchanged. 

The MultiSTAR USF 1 DSC sensor

The UFS 1 MultiSTAR sensor (Figure 2, left) is a microchip embedded in a ceramic support. The sensor is based on MEMS technology (MEMS: Micro-Electro-Mechanical Systems) and consists of two separate calorimeters (for sample and reference), which are operated like a conventional DSC.

The actual sensor with the two calorimeters consists of two identical quadratic silicon nitride membranes with a length of 1.6 mm. The thickness of the membrane is 2 µm. The membranes are mounted in a silicon frame that is 300 µm thick.

As shown in Figure 2 (right), the sample area with a diameter of 0.5 mm is in the middle of the membrane. It is coated with aluminum so that a homogeneous temperature profile is formed. The temperature of the sample area is measured by means of eight thermocouples. The sample area is in fact the actual “furnace” of the calorimeter, which is in a cold environment. The furnace can be heated and cooled at high rates of several 1000 K/s due to its low heat capacity and the temperature difference between it and the (cooled) environment. 

Sample

Typical (polymer) samples for the Flash DSC 1 have a thickness of 10 to 50 µm. Organic materials typically have a mass between 10 ng and 10 µg. In general, small disks are first cut from the bulk material. The disks are then cut to smaller pieces near the sensor under the microscope using a knife. The samples obtained are usually positioned directly on the sensor by means of a hair (Figure 2). 

Conclusions

The Flash DSC 1 is a completely new type of DSC instrument. It has been developed to obtain additional information about the behavior of metastable materials through the use of extremely high heating and cooling rates. 

Measurements can however also be performed at low heating and cooling rates. This enables direct comparisons to be made with measurements using conventional DSC – the lower heating and cooling rates of the Flash DSC 1 overlap the higher heating and cooling rates of a conventional DSC instrument. 

The UFS 1 sensor contains a complete DSC consisting of two miniaturized furnaces with temperature sensors. The UFS 1 is a DSC chip sensor based on MEMS technology. The Flash DSC 1 is used to measure fast isothermal crystallization and reaction processes. 

The wide heating and cooling rate range enables you to investigate the formation of structure and reorganization of metastable materials. If reorganization can be suppressed through rapid heating, the original material can be analyzed in its original state. The special performance features and properties of the Flash DSC 1 allow research in other application fields, for example the measurement of very small sample quantities. 

The Flash DSC 1 is therefore a very valuable addition to conventional DSC. 

_{The Revolutionary New Flash DSC 1: Optimum Performance for Metastable Materials | Thermal Analysis Application No. UC 323 | Application published in METTLER TOLEDO Thermal Analysis UserCom 32}