# Thermal and Thermomechanical Analysis of Amorphous Metals: A Compact Review
## 2 Thermal Characterization of Amorphous Metals
### Fast Scanning Calorimetry of Amorphous Metals  
#### 2.2.1 Configuration Considerations  
To overcome the challenges that the conventional calorimetry methods face when aiming to describe the amorphous metals, fast scanning calorimetry (FSC) has risen as one of the most prominent methods to study these processes. It is a modified variation of DSC that surpasses the physical and practical limits of its predecessor [52]. First off, the samples are placed directly on a micro-electromechanical system (MEMS) dual sensor chip with a ceramic frame, which holds two silicon nitride membranes: one acting as a reference and the other as the sample. Silicon nitride is widely recognized for its excellent mechanical properties, and studies have indicated that it does not affect measurement accuracy or sensitivity [53]. Direct contact of the sample to the sensor allows for better heat transfer during heating and cooling and provides an ultrafast and sensitive sensor response, making it possible to study samples that undergo subtle transformations, degrade quickly, or are unstable [54]. Two kinds of sensors are used, depending on the temperature range needed: MultiSTAR UFS1 sensor (Mettler, Toledo, OH, USA) for temperatures up to 450 \({}^{\circ}\)C and the MultiSTAR UFH1 sensor (Mettler, Toledo, OH, USA) for temperatures up to 1000 \({}^{\circ}\)C. The difference in execution of the MEMS chip lies in the area of the sample and reference: 500 and 80 \(\upmu\)m for the UFS and UFH sensors, respectively [55]. The UFH sensor is ideal for analyzing bulk metallic glasses, but the area is much smaller. FSC has proven that at high heating and cooling rates, complex composite systems, such as BMGs, often undergo only one crystallization instead of multiple transitions (Figure 1).  
This can also be observed in other studies, such as the work of [PERSON] et al., who proposed the existence of three regimes, varying from deeply undercooled to slightly undercooled liquids. They found that for the highly undercooled liquid (high heating and cooling rates), the energy of activation was independent of the heating rate as opposed to the slightly undercooled liquid [57; 58]. Generally, it can be said that in the deeply undercooled regime, crystallization is controlled only by pre-existing nuclei [59; 60]. Furthermore, the true values of the critical cooling rate can be measured with ease, and it has been shown that the critical cooling rate and general crystallization kinetics depend on the sample mass. However, the sample mass needs to be in the range of \(<\)10\({}^{1}\) ug and loaded onto a sensor chip, which complicates sample preparation [53] (Figure 2). [PERSON] et al. showed that there are various critical cooling rates, which can lead to different glasses for the same material. In their work, they utilized FSC for the analysis of two glasses, one cooled at 500 K s\({}^{-1}\) (self-doped glass) and the other at 20,000 K s\({}^{-1}\) (chemically homogeneous glass), and their findings concluded that there are various nucleation mechanisms that govern glass formation [61].  
Figure 1: Fast scanning calorimetry of MgCuGd glasses at different cooling rates. A distinct peak (glass transition) diminishes at high cooling rates, indicating a shift in the glass formation mechanism (reprinted with permission via CC Attribution 4.0 License) [56].  
Figure 2: MultiSTAR UFS 1 MEMS chip sensors for sample loading: sample and reference sensor sites are on the left, while the 14 connectors of the Flash DSC (fast scanning calorimetry instrument by Mettler Toledo) are on the right (reprinted with permission via CC Attribution 4.0 License) [54].