# Analysis of Nucleation and Glass Formation by Chip Calorimetry
## 3 Results and Discussions  
### Nucleation and Primary Crystallization  
1.1 Separation of Glass Transition Temperature and Crystallization Temperature by Increasing Heating Rate in Marginal Al-Based MG  
For most MG systems with good glass formation ability, the glass transition signal is strong enough to be detected in the heating DSC traces, which makes it possible to measure the glass transition temperature and the supercooled liquid region by the conventional DSC method. However, for marginal MGs such as the Al-based MGs, the glass transition signal is prone to be overlapped by a primary crystallization for Al nanocrystals precipitation [6; 7]. Thus, the traditional DSC is not a good thermal analysis tool to observe the glass transition of Al-based MGs. On the other hand, considering that the glass transition and crystallization are significantly different kinetic processes, they should follow different evolution paths with different heating rates so that the two kinetic signals are separated under higher heating rates. Here, we take the typical Al\({}_{92}\)Sm\({}_{8}\) MG as an example. The conventional DSC with heating rate of 0.33 K/s was applied to measure the heat flow curve shown in Figure 1a. It is clear that the conventional DSC heat flow curve only displays the primary and secondary crystallization peaks as shown in Figure 1b, and there is no clearly defined glass transition signal. In contrast, the maximum heating and cooling rates for high-rate Flash DSC instrument with chip sensors (Flash DSC2, Mettler Toledo ((Columbus, OH, USA))) are 4 \(\times\) 10\({}^{4}\) and 4 \(\times\) 10\({}^{3}\) K/s, and the temperature range is between \(-\)90 \({}^{\circ}\)C and 450 \({}^{\circ}\)C [8; 9]. The optical picture of tiny MG sample being loaded onto the Flash DSC chip is shown in Figure 1b, and the inserted optical picture gives the ribbon-like Al-based MG sample. A series of Flash DSC heat flow curves corresponding to different heating rates from 50 K/s to 1000 K/s were measured as shown in Figure 1c. For all heating rates by Flash DSC, the Flash DSC heat flow curve exhibits both the obvious glass transition and crystallization signals marked by \(T_{g}\) and \(T_{XI}\). To further study the dynamic properties of glass transition and primary crystallization for the Al\({}_{92}\)Sm\({}_{8}\) MG, the evolutions of \(T_{g}\) and \(T_{XI}\) with heating rate are analyzed based  
Figure 1: (**a**) Heat flow curve by conventional DSC with the heating rate of 0.33 K/s for Al\({}_{92}\)Sm\({}_{8}\) MG; (**b**) optical picture of tiny MG sample on Flash DSC chip (the left inserted picture gives the optical photo of ribbon-like MG sample); (**c**) a series of Flash DSC heat flow curves by Flash DSC with the heating rates ranging from 50 to 1000 K/s; and (**d**) activation energies of glass transition and primary crystallization by fitting the experimental \(T_{g}\) and \(T_{XI}\) based on the Kissinger equation. on the Kissinger equation. For MGs, the glass transition temperature and the primary crystallization temperature usually follow the Kissinger equation [7]:  
\[ln(\beta/T^{2})=(-E/(RT))+constant \tag{1}\]  
where \(\beta\) is the heating rate; \(T\) is the value of the onset temperature of primary crystallization or the glass transition; \(E_{g}\) and \(E_{X1}\) are the activation energies for the glass transition and primary crystallization, respectively; and \(R\) is the gas constant. Thus, the activation energy for the glass transition and primary crystallization for Al\({}_{92}\)Sm\({}_{8}\) MG can be calculated by fitting the experimental results with Kissinger equation and the detailed results are shown in Figure 1d. The activation energy for primary crystallization is 98.8 kJ/mol and 136.7 kJ/mol for the glass transition. These activation energy values are comparable with those of previous researches in other Al-based MG systems [10; 11; 12]. Thus, for marginal Al-based MG, the glass transition requires more activation energy than that for the primary crystallization process.