Supporting Information for Application in Nanoenergetic Materials (nEMs)
1. SEM Characterization
Figure 1 SEM images of the Co3O4 nanowalls and nanowires after Al integration: (a) top
view and (b) cross-section view
2. DTA Characterization
The exothermic reactions of the Al/Co3O4 based nEMs are first characterized by
differential thermal analysis (TA Instruments Q600 DTA) as shown in figure 2, where the
deposited Al thickness is about 800 nm. The DTA is running from 40 to 1000 °C at a heating
rate of 10 °C/min under 50 ml/min Ar flow. It can be seen that there are two exothermic peaks
associated with the thermite reactions and an endothermic peak associated with the melting of
Al. The onset temperatures of the first and second exothermic peaks are around 560 °C and
900 °C, respectively. The onset temperature of the endothermic peak is about 650 °C, which is
close to the melting temperature (660 °C) of bulk Al.
The first exothermic reaction in figure 2 is caused by the thermite reaction between the
Co3O4 nanostructures (nanowalls/nanowires) and Al, which occurs prior to the melting of Al.
This exothermic reaction is based on the solid–solid diffusion mechanism. The increased
surface energy of the Co3O4 nanostructures and nano Al enhances their reactivity and causes
the reduced onset temperature. After the melting of Al, Co3O4 and tiny CoO beneath the
Co3O4 nanostructures react with the melted Al at about 900 °C. The second exothermic
reaction is based on the liquid–solid diffusion mechanism.
Figure 2 DTA curve of the reactions of the Al/Co3O4 based nEMs
3. DSC Characterization
In order to quantitatively determine the heat of reaction, the Al/Co3O4 based nEMs are
characterized using differential scanning calorimetry analysis (TA Instruments Q20 DSC) as
shown in figure 3. The DSC is carried out from 40 to 680 °C at a heating rate of 5 °C/min
under 75 ml/min Ar flow. The exothermic peak with a peak temperature of about 560 °C
corresponds to the first exothermic peak in the DTA curve in figure 2, which is caused by the
solid–solid reaction between the Co3O4 nanostructures and the nano Al. Integration of this
exothermic peak in the DSC curve gives a heat of reaction of 1770 J/g. The endothermic peak
with a peak temperature of about 660 °C corresponds to the endothermic peak in the DTA
curve in figure 2, which is caused by the melting of Al.
By assuming that the DTA signal is proportional to the heat of reaction, we can use the
value of heat of reaction calculated from the DSC analysis in figure 3 to scale the DTA curve
in figure 2. Although this is not very accurate, because the relationship between the
temperature and the heat is not exactly linear, it allows us to roughly estimate the total heat of
reaction of the Al/Co3O4 based nEMs to be around 3100 J/g.
Figure 3 DSC curve of the reactions of the Al/Co3O4 based nEMs