Materials Research Express (Jan 2022)
Effect of MnO2 morphology on the thermal properties and combustion behavior of nano-Al/MnO2 thermite
Abstract
Al/granular MnO _2 and Al/rod MnO _2 thermite samples were prepared to investigate the effects of different morphologies of MnO _2 on the thermal properties and combustion behavior of nano-Al/MnO _2 thermite. The morphology and thermal properties of the thermite were characterized by field emission scanning electron microscopy (FE-SEM), x-ray diffractometry (XRD), and differential scanning calorimetry (DSC). DSC results show that the Al/rod MnO _2 releases 1274.39 J·mol ^−1 heat, which is 292.58 J·mol ^−1 more than the Al/granular MnO _2 . The initial reaction temperature of Al/rod MnO _2 is 567.39 °C, which is delayed by 17.39 °C versus 550 °C of Al/granular MnO _2 . Non-isothermal thermodynamic analysis was used to measure the activation energy of Al/rod MnO _2 to be 234.36 kJ·mol ^−1 , which is 46.53 kJ·mol ^−1 higher than that of Al/granular MnO _2 . This corresponds to an increase in the ignition temperature in the DSC curve and indicating a higher safety profile. In the open burning experiment, the burning time of Al/granular MnO _2 was longer and sparks sputtered around the flame. The Al/rod MnO _2 has a large combustion flame and a fast combustion rate. The light intensity peaks of the two groups of samples are close in the light intensity test. The light intensity existence time of Al/rod MnO _2 is 0.0146 s, which is 0.094 s shorter than Al/granular MnO _2 . This shows that the combustion rate of Al/rod MnO _2 is much faster than that of Al/granular MnO _2 . The closed-tube combustion experiment shows that the combustion wave velocity of Al/rod MnO _2 increases first and then decreases; the maximum wave velocity reaches 339.6 m·s ^−1 , and Al/granular MnO _2 cannot self-propagate combustion in the microporous environment. In the constant volume combustion experiment, the peak combustion pressure of Al/rod MnO _2 is 0.938 Mpa, and the peak value of Al/granular MnO _2 combustion pressure is 0.581 Mpa; the difference is obvious. This shows that the rod MnO _2 gas production performance is better. According to the duration of the pressure peak, the burning speed of Al/rod MnO _2 in the light intensity test is confirmed again to be much faster than that of Al/granular MnO _2 . The Al/rod MnO _2 is better than Al/granular MnO _2 in thermal and combustion performance and is also safer. This provides a basis for future performance and safety research on aluminothermic materials.
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