Ignition Behavior of Al/Fe2O3 Metastable Intermolecular Composites
Abstract
Nano size Al/Fe2O3 thermite system has been reported in the literature as metastable intermolecular composites (MIC). Nano Al/nano Fe2O3 MIC has been prepared in various proportions by ultrasonic method. A comparative study on heat output and thermal behavior has been made on MIC using DTA (Differential Thermal Analysis), STA (Simultaneous Thermal Analyzer) and bomb calorimeter. It has been observed that nano-size ingredients produce more heat output compared to micron size ingredients. The ignition temperature also reduces in case of MIC indicating faster release of energy at lower temperature. The impact of ignition of nano-thermite has been reported based on ignition DTA experiment. DTA analysis also shows complete reaction in case of MIC where as micron size thermite showed an endothermic peak of Al melting indicating incomplete reaction. The PXRD (Powder X-Ray Diffraction) data of combustion products has been used to establish the combustion mechanism of MIC. The activation energy of MIC has been calculated using Kissinger, Ozawa and Starink kinetic equations and compared with literature reported values.
Keywords
Download Options
Introduction
The thermite systems give very high-temperature output and are prefered as heat source for several applications. The Al/Fe2O3 thermite system is a classical thermite system and can be used for welding of railway tracks (since 1898), cutting and perforation of materials, to produce alumina liners insitu for pipes, a portable heat source, a high-temperature igniter, a pyrotechnic heat producer as an additive to explosives [1] propellants [2], gas generating compositions [3], nanoenergetic microelectromechanical systems (MEMS) platform for micro-propulsion system [4] and incendiary grenade [5]. This system has also been investigated in environmental protection processes [6], namely for the treatment and recycling of zinc hydrometallurgical wastes [7, 8] and for the treatment of by-products of steel industry [9]. Other recent applications of this reactive system are the synthesis of ceramic reinforced metal–matrix composites [10, 11], of magnetic granular films [12], of iron aluminides [13-15], of transition metal carbide/ nitrides [16], alloying/welding [17] and energetic nanocomposites [18- 20]. Al/Fe2O3 has been used for catalytic application of combustion of AP/HTPB system [21]. Recently fabrication of hybrid nano-composite from Al/Fe2O3 system has been reported in the literature [22].
Conclusion
Nano thermite compositions (MICs) were prepared by ultrasonic method using nano Al and nano iron oxide of different weight percentage which were found to be more efficient than micron size thermite composition. Heat of combustion obtained by bomb calorimeter increased upon increasing Al content. Ignition temperature measured by DTA of MICs was lower than micron size thermite composition and combustion reaction was very fast with faster release of thermal energy. In the thermo-gravimetric analysis, two transitions were observed, one for nittridation ignitation with exo followed by melting of Al with endo peak for thermite. MIC showed only one nitridation ignitation with exo peak. The activation energy was calculated using Kissinger, Ozawa and Starink kinetic equation and found to be 164, 157 and 158 kJ/mol. MIC’s are more efficient in energy release than micron size thermite composition. The mechanism of the combustion reaction was investigated by XRD of combustion products. Micron size thermite composition produced byproducts such as Al2O3 and FeAl3, whereas in case of MIC’s, hercynite was the intermediate product along with FeO and with increasing Al content in MIC, formation of Fe phase took place along with Al2O3.