Preparation And Properties Of Metastable Intermolecular Composite Al/Bi₂O₃

There is an important technical limitation in present widely researched metastable intermolecular composite(MIC), which is that it only releases a great amount of heat and produces high temperature during the thermite reaction. Because of the less gas production, outstanding pressure output performance is almost impossible to obtain, such as high pressure and shock wave. The main reaction product bismuth(Bi) has a much lower boiling point(1873 K) than the maximum thermite reaction temperature(3319 K) in nano Al/Bi2O3 composite, therefore the product evaporates and increases the output pressure and reaction speed. In this thesis, a series of nano Al/Bi2O3 composite were prepared and characterized using Bi2O3 prepared by solvothermal method.First of all, Bi2O3 were prepared by solution combustion method and solvothermal method. The samples were characterized by Scanning Electron Microscope(SEM) and X-ray Diffraction(XRD). The results show that the morphology of β-Bi2O3 prepared by solution combustion method was micro-sized irregular particle. Homogeneous nano Bi2O3 with high crystallization degree and small particle size were prepared by solvothermal method. Sufficient crystallization, particle diameter of 40-300 nm and crystal form of β-Bi2O3 and α-Bi2O3 could be obtained by controlling the precursor calcination temperature.Ultrasonic method was used to prepare Al/Bi2O3, Al/Fe2O3 and Al/CuO composites, meanwhile, Al/Bi2O3 with different stoichiometric proportions and particle sizes were prepared. The samples were characterized by SEM, XRD, DSC(Differential Scanning Calorimetry) and tested by closed bomb vessel. The XRD and SEM results show that the crystal structures of Al/Bi2O3 remain unchanged after ultrasonic vibration, particles uniformly distributed, and there are some agglomerations. The DSC analysis indicates that there are two exothermic peaks of thermite reaction and one endothermic peak of aluminum melting, and the calculated apparent activation energy Ea is 341 kJ/mol. So the main reaction of Al/Bi2O3 is liquid-solid phase reaction, and Al/Bi2O3 has low sensitivity to heat. The closed bomb tests show that the peak pressure of 4559 kPa and ?P/?t of 11.397 GPa?s-1 were generated by Al/Bi2O3, which are greater than those of Al/Fe2O3 and Al/CuO. Al/Bi2O3 has good features of high gas generation and fast reaction rate. Insufficiency or excess of Al could decrease the pressure output performance, and the pressure output performance also be decreased with the increase of Bi2O3 particle size.In order to improve the uniformity and gas generation of Al/Bi2O3, Al/Bi2O3 was prepared by self-assembly method using high polymer Poly(4-vinylpyridine)(P4VP). Al/Bi2O3/OA was prepared by ultrasonic method using binder oleic acid(OA). The results show that P4 VP improved the binding affinity of Al and Bi2O3. The main reaction of Al/Bi2O3 is solid-solid state reaction. The adding of P4 VP decreased the ignition delay time and increased Pmax and ?P/?t. The adding of OA improved the uniformity of Al/Bi2O3, and the main reaction of Al/Bi2O3 is solid-solid state reaction. The Pmax of Al/Bi2O3 could be improved by adding just enough OA, while coated OA extended the ignition delay time and decreased ?P/?t.At present, MIC material is one of the hot research topics in the field of energetic materials. Metastable intermolecular composite Al/Bi2O3 prepared in this thesis has good features of high gas generation, high pressure output and fast reaction rate, which shows the positive significance in increasing pressure output and expending the application range of MIC materials. The pressure output performance of Al/Bi2O3 could be improved by adding assembly agent or just enough binder. It gives a new way for the research of high pressure output MIC materials.