The Research Of Explosive Consolidation And Sintering Of Nanometer Ceramic Powders

The explosive consolidation and sintering powders is a novel material process or synthesis technology, which uses the energy generated from explosive and acts on the metal and nonmetal powders in the form of shock wave. During the process, the powders experience high temperature and high pressure instantaneously. In fact, it is the application of high temperature consolidation principle of porous bulk under shock wave adiabatic compact condition. This technology is called as the third research subject in the explosive process field. Investigation of ECCP (explosive consolidation ceramic powders) whether on experiment or theory, is always a challenging work. With the development of material preparation technology, the nanometer powders have been produced amply, whereas the technology of preparation of sintering bulk with nanometer morphology is still in studying. As a special powders sintering technology, explosive consolidation has broad prospect in the application of powders compact and sintering. Although many researchers have been researching on the theory and done many experiments on the ECCP, there is still lack of results involving nanometer scale. This thesis researched the ceramic powders in nanometer scale, and the main work include1. Based on the brittleness of ceramic materials and supposing particles are on the elastic state during explosive consolidation, the heat conduction behavior in particles is investigated. It is found that there is no welding sintering behavior due to friction between nanometer ceramic particles during explosive consolidation. This result can be used to judge the theory of the ECCP.2. No matter how small the ceramic particle is, the brittle character is determined by the ceramic chemical bond. Therefore, the nanometer ceramic particles may be fractured in the process of explosive consolidation with imbalance dynamic high pressure. In the two-dimensional plane, with elastic hypothesis, the acting force between ceramic particles is researched using the knowledge of elastic mechanics, and it produces, from our study, the result that there are two maximal shear stress and their corresponding positions. The possibility of the nanometer ceramic powders fracturing during explosive consolidation is confirmed with comparing and studying the three criterions of brittle failure. With the above mentioned results, we explained the phenomena that the particles incline to fracture uniformly with increasing the shock pressure. Furthermore, because one of the maximal shear stress positions in the range of 0.5nm depth from the contact surface, and the thickness of crystal boundary (interface) is usually in the same scale, there may be shear plastic flowing of particles in the shock wave condition.3. For experiments, due to the special physical and chemical characters of ITO ceramics, we propose a process using cold explosive consolidation plus subsequent sintering. The quality sintering bulk with sub-micron crystal size morphology and more density characters has been successfully obtained by adjusting the technology parameters. The preheat explosive consolidation and sintering ceramic powders is an effective route to solve the macro- and micro- cracks in explosive consolidated and sintered bulk. In this thesis, we renovated a 5kg-TNT equivalent spherical explosion-containment vessel to be protecting and supporting structure of preheat explosive consolidation set (PHECS) reference to Prümmer's PHECS. In the renovated set, we designed an ingress pipe structure for sample passed, which can protect the repetitious using components. This structure can ensure preheated sample exactly dropped into the middle of explosive compact. And it has characters of low cost and simple manufacture. For the sake of long-distance controlling, we added a signal system on the PHECS. Thus can ensure us the time when the sample dropping into the middle of the explosive compact, and initiating the explosive in time. Using our PHECS and adjusting the consolidation structure, preheat temperature and explosive shock pressure, we obtained density ITO sintering bulk. The crystal size of the bulk is in the range of sub-micron.4. The preparatory study has been performed respectively on nanometerγ-Al₂O₃ andα-Al₂O₃ ceramic powders with PHECS, and the parameters, with which theγ-Al₂O₃ powders have been qualitatively explosive consolidated and sintered, furthermore, the crystal type has been transformed to beα-Al₂O₃ crystal type, have been found out. When the preheat temperature reaching 0.5Tm or so and explosive shock pressure reaching 18.4GPa, nanometerα-Al₂O₃ ceramic powders can be consolidated to be density, but the crystal size is sensitive to the preheat temperature under the above mentioned conditions.