| Microwave sintering is a novel rapid material preparation method which is superior to the conventional sintering. It has important practical and theoretical significance to study the microwave sintering mechanism. In this paper, the importance and necessity of carrying out the SR-CT online observation of the microstructure evolution during microwave sintering was represented. According to this, a set of SR-CT technology based microwave sintering analyze system was successfully built. Depending on this system, the SR-CT experimental study on the microwave sintering of metal, ceramic and metal-ceramic hybrid materials were carried out. The microstructure evolution characteristics and the corresponding sintering mechanisms of these materials were analyzed by the comparison between different materials, as well as the microwave sintering and conventional sintering. Finally, the further discussion of the "thermal effects" and "non-thermal effects" of microwave were carried out. The main content and the innovation of this paper are:Firstly, a new synchrotron radiation CT technology-based microwave sintering experimental system was built. The online observation of microstructure evolution during the fast microwave sintering by the synchrotron radiation CT technique was realized. The highest resolution reached submicron. At present, the news about such experimental system has not been reported.1. The separated structure resolves the problem of the space limitation of the high contrast, high-resolution SR-CT experiment platform;2. The multi-dimensional precision electronic control rotary device can realize the high precise of positioning and rotation of the sample in the high-temperature microwave field, which has positive significance for conducting the SR-CT experiment under multi-field coupling or extreme conditions;3. The specially designed double insulation structure resolved the problem of light-through, heat insulation, temperature measurement and atmosphere protection. This provides technical support for expanding the application scope of this analytical system.Secondly, the first SR-CT experimental study on metals, ceramics and metal-ceramic hybrid materials were realized. The special sintering phenomena and the corresponding sintering kinetics mechanisms were analyzed. The quantitative analysis showed that there were different sintering dominate mass diffusion mechanisms between microwave and conventional sintering.1. The SR-CT online experiments and observations on the microstructure evolution of metals, ceramics, and metal-ceramic mixed materials in the microwave sintering were achieved. Various special sintering phenomena that were different from the conventional sintering were observed. The explanation for these phenomena was given from the aspects of "thermal effect" and "non-thermal effect" of the microwave;2. The statistics and analysis of the variation of particle surface bending energy of the hybrid system and the pure metal were carried out by adopting the method of B-spline interpolation. The results indicated that coupling mechanism of "microwave-material" is related to the property of materials, the microwave field is good for the decrease of particle surface bending energy.3. The watershed algorithm was used to extract the sintering-neck of metals, ceramics and metal-ceramic hybrid materials, and the sintering-neck growth kinetic curves were obtained. Then, the dominant diffusion mechanism and the corresponding microscopic mechanism were analyzed. The results show that there were dominate mass diffusion mechanisms between microwave and conventional sintering, as well as between the different materials. In addition, the study of the coupling mechanism between microwave and the surface and interface of different material systems, it was shown that the addition of ceramic materials will induce interfacial polarization, which will promote the sintering process.In addition, the "thermal effects" and "non-thermal effects" that were in connection with the intensity distribution and propagation direction of microwave were further analyzed. The result indicated that these effects will promote the mass diffusion process and induce anisotropic sintering.1. As in the aspect of "thermal effects", the main analysis was on the promotion of sintering process induced by the uneven distribution of the microwave electric field and magnetic field, as well as the microscopic configuration of the material;2. As in the aspect of "non-thermal effects", the main analysis was on the anisotropic sintering which has relation with the direction of microwave electric field and magnetic field, as well as the microscopic configuration of the material.Finally, a summary of the full text was made, the main research contents and results were given, and the research ideas and programs for the problems which need further in-depth study were raised. |
PDF Full Text Request