Research On Ceramic Sintering By Synchrotron Radiation X-Ray Computed Tomography

In this paper, the necessity and importance of investigating ceramic sintering process in real-time and non-destructive is firstly presented. The microstructure evolution process and phenomena, thermodynamic mechanisms and theoretical models, constitutive laws and governing equations about sintering process is globally reviewed. The principle and research status of Synchrotron radiation x-ray computed tomography (SR-CT) technique is generally summarized. The microstructure evolution of the sintering process is numerical simulated by phase-field method. In order to observe the microstructure evolution of sintering process by SR-CT technique, the technical difficulties of SR-CT technique was studied and a new method which can improve the quality of reconstructed images based on the windowed Fourier filter method was proposed. The sintering process of several groups of ceramic samples was investigated by SR-CT experimental and the experimental results were discussed according the sintering theory.The main content is as follows:Firstly, by summarizes the sintering theories, the 2-D and 3-D microstructural evolution during sintering process was simulated by Phase field model while there are few reports on the 3-D results.1,The material transmission mechanism, densificated process, empirical densification equation and phenomelogical densification equation about sintering process were studied.2,A summary of the numerical simulating methods of sintering process was presented.The Phase field model based on Cahn-Hilliard equation for conserved field variables and Ginzburg-Landau equation for non-conserved variables was emphatically introduced.3,By solving coupled time-dependent governing equations with Cahn-Hilliard equation for conserved field variables and Ginzburg-Landau equation for non-conserved variables, the 2-D microstructural evolution during sintering process, such as aggregation and migration of pores and grains is visually simulated.4,The 3-D microstructural evolution during sintering process was futher simulated by the Phase field model and the Correctness of the Simulation Results was confirmed by the porosity-simulation time curves and sintering theories. Secondly, a new method of improving the quality of reconstructed images based on windowed Fourier filter method was proposed.1,The SR-CT technique was discussed and the filter back-projection reconstruction algorithm was emphatically introduced.2,By analysis the filter function of the filter back-projection reconstruction algorithm and the characteristics of the synchrotron radiation x-ray,the method of improving the quality of reconstructed images based on windowed Fourier filter method was proposed.The feasibility of the methods was analysised.3,The effectiveness of the method was validated by the experimental results of two kinds of samples.Compaied with the reconstructed images that did not use Windowed Fourier filter method, the reconstructed images which use the Windowed Fourier filter method shows the high reconstruction quality. In addition, the real-time and non-destructice observation of the sintering process by Synchrotron radiation computed tomography technique was firstly realized in our country.1,The experimental scheme was performed and several groups of sample according to different components and initial porosities were prepared, the SR-CT technique was employed to explore the microstructure evolution of the samples. From these cross-section images at different sintering time, the evolution process of grains and pores could be observed, and vertical-section and three-dimensional images could also be obtained.2,The porosity of the compacted samples were obtained by treating the reconstructed images using digital image processing method.The desifacation Characteristics of different sintering stages could be clearly observed by the porosity-time and porosity- time-logarithm curves.3,From the linear relationship between Porosity and Log time in the middle stage of sintering,the relative densification rate was performed. The beginning time of the sintering process, the relative densification rate in the middle stage of sintering and the end point of sintering was discussed by analyis the porosity- time-logarithm curve of the samples with different initial porosity.At last, the whole works are summarized and the further researches are proposed.