The Grain Size Of Polycrystalline Ceramic Materials - The Circumference Of The Relationship

For the studies of the relationship between the mechanical properties and microstructure in polycrystalline ceramics, the average grain size was often used as a key micro-structural parameter and therefore received scholars'widespread attention. On the studies of functional ceramic materials, the average grain size was also used as an important parameter to analyze the impact of grain boundary effects on various performance parameters. However, it must be noted that, in the same polycrystalline ceramic samples, the sizes of different grains were widely distributed and varied greatly. Size difference during the grains was often above one or even several orders of magnitude. But in all relevant research reports, Just an average was widely used as grain size, while the statistical distribution effect of grain size actually existing in the materials was always ignored. Besides, so far, the studies on polycrystalline ceramic sintering process have been generally based on the observations of the changes in the average size of grain. And studies on the changes of grain shape during the sintering have been reported extremely rare. On the other hand, Photos of grain morphology in dense polycrystalline ceramics, which were reported in a large number of the literature, showed that the ideal grain shape of regular hexagon was very rare. So it is of theoretical and practical values to explore a new micro-structural parameter using research the relationship between structure and properties of ceramic materials, to establish a new technology characterizing grain shapes and apply to ceramic sintering.In this thesis, grain growth process and surface grain morphology during the three systems of BaTiO3-PTCR materials, cubic ZrO2 and lead-free ceramics were observed under the conditions of different sintering temperatures and different holding times. From the statistical point of view, it was confirmed that for a given material, at the same sintering system, the ratio of P/A0.5on the perimeter (P) and the square root of area(A) about the surface grain had smaller discrete than the corresponding average grain size, could more accurately and credibly descript the grain morphology. It finally confirmed that the surface grains of dense single-phase polycrystalline ceramic materials had a constant P/A0.5 value.Secondly, on the basis of above observations, the PIA0.s value of surface grains was proposed as a parameter to characterize the grain shapes. By analyzing the changes of P/A0.5 values during sintering process, the corresponding grain shapes was obtained. This made foundation for the parameter to be used in the studies of sintering behavior of materials, especially in grain growth process. Finally, grain boundary conductance activation energy Egb was measured in cubic ZrO2 ceramics. It was found that, PIA0.5 and the corresponding Egb showed opposite trends. The corresponding relationship between these two parameters seemed to indicate that the changes of grain shapes'parameter could reflect the character of the microstructure resulted in the changes of electrical properties of grain boundaries. In the research on Grain boundary effects, the changes of P/A0.5 value were expected to reveal the relationship between microstructure and the material properties.