Microstructure solid-state sintering

Typical microstructures developed by solid state sintering, liquid phase sintering and firing a porcelain are shown in Fig. 5.20. 

Fig. 3 Microstructure of a solid-state sintered mullite ceramic with a relative density >99%. The ceramic had equiaxed grains with a grain size of -1 pm and no apparent glassy phase...

Ferrites are complex because they combine two complex areas ceramic microstructures and magnetic phenomena. Ceramic microstructures, formed as a result of physico-chemical processes such as solid-state sintering, are affected by a large number of interacting variables the essentially quantum-mechanical nature of their magnetic properties makes them difficult to comprehend, since they are entirely different to macroscopic, every-day experience. The approach to ferrites their synthesis/fabrication the relationship between crystal structure, texture and physical properties the modelling of magnetic interactions, is of necessity interdisciplinary. 

Microstructural coarsening occurs with slow solid-state sintering of the solid. 

Improved reliability in sliding bearing and rotating seal application have been achieved with microstructure-taylored solid-state sintered SiC materials, which contain pores [97-100], a combination of pores and graphite [101], and/or very large grained SiC crystallites [102]. 

In general, compared with solid state sintering, liquid phase sintering allows easy control of microstructure and reduction in processing cost, but degrades some important properties, for example, mechanical properties. In contrast, many specific products utilize properties of the grain boundary phase and, hence, need to be sintered in the presence of a liquid phase. Zinc oxide varistors and SrTiOs based boundary layer capacitors are two examples. In these cases, the composition and amount of liquid phase are of prime importance in controUing the sintered microstructure and properties. 

Figure 1.4. Typical microstructures observed during (a) solid state sintering (AI2O3) and (b) liquid phase sintering (98W-INi-IFe(wt%)).

Figure 1.21 Incomplete removal of the porosity during solid-state sintering of Ce02 results in a microstructure consisting of grains, grain boundaries, and pores.

In solid-state sintered ceramic systems, densification and microstructure development can be assessed on the basis of the dihedral angle, 0, formed as a result of the surface energy balance at the pore-grain boundary intersection. 

Shi JL. Solid state sintering of ceramics pore microstructure models, densification equations and applications. J Mater Sci. 1999 34 3801-3812. DOI 10.1023/A 1004600816317... 

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