Polycrystalline materials, both dense and porous, are traditionally fabricated from ceramic, metal or composite powders via powder technology routes that include shaping and sintering steps. During shaping a compact body is formed from the granular raw material, while sintering leads to strengthening of this compact and coarsening. In this collection, the authors summarize the basic concepts and classical models used for describing solid state sintering processes. Following a brief introduction, in the second section a historical overview of early sintering theory is given, followed in the third section by an explanation of the driving force of solid state sintering. Following this, grain boundary is analyzed to discern how the spatial orientation of grains themselves may be defined generally and exactly. Additionally, one can easily understand that there is a correlation between the change in the grain orientation and grain deformation and this correlation was mathematically demonstrated. Finally, the authors interpret the quantity of grain orientation corresponding with the experimental measured value, the analysis of local deformation could be performed experimentally on the basis of their results. In closing, following an outline describing the historical development of ECAS and related techniques, the principle of ECAS is briefly described, current opinions concerning sintering mechanisms are summarized, and the problem of carbon contamination is discussed in some detail.
