In my understanding, sintering process is used for the first stage in the material processing to cyrstallize the related material. The initiate state can be amorphous to form crystal state. Annealing is the further stage of sintering that has objective to make better structures. Therefore usually annealling was done at quite longer time in compare with sintering process and in some case it usually accompanied with gas flow. The third one, calcination is used to describe the solid state reaction. For example when powder A and powder B are mixed and heated, to produce new compound.
Could any one please give comments and further suggestion or corrections?