DESIGN, ASSEMBLY AND CHARACTERIZATION OF COMPOSITE ...

2.6. Sintering
In robocasting, sintering is used after binder burnout to reduce porosity in the
particle compact and enhance the strength of the material. Both solid state sintering and
liquid phase sintering are explored in this research for co-sintering of heterogeneous
composite structures of BaTiO3 and Ni. Single component sintering is complex process
where the main thermodynamic driving force is reduction of the surface area to volume
ratio in the particle compact. The rate and extent of sintering are dependent on time,
temperature and chemical environment. When more than one material is sintered in the
same structure, the process is termed co-sintering and extra variables become important.
For instance, the rate of sintering of the two materials may differ at a given temperature,
which often leads to differential shrinkage, warping, and cracking of the overall structure.
In the case that one material needs an oxidizing environment while the other needs a
reducing environment, a compromise must be made. The following gives some basic
knowledge of sintering to assist the understanding of the complexity of co-sintering.
2.5.1 Definition
Sintering uses thermal treatment to bond compacted particles into a coherent,
predominantly solid structure via mass transport events occurring at the atomic level 38 .
Sintering processes are categorized in many ways: solid state sintering, liquid phase
sintering, pressure assisted sintering, and novel sintering techniques such as reactive
sintering, microwave sintering, and spark plasma sintering. Despite these variations, the
common characteristics of sintering processes are: 1) reduction of total surface energy
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