Characteristics of sintered ceramics

Characteristics of sintered ceramics
For sintered ceramics, the average grain size distribution and the level and type of porosity are important. Similarly, depending upon the application, second phase in the micro – structure could occur as separate grains of components dissolve in solid solutions of the matrix, so second phase at grain boundaries also become important. In the case of extruded ceramics, orientation effects also can be important.
The average grain size often closely related to the primary particle size. An exception to this is if there is grain growth due to long sintering times or exaggerated or abnormal grain growth.
Typically, ceramics with a small grain size are stronger than coarse grained ceramics. Finer grain size help reduce stresses that develop at grain boundaries due to anisotropic expansion and contraction.
Normally, starting with finer ceramic raw material produces a fine grain size. Magnetic, dielectric, and optical properties of ceramic materials depend upon the average grain size and, in these applications, grain size must be controlled properly.
Although we have not discussed this here in detail, in certain application, it is important to use single crystals of ceramic material so as to avoid the deleterious grain boundaries that are always present in polycrystalline ceramics.
Pores represent the most important defect in polycrystalline ceramics. The presence of pores is usually detrimental to the mechanical properties of bulk ceramics.
Since pores provide a pre – existing location from which a crack can grow. The presence of pores is one of the reasons why ceramics show such brittle behavior under tensile loading. Since there is a distribution of pore sizes and the overall level of porosity changes, the mechanical properties of ceramics vary. The presence of pores, on the other hand, may be useful for increasing the resistance thermal shock.