Sintering and grain growth

The effect of microstructure on properties has been neglected up to this point, mainly because the properties discussed so far, such as Young s modulus, thermal expansion, electrical conductivity, melting points, and density, are to a large extent microstructure-insensitive. In the remainder of this book, however, it will become apparent that microstructure can and does play a significant role in determining properties. For example, as shown in Table 10.1, the optimization of various properties requires various microstructures. 

As noted above, once shaped, the parts are fired or sintered. Sintering is the process by which a powder compact is transformed to a strong, dense ceramic body upon heating. In an alternate definition given by Herring.  

High strength Small grain size, uniform microstructure, and flaw-free 

High toughness Duplex microstructure with high aspect ratios 

High creep resistance Large grains and absence of an amorphous grain boundary phase 

---

In the preparation of MgO from chloride salt precursors, it was observed that the presence of any residual chloride had a detrimental effect on the surface area of the resultant MgO 29). This effect has been related to the ability of chloride to aid sintering and grain growth in the oxide 30). 

Here, however, unlike binaries or multinaries, the emf is inherently unstable273 274 as the same processes allowing for an excess emf to be measured are also allowing for sintering and grain growth (electrochemical Ostwald ripening275 273). In addition, there has to be paid attention to the fact that the emf refers to the excess chemical potential of silver directly at the electrode/electrolyte interface.273... 

Reduction of surface or interfacial energy, e.g.. sintering and grain growth... 

---