MATSE 81
Materials in Today's World

Ceramic Bonding

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Recall that the predominant bonding for ceramic materials is ionic bonding. In ionic bonding, a metal atom donates electrons and a nonmetal atom accepts electrons. This electron transfer creates positive metal ions (cations) and negative nonmetal ions (anions), which are attracted to each other through coulombic attraction. The nature of ionic bonding (creation of cations and anions) results in several differences between ionic and metallic bonding. First, ionic bonds in solids are quite directional, i.e., there are certain preferred angles. Second, to maintain charge balance the cations and anions have to be in certain ratios. Thirdly, it turns out, to form stable structures it is necessary to maximize the number of oppositely charged ion neighbors (as shown in the figure below). All of these factors make ceramic structure inherently more complex than metal structures and, as we will discuss later, also make ceramics brittle.

Formation of unstable and stable structures of ions.
Maximizing the number of oppositely charged ion neighbors to form stable structures.
Adapted from Fig. 3.5, Callister & Rethwisch 5e.

Now, please proceed to the reading for this lesson (shown on the next page).