Introduction to Materials Science and Engineering by Chung Yip-Wah;Kapoor Monica;

Author:Chung, Yip-Wah;Kapoor, Monica;
Language: eng
Format: epub
Publisher: Taylor & Francis Group
Published: 2022-02-17T00:00:00+00:00

At this point, you may wish to go outdoors. Throw both Frisbees to a height of about 3 m. What do you find (Figure 6.1)? What has this to do with ceramics? Why are these findings significant?

FIGURE 6.1 Two ice Frisbees, one with embedded paper strips and one without, before and after being dropped from 3 m. Before we get back to these questions, let us define what ceramic materials are. Traditionally, ceramics are materials that come out of clay after high-temperature firing: china, porcelain, tiles, bricks, and glassware (keramikos = burnt material). Today, we consider ceramics to be the general class of inorganic nonmetallic compounds (semiconductors excluded). Usually, a ceramic compound consists of at least one metallic element and one nonmetallic element. Such ceramics are partially ionic. As we will see later, this has a large effect on electrical and mechanical properties of ceramics.

Returning to the ice Frisbee experiment, we can consider water (hydrogen oxide) to be a special case of an oxide ceramic. The Frisbee-throwing experiment resulted in the pure oxide ceramic breaking into pieces upon the first throw (Figure 6.1). This is not surprising since we learn in an earlier chapter that ceramics tend to have lower fracture toughness and hence fail more easily with sudden impact. On the other hand, the paper-impregnated oxide ceramic can withstand multiple throws without failure. How is it possible that something as fragile as paper can impart such dramatic performance improvement to this oxide ceramic? This is a classic case of a composite material that retains the strength of the matrix but with markedly improved fracture toughness. We will discuss this point further in a later section. It is left as an exercise for the readers to determine what happens when we change the amount of paper, or replace it with metal paper clips, or little pieces of rubber bands.

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