Alumina is the most widely used ceramic material. Determine the ASTM grain size number for the polycrystalline alumina sample shown in Figure 4-25.
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![501_image100820142239.png](https://secure.tutorsglobe.com/CMSImages/501_image100820142239.png)
Figure 4-25 Microstructure of an alumina ceramic. (Courtesy of Dr. Richard McAfee and Dr. Ian Nettle ship.)