Ceramics may have which of the following structures?

• A. Be purely crystalline
• B. Be purely amorphous
• C. Be crystalline with some amorphous regions
• D. May be crystalline, partly crystalline, or amorphous

Answer: (D)

Ceramics exhibit a spectrum of microstructures. Some are crystalline, consisting of long-range atomic order and typically forming as polycrystalline aggregates with grain boundaries. Others are amorphous, lacking long-range order, like glasses formed from melts. There are also materials that are partially crystalline, with crystalline phases embedded in an amorphous matrix—glass-ceramics are a common example. Processing conditions such as cooling rate, composition, and nucleating agents determine which structure develops. Because ceramics can be fully crystalline, fully amorphous, or in between, the most complete statement is that they may be crystalline, partly crystalline, or amorphous.