Structures and Properties of Ceramics

Structures and Properties of Ceramics

Most ceramics are compounds between metallic

and nonmetallic elements for which the interatomic bonds are either totally

ionic, or predominantly ionic but having some covalent character

The term “ceramic” comes from the Greek word keramikos, which means “burnt stuff,” indicating

that desirable properties of these materials are normally achieved through

a high-temperature heat treatment process called firing.

Ceramic Structures

Because ceramics are composed of at least two elements, and often more, their crystal

structures are generally more complex than those for metals. The atomic bonding

in these materials ranges from purely ionic to totally covalent; many ceramics

exhibit a combination of these two bonding types, the degree of ionic character

being dependent on the electronegativities of the atoms.

CRYSTAL STRUCTURES

For those ceramic materials for which the atomic bonding is predominantly ionic,

the crystal structures may be thought of as being composed of electrically charged

ions instead of atoms. The metallic ions, or cations, are positively charged, because

they have given up their valence electrons to the nonmetallic ions, or

anions, which are negatively charged.

Two characteristics of the component ions

in crystalline ceramic materials influence the crystal structure: the magnitude of

the electrical charge