Ceramic Properties and Crystal Structure

Study Notes

Ionic bonding gives ceramics high melting points and hardness.
Covalent bonding in ceramics, such as silicon carbide, creates strong directional bonds, contributing to high stiffness and thermal stability.

The crystal structure of ceramics heavily influences their properties.
Ceramics can exhibit various crystalline structures, including cubic, hexagonal, and tetragonal.
Zirconia can exist in multiple phases (monoclinic, tetragonal, and cubic), each with distinct properties.

Ceramic manufacturing involves several key processes: raw material preparation, forming, drying, firing, and finishing.
Each stage plays a critical role in determining the final properties of the ceramic product.

The first step in ceramic manufacturing is the preparation of raw materials.
Common raw materials include clays, feldspar, silica, and alumina.
These materials are processed to remove impurities and achieve a fine particle size.

Forming techniques include:
- Pressing: compacting ceramic powder in a mold under high pressure for dense, uniform products.
- Extrusion: creating long, continuous shapes with a constant cross-section.
- Slip Casting: creating complex shapes using a slurry of ceramic particles.
- Injection Molding: producing intricate and detailed shapes.

Firing is the most critical stage in ceramic manufacturing, where the formed ceramic body is heated to high temperatures in a kiln.
The firing temperature and duration depend on the type of ceramic material and the desired properties.
Firing causes:
- Dehydration: removal of chemically bound water from the ceramic material.
- Phase Transformation: changes in the crystalline structure, affecting the material's properties.
- Densification: reduction of porosity and increase in density, leading to improved mechanical strength and durability.

Ceramics are non-metallic, inorganic materials that are typically crystalline in nature.
They are composed of metal and non-metal elements bonded together by ionic and covalent bonds.

The use of ceramics dates back thousands of years, with early human civilizations using clay to create pottery and tiles.
The development of high-temperature kilns and the discovery of glazing techniques expanded the utility and aesthetic appeal of ceramic products.

The chemistry of ceramics is fundamental to understanding their properties and manufacturing processes.
Ceramics are primarily composed of oxides, carbides, nitrides, and borides.
Common ceramic materials include alumina (Al₂O₃), zirconia (ZrO₂), silicon carbide (SiC), and silicon nitride (Si₃N₄).

Ceramic materials are characterized by strong ionic and covalent bonds.
In ionic ceramics, such as alumina, there is a transfer of electrons from metal atoms to non-metal atoms, resulting in positive and negative ions.