RABAYA, Janray S. ENGMATE

12.1 Classes of Materials

Most of the Engineering materials can be classified into five, these are metallic, polymeric, ceramic, composite, electronic, and advance materials. Materials can be defined as anything which satisfies the human needs. The term engineering materials is specifically used to refer materials to produce technical products. However there is no limiting line between the terms Materials and Engineering materials, they can be used interchangeably.

12.2 Electronic Structure of Materials

This include the atomic structure and the macroscopic properties of materials. At subatomic structure, electronic structure of individual atoms that defines interaction among atoms (interatomic bonding). At atomic level, arrangement of atoms in materials for the same atoms can have different properties, example are two forms of carbon: graphite and diamond. At microscopic structure, arrangement of small grains of materials that can be identified by microscopy. And at macroscopic structure, structural elements may be viewed by the naked eye.

12.3 Semiconductors

Semiconductors are widely used to make electronic devices. They are the materials that allow conductivity between metals and insulators. Mostly used in diodes and transistors. Some of the most important semiconductor devices are diodes and transistors. These semiconductor devices have changed the face of electronics today. Semiconductors find wide applications because of their compactness, reliability, and low cost. They can handle a wide range of current and voltage. One of the most important reasons of choosing transistors or any other semiconductor device is their ability to be integrated into complex but readily manufactured.

12.4 Ceramics

Ceramics are composed of compounds made of metallic and nonmetallic elements. Ceramic biomaterials include calcium phosphate ceramics, bioactive glasses, bioactive glass ceramics, alumina, and zirconia. Each of these materials is relatively hard and brittle. In fact, hardness and brittleness are typical properties of ceramics, as are excellent resistance to high temperatures and corrosive environments. The basis of these characteristics is related to the type of atomic bonds. The metallic elements release their outermost electrons to the nonmetallic atoms. This directional bond produces electrons that are localized in the structure. Thus, typical ceramic materials are good insulators, both electrically and thermally.

12.5 Superconductors

Superconductor is an element, intermetallic alloy, or compound that will conduct electricity without resistance below a certain temperature (known as the critical transition temperature. Once set in motion, electrical current will flow forever in a closed loop of superconducting material. Many materials can exhibit the phenomenon of superconductivity at low enough temperatures. Therefore there is a lot of fuss about them because they can be very useful. If they have zero resistance energy will not be lost when passing a current through the material.

12.6 Polymers and Plastics

Polymers are large molecules made up of many smaller and identical repeating units joined together by covalent bonds. These molecules are called monomers. Polymerization is the chemical process by which the monomers are joined together to form the big molecule known as the polymer. A polymer is a macromolecule that are a different property than its monomers. Polymers are divided into 2 types: Naturally occurring polymers (exist in living things) and the Synthetic polymer (man-made polymers by chemical processes).

12.7 Biomaterials

Biomaterial is a nonviable material used in a medical device, intended to interact with biological systems. It is defined by their application not by chemical make-up. It is a material intended to interface with biological systems to evaluate, treat, augment or replace any tissue, organ or function of the body. It include polymeric biomaterials, bioceramics, metallic biomaterials, biocomposite, and biologically based (derived) biomaterials.

12.8 Liquid Crystals

Liquid crystal materials generally have several common characteristics. Among these are a rod-like molecular structure, rigidness of the long axis, and strong dipoles and/or easily polarizable substituents. The distinguishing characteristic of the liquid crystal line state is the tendency of the molecules (mesogens) to point along a common axis, called the director .This is in contrast to molecules in the liquid phase, which have no intrinsic order. In the solid state, molecules are highly ordered and have little translational freedom.

12.9 Nanomaterials

Nanomaterials are materials with dimensions and tolerances in the range of 100 nm to 0.1 nm. These could be metals, ceramics, polymeric materials, or composite materials. The human hair is five orders of magnitude larger than nanomaterials. Nanomaterials comprised of many different elements such as carbons and metals. Combinations of elements can make up nanomaterial grains such as titanium carbide and zinc sulfide.