Ceramics

A ceramic has traditionally been defined as “an inorganic, nonmetallic solid that is prepared from powdered materials, is fabricated into products through the application of heat, and displays such characteristic properties as hardness, strength, low electrical conductivity, and brittleness."

Ceramics are basically amorphous or complex crystalline structure with strong ionic bonds. Due to this amorphous nature, they do not have an electron community. In absence of this, the electrical conductivity and thermal conductivities take a toll. With the strong ionic bonds between them, it takes a lot of energy to activate and displace atoms from bonds. Hence ceramics are extremely heat resistant.

The word ceramic comes the from Greek word "keramikos", which means "pottery." They are typically crystalline in nature and are compounds formed between metallic and nonmetallic elements such as aluminum and oxygen (alumina-Al₂O₃), calcium and oxygen (calcia - CaO), and silicon and nitrogen (silicon nitride-Si₃N₄).

D epending on their method of formation, ceramics can be dense or lightweight. Typically, they will demonstrate excellent strength and hardness properties; however, they are often brittle in nature. Ceramics can also be formed to serve as electrically conductive materials or insulators. Some ceramics, like superconductors, also display magnetic properties. They are also more resistant to high temperatures and harsh environments than metals and polymers. Due to ceramic materials wide range of properties, they are used for a multitude of applications. 

The broad categories or segments that make up the ceramic industry can be classified as:

• Structural clay products (brick, sewer pipe, roofing and wall tile, flue linings, etc.)

• Whitewares (dinnerware, floor and wall tile, electrical porcelain, etc.)

• Refractories (brick and monolithic products used in metal, glass, cements, ceramics, energy conversion, petroleum, and chemicals industries)

• Glasses (flat glass (windows), container glass (bottles), pressed and blown glass (dinnerware), glass fibers (home insulation), and advanced/specialty glass (optical fibers))

• Abrasives (natural (garnet, diamond, etc.) and synthetic (silicon carbide, diamond, fused alumina, etc.) abrasives are used for grinding, cutting, polishing, lapping, or pressure blasting of materials)

• Cements (for roads, bridges, buildings, dams, and etc.)

• Advanced ceramics

  • Structural (wear parts, bioceramics, cutting tools, and engine components)

  • Electrical (capacitors, insulators, substrates, integrated circuit packages, piezoelectrics, magnets and superconductors)

  • Coatings (engine components, cutting tools, and industrial wear parts)

  • Chemical and environmental (filters, membranes, catalysts, and catalyst supports)

Polymers

A polymeric solid can be thought of as a material that contains many chemically bonded parts or units which themselves are bonded together to form a solid. The word polymer literally means "many parts." Two industrially important polymeric materials are plastics and elastomers. Plastics are a large and varied group of synthetic materials which are processed by forming or molding into shape. Just as there are many types of metals such as aluminum and copper, there are many types of plastics, such as polyethylene and nylon. Elastomers or rubbers can be elastically deformed a large amount when a force is applied to them and can return to their original shape (or almost) when the force is released.

Polymers have many properties that make them attractive to use in certain conditions. Many polymers:

• are less dense than metals or ceramics,

• resist atmospheric and other forms of corrosion,

• offer good compatibility with human tissue, or

• exhibit excellent resistance to the conduction of electrical current.

Polymers are usually long chain organic macro-molecules with co-valent bonds. Each molecule is formed from a large number of unitary molecules known as Monomer. For this reason, the polymers can be bent and stretched easily. In certain polymers some of the molecules cross link with each other thereby increasing the strength across the molecules.

Their properties:

• Ductile / soft

• Translucency

• Low thermal stability

• Lightweight (But high molecular weight)

• Poor conductor of heat and electricity (With exception of PPV, etc.)

T he polymer plastics can be divided into two clas`1w2es, thermoplastics and thermosetting plastics, depending on how they are structurally and chemically bonded. Thermoplastic polymers comprise the four most important commodity materials – polyethylene, polypropylene, polystyrene and polyvinyl chloride. There are also a number of specialized engineering polymers. The term ‘thermoplastic’ indicates that these materials melt on heating and may be processed by a variety of molding and extrusion techniques.

Rubber is a natural occurring polymer. However, most polymers are created by engineering the combination of hydrogen and carbon atoms and the arrangement of the chains they form. The polymer molecule is a long chain of covalent-bonded atoms and secondary bonds then hold groups of polymer chains together to form the polymeric material. Polymers are primarily produced from petroleum or natural gas raw products but the use of organic substances is growing. The super-material known as Kevlar is a man-made polymer. Kevlar is used in bullet-proof vests, strong/lightweight frames, and underwater cables that are 20 times stronger than steel.

• What are the main ways to classify plastics ?

• What is the main difference between thermoplastics and thermosets?

• Which of these two- a piece of butter or a pancake behaves more as a thermoplastic or as a thermoset when heated?

• What mechanisms explain different behavior of these materials?