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Categories of Materials

• Organics• Metals and Alloys• Polymers• Ceramics• Composites

Organics

• Organics are or were living organisms• Composed of mostly carbon and

Hydrogen• Structure depends on the way cells

developed not by human manipulation• Renewable, sustainable • Infinite variety• Genetically alterable

Metals and Alloys

• Metals are pure elements which comprise about three-fourths of the periodic table

• Few are used in their pure form because of: – Hardness; too hard or too soft– Cost; scarcity of element– Engineers need certain characteristics that can

only be accomplished by a blending of basic elements

• Metallic materials include alloys, which are combinations of metals and other elements

Metals

• Possess material properties, including:– high strength and toughness– high electrical conductance– high thermal conductance– luster

• Examples– aluminum - copper - gold - zinc - iron - lead -

nickel– silver - thorium - chromium - tin - beryllium

Alloys

• Consist of materials composed of two or more elements, at least one being a metal

• This combination of elements gives the material a combination of properties from each element

• Examples– Steel- iron, carbon and impurity elements such as

boron copper or silicon – Brass - copper, zinc– Stainless Steel - nickel,iron– Monel - nickel,copper

Types of Metallics

Ferrous Metallics - iron and alloys which contain at least 50% iron (e.g. wrought iron, cast iron, steel, stainless steel)

Nonferrous Metallics - Metallic elements other than iron (e.g. copper, lead, tin, zinc, titanium, beryllium, nickel)

Powdered (Sintered) Metals (ferrous or non-ferrous)• Sometimes called sintered metal. A process of producing

small (powdered) particles which are compacted in a die and then “sintered” (applying heat below the melting point of the main component)

Examples: trigger on gun, gears, bearings, carbide tool inserts

Polymers

• Polymers– Chain-like molecule made of many (poly)

smaller molecular units (mono”mers”)– Chaining (polymerization) is responsible for

the formation of natural fibers, wood, lignin, rubber, skin, bone and the tissues of animals, humans and insects

Plastics

• Plastics– Human-made polymers– Plastics are workable or moldable

• Thermosetting plastics are formable once (e.g. epoxy, phonelic (Bakelite), polyurethane)

• Thermoplastics can be heated repeatedly and

formed into new shapes (e.g. polyethylene, nylon, Plexiglas)

Elastomers

• Elastomer– amorphous (shapeless) structure consisting of long

coiled-up chains of entangled polymers– can be stretched at room temperature to at least twice its

original length and return to its original shape after the force has been removed

• Process to strengthen an elastomer: vulcanization– a chemical process used to form strong bonds between

adjacent polymers to produce a tough, strong, hard rubber (automobile tires)

Ceramics

• Crystalline compounds combining metallic and non metallic elements

• The absence of free electrons make ceramics poor electrical conductors.

• Because of the strength of the bonding, ceramics have high melting temperatures

Ceramics(continued)

Categories: Clay

Refractory

Electrical and Magnetic

Glasses

Cermets

Ceramics(continued)

Clay Products• Inorganic material which is shaped, dried

and fired.Examples: brick, floor and wall tiles, drainage tile, roof

tile, sewer pipe, chimney flue, china, and porcelain.

Ceramics(continued)

Refractory Materials• Ceramics designed to provide acceptable

mechanical or chemical properties while at high temperatures.

• Most are based on stable oxides such as carbides, nitrides, and borides.

• An example of a refractory is the machinable all-silica insulating tiles on the U.S. space shuttle

Ceramics(continued)

Electrical and Magnetic Applications

• Ceramics are used as resistors and heating elements for furnaces (silicon carbide)

• Semiconductor properties:– Thermistors- as they heat-up allow current to flow.– Rectifiers- allow current to flow in one direction– Clay based ceramics for high-voltage insulators

Ceramics(continued)

Glass• Based on silica with additives that alter the structure or

reduce the melting point, optimize optical properties, thermal stability and resistance to thermal shock

Cermets

Combinations of metals and ceramics(oxides, nitrides, or carbides) bonded together in the same way powdered metallurgy parts are made.

Examples: crucibles, jet engine nozzles

Composites

• Laminar or Layer Composites - alternate layers of materials bonded together. (e.g. plywood, safety glass, Formica, bimetallic strips)

• Particulate Composites - discrete particles of one material surrounded by a matrix of another material. (e.g. concrete, asphalt, powdered metals and ceramics)

• Fiber-Reinforced Composites - composed of continuous or discontinuous fibers embedded in a matrix of another material. (e.g. Kevlar, rayon, steel reinforced tires, fiberglass, graphite-epoxy)

Review

• Organics• Metals and Alloys• Polymers• Ceramics• Composites

Major Categories of Materials