Section 1: Materials with a Past

• Alloy: a mixture of elements that has metallic properties.

  • Advances in metal processing are still occurring as scientists continue to improve the art of blending metals, or making alloys, to make better metal products.

  • Alloys can produce materials with improved properties such as greater hardness, strength, lightness, or durability.

  • Other alloys also have been developed through the ages, giving people a large selection of materials to choose from today.

• Properties of Metals and Alloys

  • Alloys retain the metallic properties of metals.

  • Luster: reflect light or have a shiny appearance

  • Ductility: can be pulled into wires.

  • Malleability: the property that allows metals and alloys to be hammered or rolled into thin sheets

  • Conductivity: heat or electrical charges can move easily through the material.

  • Metals and alloys usually are good conductors of heat and electricity because of these loosely bound electrons.

  • Gold is a bright, expensive metal that is soft and bends easily.

  • When gold and copper are melted, mixed, and allowed to cool, an alloy forms.

• Uses of Alloys

  • If you see an object that looks metallic, it is most likely an alloy.

  • Automobile and aircraft bodies that require strong materials are constructed of alloys that are corrosion resistant and lightweight but able to carry heavy loads.

  • The classes of steel have different properties and therefore different uses.

  • Steel is a strong alloy and is used often if a great deal of strength is required.

  • Bridges, overpasses, and streets also are reinforced with steel.

  • Ship hulls, bedsprings, and automobile gears and axles are made from steel.

  • Another class of steel, called stainless steel, is used in surgical instruments, cooking utensils, and large vessels where food products are prepared.

• New Alloys

  • Steel is not the only common type of alloy.

  • The new alloys are strong, lightweight and last longer than alloys used in the past.

  • Titanium alloy panels, developed for the space shuttle heat shield, might be used on future reusable launch vehicles that are designed to carry payloads to the International Space Station.

Section 2: Versatile Materials

• Ceramics: materials that are made from dried clay or claylike mixtures.

  • Pottery, bricks, glass, and concrete are examples of ceramics.Traditional ceramics are made from easily obtainable raw materials—clay, silica (sand), and feldspar (crystalline rocks).

  • After the raw materials are processed, ceramics usually are made by molding the ceramic into the desired shape, then heating it to temperatures between 1,000°C and 1,700°C.

  • The heating process, called firing, causes the spaces between the particles to shrink.

  • Ceramics are known also for their chemical resistance to oxygen, water, acids, bases, salts, and strong solvents.

  • These qualities make ceramics useful for applications where they may encounter these substances.

  • Traditional ceramics also are used as insulators because they do not conduct heat or electricity.

  • Changing the composition of the raw materials or the manufacturing process changes the properties of the ceramic.

  • Ceramics can be used in the body because they are strong and resistant to body fluids, which can damage other materials.

• Semiconductors: poorer conductors of electricity than metals but better conductors than nonmetals, and their electrical conductivity can be controlled.

  • Another class of versatile materials is semiconductors.

  • Semiconductors are the materials that make computers and other electronic devices possible.

  • Adding other elements to some metalloids can change their electrical conductivities.

  • If the added atoms, called impurities, have fewer electrons than silicon atoms, the silicon crystals will contain holes, or areas with fewer electrons.

  • Doping: The process of adding impurities or other elements to a semiconductor to modify the conductivity.

  • If the impurity causes the overall number of electrons to increase, the semiconductor is called an n-type semiconductor.

  • If doping reduces the overall number of electrons, the semiconductor is called a p-type semiconductor.

  • By placing n-type and p-type semiconductors together, semiconductor devices such as transistors and diodes can be made.

  • These devices are used to control the flow of electrons in electrical circuits.

  • Integrated Circuit: contains many semiconducting devices.

  • Integrated circuits as small as 1 cm on a side can contain millions of semiconducting devices.

  • Because of their small size, integrated circuits are sometimes called microchips.

  • Semiconductors make today’s computers possible.When a computer system is functioning properly, the hardware and software work together to perform tasks.

Section 3: Polymers and Composites

• Polymers: a class of natural or manufactured substances that are composed of molecules arranged in large chains with small, simple, repeating units called monomers.

  • Monomer: one specific molecule that is repeated in the polymer chain.

  • Not all polymers are manufactured. Some occur naturally.

  • Synthetic: the polymer does not occur naturally, but it was manufactured in a laboratory or chemical plant.

  • In the 1800s, scientists began developing processes to improve natural polymers and to create new ones in the laboratory.

  • Today, so many types of synthetic polymers exist that they tend to be divided into groups such as plastics, synthetic fibers, adhesives, surface coatings, and synthetic rubbers.

  • Today, synthetic polymers usually are made from fossil fuels such as oil, coal, or natural gas.

  • Fossil fuels are composed primarily of carbon and hydrogen and are referred to as hydrocarbons.

  • The reason that polymers can be used for so many applications is directly related to the ease with which their properties can be modified.

  • The number of carbon atoms in the polymer can be high, and each bonding site represents a possibility of a change in properties.

  • Plastics are usually lightweight, strong, impact resistant, waterproof, moldable, chemical resistant, and inexpensive.

  • Most synthetic fibers are composed of carbon chains because they are produced from petroleum or natural gas.

  • Synthetic polymers are used to make adhesives that can be modified to provide the best properties for a particular application

  • Synthetic rubber is a synthetic elastic polymer.

• Composite: a mixture of two or more materials—one embedded or layered in the other.

  • Glass fibers are used often to reinforce plastics because glass is inexpensive, but other materials can be used as well.

  • Composite materials are used in the construction of satellites.

  • Aircraft made of composites also benefit from the strong yet lightweight properties of composite materials.