Chapter 22- New Materials Through Chemistry Section 1- Materials with a Past
Alloys • An alloy is a mixture of a metal with one or more other elements where the mixture retains the properties of the metal. • Starting in 3500 B.C. the first known mixture of metals (alloy) became so popular and widely used that a 2,000 year span of history is known as the Bronze Age.
Properties of Metals and Alloys • Metals have Luster, which means they reflect light or have a shiny appearance. • The shiny appearance of aluminum foil and copper wire demonstrates the property of luster.
Properties of Metals and Alloys • Malleability is the property that allows metals and alloys to be hammered or rolled into thin sheets. • Aluminum foil that is used in food preparation and food storage demonstrates the malleability of aluminum.
Properties of Metals and Alloys • Conductivity means that heat or electrical charges can move easily through material. Metals and alloys have high conductivity because some of their electrons are not held tightly by their atoms. • Metals and alloys are usually good conductors of heat and electricity.
Important New Alloys • Aluminum and Titanium alloys to build large commercial aircraft. • Titanium Alloy is used for space shuttles and launch vehicles during space missions. • The original heat shield on space shuttles was made of ceramic tiles that are prone to cracking as a result of the high temperature and stress they experience during reentry into Earth’s Atmosphere. Each broken ceramic tile must be removed carefully and a new one glued into place. • The new titanium alloy panels are much larger and attach to the heat shield easier, lower maintenance cost, and will last as just as long.
Chapter 22 New Materials Through Chemistry Section 2: Versatile Materials
Ceramics • Ceramics are materials made from dried clay or clay-like mixtures. • Ceramics have been around for centuries. The earliest clay pottery was from 10,000 B.C. • Ceramics are made from a mixture of clay, silica (sand), and feldspar. • Examples of Ceramics: Pottery, Bricks, Glass, and Concrete
Semiconductors • Semiconductors are the materials that make computer devices possible. • Semiconductors can be found on the periodic table in the metalloids. • Metals conduct electricity too well to be a semiconductor and nonmetals do not conduct electricity well enough. Metalloids conduct electricity just right as their electrical conductivity can be controlled. The ability to control the electrical conductivity makes semiconductor devises useful and versatile.
Semiconductors • The process of adding impurities or other elements to a semiconductor to increase the conductivity is called Doping. • Depending on the element/semiconductor the overall number of electrons is increased or decreased. • If the impurity or doping causes the number of electrons to increase the semiconductor is called an n-type semiconductor. • If the impurity or doping causes the number of electrons to decrease the semiconductor is called a p-type semiconductor.
Integrated Circuits • By placing n-type and p-type semiconductors together devices such as transistors and diodes can be made. • An integrated circuit contains many semiconducting devices. • Integrated circuits are known as microchips.
Chapter 22 New Materials Through Chemistry Section 3: Polymers and Composites
Polymers • Polymers are a class of natural or manufactured substances that are composed of molecules arranged in large chains with small, simple, repeating units called monomers. • A monomer is one specific molecule that is repeated in the polymer chain. Ex. Polypropylene may have 50,000 to 200,000 monomers in its chain. • Synthetic means that it does not occur naturally, but was manufactured in a laboratory or chemical plant.
History of Natural and Synthetic Polymers • Ancient Egyptians soaked their burial wrappings in natural resins to help preserve the dead. • In 1839, Charles Goodyear, an American inventor found that heating sulfur and natural rubber together improved the qualities of natural rubber. A few years later Charles Goodyear started Goodyear tires. • Today Synthetic polymers are usually made from fossil fuels such as oil, coal, or natural gas. • Fossil fuels composed primarily of carbon and hydrogen and are referred to as hydrocarbons.
Plastics • Plastics are used widely because they have desired properties. Plastics are usually lightweight, strong, impact resistant, waterproof, moldable, chemical resistant, and inexpensive. • Polyethylene (plastic grocery bag) is an example of a plastic made from hydrocarbons.
Synthetic Fibers • Nylon, Polyester, Acrylic, and Polypropylene are example of polymers that can be manufactured as fibers.
Composites • A composite is a mixture of two or more materials-one embedded or layered in the other. • Fiberglass and Carbon Fiber are great examples.