Transcript Chapter 22

Chapter 22
New Materials Through Chemistry
Alloys-Section 1
• Alloy-a mixture of a metal with one or
more other elements where the
mixture retains the properties of the
metal
• Alloys are produced to obtain
improved properties; ex: hardness,
strength, lightness, etc.
Alloys through time
• 3500 b.c.—historians believe that
ancient Sumerians in the TigrisEuphrates Valley (Iraq) accidentally
discovered bronze
• This 2,000 yr time span is known as
the Bronze Age (3500 b.c. to 800 b.c.)
• Processing of Bronze has greatly
changed since this time period as
well as new alloys being developed
Properties of Metals and Alloys
• Alloys retain the metallic
properties of metals
• Metals have/are:
• Luster-shiny
• Ductility-can be pulled into wires
• Malleability—can be hammered into
sheets
• Conductivity-heat or electrical charges
move through them
What prop’s of an alloy are most important?
• Depends upon how it will be used
AND which characteristics are most
desirable
• Ex: gold jewelry-mostly made from
gold alloys
• Gold—bright, expensive, soft, bends
easily
• Copper-inexpensive, harder than gold
• When gold and copper are melted,
mixed, and cooled, an alloy forms
• Figure 3—pg. 674
Other Factors to consider
• When choosing the type of alloy that
would be best these types of
questions might also arise:
• 1. Characteristics of the desired final
product
• How hard does the alloy have to be
to prevent the object from breaking
• Will the object be exposed to
chemicals that will react with the
alloy?
Uses of Alloys
• Common Alloys and their
Composition and Uses are listed on
pg 675 in the book-Gigure 4
• Bronze
• Brass
• Sterling Silver
• Pewter
• Solder
• Wrought Iron
Steel-An Important Alloy
• Different forms of steel alloys
perform different functions
• Classes of steel are classified by the
amount of carbon and other
elements present, as well as by the
manufacturing process used to
refine the iron ore
• Ex: stainless steel, steel used in
construction, etc.
Aluminum Alloys
• Aluminum is familiar because it is
used to make soda cans and cooking
foil
• Other uses: commercial aircraft, etc.
• Titanium—used in the development
of space shuttle panels as a heat
shield that might be used in place of
traditional ceramic tiles
• (imp. Upon re-entry into Earth’s
atmosphere from space)
Section 2-Ceramics
• Ceramics—materials made from
dried clay or clay-like mixtures.
• Ceramics have been around for centuries
The first walled town, Jericho, built about
8,000 b.c. was built from these materials
Around 1500 b.c. the first glass vessels were
made and kilns were used to fire and glaze
pottery
By 50 b.c., Romans developed concrete and
used it as a building material
More on Ceramics
• 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)
Firing Ceramics
• Ceramics are known also for their
chemical resistance to oxygen,
water, acids, bases, salts and strong
solvents
• Traditional ceramics are used also as
insulators because they do not
conduct heat or electricity
• Manufacturing ceramics is similar to
manufacturing alloys –desired
properties are important
Modern Ceramics
• Ceramics traditionally are used as
insulators, but some ceramics have
superconductive properties.
• Ceramics also have medical uses
ex: hip and joint replacements,
tooth replacements, repair and
braces.
Semiconductors
• Semiconductors are materials that
make computers and other electronic
devices possible
• Ex: silicon and germanium are
semiconductors—poorer
conductors of electricity than
metals but better conductors than
nonmetals and their electrical
conductivity can be controlled
Controlling Conductivity
• Adding impurities to some metalloids
will alter their conductive properties
• Ex: silicon is used to make
semiconductor devices
• Its electrical conductivity can be
increased by introducing impurities,
such as atoms of arsenic or gallium into
its crystal structure
Doping and Integrated circuits
• Doping—the process of adding
impurities or other elements to a
semiconductor to increase the
conductivity
N-type-has increased # of
electrons
P-type-has decreased # of
electrons
Integrated Circuits
• Integrated circuits-contain many
semiconducting devices/are very
small in size/sometimes called
microchips
• Pg. 683 –History of the Computer
• (shows how size of computers has
changed throughout history as
memory storage has become
smaller)
Semiconductors and Computers
• Semiconductors make computers
possible
• A desktop computer is an example of
a device that uses semiconductors
• 3 main jobs of computers:
• Receive and store info
• Follow instructions to perform tasks
• Communicate info to the outside world
Section 3-Polymers and Composites
• Polymers-a class of natural or
manufactured substances that are
composed of molecules arranged in
lg. chains
• Monomers—one specific molecule
that is repeated in the polymer chain
• ex: polypropylene has 50,000 to
200,000 monomers in its chain
Synthetic—means that the polymer does
not occur naturally/but was made in a
lab or chemical plant
More on monomers and polymers
• Fig. 2 on pg. 685
• History of Synthetic Polymers• Ancient Egyptians soaked burial
wrappings in natural resins for
preservation
• Charles Goodyear, heated sulfur and
natural rubber together to improve
qualities of natural rubber
• TODAY-carbon and hydrogen are the
primary components of most
synthetic polymers because
polymers are made from
hydrocarbons
• Chart-pg. 686
• Changing Properties: if the
composition or arrangement of
monomers is changed, then the
properties of the material will change
Plastics
• Plastics are widely used for many
products because they have
desirable properties
• Plastics are usually lightweight,
strong, impact resistant, waterproof,
moldable, chemical resistant, and
inexpensive.
• Plastics are transparent, melt at high
temp’s and are flexible –sometimes.
Synthetic Fibers
• Most synthetic fibers are composed
of carbon chains because they are
products of petroleum or natural
gas/they can be mass produced
• Ex: nylon, polyester, acrylic and
polypropylene
Aramids—a special family of nylons
w/fireproofing properties(light and five
times stronger than steel)
**used by: firefighters/motorcycle and
race car drivers, etc.
Adhesives
• Synthetic polymers are used to make
adhesives that can be modified to
provide the best properties for a
particular application.
• Ex: contact cements, structural
adhesives, etc.
• Silicone-used to seal windows and
doors to prevent heat loss in homes and
other buildings.
Surface Coatings and Elastic Polymers
• Polyurethane—popular polymer that
is used to protect and enhance wood
surfaces
• COMPOSITES—a mixture of 2 or
more materials-1 embedded or
layered in the other
• Composite materials of plastic are
used to construct boat and car
bodies, etc.
• Ex: fiberglass
• Look Over Composites in Flight-pg. 690