Lecture: 2
Structure Levels:
• Subatomic level
Electronic structure of individual atoms that
defines interaction among atoms (interatomic
bonding).
• Atomic level
Arrangement of atoms in materials (for the same
atoms can have different properties, e.g. two forms
of carbon: graphite and diamond)
• Microscopic structure
Arrangement of small grains of material that can
be identified by microscope.
• Macroscopic structure
Structural elements that may be viewed
with the naked eye.
Properties:
Properties are the way the material responds to the
environment and external forces.
Mechanical properties – response to mechanical forces,
strength, etc.
Electrical and magnetic properties - response electrical and
magnetic fields, conductivity, etc.
Thermal properties are related to transmission of heat and heat
capacity.
Optical properties include to absorption, transmission and
scattering of light.
Chemical stability in contact with the environment - corrosion
resistance.
Types of Materials:
Let us classify materials according to the way the atoms are
bound together.
Metals: valence electrons are detached from atoms, and spread
in an 'electron sea' that "glues" the ions together. Strong,
ductile, conduct electricity and heat well, are shiny
if polished.
An alloy is a combination of two or more metals usually
produced to have new materials with improved properties.
Alloys like : Cu-Zn (brass) , Fe-C (steel) , Sn-Pb (solder) .
Semiconductors: the bonding is covalent (electrons are
shared between atoms). Their electrical properties depend
strongly on minute proportions of contaminants.
Examples: Si, Ge, GaAs.
Ceramics: atoms behave like either positive or negative ions,
and are bound by Coulomb forces. They are usually
combinations of metals or semiconductors with oxygen,
nitrogen or carbon (oxides, nitrides, and carbides). Hard, brittle,
insulators.
Examples: glass, porcelain.
Polymers: are bound by covalent forces and also by weak van
der Waals forces, and usually based on C and H. They
decompose at moderate temperatures (100 – 400 C), and are
lightweight. Examples: plastics rubber.
Composite Materials: Consist of more than one material
type (such as fiberglass) , display a combination of the best
characteristics of each of the individual material.
Examples: Continuous carbon fibers in one or more
orientations in a polymer matrix.
Concrete is another structural composite obtained by
combining cement, sand, gravel.
Composites are classified according to their matrices into:
1- polymer-matrix composites : used for lightweight structures
(aircraft, sporting goods, wheelchairs, etc.) in addition to
vibration damping.
2- Cement matrix composites
3-Metal-matrix composites : with aluminum as the matrix are
used for lightweight structures, but they have a high cost of
fabrication.
‫المواد المتراكبة المقواة بااللياف‬
‫المادة االساس‬
‫االلياف‬
‫المادة المتراكبة‬
‫المادة االساس‬
‫المواد المتراكبة المقواة بالدقائق‬
‫المادة الدقائقية‬
‫المادة المتراكبة‬
‫المادة االساس‬
4 - Carbon-matrix composites : relatively expensive because
of the high cost of fabrication and they are important for
lightweight structures (like the Space Shuttle) and components
that need to withstand high temperatures (such as aircraft
brakes).
5 - Ceramic-matrix : superior to carbon-matrix composites in
oxidation resistance, but they are not as well developed.
Biomaterials: Implanted in the human body for eplacement
of diseased or damaged body parts. They are must be:
1- Not produce toxic.
2- Compatible with body tissues.
Engineering Classification of Materials
Material
Non-single (composite)
Non-metallic bonds
Organic (polymers)
single
Metallic bonds (metals)
Non-organic (ceramic)
Future of materials science :
Design of materials having specific desired characteristics
directly from our knowledge of atomic structure.
• Miniaturization or "Nanotechnology ": “Nanostructured"
materials, with microstructure that has length scales between 1
and 100 nanometers with unusual properties. Electronic
components, materials for quantum computing.
• Smart materials:
Materials that are able to sense changes in their environments
and then respond to these changes in predetermined manners.
■ Airplane wings that deice themselves
■photosensitive glass, which darkens in response to sunlight.
The process is similar to the way that photographic films
darken, but is reversible. The glass contains dispersed silver
halide crystals doped with copper.
■ Buildings that stabilize themselves in earthquakes .
■Actuators : able to change shape , position , natural
frequency , or mechanical characteristics in response to
change in temp. , electric field , and / or magnetic field .
Four types of materials used for actuators:
1- Shape memory alloys : ∆T
∆ Shape
Ex: Ni/Ti alloys such as Nitinol, Cu/Zn/Al Alloys, and
Cu/Al/Ni Alloys.
2- Piezoelectric ceramics : ∆ Voltage
expand &
contract, also ∆ dimensions
generate an electric
field.
Ex:
Piezoceramics (Lead Zirconate Titanate,PZT) are used
extensively as actuators and sensors, for a wide range of
frequency including ultrasonic applications.
3-Magnetostrictive materials : Magnetic field
4- Electrorheological & Magentorheological Fluids :
Electric & Magnetic fields
∆ Viscocity .
■Sensors
Smart System as used in helicopters to reduce noise.
• Advance Materials :( High-Tech.)
- Leaser
- Integrated Circuits (IC)
- Magnetic information Storage
- Liquid Crystal Display (LCDs)
- Fiber Optics.
- Thermal Protection System for the Space Shuttle Orbiter.
• Environment-friendly materials: biodegradable or
photodegradable plastics, advances in nuclear waste processing,
etc.
• Learning from Nature: shells and biological hard tissue
can be as strong as the most advanced laboratory-produced
ceramics, mollusces produce biocompatible adhesives that we
do not know how to reproduce…
• Materials for lightweight batteries with high storage densities,
for turbine blades that can operate at 2500°C, room-temperature
superconductors? chemical sensors (artificial nose) of extremely
high sensitivity, cotton shirts that never require ironing…