Transcript What has been presented?

What has been presented?
Classification of Matter
Matter
• has mass and
• takes up space (has mass and volume) and
• made up of atoms
Atom - smallest particle of an element that has the
properties of the element
States of Matter:
Solid
Gas
Liquid
Plasma
Phase Changes of Matter- due to changes in energy with
and or without changes in temperature
Types of Matter
Elements
Compounds
Pure substances
•Constant, defined compositions
•Physically cannot be separated
•Elements, compounds
Mixtures
Mixtures
Composed of one or more
elements or compounds
Can be separated
Know what an element, compound or mixture are
Mixtures
Homogeneous
Heterogeneous
Types of Elements
Metals
Nonmetals
Metalloids
(semimetals)
Metals
left side of periodic table
most numerous solids
lustrous
conductors
workable
Non Metals
right side of periodic table
all 3 states of matter
not lustrous (dull)
tend not to be conductors brittle
Metalloids (Semimetals)
on border between metals and nonmetals (stair step line)
fewest # of elements
solids
intermediate properties
Structure of Materials
Atomic structure: bonding between the atoms,
arrangement of atoms
Microstructure: crystalline structure -features that can be
seen using a microscope
Macrostructure Cracks, - can be seen by the naked eye
Microstructure:
Crystalline Materials
Amorphous Materials
Atoms
Electrons
Protons
Neutrons
Nucleus
Atomic Mass Units
Atomic Number
Atomic Mass
Isotopes
Atomic Bonding
Metallic Bonding bonding between atoms within metals
Ionic Bonding a metal and a nonmetal ion through
electrostatic attraction
Covalent Bonding a chemical link between two atoms via
sharing electrons
Van der Waals attractive or repulsive forces
between molecules
Valence electrons
Core electrons
The Periodic Table
•A representation of the elements
•arranged by increasing atomic number
•Rows called periods
tells number of electron shells
number them down the left side of the
periodic table –1 through 7
•Columns called families or groups
elements in same column have similar
chemical properties
same number of valence electrons
Atoms tend to decrease in size as you go across a
period
Types of Elements in the Periodic Table
Metals
Nonmetals
• 1 to 3 valence electrons
• 5 to 8 valence electrons
• givers of electrons
• takers of electrons
• lose electrons
• gain electrons
• make (+) ions
• make (-) ions
• left side of periodic table
• right side of periodic table
Ions
Noble gases –full valence band
- very stable –low reactivity
- don’t want to form compounds
or bonds
- under standard conditions, they
are all odorless, colorless, monatomic
gases
Halogens – have s2p5 electron
configuration
- want one more electron
- most reactive nonmetals
- Found as ions in compounds
because of high reactivity
alkali metals –1 s electron in
valence band
- want to give away one
electron
- most reactive metals –
highly reactive with water
Alkaline Earth Metals
- React with halogens to form ionic
salts
- Form Oxides that are very stable
at high temperatures
- 2 electrons in s orbital
Transition Metals
- Have incomplete d subshells in valence
orbitals
- Multiple oxidation states –can form multiple
compounds with same elements
Properties of Metals
Chemical Properties
Physical Properties
- Thermal Properties
- Mechanical Properties
Force – Stress – Strain – Workability
Brittleness – Hardness - Elasticity
Plasticity - Toughness - Strength
Stresses and Forces
 Tension: the pulling force
stretches materials
 Compression: a pushing
force squashes materials
 Torsion: a twisting force
 Shear: opposing forces
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Mechanical Properties
• workability
malleability – can be flattened
ductility – can be drawn into
wire (stretched), bent, or
extruded
• brittleness
breaks instead of deforming when
stress is applied
• hardness
resistance to denting or
scratching
Mechanical Properties
• elasticity
ability to return to original shape after
being deformed by stress
Young's modulus is a measure of
the stiffness of an elastic material and is a
quantity used to characterize materials
• plasticity
retains new shape after being deformed by
stress
• toughness
– ability to absorb energy
• strength
– resistance to distortion by stress or force
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Absolute Temperature – Minimal Energy
Phonons - Elastic Wave that transfer energy in materials
Thermodynamics
- First Law - ΔU = Q –W
- Energy of Phonons – E = hc/l = hv Materials gain
or lose heat by gaining or losing phonons
- Heat Capacity - Energy required to raise the
temperature of one mole of a material by one degree
- Specific Heat - energy required to raise
temperature of a mass of material by one degree
- Thermal Expansion – As atoms gain energy they
vibrate more, expanding the crystal lattice
- Coefficient of Linear Expansion - DL = La DT
If material expansion is restrained, thermal stress
developed
Causes of Thermal Stress
Design of Materials - Joining of Materials
Thermal Conductivity
- Measure of the rate at which heat is transferred through a
material (K)
K DT/Dx = Q/A (Heat Flux)
Heat Flux flows in the direction of decreasing temperature
Electric Properties
Thermal Properties: transport of heat through Phonons in a
material
Electrical Properties: transport of electrons through a
material
Electrical Conductivity: how well a material accommodates
the movement of an electric charge
Electrical Resistivity: opposition of a body or substance to
the flow of electrical current through it
Insulator vs. Conductor
Insulators: materials are not good conductor. Minimal current
exists when a potential is applied to the material
Conductors: materials that conduct electricity. A current will
be generated when a potential is applied to a material
Ohm’s Law – V = IR
Resistivity - resistance dependent on material properties
resistivity - ρ of a material: resistance (R) per unit
length (L)and cross-sectional area (A)
r = RA/L
Conductivity
s = 1/r
Power
P= V I
Crystals
Many materials used in technological applications are
made up of one or more crystals
Crystalline Materials have Long Range Order
Classification of Solids
Metals: Steel sheets to make cars or Copper wire
Ceramics: Tableware, components in cell phones, glass
Polymers: Plastics (short-range order and long-range
order)
Semiconductors: Electronics
Crystallography
- science of the
arrangement of atoms in solids (or crystals)
- physical properties are often controlled by crystalline
structure and differences in structure
Crystal Lattices and Crystal Structures
Crystal Lattices –set of points (atoms) arranged in a
repeating manner
Crystals are THREE DIMENSIONAL (3D)
Crystal Lattices and Structures
Structures are obtained by placing one or more atoms at
each crystal point
Unit Cell
The smallest piece of a crystal lattice that contains all the
information to make the whole lattice is called a Unit cell, also
called the “Single repeating unit” in the lattice
Three Basic Cubic Lattices
Cubic Lattice Structures
A simple cubic lattice consists of one lattice point on each of the
eight corners…few materials have this configuration
A body-centered cubic lattice consists of a lattice point on each of
the corners with one additional lattice point associated n the middle
of the lattice.
Some Elements: Fe, Mo, W
A face-centered cubic lattice consists of eight lattice points located
at the corners and has an additional lattice point on each face of the
cube in its center.
Some Elements: Cu, Pt, Ni
Miller Indices for Cubic Structures
Lattice planes –planes in crystal structures that cut through the unit
cell in different ways.
Miller indices use the x, y, z to describe
directions in crystal coordinates and to
describe the planes.
Crystallographic Planes
• (110) plane is shaded in grey
• Plane is in z direction
Atomic Positions in Crystals
- For each plane, the atoms have a particular arrangement
- EXAMPLE: FCC (100)
Number of Atoms in a Unit Cell
There are different number of
lattice points associated with the
unit cells of different lattices.
•The corner of each lattice
are shared by eight unit cells.
Subsequently, ONLY one eighth of
each corner atom belongs to any
one unit cell.
Atomic Packing
Atomic Packing informs us of how
many atoms that can be places in a
given space or volume.
We are going to determine the
amount of used volume in a cubic
from placing the “round” atoms in
it.
FCC Unit Cell
Since there are 6 faces each
face shares a unit atom with an
adjoining cubic lattice, so there
are 3 atoms per unit cell.
Body Centered Cubic: Packing Density 68% filled
Face Centered Cubic ……….74% filled
Defects in Crystals
Three main types:
Point Defects
Line Defects
Interfacial Defects
Crystal Defects
Simplest point defect is a vacancy. A vacancy is merely a
missing atom in the crystal
Three types of Point Defects
Substitution
Interstitial
Vacancy
Dislocation (Line Defects)
regions in crystals where atoms are not perfectly aligned –
an extra partial plane
Defects can move
a small number make a metal more workable
a large number make a metal harder to work
dislocations can get “jammed” or “pinned” makes
the metal harder = work-hardening
The most common type of line defect is a dislocation.
Plane of atoms that does not extend all the way through
the crystal but terminates abruptly in the crystal
As the distance from the dislocation increases, atom
positions become closer and closer to their lattice sites
Shear stress applied to a dislocation will result in the formation of
a step
Dislocation is now on outside of crystal
Grains –portion of a material within which the arrangement of
atoms is identical
Grain Boundaries –interface where grains of a polycrystalline
material meet
Interfacial Defects
A grain boundary is the interface between two grains in a
polycrystalline material. Grain boundaries disrupt the motion of
dislocations through a material, so reducing crystallite size is a
common way to improve strength
Grain Sizes
Sample Preparation can affect grain sizes.
Quick Cooling -smaller grain size
Slow Cooling –larger grain sizes
Smaller Grain sizes →more grain boundaries
Larger Grain sizes →fewer grain boundaries
At low temperatures: Smaller grains increases the strength of a
material because the amount of grain boundaries increases. Grain
boundaries act as barriers to dislocation movement (at regular
temperatures)
At high temperatures: Smaller grains decreases the strength of a
material because grain boundary sliding may occur. Grain
boundaries become regions of weakness
Grain boundaries can affect other materials properties.
High energy –sites for onset of corrosion Corrosion
Can improve strength by reducing dislocation movement
Decrease the electrical and thermal conductivity
What is Diffusion?
Mechanism by which matter is transported through matter
Diffusion Speed
Gases > Liquids > Solids
Diffusion required for:
Heat treatment of metals
Manufacture of ceramics
Solidification of materials
Types of Diffusion
Self-diffusion: movement of atoms through their own
lattice
Interdiffusion (impurity diffusion): diffusion of species not part of
the crystal structure
Example: movement of Ni through the lattice of Cu
Mechanisms of Diffusion Vacancy: involves vacancies in crystal
structure
Interstitial: involves atoms in interstitial locations in crystal
Conditions for atom migration: empty adjacent site.
Atom must have enough energy to break bonds and cause
lattice distortion during displacement.
Interstitial Diffusion
Migration of interstitial atoms from and interstitial position to
adjacent empty one
•Diffusing atoms are small compared to atoms in crystal–