SPH 203: STRUCTURE AND PROPERTIES OF MATTER Course Instructor: Dr Justus Simiyu
SPH 203: STRUCTURE AND PROPERTIES OF MATTER
Course Instructor:
Dr Justus Simiyu
ATOMIC AND MOLECULAR BONDING
Bond Strength
measure of the energy required to break a bond, that is, the amount of energy required to
vapourize the solid and hence separate the constituent atoms. From the measure of heat
required to vapourize 1 Kg mole
Bond Strength and Melting Point.Material Atomic Number Melting Point
(C)Carbon(diamond)
6 3,750
Silicon 14 1,421
Germanium 32 937
Tin 50 232
Thus melting point occurs when the vibration becomes so great
that the bonds are broken and the atoms become mobile.
PHASES OF MATTER
GasesIdeal Gase (Assumptions)• behave as small elastic spheres• The molecules
•are all alike-hence the homogeneity of a gas.•are in constant motion-hence the diffusion.•exert no force on each other except when in actual contact.
• volume occupied by the molecules is small compared to the total volume
• exerted Pressure is due to collisions of the molecules with the walls of the container.
Mean Free Path
• average distance between successive
collisions of molecules u
vw
u
u
-u
v
w
-w
w
u
c
c
c
Gas Mean free path (m)
Hydrogen 16.3x10-8
Nitrogen 8.5
Oxygen 9.6
important for gas transport properties e.g. thermal conductivity
Liquids
Surface tensionelastic tendency of a fluid surface which makes it acquire
the least surface area possibledecreases with temperature rise
Composed of molecules with much less free space
Substance Surface tension (Nm-1)
Water 0.070
Alcohol 0.025
Molten aluminum 0.500
Molten iron 1.500
Eg. Water striders
Eg. Water striders
Solids
array of atoms whose mean positions do not change with time
Characterization of solids
• x-ray diffraction
sin2dn
METALS/NON-METALSInter-atomic Forces in Solids
r
F
rro
U
Young’s Modulus
Mat
erial
Bonding Young’s modulus (Nm-2)
MgO ionic 30 x 1010
Copper Metallic 13 x 1010
Diamond Covalent 54 x 1010
MECHANICAL TESTSTensile tests
• Subject specimen to tension
Extension
Load
A
BC
E
F
O D
Hardness test
Classified into:
• Resistance to indentation by a particular shape of indenter.
• Resistance to scratching.
• The rebound of a steel ball from the surface.
Brinell Hardness (HB), test
• Steel ball pressed onto the surface under steady load, maintained for few seconds and indenter removed
Hardness:• Ratio of applied weight to diameter of indentation
22 11
2
DdD
WHB
Vickers Hardness (HV).
• Similar to HB but the indenter is always Diamond
• Hardness: ratio of weight to surface area of indent
2854.1
d
WHW
Rockwell Hardness: (HR)A, B, C
• Applied on soft materials
• Using different types of indenter
• A: cone shaped diamond indenter (tungsten)
• B: Steel sphere (Soft steels, Al, Brass)
• C: cone shaped diamond indenter (Harder steels)
• Hardness:
• d is the depth, N & s are scale factorss
dNHR
NON-METALSInorganic materials (Ceramics)
Eg. Magnesia (MgO)
aluminum oxide
(Alumina) – Al2O3,
Silicon Carbide (SiC)
Mostly ionic bonded e.g. MgO, or covalently bounded e.g. SiC.
Unique properties
• high melting points, • high corrosion resistance • chemical stability (chemically resistant to most acids
and alkalis), and resistance to abrasion. • Most ceramics do not have free conducting electrons
as a result have relatively low thermal and electrical conductivities,
• have high compressive, and mechanical strengths at high temperatures.
• Low densities of ceramic materials are also low in comparison to those of most metals; hence they have strength-weight ratios (Light but strong)
Ceramics
Property
Melting Point
(0C)
Density x
103Kgm-3
Thermal
Conductivity
(Wm-1K-1)
Tensile Strength
(MPa)
Young’s Modulus
(GPa)
Magne
sia
(MgO)
Sintered
Alumina
Al2O3
Vitreous
Silica
(SiO2)
Hot pressed
SiC
Hot pressed
Si2N4
Hotpressed
(Si2N4)
2800
3.6
36-45
100
210-
310
2040
3.9
12-32
400-500
350-380
1710
2.5
1-2
80-160
70
Decompose
s at 2300
3.2
100
350-800
350-470
Sublimes at
1900
3.2
10-16
500-900
150-320
Sublimes
1900
3.2
10-16
500-900
150-320
Organic Materials (Polymers)
Polymers
• atoms aggregate together into molecules,
• held together by either Van der Waal or hydrogen bonds
• Have long chain or repeating units that make up its molecule.
• The smallest unit is known as a monomer
• repeating network unit forms the polymer.
•
Composites
• consists of two or more components that can be distinguished from one another under a microscope.
• Target: superior material whose property of interest is superior to those of the individual components.
• Example combination of strength & ductility may be realized in solids that comprise fibres or precipitated particles embedded in a ductile host material.
• Polymers are most suitable materials to host fibres. Example fibreglass roof covers of pick-up trucks or car-bumpers that are made of composites.
Plywood
Composites
Examples
Natural composite
materials
Wood, bone, bamboo, muscle and
other tissues
Microscopic
materials
Metallic alloys: eg., steels,
toughened thermoplastics e.g.
impact polystyrene
Macrocoposites Galvanised steel, reinforced
concrete, helicopter blade, car
bumpers, pick-up truck roofs, skis
etc
FRACTURE AND OXIDATION
Fracture
Break in continuity of a surface of a materialEg: wood, bone, stone etc
Fracture vs Failure
• Fracture is a major mechanical property of metals• The study of this property aims at improvement of
mechanical properties of metals• For safety (to prevent fracture due to stress)• Fracture is caused by Failure• Failure is for specific purpose eg.
Fractures Types Ductile
• Necking before fracture
• Cup-&-cone shapes of the two new surfaces created
• Most metals are ductile
Brittle
• No necking
• E.g. ceramics, glass, extra cold metals
Scientific explanation of Metal Failure
• Metals contain voids
• Some only seen through microscopy
• When subjected to tress, voids increase in size
• Get close to each other
• Weakens the bond
• Leads to breaking (fracture)
Prevention of Brittle Fracture
• Etching (Chemical process of filling cracks and voids)
• Polishing (Physical process of filling the cracks)
• Introduction of ductile fibers in micro cracks
– Mainly composites (commonest: concrete)
– Prevents crack growth
– Construction industry
Causes of Failure
• No single cause of failure
• Important for safety (construction, transport – air etc)
• Causes:
• thermal shock,
• wear,
• corrosion,
• stress corrosion cracking,
• fatigue
Corrosion
• Chemical process of conversion of a metal from a refined state to a more chemically stable
• Formation of compounds on a metal surface when exposed to air, water, or an electrolyte
• Common terminology: Rusting
• Its an irreversible process
The Process
• It’s a chemical process• one of the reactants must be
at a higher energy state• natural process involves
transition from high to low level
• Hence energy absorbed: +ve• energy released: –ve• For spontaneous reaction: G = –ve.
fb eeG
e: Activation energy (energy required to overcome a barrier)
(Free Energy)
Factors affecting corrosion
• Temperature of the surrounding
• The diffusion rates of the reaction products
• The equilibrium concentration of the ions or reaction products in the solution;
• The pH value of the solution
• Electrolyte velocity
• Solid or dissolved pollutants
• Relative humidity.
Types of Corrosion
• Direct corrosion by dry gases
• electrochemical corrosion
• galvanic or bimetallic) corrosion
Manifestation of corrosion• Uniform attack
• Pitting-
• Crevice corrosion-
• Intergranular
• Stress corrosion-
• Corrosion fatigue-
• Fretting
Corrosion hazards
Prevention/Control of Corrosion
• Painting
• Galvanization
• Environmental control (pH, humidity, air quality)
• Appropriate choice of materials
• Cathodic and anodic protection
• Sydney Opera House
Sydney Opera House
THERMODYNAMICS
a b c
d e
f g h i
(Adiabatic )
Definitions System
Phase
Surrounding (Kitchen)
Rigid boundary
isolated system
Equilibrium state
one state in which all the bulk physical properties of a system are uniform
throughout the system & do not change with time.
• e.g. Temp, Pressure, concentration, volume, magnetic field, etc
• Min. of two variables required for specification
Zeroth Law (Temperature)
Diathermal wallAdiabatic wall
A B C
A AB C
REVERSIBLE, IRREVERSIBLE, QUASISTATIC AND ADIABATIC
PROCESSES
Thermodynamic reversibility
1. the process must be quasi-static (equilibrium state is always maintained)
2. there must be no hysteresis (i.e., no dissipation of energy).
Reversible
(P1,V1)
P2,V2
P
Work & Volume changes(for reversible Process)
Atmospheric thermodynamicsP
V
1
2
3
V1 V2
P2
P1
Isotherm at T
FP
AGas
CSA=A
dx
PAF
PdVPAdxdW
nRTPV
work done is path dependent 12231 VVPW
2
1
2
11
2
21 lnV
V
V
V V
VnRT
V
dVnRTPdVW
INTRODUCTION TO QUANTUM THEORY
Classical vs Quantum
• Newtonian mechanics:
• Interested in
x, v, a, p
• Light as a wave
• Quantum mechanics:
• Interested in
• Pos, energy, momentum
• Light as a particle
FmaF , txt
itxxm
,,2 2
22
Photoelectric Effect
• Proof of Quantum (or particle) nature of light
ejection of electrons from the surface of a metal when a beam of monochromatic light of some frequency () is shone on the surface.
Other phenomena• Heat Capacity of Solids
• The Atomic Spectra (The Hydrogen Atom)
Wave-Particle duality & the Complementarity’s Principle
the particle and wave models are complementary; if a measurement confirms
the wave nature of radiation or matter, then it is impossible to prove the particle nature in
the same experiment, and vice-versa.
WAVE MECHANICS AND SCHROEDINGER’S EQUATION
wave function (),
• , a complex function, that it is, it has a real part and an imaginary part.
• Is used to find probability that a particle is somewhere (in volume element dV)
Schrödinger Equation
• Time – dependent
• In a potential (V(x))
txt
itxxm
,,2 2
22
txVxmti
,2 2
22
mE
xEti
e2
2
22
2
222
82 mL
hn
mL
nEn
Wave - Particle
Position - Wave (Continuous)
Energy – Particle (quantized)
mE
xEti
e2
2
22
2
222
82 mL
hn
mL
nEn
PHYSICS CAREER DAY WORKSHOP
DATE: JULY 6 2018
VENUE: MH1
TIME 8.00am
KEY NOTE ADDRESS:
Rose M. Mutiso, Ph.D.
Co-Founder and CEO The Mawazo Institute
Rose M. Mutiso, Ph.D.
• Co-Founder and CEO of The Mawazo (“Ideas”) Institute, a Nairobi-based think tank.
• Scientist, researcher & practitioner working on technology & policy aspects of energy, environment & innovation issues in North America, South Asia, & Sub-Saharan Africa.
• Materials Scientist by training with research experience in the fields of nanotechnology & polymer physics.
• Passionate about harnessing science & technology to improve lives