Chemistry of Materials

What are A and X in zAX

A: Mass number, number of electrons and neutrons

B: Atomic Number, number of protons

number of electrons is usually equal to protons

Maximum number of electrons per orbital
2
Order of Shells
1s 2s 2p 3s 3p 4s 3d 4p
Define Ionisation Energy
The minimum energy required (to be added to the atom) to remove the outermost electron from the ground state of an isolated (eg. gaseous) atom
In what directions Ionisation Energy increases/decreases
Decreases from top to bottom
Increases from left to right
Three properties of ionisation energy
-Increases as successive electrons are removed
-Sharp increase when an inner-shell electron is removed
-High values of IE are why only valence electrons are involved in bonding
Define Electron Affinity
The energy change that occurs when an electron is added to a gaseous atom – measures attraction of atom for the added electron
Properties of Electron Affinity
-Typically, energy is released when an electron is added (negative value)
-Typically increases (more negative) left to right
-Noble gasses are positive
-typically is positive (energy gained) when the added electron begins a new shell (eg. noble gasses, Be, Mg)
Define Electronegativity
The ability of an atom in a molecule to attract electrons to itself
In what directions Electronegativity increases/decreases
Increase from left to right
Decrease from top down
Describe Hydrogen Bonding
when the molecules in a molecular compound have both a hydrogen atom and at least one “lone pair” of electrons, the hydrogen of a molecule will be strongly attracted to the lone pair on an adjacent molecule, creating above average inter-molecular force.
http://chemwiki.ucdavis.edu/Physical_Chemistry/Quantum_Mechanics/Atomic_Theory/Intermolecular_Forces/Hydrogen_Bonding
Formal Charge formula

F = V – (N + B/2)

V = Valence Electrons

N = Non-Bonding Electrons

B = Bonding Electrons

applying formal charge
The four types of solids
Molecular
Covalent Network
Ionic
Metallic
Properties of Molecular Solids
-Intermolecular forces are weak
-Thus low melting point
-Room temperature gases and liquids usually form molecular solids at low temperature
Crystalline solid:
well-ordered, definite arrangements of molecules, atoms or ions. Crystals have an ordered, repeated structure
Amorphous solid:
no ordered structure,
e.g. rubber, glass
Properties of Covalent Network Solids
-Atoms held together in large networks by covalent bonds
-Examples: diamond, graphite, quartz (SiO2), silicon carbide (SiC), and boron nitride (BN)
About Carbon Nanotubes
-Example of covalent network
-Long cylindrical structures
-Either single or multi walled
-Potential structural applications in high strength materials
-Applications in a range of conductive materials
Properties of Ionic Solids
-Regular structures, packing of positive and negative ions around each other
-Hard, brittle, high melting points
-Poor electrical conductors
Properties of Metallic Solids/Bonding
-Metal ions in a sea of delocalised valence electrons –> good electrical conductor
-Strong bonding
-Without any definite directions for bonds, the metals are easy to deform
coordination number of simple cubic, body-centred cubic and fcc
6, 8, 12
occupation of simple cubic, body-centred cubic and fcc
52%, 68%, 74%
Example of simple cubic
?-Po
Examples of body-centred cubic
Ba, Cr, Fe, W, alkali metals
examples of fcc
For example: Ag, Al, Au, Ca, Cu, Ni, Pb, Pt
Images of cubic unit cells
[image]
For CCP, the stacking pattern that produces hexagonal close packing
ABABABAB,
rather than ABCABCABCABC for Cubic Close Packing
picture of hexagonal close packing
[image]
The two packing types for FCC
Hexagonal close packing
Cubic close packing
Differences between Hexagonal close packing and Cubic close packing
Cubic: Ductile
Hexagonal: Brittle
Properties of Metals vs Non-Metals
Metals:
-Low ionisation energy rather than High
-Malleable rather than usually brittle
-Good electrical conductors
about heterogeneous alloys
components not dispersed uniformly
Two types of Solution alloys
-Substitutional alloys – solute atoms disperse main atoms
-Interstitial alloys – solute atoms occupy empty space between main atoms
about Substitutional alloys
-All atoms radius within 15% of each other
-Elements must have similar bonding characteristics
-Elements Must have same crystal structure
-Elements Must have Similar Electronegativity
about Interstitial alloys
-One element must have a significantly smaller radius than the other
describe triple point
P and T at which all three phases
are in equilibrium
what is abnormal about water phase diagram
the solid-liquid line goes backward (i.e. solid is less dense than liquid)
what is a supercritical fluid
a fluid that is beyond the temperature and pressure of the critical point. has a density of liquid and viscosity of gas.

explain the steps:

[image]

Energy is released by the changing of bonds as the iron changes phase, and so the material does not overall cool down at during these phase changes.
how to read binary phase diagram (picture)
[image]
what is silica
Silicon Dioxide
what is Carbonate
(CO3)2-
what is Silicate
(SiO4)4-, tetrahedra
basic steps for making portland cement
[image]
About setting cement
-Reaction of clinker materials with water to give gelatinous calcium silicates, solid Ca(OH)2, complex silicates, calcium aluminates, etc
-In concrete, the hydrated materials bind to solid aggregates (stones)
-Hydration reaction of Portland cement results in hardening
-There are rapid reactions within hours, and slow reactions over years
a few examples of things made from petroleum/crude oil
-liquid Fuels
-plastics
-detergents
-soaps
-drugs
picture of crude oil reservoir
[image]
Elements/percentages in petroleum
-Carbon 84%
-Hydrogen 14%
-Sulfur 1-3%
-Nitrogen, oxygen, metals, salts <1% each
Hydrocarbons in petroleum
-Alkanes ~30%
-Cycloalkanes ~50%
-Aromatics ~15%
General formula of alkanes
CnH(2n+2)
the three basic steps of crude oil before final use
-Washing/desulfurisation: REMOVAL OF SALTS AND MINERAL CONTAMINANTS
-Seperation: Fractional Distillation
-Conversion: Reforming, Cracking, Alkylation and Isomerisation
Details of fractional distillation
Crude oil is heated to ~600C and blasted into a distillation tower. The fuels come out in broad fractions based on number of carbons
Basics of the four conversion processes
-Reforming: changes alkanes and cycloalkanes to more valuable aromatics (reformer)
-Cracking(Pyrolysis): breaks large hydrocarbons to smaller ones (coker)
-Alkylation: Changes alkanes and alkenes to larger branched alkanes (alkylation unit)
-Isomerisation: Alters arrangement of atoms in molecule
details of Reforming

-Uses heat, pressure and a catalyst

[image]

schematic of reforming unit
[image]
three types of cracking

Catalytic cracking

Hydrocracking

Steam/Thermal cracking

about catalytic cracking

-Catalysts help reactions

-Typically ~900C and 10-20psi

-Three basic functions:

–Reaction of catalyst and feedstock cracks feedstock into    different hydrocarbons

–catalyst is reactivated by burning off coke

–new hydrocarbons are distilled into different weights

Example chemical reaction of catalytic cracking
C15H32 –> 2C2H4 + C3H6 + C8H18
about fluid catalytic cracking
-Feedstock is vaporised and mixed with a fluidised powdered catalyst (very very fine behaves like liquid)
-Carbon is deposited ON the catalyst, requiring it to be “regenerated” occasionally
-Modern implementations use a continuous loop system so the process can run while catalyst is regenerated
schematic of fluidised-bed cracking plant
[image]
about hydrocracking
-Uses elevated partial pressure of hydrogen gas and catalysts
-Pressure of 1000-2000 Psi
-Temperature of 400-800 C
-Produces only saturated products
about thermal/steam cracking
-Hydrocarbon diluted with steam and briefly heated in furnace without O2
-850°C, slightly above atmospheric pressure
-Residence time very short in reactor # milliseconds
about alkylation
-Uses strong acid catalyst (sulfuric or hydrofluoric acid) and temperatures 0-30C
-High ratio of alkane to alkene
-Upgrades low molecular weight alkanes and alkenes to branched alkanes with increased molecular weight
Example equation of alkylation
[image]
details of isomerisation
-rearrangement of straight chain alkanes to branched alkanes
-Uses hydrogen, chloride and catalyst
-creates extra alkane feed for alkylation
-improves the octane of straight run alkanes
example euqation of isomerisation
[image]
Define Fuel
Fuel is any material that is burned or altered to obtain energy to do work through a chemical reaction.
Fuel Classification
6 classes: class 1(light) to 6(heavy)
light/heavy as in length of carbon change and increase in boiling point and viscosity
about virgin/straight-run gasoline
not suitable for modern engines, but is the main part of the fuel blend
the four stroke gasoline cycle (image)
define is compression ratio
is equal to V/v,
V = Volume of cylinder at the bottom of the cyle
v = volume of the cylinder at the top of the cycle
about compression ratio
-Increases efficiency, somewhat logarithmically
-Modern cars R = ~9:1
-High compression ratio means fuel/air can spontaneously ignite –> knocking
-knocking prevented by high octane fuel
about octane number
-ON measures a fuel’s resistance to auto-ignition
-modern cars require ON>~90
what is octane rating of straight-run gasoline
~60
how Octane Number is measured
-Measured in a test engine
-iso-octane has the benchmark ON of 100
-n-heptane (plain C7H16) has ON of 0
e.g. gasoline with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90
how octane ratingincreases for different hydrocarbans
tyeps of fuel additives
Anti-knock
Lead replacement
antioxidants
de-icers
rust inhibitors
about anti-knock additives
-lead is a cheap anti-knock additive, but obvious health dangers AND incompatibility with catalytic converters
-lead replaced by hydrocarbons of higher octane rating
about antioxidant additives
-often amines
-prevent build up of gum, which can lead to engine damage and performance decrease
about cetane number
-opposite of octane number
-measures ease at which fuel will undergo compression ignition
-for typical use CN = ~50
approximate carbon chain length of gasoline
4-12
approximate carbon chain length of diesel
8-21
what is biodiesel primarily made of
triglycerides – triesters of glycerol with 3 long chain fatty acids
reaction for production of biodeisel
TRANSESTERIFICATION
triglyceride + Methanol –> Biodiesel + Glycerin
advantages/disadvantages of biodiesel
-Works in most diesel engines, Sustainable, less pollutants than fossil fuel, safer to handle than fossil fuels
-Can be problematic in some engines, lower fuel economy than fossil fuel
blending of biodiesel
Can be used pure of blended with petroleum
“B-factor”:
100% biodiesel is referred to as B100;
20% biodiesel = B20
What is an explosive
Substance containing a tremendousamount of poten0al energy stored in chemical bonds.
what makes an explosion
rapid release/expansion of gasses -> pressure
production of heat
quick release of energy
produces more stable substances (mainly gasses)
difference between fuels and explosives
Fuels react in a controlled manner
explosives react rapidly and violently
define high explosive. examples
speed of reaction is faster than the speed of sound
Dynamite, TNT, plastic explosives
define low explosive. example
speed of reaction slower than speed of sound
Black Powder
Two useful specification tests for explosives, units
Explosive Strength (cal/qty)
velocity of Detonation (m/s)
Trauzl test – brief description
10g of explosive is placed in a cavity in a lead block, covered with sand and then detonated.
Resulting volume of cavity is compared to the Standard Volume produced by gelignite
basic methods of determining velocity of detonation
optical or electrical
an explosive may consist of either:
a chemically pure compound
a mixutre of fuel and oxidzer
common oxidizers
ammonium”nitrate,”sodium”nitrate,”calcium”nitrate
two necessary structural features of molecular explosives
at least on chemical bond that can easily be broken
A high proportion of oxygen required for explosion within the molecule itself
examples of weak bonds for molecular explosives
N-O
N-N
N-Cl
O-Cl
about oxygen balance
indicates degree to which an explosive can be oxidised
-Zero: exactly enough oxygen
-Positive: more than enough oxygen
-Negative: Not enough oxygen
Maximum explosiveness as oxygen balance approaches zero
how to tell if reaction has positive or negative oxygen balance
Pos: O2 produced
Neg: C or CO produced
about primary explosives. Example
-Very powerful
-Very sensitive
-Usually used as only a detonator
-Mercury Fulminate
About Secondary Explosives. Example
-aka high explosives
-Most explosives are secondary explosives
-nitroglycerin
-PETN – Benchmark. More explosive than PETN in primary explosive
-RDX
-Semtex
About tertiary explosives. Example
-Not explosive unless mixed with other combustibles.
-Inexpensive
-must be detonated by secondary explosives
-ANFO (Ammonium Nitrate + Fuel Oils)
Use of explosive mixture allows control of
-Strength
-V.O.D.
-Cost
-Safety
what is a polymer
made up of many repeating monomers.
High molecular weight
Polymerisation
the process of linking monomers
advantages of polymers
-Ease of processing
-Light Weight
-Tough
-Low Friction
-Flame retardant
-Insulating
-Appearance
-Weather/chemical resistance
how increasing polymer chain length affects physical properties
as chain length increases:
-melting and boiling point increase
-impact resistance increases
-viscosity increases
-chain mobility decreases
-strength and toughness increase
how polymer branching affects physical properties
can be linear, branched, cross-linked
affects chain packing and polymer density
how interchain interactions affects physical properties
-Interaction of chains through hydrogen bonding etc,
-rotation of carbon bonds
-affects strength and rigidity
about polymer non-uniform/disordered packing
-amorphous
-less rigid – malleable
-weaker
about polymer crystalline packing
– crystalline-like
-increased regidity, strength and opactity
-more brittle
about vulcanisation
vulcanisation: to natrual rubber heat and add sulfur. sulfur cross-links to make more rigid. 30% cross-linking is very rigid rubber.
Glass transition temperature
the temperature at which the transitionin the amorphous regions between glassy and rubbery occurs
How chain mobility affects Tg
more immobile chain –> higher Tg
How chain length affects Tg
Tg increases with increasing chain length
about plasticisers
-can be added to a polymer
-increase rubberyness of polymer
-decreaes Tg
atactic side chains
side chains are randomly distributed
isotactic side chains
side chains are all on the same side
syndiotactic side chains
side chains are on alternating sides
five factors affecting Tg:
-stiffer chain groups raise Tg
-strong intermolecular forces raise Tg
-side group restrict rotation, raise Tg
-cross linking raises Tg
-plasticisers lower Tg
how to identify addition polymer
the repeating unit is always the same as the monomer from which the polymer is made
The four addition polymerisation procedures
-Radical Polymerisation
-Cationic Polymerisation
-Anionic Polymerisation
-Coordination Polymerisation
General characteristics of radical addition polymerisation
-Polymer chains form rapidly
-Extremely Exothermic
-Branching and cross-linking is common
what is copolymer
polymer with more than one repeating monomer
statistical copolymer
different monomers are distributed randomly
alternating copolymer
different monomers are alternating
ABABABABABABAB
block copolymers
different monomers occur in blocks
AAAAAABBBBBBBAAAAAAAAAAAAAAABBBBBAAA
graft copolymers
one monomer is main chain, another is a side chain
about ABS
-very tough and strong
about SBR Styrene Butadine Rubber
-tyres, chewing gum
-replacement for natural rubber
applications of polyamides
-heat resistant
-strong synthetic fibres
-aerospace
-military
-kevlar
about epoxy-resins
-strongest known adhesives
-chemical and heat resistant
about dental polymers
slowly begin to cross-link, so time to shape around teeth
about thermoplastic polymers
-can be heated to softening without degradation
-not cross-linked
-difunctional monomers
about thermosetting polymers
-very hard and rigid once formed
-degrade when melted
-highly cross-linked
examples of thermoplastics
Nylon, polystyrene
about bioplastics
-made from renewable biomass
can degrade…
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