Corrosion examples in shuttle mat'ls
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Corrosion examples in shuttle mat'ls
1x 60x
235x 1180x
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Corrosion examples in shuttle mat'ls
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Corrosion examples in shuttle mat'ls
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Corrosion examples in shuttle mat'ls
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Corrosion examples in shuttle mat'ls
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Corrosion area effect
Area effect:
large cathode & small anode - corrosion accelerated
electrochemical cell current density high
try to keep potential anodic areas large relative to cathode
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Polymers - the nightmare begins
I am inclined to think that the development of polymerization is, perhaps, the biggest thing that chemistry has done, where it has the biggest effect on everyday life
LORD TODDPresident of the RoyalSociety of London
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What are polymers?Why important ?
• Long chain molecules
• Extraordinary range of physical properties
• Many (not all) are cheap
• Low densities
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Question: if chain has a molecularweight of 420,000, how many ethylene units does it contain ?
A. 30,000B. 15,000C. 150,000
Because only 200 ethylene units in this chain (200 - mer), molecular weight only 5,600 (= 28 x 200).
Ethylene PolyethyleneCH2= CH2 [-CH2- CH2-]n
Check out chain of beads at right. Imagine each bead is an ethylene unit;
How big is n ?
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How big is n ?
Commercially produced polyethylenesoften have MWs of hundreds of thousands. If ethylene unit is 1" instead of a few angstroms
Length of fully stretched outMW 420,000 chain is almost 1/4 mile!
[-CH2- CH2-] = 1 inch
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Some Basic Chemistry:Single and Double Bonds
CC C –– ––
H
HH H CH4
CC C –– ––
H
HH C ––
–
H
HH C2H6
C C C –––
H
HC–
–
H
H– C2H4
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Functional groups - small groups of atoms held together in specific arrangement by covalent bonds
Responsible for principal chemical properties of molecule
Some Basic Chemistry:Functional Groups
CH2=CH2
Ethylene
R–OH R–C–OH
=O
R–C–O–R+Alcohol Carboxylic Acid Ester
=O
R–NH2 R–C–OH R–C–NH–R+Carboxylic AcidAmine Amide
=O =O
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Some Basic Chemistry:Condensation Reactions
Acetic Acid
Ethyl Alcohol or Ethanol reversible
reaction
Ester linkage
O
Ethyl Acetate
OCH3 - C - OH + CH3 - CH2 - OH
CH3 - C - O - CH2 - CH3 + H2O
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Except, reaction goes step-wise
Now…to make a Polymer
The molecules are monofunctional:
+
To make linear chains need bifunctional molecules:
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O O
HO - C - (CH2)n - C - O - (CH2)m - OH + H2O
O O
Polyester - step 1
HO - C - (CH2)n - C - OH + HO - (CH2)m - OH
Dimer
Monomers
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Polyester
HO - C - (CH2)n - C - OH
O O
HO - C - (CH2)n - C - O - (CH2)m - OH +
O O
HO - C - (CH2)n - C - O - (CH2)m - O - C - (CH2)n - C - OH
O OO O- H2O
Trimer
M1 + M1 M2
M2 + M1 M3
M2 + M2 M4
M3 + M1 M4
M4 + M1 M5
M3 + M2 M5
M5 + M1 M6
Etc.
Reacting diacid & dialcohol give polyester!
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Nylons
H2N - (CH2)6 - NH2 + HO - C - (CH2)4 - C - OH
O
H2N - (CH2)6 - N - C - (CH2)4 - C - OH + H2O
OO
O
Adipic AcidHexamethylene Diamine
Amide Group
H
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Nylon 6,6 - N - (CH2)6 - N - C - (CH2)4 - C -
O O
n6 6
H H
“I am making the announcement of a brand new chemical textile fiber ---derivable from coal, air and water -- and characterized by extreme toughness and strength --” Charles Stine V.P. for research, Du Pont, 1938
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Nylon
“I am making the announcement of a brand new chemical textile fiber ---derivable from coal, air and water -- and characterized by extreme toughness and strength --” Charles Stine V.P. for research, Du Pont, 1938
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Nylon
May 15 1940 - “Nylon Day” Four million pairs go on sale throughout US Supply
exhausted in 4 days.
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Nylon Parachute WWII
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Post WWII stocking sale, San Francisco.