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Additive components
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Outline
• Overview of Additives• Why they’re used• Functions of engine oil• The Challenge
• Basic Concepts• Polarity, Surfactants, and Micelles• Colloids and Emulsions• Radicals and Reactions
• Engine Processes and Additives• Oxidation and Antioxidants• Acids and Detergents• Deposits and Dispersants• Wear and Anti-Wear• Friction and Friction Modifiers
• Formulation• Putting it all together
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What’s in the bottle*?
Additive Package
Base Stock
Viscosity Modifier
Dispersant
Detergent
Anti‐Oxidant
Anti‐Wear
Friction Modifiers
Others
Ensures fluidity andadds performance
Changestemperature response
Keeps everything soluble
Neutralizes acids andprevents deposits
Reduces and delaysoxidation
Reduces abrasive wear
Reduces (or increases)friction
As needed for specialized products
Hydraulic Oils &MonogradeEngine Oilsdon’t haveVM
*Not all oils haveall components
=**Many other, morespecialized additives
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Functions of additives
• Make “oil” work
• Base stock by itself is not good enough for most applications
• Tailor base oils for different applications
• The same base stock can become PCEO, HDDO,ATF, Industrial Oil, etc., depending which additives are used
• There are some limitations
• Perform two critical functions:
• Minimize destructive processes
• Oxidation, wear, friction, corrosion, etc.
• Confer beneficial properties
• Lubricity, cleaning, etc.
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OH H
Polarity
• Oil and Water Do Not Mix!• Water is a polar molecule
• Oxygen has greater affinity for electrons• Becomes partially negative
• Hydrogen becomes partially positive
• Molecule is neutral, but has separation of charge
• Oil is a non-polar molecule
• Carbon and hydrogen have roughly same affinity for electrons
• Molecular symmetry further reduces polarity
+
SN
Water
Oil
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The challenge
• Engine lubricating oils are non-polar• Hydrocarbons
• Engines and their contents are polar• Metal surfaces
• Oxidation products
• Soot
• Sludge
• Varnish
• etc.
• How to make them mix?
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Surfactants
• Molecules with both polar and non-polar sections
• Will orient based on polarity of medium• Interface
• Where two phases meet
• e.g., oil and water
• Polar ends in water
• Non-polar ends in oil
• In bulk liquid
Polar ‘head’ Non-polar ‘tail’
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Micelles
• In three dimensions these form a spherical environment• Solid in the middle = colloid
• Liquid in the middle = emulsion
In Oil In WaterPolar core
Non-polar core
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Chemistry shorthand
= RH RH is really R:HR:H R• + H•
Unpaired electron = Radical
C5H12 =(pentane)
CC
CC
C
H
H
HH
H
H
HH
H H
H
H
CC
CC
C
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Oxidation
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Chemically, what is oxidation?
• Destruction of molecules by exposure to oxygen atelevated temperatures
• Technically, oxidation can occur without oxygen, but we don’t need to consider those cases
• Initiated by Radicals
• Molecular fragments with an unpaired electron
• Very unstable and reactive
• Radicals attack and “pull apart” the base stock molecules
• To pair their lone electron
• The process can be catalyzed by metals
• Catalyzed = Accelerated
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C
H
How to measure oxidation
Carbonyl
Polar
Acid
Larger molecule(higher viscosity)
1. Oxygen Uptake2. Infrared3. Acid Number4. Insolubles5. Viscosity Growth
+O2
+O2
Chain Breaking Chain Growth
Radical
OH
OH
H
C
O
C
H
H
C
O
OH
C
H
C
H
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Indicators of oxidation
Aluminum Beaker Oxidation Test (ABOT)
0 10050
Test Hours
300250 350200150-10
0
10
20
30
40
50
Ch
ang
e (I
R,
Vis
cso
sity
)
-1
0
1
2
3
4
5
Ch
ang
e(P
entan
e, Acid
)
Infrared
AcidNumber
Viscosity
PentaneInsolubles
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Runaway oxidation
Viscosity changes due to oxidation
Polymer Thickened Fluid
NOT TO SCALERelative sizes and
timings of decrease and
increase will vary
Chain breaking of
VMChain growth of base
stock
Break Point
Oxidation Inhibitor
Consumed
Vis
cosi
ty
Time
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Anti-oxidant example
Source: Igarashi, et. al., J. Am. Chem. Soc. 1992, 114, 7727-7736
0 1000 2000 3000 4000 5000Time, seconds
0
50
100
150
200
250
Ext
ent
of
Oxi
dat
ion
, m
M[
–OO
H]
• Anti-oxidant displays “Induction Time” to delay onset of oxidation
– Followed by “Break Point” and resumption of oxidation
n‐hexadecane160C1 atm O2
1.2 mM BMPadded at 620 s
OH
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Effect of temperature
Rule of thumb - every 10C increase in temperature doubles the rate of oxidation
140C
Test Temperature
This data set: Rate doubles
every 7°C
163°C
155°C
Aluminium Beaker Oxidation Test (ABOT)
170C
Test Hours
150 250200 300
Aci
d N
um
ber
Incr
ease
10
2
0
8
6
4
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Oxidation inhibitors (or anti-oxidants)
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Anti-oxidant
• Oxidation– Destruction of molecules by exposure to oxygen at elevated temperatures
• Negative consequences of oxidation– Viscosity increase– Acid formation
• Attack engine surfaces– Particularly copper-lead bearings
– Insolubles• Form deposits
– Sludge and varnish– Additive depletion
• Function of anti-oxidants– Reduce and control oxidation
• Compositions– Hindered Phenol– Alkylated DiPhenyl Amine– Some sulfur compounds– Certain metal compounds (e.g., Molybdenum)
HO
RHindered Phenol
N
R R
H
Alkylated DiPhenyl Amine
Hydrocarbon“tail” forsolubility
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O
R
HH
C
C
HHH
HC
HH H
C
C
C
HH H H
H
H
HH H
OH
R
How do hindered phenols work?
• Easily lose a hydrogen to form a stable radical
• Stabilized by aromatic ring
• Further reaction inhibited by molecular structure
Is really
Hindered
Hydrocarbon tail for solubility
Bulky groups reduce further reactions
Weakly bonded hydrogen
Aromatic ring stabilizes radical
H.
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Detergents
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Detergents
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Detergents
• Functions• Neutralize acids
• Combustion products: Sulfur and Nitrogen (strong) acids
• Oxidation products: organic (weak) acids
• Reduce high-temperature deposits• Prevent piston ring sticking
• Lacquer, varnish, and carbon
• Prevent bore polish (abrasive or corrosive liner wear)
• Mechanisms• Basic (alkaline) to neutralize acids
• Surface-active to reduce deposits
• Composition• Basic metal with organic “tail”
• Sulfonate
• Phenate
• Salicylate
Ca, Mg, Na, Ba, ….
Deposit prevention
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Function of detergent
• Acid neutralization
OEM minimum
Bas
e N
um
ber
by
D47
39
0
3
6
9
0 20,000 40,000 60,000Miles
OEM oildrain interval
Oil AOil B
Oil C
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Function of detergent
• Piston cleanliness
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Detergents
Neutral
Basic
Overbased
'Soap'
'Core' (metal carbonate) (metal hydroxide)
H– O – M – O –H
H– O – M – O –H
CaCO3
Mg(OH)2
StrongInorganic
BaseH– O – M – O –H
“M” is a metal, such as calcium, magnesium, sodium, etc.
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Typical lubricant detergents
M+
–O
R
O C
OH
O
M+
–
R
O S O
O
M+
–
R
Sulfonate Phenate Salicylate
“M” is a metal, such as calcium, magnesium, sodium, etc.“R” is a hydrocarbon “tail” for solubility
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SASH and ash
• Detergents contain metal– Calcium, magnesium, sodium, etc.
• When burned, they leave a residue– Called “Ash”
• Typically measured as ”sulfated ash”
• React the oil with sulfuric acid and burn it• Simulates burning in the presence of fuel
• Metals become metal sulfates• Hydrocarbons burn completely
• Indirect method of measuring metal content• ASTM D874
• Note: There is also a test for ”ash”
• without sulfuric acid• ASTM D482
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Base number
• Base Number (BN) is a quantitative measure of alkalinity• Formerly known as Total Base Number (TBN)
• Concentration of base• Expressed as equivalent KOH neutralizing ability (mg KOH/g units)
• Add acid until solution is neutralized• Two test methods
• ASTM D2896• Uses perchloric acid, an extremely strong acid• Measures “everything”
– Strong bases, weak bases, some salts, etc.• Gives higher numbers• Used for fresh oils
• ASTM D4739• Uses hydrochloric acid, a strong acid• Measures “effective”
– Strong bases• Gives lower numbers• Used for in-service oils
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Dispersants
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Dispersants
• Definition– Also called “Ashless Dispersants”– “Ash” really means “SASH” means “contains a metal”
• Sodium, calcium, magnesium, zinc, etc.• Dispersants don’t contain metals
• Only carbon, hydrogen, nitrogen, oxygen, boron, etc.
• Functions• Suspend (dissolve) soot• Inhibit and suspend sludge
• Sludge = oil + water + oxidation + dirt = “black mayonnaise”• Reduce formation of deposits• Keep things clean
• Engine oil is a trash collector• Oil change is “taking out the garbage”
• Composition• Long chain hydrocarbon for solubility• Small (non-metal) polar “head group” to stick to soot and deposits
Fuel additives callthese “detergents”
Detergent
Dispersant
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N
O
O
Poly IsoButylene
Polar head
= PIBSA/PAM
Dispersants – composition
Non-Polar tail
Example:
PolyAMineIsoButylene
N N N NN
BridgingGroup
SuccinicAnhydride
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Dispersant example
Bad Results Good Results
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Friction and wear
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Friction and wear
• Both are caused by relative motion between surfaces
• Friction is a loss of energy
• Dissipated as heat
• Heat can do damage
• Wear is a loss of material
• Changes geometry of contacts
• Changes equipment performance
• Introduces metal oxidation catalysts
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Antiwear agents
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Antiwear agents
• Function• Reduce surface-on-surface wear
• Mechanism• Decompose on the surface to form protective film• Heat caused by friction• “Anti-Flux” – dirty surface prevents adhesion
• Composition• Zinc-containing (ZDDP)
• Engine oils• Ashless phosphorus based
• ATF, gear, aviation• Ashless non-phosphorus
• Railroad and other special cases• Extreme pressure
• Gear oils
Consequence:
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Phosphate
Dialkyl
Zinc Dithio
Zinc Dialkyl DithioPhosphate (ZDDP)
Note: Not exact chemical structure; for illustration only
RO ORS S
RO ORS S
P Zn P
Hydrocarbon 'tail' for solubility.Can be varied to affect performance
More detail about “R” group later
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ZDDP “alkyl” structures
Alkyl type, length, and branching affect ZDDP properties
Primary ZDDP – one
‘alkyl’ group
Secondary ZDDP – two
‘alkyl’ groups
Aryl ZDDP – aromatic
group
ZnS
SP
OR
O Z
ZnS
SP
OR
O C
H
H
X
ZnS
SP
OR
O C
H
Y
X
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0
20
40
60
80
100
150 200 250 350300
Wei
gh
t R
emai
nin
g, P
erce
nt
Temperature, Celsius
Thermo-Gravimetric Analysis (TGA)
ZDDP decomposition
ZDDP decomposition temperatures highly dependent on method and conditions
Good for passenger car sliding valve trains
Good for gas engine ring-liner wear
Good for marine cylinder oils
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Ashless phosphorus type
• Tri-cresyl phosphate (TCP)• And variations
• Can substitute other chains for CH3
• Can substitute sulfurs for oxygens• Thiophosphate
• Can remove one oxygen to make phosphite
OCresyl
H3C CH3
CH3
O P O
O
Cresyl
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Extreme pressure (EP) additives
• ‘Extreme’ is a relative term
• ZDDP sometimes called ‘EP’
• EP more commonly refers to
• Additives for high loads in gear oils
• Chlorine-containing molecules
• Highly reactive sulfur or sulfur-phosphorus compounds
• Work similar to ZDDP, but
• More active
• More corrosive
• Balance EP protection with corrosion
H3CCH3
Cl Cl Cl Cl
Cl Cl
Short-chain chlorinated paraffin
H3C CH3
Cl
Cl
Cl
Cl
Cl
Cl Cl
Medium-chain chlorinated paraffin
O
OClCl
Cl
Cl
Cl
Cl
O
O
R
R
Ester ofchlorendic acid
Trichloromethyl esterof thiophosphoric acid
PS S
O
SO
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
O
O
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Friction modifiers
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Metal surface
What are friction modifiers?
• Function• Reduce friction between contacting surfaces in relative motion
• Mechanism• Form a “springy” layer
• “Plush Carpet” effect
• Composition• Straight-chain stiff
hydrocarbons withpolar end groups
• Bond to metal surfaces
• Rather than soot, for example
Consequence:
FrictionModifier
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Friction modifier example
• Stribeck curve• Friction modifier extends the hydrodynamic region
• Enabling protection at lower viscosities
Viscosity
Fri
ctio
n C
oef
fici
ent
(Po
wer
Lo
ss)
Without FM
With FM
Ref: Passut, C.A. and Kollman, R.E., SAE paper 780601
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Typical friction modifiers
OH
O
O
OP OH
O
C O OH
C O
O
Oleic acid
Dioleyl phosphite
Glycerol dioleate
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Solid friction modifiers
• ‘Flat Plate’ molecular geometry
• Planes glide over each other
• Graphite (Carbon)
• Molybdenum DiSulphide (MoS2)
• Polytetrafluoroethylene = PTFE
• Teflon®
• Strong terminal bonds don’t stick to other things
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Comparison of additives
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Relative sizes of things
Atom
Soap Molecule
Friction Modifier
Detergent Colloid
Virus
Dispersant
Viscosity Modifier
Surface Roughness
Soot Particles
Oil Film Thickness
Bacteria
Human Hair
Log (Meters)-10 -9 -8 -7 -6 -5 -4 -3
millionth inch
Ångstrom = Å
nanometer = nm
Oil Filters
Wear Particles
ISO Scale
micrometer= micron= µm
thousandthinch
millimeter = mm
billionth inch
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Formulation(Putting it all together)
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Formulation science
The key is balancing the additives for the application:
Antioxidants LOFI
Antiwear VM
Antirust Base Stock
Detergent
'The Oil'
Dispersant FM
ATFPCMO
HDEO2T
Gear
RRGEO
Indoil
For more information:“Lubricant Additives, Chemistry and Applications,” L. R. Rudnick (ed.), Marcel Dekker, Inc., 2003“Lubricant Chemistry, Technology, Selection, and Design,” S.Q.A. Rizvi, ASTM MNL59, 2009“Automotive Lubricants Reference Book (2e),” R.F. Haycock and J.E. Hillier, SAE PT‐111, 2004
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