effective use of organomolybdenum additives in lubricants · solid modtc • dark green to brown...

WEBINARS

Effective use of organomolybdenum additives in lubricants

These versatile and non-toxic chemistries solve difficult friction problems and enhance the performance of other additives.

KEY CONCEPTS

Molybdenum’s versatile chemistry lets it

serve a variety of functions and helps make

molybdenum compounds more soluble in

lubricant formulations.

Molybdenum compounds can produce

beneficial synergistic effects in properly

formulated additive packages and lubricants.

Molybdenum and its compounds do not poison

or leave deposits on automotive exhaust

catalysts.

By Dr. Nancy McGuire

Contributing Editor

O©

Can

Sto

ck P

hot

o /

mto

ome

2 4 • N O V E M B E R 2 0 1 8 T R I B O L O G Y & L U B R I C A T I O N T E C H N O L O G Y W W W . S T L E . O R G

rganomolybdenum lubricant additives solve a wide range of lu-brication challenges. In greases and engine oils, these additives have a track record of reducing friction and improving fuel economy, but there are many more applications. Their multifunctional and synergistic nature

-able: this transition metal is not only non-toxic, it serves as a micronutri-ent in living organisms. Molybdenum additives also are compatible with passenger car catalyst systems.

Molybdenum is a very versatile element. Its abundance in the Earth’s crust is similar to that of tin, tungsten and lead. This transition metal forms ions and compounds with an oxidation state ranging from -2 to +6 and it bonds with 4-6 other atoms in coordination compounds. Molybdenum compounds have a wide variety of stereo-chemistries and reactivities, and molybdenum can form compounds with most organic and inorganic ligands. This is useful for overcoming solubil-ity challenges associated with incorporating Mo effectively into a lubrication system.

Molybdenum has an exten-sive sulfur chemistry. Sulfur is an important lubricant component in its own right, and molybde-num compounds that include sulfur often exhibit beneficial properties from both elements.

Molybdenite (MoS2), the principle ore form of molybde-num, is readily available as an

important industrial catalyst as well as a lubricant additive. Mo-lybdenite can be roasted in air to form molybdenum trioxide. This oxide can be reacted with an aqueous solution of either sodium hydroxide or ammonia to form Na2MoO4, (NH4)2Mo2O7 or (NH4)6Mo7O24, which can react more easily with organic ligands and solubilize more eas-ily in a lubricant system. These

compounds serve as the basis for further reactions to form or-ganomolybdenum compounds.

Molybdenum provides effec-tive solutions to a variety of difficult lubricant formulation problems. Small amounts can produce large benefits with-out detrimental side effects. Organomolybdenum additives

can serve several functions at once: antioxidancy and deposit control; antiwear and extreme pressure performance; and fric-tion reduction, which improves fuel economy (see Figure 1). Fur-ther, these compounds can work synergistically with other addi-tives, including antioxidant and antiwear additives, to provide more effective lubricant and machinery protection. Organo-

MEET THE PRESENTER

This article is based on a Webinar presented by STLE Education on June 28, 2017. Effective Use of

Organomolybdenum Additives in Lubricants is available at www.stle.org: $39 to STLE members, $59

for all others.

Dr. Vincent Gatto has worked for 32 years as a research, applications, technical service and

product-development scientist in lubricant, fuel and polymer additives. He is research director

for Vanderbilt Chemicals, LLC (Norwalk, Conn.), where he is responsible for the management and

strategic direction of a team of synthetic organic chemists. His team works on the discovery and

development of new chemicals for use as additives in the lubricant, rubber and plastics industries.

He also directs and prioritizes projects in the petroleum applications laboratory.

Gatto received his doctorate in chemistry from the University of Maryland and held a

postdoctoral position at the University of Miami. He joined the staff at Ethyl Corp. (now Afton

Chemical Co.), where he worked for 16 years as a technical service advisor and additive scientist. He

then worked for 11 years as an R&D technical service manager at Albemarle Corp. before starting

work at Vanderbilt.

Gatto holds 125 U.S. patents, patent applications and technical publications in the areas of

chelation additives and additives for polymers, lubricants and fuels. He has delivered numerous

presentations on the applications of additives in industrial fluids and engine oils.

You can reach Gatto at [email protected].

Vincent Gatto

W W W . S T L E . O R G T R I B O L O G Y & L U B R I C A T I O N T E C H N O L O G Y N O V E M B E R 2 0 1 8 • 2 5

Application Molybdenum Type Performance Attribute

Grease Molybdenum Disulfide Solid MoDTC Liquid MoDTP

Antiwear, EP and Friction Modifier

Engine Oils Molybdenum Carboxylates* Liquid MoDTC Liquid Ester/Amide

Antiwear, Friction Modifier, Antioxidant and Deposit Control

* Rarely used due to corrosion and severe discoloration

Figure 1. Applications of organomolybdenum in lubricants. (Figure courtesy of Vanderbilt Chemicals, LLC.)

molybdenum additives can de-

in performance at low treatment levels, and they are compatible with automotive catalyst and emission control systems.

In the late 1960s, the Vanderbilt Co. became the

-lybdenum lubricant additive technologies still in use today, and other companies have got-ten into the f ield since then. A recent patent search shows that 67% of patents for molyb-

grease applications, 15% are for engine oil applications, and the remainder are for hydraulic, gear, transmission, transform-er, turbine, metalworking and

Engine oil applications commonly use liquid molybde-num dithiocarbamate (MoDTC) or liquid molybdenum ester compounds. The choice of or-ganic ligands used to make the MoDTC determines whether the product is liquid or solid; compounds with longer and branched organic chains are more likely to be liquid at am-bient temperatures. MoDTC is phosphorus-free, and it con-tains alkylamine groups that give it excellent solubility in oils. Molybdenum esters con-tain neither phosphorus nor sulfur; these compounds also serve as antioxidants, antiwear

Molybdenum esters have low toxicity, are biodegradable and are a relatively low-cost source of molybdenum (see Figure 2).

Solid MoDTC has a low sol-ubility in oil, but it is commonly used in greases because it can be dispersed relatively eas-ily. Because the solid MoDTC compounds use smaller or-ganic ligands, molybdenum forms a higher percentage in these compounds, and less ad-

ditive can be used to provide

and liquid MoDTC serve as antioxidants, antiwear agents

solid form also is an extreme pressure agent. Solid MoDTC is superior to inorganic molyb-

denum compounds (e.g., MoS2)

for antioxidant and antiwear performance.

Liquid molybdenum di-thiophosphate (MoDTP) compounds are dark green to brown liquids that have excel-lent oil solubility. These com-

pounds are used in greases, and their molybdenum, sulfur and phosphorus components all provide benefits. MoDTP compounds have antioxidant, antiwear, extreme pressure

-ties (see Figure 3).

WEBINARS


Liquid MoDTC Liquid MoEster

• Brown liquid• Sulfur- and phosphorus-free• Antioxidant, antiwear and friction modifier• Low toxicity and biodegradable• Relatively low cost source of molybdenum

• Amber to brown liquid• Phosphorus-free• Antioxidant, antiwear and friction

modifier• New amine technology delivers excellent

oil solubility

Specification MOLYVAN 3000

Molybdenum Content 9.1 – 11.2%

Sulfur Content 9.4 – 12.1%



Sulfur Content Not Present

Figure 2. Applications of organomolybdenum in lubricants. (Figure courtesy of Vanderbilt Chemicals, LLC.)

Figure 3. Molybdenum products for grease. (Figure courtesy of Vanderbilt Chemicals, LLC.)

Solid MoDTC

• Dark green to brown liquid• Excellent oil solubility• Antioxidant, antiwear, extreme pressure and

friction modifier• Also useful in automotive and industrial gear oils

Liquid MoDTP

• Yellow powder, low oil solubility• Phosphorus-free• Antioxidant, antiwear, extreme pressure

and friction modifier• Superior to inorganic molybdenum for

antioxidant and antiwear performance

Specification MOLYVAN A






Phosphorus Content 6.3%

Antioxidant additives, including molybdenum compounds, are used to reduce the rate of lubri-cant oxidation and, thus, delay or prevent lubricant degrada-tion that leads to wear, sludge and deposits (see Figure 4).

Organomolybdenum addi-tives can be used to control oxi-dation and deposits in engine

based on their synergistic ef-fects with other additives, including alkylated diphenyl-amines or sulfur compounds.

Organomolybdenum additives can be effective at fairly low levels (50-150 ppm delivered Mo), but their ability to control deposits is very system depen-dent; at very high temperatures they can actually promote de-posit formation. The mecha-

nism of action of these addi-tives as antioxidants is not well understood.

High levels of molybde-num additives like MoDTC and molybdenum esters can sometimes induce corrosion in engine oils, but combining these additives with novel tri-azole corrosion inhibitors (a relatively new technology) can almost eliminate the corrosion problems caused by high levels of Mo additives (see Figure 5).

Molybdenum compounds are primarily used as anti-

-tion (FM) and extreme pres-sure (EP) additives in engine oils and greases. These com-pounds act synergistically with other additives, including zinc dialkyldithiophosphates (ZDDP) and sulfurized EP ad-ditives. Compounds that have both molybdenum and sulfur in their chemical makeup can function in all three modes: AW, FM and EP. Organomolybde-

-tive in this capacity at 25-1,200 ppm Mo in engine oils and 400-5,000 ppm Mo in greases.

Fuel economy, which comes from friction reduction, is one key driver encouraging the use of molybdenum additives in engine oils. These additives are

friction in the boundary and mixed lubrication regimes (see Figure 6 on Page 28).

Various organomolybde-num additives reduce friction using different mechanisms. For example, MoDTC, which

decomposes to the layered in-organic solid MoS

2. Under high temperatures and loads, MoS2 forms stacked sheets in the

past each other under shear. Oxidation of the MoS2 sheets causes them to fragment, re-


Figure 4. How sludge, varnish and deposits form. (Figure courtesy of Vanderbilt Chemicals, LLC.)

Figure 5. Triazole corrosion inhibitors (new triazole CI) can almost eliminate copper and lead corrosion products caused by high levels of Mo additives in engine oils. DMTD = dimercaptothiadiazole. (Figure courtesy of Vanderbilt Chemicals, LLC.)

99

3

378

4

46.5

101.5 108

1.5 0

20

40

60

80

100

120

140

160

Engine Oilwith Mo

plus oldtriazole CI

plusDMTD CI

plus newtriazole CI

Met

al (p

pm)

Cu Pb

(ASTM D6594, Standard HTCBT Conditions, 0.2% CI)

Molybdenum source is 0.20% MoEster (160 ppm Mo) & 0.163% MoDTC (160 ppm Mo)

US Patent Application 2017/0044457

sulting in a loss of friction-re-duction properties. The oxida-tion product, MoO3, is not an

-lybdenum esters act through an adsorption and decomposition mechanism, and these com-pounds are more effective in aged oils. Organomolybdenum friction-reducing additives are

ppm delivered Mo, which is a higher level than is used for antiwear and antioxidant prop-erties.

Molybdenum compounds can be used in combination with a variety of other compounds

that is, the total measured ef-fect is greater than the sum of

-dependently. The performance of these additives is highly de-pendent on the composition

They can have antagonistic ef-fects when they are combined with other surface additives like ZDDPs or organic friction

formulated properly. Proper formulation also is essential to preventing compatibility problems with other additives, including organic friction modi-

-sion at high additive levels.

Some molybdenum-based additives have limited solubil-ity, especially in high quality

(see Figure 7). Newer technologies, which use highly branched alkylamines, can im-prove solubility across a wide range of additive levels and base oils (see Figure 8).

Molybdenum-based additives, when added at levels of a few percent, increase EP perfor-mance in greases, as well as reduce friction and wear (see Figure 9 on Page 30). Friction

measurements using a mini-traction machine (MTM) for a lithium complex grease with 2% of a liquid MoDTC addi-tive containing 10% molybde-num showed that the additive reduced friction best at higher temperatures (120 C versus 60

C). Well-designed formulations

that combine molybdenum additives with other additives, in-cluding ZDDP and dimercaptothiadiazole (DMTD) dimer complexes, can signif icantly improve overall results with

respect to friction reduction and load-carrying capability (see Figure 10 on Page 30). Tests

of using additive combinations to improve grease performance (see Figure 11).

WEBINARS


Figure 6. Molybdenum-based additives in engine oils reduce friction in the boundary and mixed lubrication regimes. (Figure courtesy of Vanderbilt Chemicals, LLC.)

Figure 7. Newer fluid technologies, including highly branched amine additives (left), can improve the solubility of molybdenum-based additives over older amine technologies (right) across a wide range of base oils and additive levels. (Figure courtesy of Vanderbilt Chemicals, LLC.)

350 ppm Mo 700 ppm Mo 350 ppm Mo 700 ppm Mo

MoDTC With Old Amine TechnologyMoDTC With New Amine Technology

350 ppm Mo 700 ppm Mo




Group II

Group III

PAO PAO

Group III

Group II

US Patent 9,012,383


90 Days (Group III 0W-20 Engine Oil, 700 ppm Mo, 750 ppm P) Ambient -

New Technology 10 % MoDTCw/ Primary ZDDP Clear Clear Clear w/ Secondary ZDDP Clear Clear Clear Old Technology 10 % MoDTCw/ Primary ZDDP Clear Clear Very Hazy w/ Secondary ZDDP Clear Clear Very Hazy

Symmetrical highly branched amine exhibits improved compatibility compared to asymmetrical branched amine alternatives

US Patent 9,012,383

Figure 8. Symmetrical, branched amine compounds keep molybdenum-based additives in solution in engine oil, even after 90 days. (Figure courtesy of Vanderbilt Chemicals, LLC.)

SYNTHETIC BASE STOCKS • ADDITIVE COMPONENTS & PACKAGES

• Technical Service • On-Staff Chemists • Formulation Assistance • Logistics Expertise

Call now to see how your supply chain benefits when service gets personal.

USA +1 281 587 0900 | +1 800 275 8580CANADA +1 613 966 8881

ARGENTINA +54 9221 511 9100/9003

[email protected] | soltexinc.com

With The Personal TouchWe specialize in meeting unique needs like custom blends and special packaging - all while delivering exceptional customer service - so you can focus on meeting tight deadlines, solving problems and reducing your costs.

WEBINARS

As versatile as molybdenum is for grease applications, it has even more applications in en-gine oils. Molybdenum-based engine oil additives are used for controlling oxidation and deposit formation, reducing friction and wear and improv-ing fuel economy.

Molybdenum ester com-pounds can act synergistically with antioxidants like alkylat-ed diphenylamines (see Figure 12). Combining these additives postpones the onset of oil oxi-dation, and it helps keep aged oils from becoming more vis-cous (a sign of oxidation). Fig-ure 13 on Page 32 shows the benef its of organomolybde-num additives for controlling deposits that can form when oils oxidize.

Molybdenum additives also act synergistically with other AW additives, including various phosphate compounds. Additive combinations, without

(see Figure 14 on Page 32).

Timing chain elongation, an indicator of wear, is one test for compliance with the GF-6 specif ications for passenger car motor oils. The presence of zinc actually increases chain elongation, but molybdenum signif icantly reduces elonga-tion. Combining zinc and mo-lybdenum additives produces an even greater reduction as molybdenum cancels out nega-

(see Figure 15 on Page 33).

Molybdenum additives also act, alone or in combination with other additives, to reduce friction. The proper formula-tion is key to achieving the greatest reduction in the coef-


Figure 9. MoDTP grease additives improve EP performance. (Figure courtesy of Vanderbilt Chemicals, LLC.)

Figure 10. Combinations of additives can reduce the coefficient of friction (CoF) and increase the load-carrying capa-bility (higher weld point) of grease formulations. (Figure courtesy of Vanderbilt Chemicals, LLC.)

0

20

40

60

80

100

120

140

650 SN Base Oil Li Complex Grease

Last

Non

-Sei

zure

-Loa

d, k

gf

No Additive1% MoDTP2% MoDTP3% MoDTP

Ma, A.; Gu, M.; Yao, J.; Zhang, R.; 16th Lubricating Grease Conference, NLGI India Chapter, February 3, 2014

(ASTM D2509, Timken Method)

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

CoF

Li-Complex Grease +3% MoDTP+2% MoDTP + 1% DMTD Dimer +1% MoDTP + 2% DMTD Dimer+1% MoDTP + 1% DMTD Dimer Complex +1% MoDTP + 2% DMTD Dimer Complex

050

100150200250300350400450

Weld Point, Kgf

Ma, A.; Gu, M.; Yao, J.; Zhang, R.; 16th Lubricating Grease Conference, NLGI India Chapter, February 3, 2014

(Four-Ball EP) (Four-Ball Friction)


Figure 11. The right additive combinations can significantly improve the friction-reducing capability of a grease for-mulation. (Ca salt of ox. wax is a soap used in grease formulations.) (Figure courtesy of Vanderbilt Chemicals, LLC.)

Figure 12. Measurements of oxidation induction time (OIT) by pressurized differential scanning calorimetry (left), and increase in viscosity (right) show that a combination of molybdenum ester and alkylated diphenylamine (ADPA) additives works better than either additive alone. (Figure courtesy of Vanderbilt Chemicals, LLC.)

-35

-30

-25

-20

-15

-10

-5

0

5

Lithium Grease Plus 3% MoDTP Plus 1% ZDDP Plus 3% MoDTP+ 1% MoDTC +

1% ZDDP

Plus 3% MoDTP+ 1% MoDTC

+1% ZDDP + 2%Ca Salt of Ox.

Wax

% R

educ

tion

in A

vera

ged

Axia

l For

ce

(Averaged CoF by SRV in brackets)

(0.033)

(0.037)

(0.080)

(0.045)

(0.082)

US Patent 5,516,439

0

20

40

60

80

100

120

OIT By PDSC (min)No AdditivePlus 0.1% ADPAplus MoEster @ 200 ppm Mo0.1% ADPA + MoEster @ 200 ppm Mo

0

100

200

300

400

500

600

Bulk Oil Oxid. (Vis. Inc. after 64 h)No AdditivePlus 0.1% ADPAplus MoEster @ 200 ppm Mo0.1% ADPA + MoEster @ 200 ppm Mo

500 psi 175oC

Fe catalyst

10 L/h air 160oC

Fe catalyst

US Patent 9,012,383

(SAE grade 5W-30 engine oil containing 1.2 wt. % ZDDP)

for fresh or aged oils.Additive combinations can

be better than single additives at reducing friction across a range of conditions. For exam-ple, liquid MoDTC keeps fric-tion low in fresh oils and oils at elevated temperatures. Most commercially available MoDTC

in aged oils, but molybdenum ester additives excel in aged oils and at elevated tempera-tures. Glycerol mono-oleate, an organic compound with no metal, sulfur or phosphorus, functions best in fresh oils at low temperatures but loses its

begins to age (see Figure 16 on Page 33).

Oxidation prevention, maintaining the proper viscos-ity and reducing friction all contribute to improving vehi-cle fuel economy. Here again, getting the formulation right is key. For example, molybdenum and phosphorus can be antag-onistic, but using low levels of phosphorus for a given mo-lybdenum concentration can improve the reduction in fuel consumption by enhancing the performance of molybdenum. Low-phosphorus, high-molyb-denum (LPHM) formulations are being developed to push the envelope for fuel economy contributions from next genera-tion oil formulations (see Figure 17 on Page 33).

More recently, molyb-denum additives have been shown to reduce low-speed pre-ignition (LSPI), a problem that occurs in newer engines using turbochargers and direct

-nites before the spark plug is triggered. Reducing LSPI is of particular interest in light of

-ly to gain importance in future

-

WEBINARS

rus (ZDDP) and molybdenum (MoDTC) have been shown to reduce LSPI frequency while calcium increases it.

Unavoidably, a smal l

way into a vehicle’s exhaust system. Fortunately molyb-denum additives in passenger car engine oils do not poison catalytic converters. In one study, several Las Vegas taxi cabs using either a GF-5 oil formulation or a newer LPHM formulation were put through

test, the exhaust catalysts contained deposits of phos-phorus, calcium and zinc. Molybdenum levels were es-sentially zero for both formu-lations even though both oils contained a relatively high level of molybdenum. Phos-phorus deposits on catalysts exposed to the LPHM formu-lation (42 g/cubic foot) were less than one-third of the level for the GF-5 formulation (158 g/cubic foot), probably be-cause the phosphorus level in the LPHM oil was lower to begin with. Calcium deposits were about one-third higher for the LPHM formulation (46 g/cubic foot) than for the GF-5 formulation (36 g/cubic foot).

In addition, tests show that molybdenum allows the

exhaust emissions like diesel soot) at a lower temperature than for the untreated base oil or other fuel-soluble metals including strontium and man-

the catalyst to operate more ef-

In summary, molybdenum addi-tives can solve a wide range of lubrication challenges because of their multifunctional nature


Group I Engine Oil

05

10152025303540

BaselineNo Mo

plusMoEster

plusMoDTC -

A

plusMoDTC -

B

Tota

l Dep

osits

(mg)

(990 ppm P, 160 ppm Mo, 0.5% NDPA)

Group II Engine Oil

05

10152025303540

BaselineNo Mo

plusMoEster

plusMoDTC -

A

plusMoDTC -

B

Tota

l Dep

osits

(mg)

(530 ppm P, 160 ppm Mo, 0.7% ODPA)

Figure 13. The TEOST® MHT test is a specification test for engine oils that measures deposit formation on a stan-dardized rod. (NDPA and ODPA are alkylated diphenylamines.) (Figure courtesy of Vanderbilt Chemicals, LLC.)

Figure 14. MoDTC and an ashless thiophosphate (ASP) act synergistically to reduce camshaft wear and tappet scuff-ing (high figure of merit indicates less scuffing). (Figure courtesy of Vanderbilt Chemicals, LLC.)

Standard engine oil formulations excluding ZDDP. Test rig equivalent to TU-3 engine test CEC L-38-T-87

0

10

20

30

40

Camshaft Wear ( m) No AdditiveMoDTC @ 500 ppm MoASP @ 300 ppm PMoDTC @ 100 ppm Mo + ASP @ 300 ppm P

0

2

4

6

8

10

Tappet Scuffing (Merit)No AdditiveMoDTC @ 500 ppm MoASP @ 300 ppm PMoDTC @ 100 ppm Mo + ASP @ 300 ppm P

US Patent 6,187,723

Data from Tribology & Lubrication Technology, October 2003, Vol 59, No 10, p 40-47

and their synergistic behavior with other additives. In a prop-erly formulated lubricant, these additives are cost effective, and they can be extremely ef-fective even at low treat rates. Molybdenum-based additives are nontoxic and compatible with automotive catalytic con-verters.

Nancy McGuire is a free-lance writer based in Silver Spring, Md. You can contact her at [email protected].

Figure 16. Liquid MoDTC (green line) keeps friction low in fresh oils, while a molybdenum ester additive (purple line) excels in aged oils. (Figure courtesy of Vanderbilt Chemicals, LLC.)

Oil HZLM HZHM LZLM LZHM

Mo, ppm 100 684 102 674

Zn, ppm 757 755 248 249

Mo:Zn 0.13 0.91 0.41 2.7

-0.2-0.15

-0.1-0.05

00.05

0.10.15

0.20.25

Zn Mo Zn:Mo

% C

hain

Elo

ngat

ion

Effect

Main Effects & Interactions

0

0.03

0.06

0.09

0.12

0.15

5 50 500 5000

CoF

Speed (mm/s)

140 C

0

0.03

0.06

0.09

0.12

0.15

5 50 500 5000

CoF

Speed (mm/s)

140 C

BB w/o FM Liquid MoDTC (320 ppm Mo) Mo Ester (320 ppm Mo) GMO (0.5wt.%)

Fresh Oil Condition Aged Oil Condition

Group III 0W-20 Engine Oil, One Friction Reducer

1.490.8

2.291.49 1.26

2.75

1.931.52

3.45

0

0.5

1

1.5

2

2.5

3

3.5

4

FEI 1 FEI 2 FEI Sum0W-20 GF-5 Prototype LPHM LPHM Next Generation

1.4min 1.2min

2.6min

Fully formulated passenger car engine oils (Group III basestock)

US Patent 9,546,340 and US Patent Application 2015/013352

Figure 15. Effects of high (H) and low (L) levels of molybdenum ester- and zinc-based additives on timing chain wear shows that a combination of additives produces a synergistic effect. (Figure courtesy of Vanderbilt Chemicals, LLC.)

Figure 17. LPHM lu-bricant formulations are being developed to increase fuel economy. (Figure courtesy of Vander-bilt Chemicals, LLC.)


effective use of organomolybdenum additives in lubricants · solid modtc • dark green to brown...

Documents