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#4806296 - 07/05/18 09:43 PM Zinc vs molybdenum
mx5miata Offline


Registered: 03/28/10
Posts: 549
Loc: NY
What's zinc and molybdenum, how they differ or if have similarities?
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#4806301 - 07/05/18 09:47 PM Re: Zinc vs molybdenum [Re: mx5miata]
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Registered: 03/04/17
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#4806303 - 07/05/18 09:49 PM Re: Zinc vs molybdenum [Re: mx5miata]
mx5miata Offline


Registered: 03/28/10
Posts: 549
Loc: NY
Okay
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#4806314 - 07/05/18 10:01 PM Re: Zinc vs molybdenum [Re: mx5miata]
Reddy45 Offline


Registered: 08/15/08
Posts: 3025
Loc: USA
I'm not a pro at this stuff, but to give you a somewhat useful answer...

Moly provides cushion/lubrication between SLIDING surfaces (like cam journals). It breaks apart at very microscopic levels and retains its form, and glides between opposing surfaces.

Zinc.. I think works best when in combo with Phosphorous? ZDDP which is a well known anti-wear additive. I forgot the actual mechanism but it constantly forms a sacrificial layer between surfaces that takes the brunt of the friction.. something like that.

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#4806330 - 07/05/18 10:16 PM Re: Zinc vs molybdenum [Re: mx5miata]
PimTac Online   content


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There is a lot of information right here on BITOG.
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#4806427 - 07/06/18 04:58 AM Re: Zinc vs molybdenum [Re: Reddy45]
mx5miata Offline


Registered: 03/28/10
Posts: 549
Loc: NY
Originally Posted By: Reddy45
I'm not a pro at this stuff, but to give you a somewhat useful answer...

Moly provides cushion/lubrication between SLIDING surfaces (like cam journals). It breaks apart at very microscopic levels and retains its form, and glides between opposing surfaces.

Zinc.. I think works best when in combo with Phosphorous? ZDDP which is a well known anti-wear additive. I forgot the actual mechanism but it constantly forms a sacrificial layer between surfaces that takes the brunt of the friction.. something like that.


Thank you.
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#4806450 - 07/06/18 06:05 AM Re: Zinc vs molybdenum [Re: Reddy45]
Trav Offline


Registered: 11/20/06
Posts: 19298
Loc: MA, Mittelfranken.de
Originally Posted By: Reddy45
I'm not a pro at this stuff, but to give you a somewhat useful answer...

Moly provides cushion/lubrication between SLIDING surfaces (like cam journals). It breaks apart at very microscopic levels and retains its form, and glides between opposing surfaces.

Zinc.. I think works best when in combo with Phosphorous? ZDDP which is a well known anti-wear additive. I forgot the actual mechanism but it constantly forms a sacrificial layer between surfaces that takes the brunt of the friction.. something like that.


That's how I understand it also. I use Rislone ZDDP additive a lot, it also contains Phosphorous, half a bottle in a 5qt sump brings the SN oils up to 1200 ppm and the bearing wear levels dropped significantly in one particular high output engine, so it does a lot more than than just protect the cam and the numbers prove it.

Like anything else though people get carried away, if 6 oz works well then the who bottle will work better (it doesn't) and that's where the problems start. It is not needed in new engines that use different bearing materials and OHC with light loads but engines that spec SF, SG and so on really seem to benefit from a little extra zinc.
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#4806483 - 07/06/18 07:09 AM Re: Zinc vs molybdenum [Re: mx5miata]
SR5 Offline


Registered: 07/07/15
Posts: 4516
Loc: Down Under
It depends on the concentration and the actual formulation. Plus there is certainly some overlap in their job

But I think of moly as a friction reducer that makes an engine run smoother.

For zinc (ZDDP) it is an anti-wear agent that protects the metal in high pressure parts of the engine when the oil film is squeezed out.

They both coat the metal surface, the difference is in the force required to remove the sacrificial layer formed. Lower force for a friction reducer & higher force for a wear protector.
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#4806549 - 07/06/18 08:25 AM Re: Zinc vs molybdenum [Re: mx5miata]
Brian553 Online   content


Registered: 01/30/18
Posts: 85
Loc: Central Texas
ZDDP is consumed from the oil blend at the surface of contact between to surfaces. It is activated by high heat/pressure and the reaction creates a compound on the surface that can plastically deform. The film can only plastically deform so much before fracturing, or spalling off the surface. Moly FMs can step in (and step in well for the pressures/temperatures of these environments) to reduce friction between the two surfaces. This then helps to reduce the shear stress in the film, thereby helping to reduce deformation and spalling of the film. Once spalled, the film is "consumed," or lost its ideal functional purpose. This is as best that I understand it; I am not a tribologist.
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#4806621 - 07/06/18 09:33 AM Re: Zinc vs molybdenum [Re: mx5miata]
MolaKule Offline


Registered: 06/05/02
Posts: 19133
Loc: Iowegia - USA
Originally Posted By: mx5miata
What's zinc and molybdenum, how they differ or if have similarities?


Brian553 gave an excellent explanation.

Molybdenum and Zinc are basic elemental metals.

I think you are referring to the ZDDP (Zinc DiarylDiThioPhosphate) and the MoDTC (Molybdenum DiThioCarbamate) in engine oils and other lubricants. ZDDP is a molecule in the form of an ester which is composed of Phosphorus, Zinc, and Sulfur atoms.

The "Moly" is primarily a Friction Modifier agent in additive packages whereas ZDDP is a Multi-Functional agent in Additive packages. ZDDP acts as both an Anti-Wear and Anti-Oxidant.


Edited by MolaKule (07/06/18 09:37 AM)

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#4806717 - 07/06/18 11:22 AM Re: Zinc vs molybdenum [Re: mx5miata]
RichR Online   content


Registered: 02/21/03
Posts: 625
Loc: Chicago
Brian553 its nice to see great information.

And it's nice to have MR Kule back on board!
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#4807004 - 07/06/18 05:34 PM Re: Zinc vs molybdenum [Re: mx5miata]
JAG Offline


Registered: 10/23/05
Posts: 4885
Loc: Fredericksburg, VA
A very good paper on ZDDP:
https://pdfs.semanticscholar.org/e2dc/da55f2a51bde3dabb2ef06543fc401d61ed4.pdf

Paper on ZDDP and MoDTC:
https://www.mgexp.com/phile/1/291112/ZDDP_Paper_Leeds.pdf

There is something that I think does not receive enough recognition by people who discuss ZDDP. Many will just look at Zn and P concentrations and think that is all that matters, without considering the reactivity of the ZDDPs varies by type. Its stated in the second paper above:
The type of ZDDP is defined by the organic alcohol used to synthesize it: alkylphenols for aryl ZDDP, primary alcohols for primary ZDDP (CH3CH2CH2CH2O), and secondary alcohols for secondary ZDDP (CH3 CH2 CH(CH3 )O). Primary and secondary alkyl ZDDPs have different thermal stabilities, primary ZDDP being more thermally stable than secondary ZDDP. Their different thermal stabilities affect the rate of film formation [5860] and in turn the antiwear performance [61]. In general, the primary ZDDPs are preferred for use in diesel engines while the secondary ZDDPs are preferred for use in gasoline engines [62].

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#4807054 - 07/06/18 06:28 PM Re: Zinc vs molybdenum [Re: mx5miata]
Hammehead Offline


Registered: 03/31/18
Posts: 98
Secondary esterified ZDDP poisons Catconverter more readly than primary, thats why is used in minor concentrations. Primary are more expensive and secondary are the ones most used in bottle additives.


Edited by Hammehead (07/06/18 06:30 PM)
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