Small Particle MoS2 Settling Time

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JHZR2

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I figured I'd go ahead and do the calculation so that everyone isnt just speculating. I havent seen anyone else attempt it, so I wrote it out in Mathcad, saved the pages as a JPG, and here it is. As usual, Photobucket ruins the images by funky compression, but I think you can make it out. Ill see if I can serve them from somewhere else so that they may load clearer. The basis for the calculation I have firsthand experience with in the lab, and is shown in greater detail in Grant Bunker's book on X-ray Absorption Spectroscopy. A simple version which I used can be reviewed in slide 46-48 of this: gbxafs.iit.edu/training/XAFS_sample_prep.pdf Now, keep in mind that if the particles are somehow surface stabilized or have some form of chemistry to keep them in solution and in small size (e.g. some kind of polymer, surfactant, etc.) then this may be less valid. More technical conversation would be necessary with LM, as well as to optimally run the experiment by vigorous mixing of LM doped appropriately into a virgin and used motor oil, then allow them to sit in a glass jar for timescales as shown below and observe. Enjoy and discuss!

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This is interesting, thank you for posting it. I admit some of it is beyond me. I see the fastest settling time in your figures is about 8 days. Would it be safe to say that if one runs his car at least every 8 days (8.38) that the particles will stay in suspension? Or am I coming to the wrong conclusion?
 
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JHZR2

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8 days was based upon a larger-size particle (it would assume based upon what LM told us, that all particles are the highest end of the distribution, which is false - most all of them are NOT that big), in a very non-viscous oil. Also that assumed a deep sump - 4 in from the top of the oil to the bottom, so a shallower sump may be faster. But I think your basic take-away is correct, based upon what we currently know.
 
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I did not think the main concern was settling, but rather the larger particle clumps being filtered out. As you point out, the stabilization can be enhanced, perhaps the clumping can as well. At 0.25um, individual particles should not be filtered out. I guess it's just a $ trade off to use an organic/thio Mo complex or MoS2.
 

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Originally Posted By: Pablo
I did not think the main concern was settling, but rather the larger particle clumps being filtered out. As you point out, the stabilization can be enhanced, perhaps the clumping can as well. At 0.25um, individual particles should not be filtered out. I guess it's just a $ trade off to use an organic/thio Mo complex or MoS2.
Some of us have had the desire to use MOS2 in seldom-used cars as a way to ensure that there is some level of surface protection at startup after sitting, etc. However there are concerns with what the settling and coming out of solution time may be. I HIGHLY doubt that the particle energetics are such that they would agglomerate to form hard particles that under shear from sitting someplace with oil flowing rapidly past would not come apart. That is my opinion of the case no matter what - so to me, large, stable particle formation that clogs a filter is unlikely unless some other funky chemistry is going on in there. But the concern is more of having a goop of MoS2 at the bottom of your sump with different characteristics than an oil. We also need to start to understand the surface characteristics of MoS2 versus carbon soot, to understand how it would react with the dispersant package in an HDEO. If the MoS2 is highly surface stabilized, it may be a non-issue, but who knows?!?
 
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Nice job. A little information for you. MoS2 forms it's slick surface from the non-interactive exposed sulfur groups. It is NOT reactive towards dispersants/detergents, as it is not acidic. It is difficult to disperse in an oil as the sulfur/sulfur Van der Waal forces cause agglomeration (as well as its low coefficient of friction). I have tested it quite thoroughly at Exxon, as many have done before me, and found it essentially useless in motor oil. It settles out in a similar manner to sub-micron lead chloride particles (when burning leaded fuel). It works very well in grease. Ed
 
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i been saying this for along time but not in a scientific manor ed stated.. i have noticed this in my experience and other at the track..again, i wouldn't waste money with lubro moly additive!!
 
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Thanks JHZR2 for the effort and thanks Edward for the input. Like Boxcartommie22, I have also reported here that I have observed settling (transfer case application). In generally, BITOGers don't seem to believe me.
 

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Originally Posted By: Edward Kollin
Nice job. A little information for you. MoS2 forms it's slick surface from the non-interactive exposed sulfur groups. It is NOT reactive towards dispersants/detergents, as it is not acidic. It is difficult to disperse in an oil as the sulfur/sulfur Van der Waal forces cause agglomeration (as well as its low coefficient of friction). I have tested it quite thoroughly at Exxon, as many have done before me, and found it essentially useless in motor oil. It settles out in a similar manner to sub-micron lead chloride particles (when burning leaded fuel). It works very well in grease. Ed
Ed, GREAT response, thanks so much! So there we have it, it will fall out of solution, and IMHO, the timescales shown give indication of what one might expect. Out of curiosity, do you think the particle sizes cited are practical? 250nm is in the DLVO range for interparticle interactions and so I find it tough to believe that they can mill it that fine. It settles out far faster per the calculations at 500nm, and imagine 1.5um! What size range were you studying?
 
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We tried size distributions of less than 100nm to 1 micron. The larger particles settled out in low flow areas of the engines and the very small particles seemed to agglomerate into larger particles which settled out in low flow areas of the engines. We worked quite a bit on the dispersing of the primary particles with a wide variety of base oils and a great number of surfactants. Even at high loadings solid MoS2 did little. However, this work should be included as part of the prelude to the development of the oil soluble moly trimer (incredible additive) that we developed at Exxon and I got the opportunity to perform the initial engine testing. Ed
 
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JHZ & Ed great job guys-for the moly trimer, can you tell us any observations from the initial engine tessting? decreased oil temp, less time to increase a certain number of rpm, decreased/increased wear rates, fuel consumption, oil condition, and let's not forget oil filter condition final Question: after reading a lot about the moly trimer like it was the Holy Grail, where is it now, and will we ever see it mass produced as an additive or added to off the shelf motor oil? Thanks Steve
 
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The Moly trimer provides better fuel economy retention and better wear protection than Moly DTC. It is three times the price of Moly DTC and is typically used at 50-100 ppm. I don't know yet which oils use it. I use it in specific racing applications and as a reactant to produce another additive. Ed
 
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i believe thats why to equal the performance of moly trimer,one has to use alot higher ppm's of moly dtc to equal what trimer does with low amts.why i love this place too!!
 
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JAG

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Thanks for the interesting thread. This makes me want to put into a clear container some LM MoS2 additive in virgin motor oil in the recommended ratio. I've had the additive for years and it is still very gray/black even at the top of the container. So some of the particles could be much smaller than the sizes you assumed. After hearing what Edward said, I still wouldn't use the additive whether I saw any settling or not.
 
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LM MoS2 will do fine in DD car and weekend car. Look at some old clear oil containers at Walmart- they have "flakes" on the bottom. I think, moly falling out is the last thing to worry about if your car sits forever in one spot. Soon as you start engine it will be mixed in oil again.
 
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For a DD I think it would be fine. What about the moly that "plates" after a short drive? Once it "plates" or "coats" a surface it is not going to fall out of suspension. I'm not disputing the fact that some of the product does settle out of suspension, from what we see here it takes ~8 days. I've seen it coating the dipstick of my mower a month or more after not using or moving the machine, so some if it is staying put. Then turn the key and whatever fell out of suspension is suspended again. JMO
 

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Originally Posted By: mechtech2
40c is the worst case scenario? Are you kidding? That isn't even warmed up. I wonder why settling is not found in real life car use.
This is a timescale exercise. Given that we are talking 8-100+ days, the few hours that the oil is >40C is very small compared to the total time. Ill run the calculations at 9 cSt for comparisson, but remember that even then sitting, thermal gradients will caus hast rates of diffusion and mobility of fine particles in solution due to convection and thermal gradients. The bulk oil temp in my 91 318i isnt higher than 160F (which is around 70C), and drops lower pretty quick. Not all bulk full temp oil is trul at 100C or higher.
 
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