Origin of black particles on roller chain

silva

Well-Known Member
Location
Belgium
A dirty chain appears black, that's nothing new, but I just now decided to wonder about it.
New drivetrain (read: chainring, rear cog and chain), no rain has passed, no dirt has been throwed yet.
Still, the (nearly new) oil quickly starts to contain some black particles.
When allowing it to dry up, it forms a black grit on the rollers.
Recently, and also the trigger for this question, I've read this:
https://www.cyclechat.net/threads/why-paint-aluminium.246783/#post-5564000
Depends on the Aluminium alloy, some alloys oxidize quickly and you'll be covered in black oxidized aluminium every time you touch the frame.
This post links "black oxidized" to aluminium.
First, so far I was unable to find a source explaining aluminium oxidizing to black. Instead, silver/grey is mentioned. But in case, the only aluminium in the drivetrain is the chain ring so wear of that part would have to be the source for the black particles.
Second, those black particles, if they are from a hard/harder material (ie oxidation increasing the hardness), they would accelerate wear. Question then is, how hard.
Third, IF chainring wear is the origin, would a steel chainring not have such a / similar drawback?
And last, the steel chainrings I found, seem to be quite expensive related to alu ones. Yet, alu is more expensive than steel, which should mean the opposite?
 

twentysix by twentyfive

Clinging on tightly
Location
Over the Hill
What oil did you use?
 

rogerzilla

Legendary Member
It is mostly dust. I've filtered the solvent used to clean a dirty chain, and none of the black filter cake stuck to a magnet.
 
Location
Loch side.
Silva, you are asking some deep questions and not many people have asked, nor thought about it.

Your reasoning is solid. Alu oxide is not black and iron oxide is as we know, reddish. So what is that black stuff in chain oil?

It is mostly steel molecules (not even particles, much smaller) and some aluminium as well. It is interesting to note that iron/steel and aluminium at the molecular level does not resemble its bulk form even remotely. Steel and aluminium molecules suspended in oil (where they cannot oxidise) appears black. No shinyness, no glint, just black.

On rim brakes where the rubber abrades the aluminium and suspends it in water when riding in the wet, you'll also find a pure black suspension coming off the rim. That's pure aluminium molecules suspended in water. It isn't rubber, even thought the pads are black rubber. If you use green, yellow or red rubber pads the suspension is still black - aluminium.

Metals in their molecular form don't resemble, nor react like that in its bulk form. The colour has nothing to do with the type of oil used.

Naked aluminium, such as a polished crank or rim, does oxidise very quickly and then passivates (the top layer is oxides and it can oxidise no further) . The colour of that is dull grey, not black.
 

ericmark

Active Member
Location
North Wales
Isn't iron (II) Oxide black?
I was taught there was ferric and ferrous oxides of iron one yellow and one black and rust is a mixture of the two, there are also hydrates however there are also many additives in steel which will likely have an effect on colour.
The same applies to oil, I remember years ago getting molislip which was claimed to reduce wear and adding it to gear box of a washing machine, it was so good the free wheel worked in both directions. Had to completely strip is down and steam off all the oil and refill with correct oil.
But the main point is, does it matter what colour the chain is?
 

Globalti

Legendary Member
Anybody who has changed the oil in a car engine or sharpened a chisel on a stone will know that as metal wears it blackens the oil.
 

winjim

✊🏻✊🏾 🌈 😷
Silva, you are asking some deep questions and not many people have asked, nor thought about it.

Your reasoning is solid. Alu oxide is not black and iron oxide is as we know, reddish. So what is that black stuff in chain oil?

It is mostly steel molecules (not even particles, much smaller) and some aluminium as well. It is interesting to note that iron/steel and aluminium at the molecular level does not resemble its bulk form even remotely. Steel and aluminium molecules suspended in oil (where they cannot oxidise) appears black. No shinyness, no glint, just black.

On rim brakes where the rubber abrades the aluminium and suspends it in water when riding in the wet, you'll also find a pure black suspension coming off the rim. That's pure aluminium molecules suspended in water. It isn't rubber, even thought the pads are black rubber. If you use green, yellow or red rubber pads the suspension is still black - aluminium.

Metals in their molecular form don't resemble, nor react like that in its bulk form. The colour has nothing to do with the type of oil used.

Naked aluminium, such as a polished crank or rim, does oxidise very quickly and then passivates (the top layer is oxides and it can oxidise no further) . The colour of that is dull grey, not black.
Steel and aluminium molecules?
 
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Location
Loch side.
It doesn't make sense to talk about metal and alloy molecules since they don't have molecular structure, so I wonder if you could clarify what you mean.
Submicron to about 30 micron particles. I didn't want to use a term like "individual crystals" since that's confusing. Most people don't associate metal as a crystalline structure. I suppose "molecules" is a no-no with you chemists. Perhaps you can suggest the right word?

I didn't use the word alloy, because that confuses the issue. Perhaps you mean aluminium?
 

winjim

✊🏻✊🏾 🌈 😷
Submicron to about 30 micron particles. I didn't want to use a term like "individual crystals" since that's confusing. Most people don't associate metal as a crystalline structure. I suppose "molecules" is a no-no with you chemists. Perhaps you can suggest the right word?

I didn't use the word alloy, because that confuses the issue. Perhaps you mean aluminium?
I wrote 'alloy' just to differentiate it from 'metal', by which I mean pure metal.

As for what you'd call the particles, I guess I'd say just that, particles. I do agree that most people wouldn't associate metals with having a crystalline structure so that would indeed be confusing.
 
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rogerzilla

Legendary Member
Anybody who has changed the oil in a car engine or sharpened a chisel on a stone will know that as metal wears it blackens the oil.
That's carbon from burnt fuel. Diesels turn their oil black after the first run because they create so much soot.
 
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