2001 Jeep Cherokee Front Brake Rotors

Actually I dont know for sure, and dont really thing it is germane to the discussion. I have not been able to find that the pad manufacturers specify conductivity as a QC parameter.

I did manage to find one reference to metallic pads as being absorbent to water, and therefore giving better wet weather performance than organic pads which do not absorb water. (I find that a little unusual, maybe).

If they absorb and hold water, then this may be the answer you are looking for. Not ground loops and galvanic corrosion.

Thanks, I wasn't looking for an answer. It was a hypothetical cause for a non existent effect.

-jim

Yeah, but from our feedback, you could see that neither of us liked your hypothetical corrosion conclusion.

..... As far as i remember rotors rusted just the same even when the brake material was mostly asbestos. I suppose it is iron dust from the engine rings that causes exhaust pipes to rust to the point that they won't come apart also? _________________________________________________________________

It has nothing to do with the brake pad material. It's the heat. Heat accelerates chemical reactions such as corrosion, and the high heat in exhaust pipes and brake rotors rusts them fast.

Rodan.

Heat, salt, and water. Things dont corrode very traditionally if there is no water present. Almost all chemical reactions increase as the temperature increases. And dissolved salts increase the conductivity of the aqueous corrosion cell, increasing the rate of corrosion...usually.

Thoroughly explaining why vehicles used for short trips experience faster exhaust system failure (rust out) versus ones that are driven longer distances.

Not.

Actually, it is _your_ fantasy.

"As far as you remember?" So, it's what you "remember" versus what I see every day of the week?

Why would there be iron dust from the "engine rings" (whatever those are) to begin with?

Yup I only remember asbestos pads. It has been almost 30 years since they quit selling them around here.

Rings, pistons, block - I suppose you never heard of any of those? Rings are usually made of iron, and some of that iron ends up in the exhaust. Using that to explain the rust in the exhaust system makes about as much sense as explaining the rust on rotors coming from the iron in the pads.

-jim

Well, if that's all you remember, than you wouldn't be able to remember ever seeing orange rust stains on some wheels but not others. You probably wouldn't be able to remember that sometimes the stains on wheels were a darker almost black color. Maybe you do remember the orange rust stains but attributed it to spilled carrot juice.

Yes, I've heard of them. Never heard of "engine rings" though. Where by chance might they be used?

Hematite, magnetite or siderite?

Except that your comparison is ludicrous.

I agree that there are often a significant amount of iron oxides in the dust from brakes. And the colors that you see are different forms of iron oxides which comes in red, yellow, brown and black colors. Those oxides are often used as paint pigments especially in primers. This is because the iron oxides are good rust inhibitors.

There are a number of problems with your reasoning. Iron oxides are more or less inert unlike the base iron in the rotor. If anything a coating of iron oxide powders on top of iron is a good protection against corrosion. It would not cause of corrosion. There are 2 mechanisms by which an iron or steel OD gets welded to ID such as on a rotor or an exhaust pipe. One is that when the iron on the surface of the OD and/or ID oxidizes it takes up more space than the metal did before oxidation. If the fit is fairly close to begin with this expansion of material turns what started as a slip fit into an interference fit. The other thing that is happening is expansion of the rotor due to heat. The rotor expands when hot. That means the OD will get bigger and when oxidation occurs while it is in that state and then when the rotor cools you have a OD to ID shrink fit. That can mean it may take a large amount of force to get them apart because of the large amount of built up tension these 2 mechanisms can cause.

Bottom line is even when you use ceramic pads the rotor can become stuck. It is quite likely that the OP who asked the original question had ceramic pads. It is not as if they are rare.

Cast iron. Probably some mix of ferrite and pearlite.

Yes that was the point of making the analogy.

And because it's a relatively cheap filler material, the cheaper pads tend to use higher concentrations of it.

You can't be serious. Paint primers are meant for adhesion, not rust protection.

Then the rotors wouldn't corrode as you claimed earlier.

I never once said that it "caused" corrosion.

I thought I was pretty clear in describing that it was the iron dust sloughing off the pad as it wears that builds up, finds its way into every nook and cranny and then creates the situation much as you describe in your next paragraph.

Do you know what this tool is for Jim?

I own this tool, have for years. Anyone who has one and has used it knows that the rust it is designed to remove comes from somewhere else besides the parts it is being used on. How do they know this to be true, because once the parts are cleaned, the parent metal is undisturbed, IOWs, you can still see the original machining marks from when the parts were turned. What about stainless steel slider pin sleeves such as those commonly used on GM vehicles, they come in with rust caked on them, it's more rust than can be attributed to wear off of the rotors and is for the most part seen when bargain brand cheap brake pads are used. Dig farther, the stainless steel caliper piston, caked with rust. Phenolic caliper pistons, caked with rust. The caliper piston dust boot which is either rubber or plastic, caked with rust. These parts didn't used to contaminate this bad back when asbestos brake linings were popular, they don't contaminate as badly now if ceramic or carbon based brake pads are used under the exact same climatic conditions.

Two wheel drive would have been OE ceramic, four wheel drive would have been OE semi-metalic.

People can choose to believe the person who actually knows that little factoid or they can choose to believe the one that talks about paint and ground loops in the brake pads.

Quite the opposite of aluminum oxide (for instance), an iron oxide layer DOES NOT provide for corrsion resistance as anyone who's ever experienced rust through could well attest.

Thin films of magnetite, Fe3O4, are often seen on boiler plate and they definitely can provide for corrosion resistance. It is somewhat like bluing a gun barrel, not using the sulfide process.

Even carbon dioxide attack in such systems can be significantly retarded.

Rust, usually limited to Fe2O3, can cause corrosion to become worse because it deprives the surface of oxygen and forces areas to become anodic. Pitting, tubercles, local attack is common.

And, the corrosion is always worse, in oxygenated systems, where the oxygen ISNT.

(Note...in boiler systems, water has little or no oxygen.)

Corrosion systems can be very specific and very complicated. It is useless to paint with too wide a brush as your header statement did.

Magnetite doesn't occur in human life spans in any appreciable amounts at or near STP.

What an incredibly clumsy statement from a "chemist". Water ALWAYS comprises oxygen, whether it exists as a solute or not is a competely different matter.

Hardly. In the application being addressed my assessment is considerably more appropriate than your ode to obfuscation.

The only thing you have made clear is your ignorance.

The mechanism I described does not happen by getting iron oxide dust into cracks and adding water. The surface of the rotor or hub has to become oxidize which causes the increase in volume. That expansion in is what causes the excessively tight fit. Simply adding water to iron oxide powder just makes a muddy goo which when dried is not a very strong adhesive. I can guarantee you that if the guy is whacking on his rotors with a sledge hammer and they still don't budge they are not just glued on with mud. Iron expands 5 to 10 times its original volume when it corrodes. So if you have a OD that fits over a ID with 002" clearance that will slip on fairly easy. When you get just half a thou of surface iron turn to rust it will become a very tight fit. With a rotor on a hub both surfaces can rust. Any additional rust beyond filling the void, starts to compress metal to make room for the rust.

-jim

Now you are full of it. Magnetite exists in corrosion systems, in nature, and even in some animals. You have no credibility at all. Ever heard of "lodestone".

I should have said free oxygen, but from the context it was very clear that this is what was referring to.

You have no idea what you are talking about, I suspect. You try to keep this thread running down a seam that was pretty much stupid from the beginning.

Smoke and mirrors, wild claims, and painting with a broad brush seem to be your specialities.

As with most compounds that haven't undergone refinement ferrous-ferric oxide.can occur in conditions that produce ferrous oxide. Now address the entirety of my response by admitting the actual proportions that in which the former occurs with repsect to the latter at or near STP consitions.

Yes, and from the context it could have hardly been more clear that ferrous oxide is what was being discussed

And you're quite conspicuously a classic, third rate bullshit artist.

And you are a high school level idiot.... You have only a very superficial idea of what you are trying to talk about. And are too big of a coward to partially identify yourself. Maybe you are Mike Hunt... Cox network fits you pretty well.

Hey, c*ntface.... See above... You referenced "iron oxide", not ferrous oxide. Cox indeed ;>)