That makes my point exactly. I used to do AAS plus KF and acid titrations for the fluid power and automotive engineering departments in college. The maximum particle size detectable was related to the residence time in the plasma (and of course the diameter of the aspiration tube into the machine) and I would agree it is less than 10 microns.
Your post said that you would change the oil at 75ppm iron because that iron in the oil was disintegrating and causing damage. What I said (and what your response reinforced) was that the iron and other elements detectable through AAS or ICP analysis is not the material that is damaging the engine. In fact, I'd go as far as saying that the detectable elements in an analysis may be irrelevant in regards to initiating engine damage. It is an indicator but not a cause.
We found that a significant portion of the elements detected by AAS were at the sub-micron level. A critical factor in an oil was the level of water which became acidic due to combustion byproducts. This caused corrosion and those corrosion products were atomic in size but still show up on the analysis.
Bottom line, once the problem is showing up on an AAS or ICP the damage (if any) is already done. Those elements showing up on the analysis aren't the ones then doing further damage, they are too small. An engine that is destroying itself may shed large particles but those are not detectable by analysis. If you are going by "ppm wear metals" alone you would think the engine is running just fine when in fact it may be on the verge of failure. Doing a wash-down of the filter and an examination of the residue under an electron microscope will show you those particles.
Originally Posted By: Ihatetochangeoil
Iron is a wear metal detected with Elemental Analysis by ICP (inductively-coupled plasma), which detects up to 24 metals, measuring less than 10 microns in size, that can be present in used oil due to wear, contamination or additives. Wear Metals include iron, chromium, nickel, aluminum, copper, lead, tin, cadmium, silver, titanium and vanadium. Contaminant Metals include silicon, sodium, and potassium. Multi-Source Metals include molybdenum, antimony, manganese, and lithium. Additive Metals include boron, magnesium, calcium, barium, phosphorous and zinc. Elemental Analysis is instrumental in determining the type and severity of wear occurring within a unit as is performed by both Blackstone and Polaris.
"That 75ppm of iron that shows up is not in itself doing any damage to your engine. It may mean that damage is occurring (which wouldn't be helped by changing the oil), but the elements that show up on the analysis as being in the oil aren't the ones causing the damage."
Really? So 75 ppm iron are OK with what mileage on the oil? Further information and stated conditions please sir.
The comments I posted regarding Iron and Silicon are quotes from Alan Bender, Technical Lab Director at Oil Analyzers. I am a long time customer and I'm sure I can obtain his phone number and I'm sure he would be happy to discuss his positions and reasons with you sir.