Varnish is present in oxidized oil and cause a real trouble. Can anyone tell me the size of this molecule and the reagent used to measure this parameter if a filter (as a patch) is used?

Djaouida

kumartr@enoc.com
Do you mean soot level? If yes, there is a method to find Soot level throgh TGA (Thermogravemetric Analysis) also throgh FTIR.
The equipment manufacturers provide test method procedures and also warning limits.

HI Kumar,
I do not mean soot. I mean by-product of degradation, peroxides and hydroxides products after oil oxidation. These by products agglomerate together to form polymers and resin. In lubrication, we call these "Varnish"
Djaouida

Djaouida
Check out two links below on Oil Analysis page - Turbine Sweetening ang RULER Analysis - alot of discussion on various techniques to monitor varnish potential in turbine oils. 2007 March(?) Practicing Oil Analysis - check out NORIA home page to see electronic copy - believe article was entitled something like "Looking Forward to Oxidation" discusses many techniques used to monitor remaining oxidative stability and varnish potential. ASTM has established a working group to develop a standard method for measuring varnish

Thank you Bob, I'd read these articles and more. Spectro Inc with the QSA program (Quantitative Spectrophotometric Analysis), Fluid life , Insight services etc..They are using a filtration operation (0.45 micron filter) as a patch test, combinate with centrifuge, and according to the weight and coloration, they evaluate the rating which is from 1 to 10, where 10 is the max presence of potential varnish. So, the molecules of varnish should have .45 micron or more. The question is : what is the reagent to use with the oil, to dissolve the rest of oil, without rinsing these molecules of varnish. In the ASTM method (D893)for insolubles, they use the coagulant N-butyldiethanolamine (98%) to agglomerate molecules. I'd already use it with 1% solution of this reagent, but who can tell me that what I did is the way we should do, or should we increase the concentration of the N-butyl..If the ASTM has established a working group to develop the method, I think, that could be completely different than ASTM D893.
Djaouida

I just read the abstract for ASTM D893 - the coagulant is to be used for oils containing detergents - so I don't believe would be suitable for turbine oils. Toluene would probably dissolve many of the suspended particles Group II/III + toluene = solvency of Group 1. So I would think pentane would be the best choice for isolating the particles. Doing work with submicron wear debris awhile back saw big increase in filter efficiency if oil was diluted first with pentane - reduction in viscosity allows particles to interact/agglomerate. Also was able to drop initial oxidation polymers out of ester based aircraft oils with pentane - reduced solvency.
Hopefully Greg or one of the varnish potential experts on this site can give you a more exact choice for the solvent

Dear Djaouida

Bob's suggestion of using pentane is good. Petroleum ether works very well. This helps agglomerate some of the particles that are less than 0.45-microns so that they can be measured.

The average size of a soft contaminant is 0.08-microns, however these have the ability to agglomerate together to form 1.0 micron size particles.

Djaouida
Check out two links below on Oil Analysis page - Turbine Sweetening ang RULER Analysis - alot of discussion on various techniques to monitor varnish potential in turbine oils. 2007 March(?) Practicing Oil Analysis - check out NORIA home page to see electronic copy - believe article was entitled something like "Looking Forward to Oxidation" discusses many techniques used to monitor remaining oxidative stability and varnish potential. ASTM has established a working group to develop a standard method for measuring varnish
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