aic@s.cc.purdue.edu (George A. Basar) (10/11/88)
I am looking for some pointers to information on the subject of
anodic/cathodic(terminology please) system of rust prevention/inhibition.
Preferably, I need technical information on the chemistry involved in
both the sacrificial and non-sacrificial systems. Also on the difference
between gel-cel and solid(metallic ?) systems.
Any opinions on the workability,reliability and general perform-
ance of these systems would be appreciated.
All of the above should reference the automotive industry, although
general information on marine systems would be helpful, also
EMAIL if at all possible.
Thank you in advance.
George A. Basar
aic@s.cc.purdue.edu
BASAR@PURCCVMornitz@kodak.UUCP (barry ornitz) (10/13/88)
In article <3596@s.cc.purdue.edu> aic@s.cc.purdue.edu (George A. Basar) writes: > I am looking for some pointers to information on the subject of >anodic/cathodic(terminology please) system of rust prevention/inhibition. > All of the above should reference the automotive industry, although >general information on marine systems would be helpful, also Similar questions to these were posted to rec.autos several months ago. I do not see how electrolytic protection (cathodic protection) is applicable to automobiles as they are not generally in a conductive or electrolytic environment. The common use for cathodic protection is in ships or underground piping where the material to be protected is surrounded by water or moist soil which is electrically conductive. In any event, the following references should help George any anyone else interested in this form of corrosion protection. "Fundamentals of Cathodic Protection", "Corrosion Cathodic Protection and Common Sense", and "Cathodic Protection - One Way to Prevent Underground Corrosion". These three papers were written by B. Husock of Harco Corporation, Cathodic Protection Division, 1055 West Smith Road, Medina, Ohio 44256. Harco can provide copies of these papers for a small fee. These references are somewhat dated and I do not know if Harco is still in business. If you cannot locate them any other way, I can provide a copy. Barry ----------------- | ___ ________ | | | / / | | Dr. Barry L. Ornitz UUCP:...!rochester!kodak!ornitz | | / / | | Eastman Kodak Company | |< < K O D A K| | Eastman Chemicals Division Research Laboratories | | \ \ | | P. O. Box 1972 | |__\ \________| | Kingsport, TN 37662 615/229-4904 | | -----------------
al@cs.strath.ac.uk (Alan Lorimer) (10/14/88)
In article <1450@kodak.UUCP> ornitz@kodak.UUCP (barry ornitz) writes: >In article <3596@s.cc.purdue.edu> aic@s.cc.purdue.edu (George A. Basar) writes: >> I am looking for some pointers to information on the subject of >>anodic/cathodic(terminology please) system of rust prevention/inhibition. . . . >Similar questions to these were posted to rec.autos several months ago. I do >not see how electrolytic protection (cathodic protection) is applicable to >automobiles as they are not generally in a conductive or electrolytic >environment. . . I don't think this is quite right - was not the whole reason for switching cars from positive earth systems to negative earth systems purely to provide a degree of cathodic protection for the bodywork, since positive earth systems actually encouraged the vehicle to rust. I remember a circuit which was designed to protect your vehicle: _______________ _______________ | | | | __|_ + 12V - _|__ _/ \__ |-------| _/ \__ |O------O-| |_______| |O------O-| Someone else's car Your Car Go on try it on your neighbour's car :-) Regards, Al. -- ____________________________________________________________________________ Alan G. Lorimer, Strathclyde University, 26 Richmond Street, Glasgow G1 1XH. UUCP: ...!uunet!mcvax!ukc!strath-cs!al DARPA: al%cs.strath.ac.uk@ucl-cs JANET: al@uk.ac.strath.cs
commgrp@silver.bacs.indiana.edu (10/19/88)
In article <1450@kodak.UUCP> ornitz@kodak.UUCP (barry ornitz) writes: >In article <3596@s.cc.purdue.edu> aic@s.cc.purdue.edu (George A. >Basar) writes: > I am looking for some pointers to information on the subject of >anodic/cathodic(terminology please) system of rust prevention/inhibition. >Similar questions to these were posted to rec.autos several months >ago. I do not see how electrolytic protection (cathodic protection) >is applicable to automobiles as they are not generally in a conductive >or electrolytic environment. Such environments exist in coastal areas and near steel mills, also in the frozen wasteland north of the Ohio River, where city streets are covered with salt whenever there is snow. It's rumored that car dealers subsidize the application of the stuff. :-) Warshawsky/J.C. Whitney Auto Parts of Chicago used to sell blocks of magnesium to be bolted to the undersides of cars to act as a sacrificial metal to prevent corrosion of the steel. I don't know how well they worked. Testing would be simple; suggest it next time a kid needs a science-fair project. -- Frank Reid reid@gold.bacs.indiana.edu
ornitz@kodak.UUCP (barry ornitz) (10/20/88)
In article <7200017@silver> commgrp@silver.bacs.indiana.edu writes: >In article <1450@kodak.UUCP> ornitz@kodak.UUCP (barry ornitz) writes: >>Similar questions to these were posted to rec.autos several months >>ago. I do not see how electrolytic protection (cathodic protection) >>is applicable to automobiles as they are not generally in a conductive >>or electrolytic environment. > >Such environments exist in coastal areas and near steel mills, also >in the frozen wasteland north of the Ohio River, where city streets >are covered with salt whenever there is snow. It's rumored that car >dealers subsidize the application of the stuff. :-) > >Warshawsky/J.C. Whitney Auto Parts of Chicago used to sell blocks of >magnesium to be bolted to the undersides of cars to act as a >sacrificial metal to prevent corrosion of the steel. I don't know how >well they worked. Testing would be simple; suggest it next time a kid >needs a science-fair project. >Frank Reid Yes, corrosive environments are common as you describe. However, to be effective both the body metal and the sacrificial anode must be electrically connected *as well be immersed in the electrolyte*. I did not state this explicitly enough in my original posting. Corrosion will usually occur near where disimilar metals are in contact and immersed in an electrolyte (galvanic corrosion). Damp mud with road salt is suitable as the electrolyte. The problem with bolting sacrificial metal to the undersides of cars is that a low resistivity electrolytic path must exist between the sacrificial anode and the rest of the car. If your car were totally immersed in salt water, this would be a good protective system; other- wise the high resistivity of the surface dirt would prevent the sacrificial anode from having much effect. This is why in moist air the zinc galvanizing on metals can prevent a scratch through the zinc down to bare metal from rusting, but cannot protect a large area several inches away from the zinc. In a highly conductive electrolyte, the zinc will provide protection until it is consumed. To give some better numbers on this, zinc is rarely effective as a sacrificial metal in environments with resistivities higher than about 1000 ohm-cm. Magnesium can be used effectively up to 5000 ohm-cm. Sea water, which is quite corrosive, has a resistivity of about 15 to 35 ohm-cm, and clean, dry sand has a resistivity of more than 1E6 ohm-cm. The effectiveness of cathodic protection can be increased by providing add- itional potential between the sacrificial anode and the metal to be protected. This works fine where underground pipes must be protected. The anode is buried near the pipe to be protected and is connected to the positive side of a power supply. The negative side of the supply is connected to the pipe. The soil conductivity completes the path. The absence of a low resistivity, uniform electrolytic path surrounding the automobile is what makes this protection method unsuitable for cars. J.C. Whitney sells lots of things of marginal effectiveness, however. This *would* be a good science fair project but waiting ten years or more for the results to be conclusive might delay graduation a bit. ;-) Corrosion is enhanced in areas of mechanical stress, a phenomena well known to the chemical industry. And before anyone suggests stainless steel for auto bodies, chlorides (salt) are very corosive to stainless. The best thing is to keep the moisture from getting to the metal with proper paints and undercoats. Barry ...rutgers!rochester!kodak!ornitz