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51c8Joe

Aluminum and acetone reactions?

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The data plate on my 35 Pontiac had been painted with at least three coats of paint.I removed the plate and put it in an acetone bath overnight. The paint came off easily, but the acetone appears to have left a uniform light grey coating on the plate. The back of the plate was bright and shiny before the bath, but now is grey. Supposedly acetone does not react with aluminum, but something sure did. I had used the bath container before and it may have had some engine oil residue when I added acetone. The grey coat can be removed with steel wool, but takes a lot of scrubbing. Any ideas on what happened and what may remove the coating? Thanks for your help.

Joe

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I found this answer on the web which might explain what you saw.

"Pure acetone cannot corrode aluminum or other metals. However, technical grades of acetone could possibly have acidic, or basic impurities impurities that might attack aluminum Al is attacked for instance by HCl to form AlCl3, but NaOH also attacks it to form NaAlO2. Both reactions produce hydorgen".

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Thank you Commodore for your response. I guess I had something in the can I used for the bath. I'll know better next time. Back to the steel wool and polish.

Joe

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Not sure in this case but I seem to remember reading some of these data plates are made of zinc, maybe that's why the reaction?

Howard Dennis

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AHA! That is the most likely explanation. I'll try to polish this one out, or else find a repro source. Thank you for your help.

Joe

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Yes, if you can see the stamping from the back side the plate is made from a zinc alloy, the aluminum would crack if stamped that thin and sharp. The zinc alloy is softer, but a sacrificial element, so it needs to be coated anywhere where it makes a steel contact. The body is painted under the plate and the rivets are brass, so no direct steel contact.

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Yep, it's zinc, and short of spending my remaining years trying to polish of the grey residue I'll have a repro made. A. G. Backeast can make or repair just about any tags or plates.

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