Letter 2492

--

Hello. I am a high school student in my final year, and for a Chemistry lab I did a basic electroplating experiment in which I plated copper onto a quarter in a solution of vinegar, salt, and ethylene glycol. I conducted the experiment with and without the ethylene glycol, and noticed an appreciable difference in the quality and speed of the plating. I do not understand the purpose of the ethylene glycol, as it is not part of the electrolyte. Is it a catalist? Or does it somehow participate in the reaction? Any help would be appreciated.

James Kent

The ethylene glycol is serving as a surface active agent (surfactant). It lowers the surface tension at the metal interface, and allows the metal ions to migrate to surface easier.

Hope the teacher likes the answer and you get an "A"!

Richard Zuendt
Garfield, New Jersey

In this case it was probably used as a brightener. It is a bit unusual, but obviously effective. An acetate (vinegar) is a bit unusual, but forms a nice complex which would allow a reasonable plate, but certainly not commercially feasable.

Many brighteners work as a poison to cause the bath to plate out slower and more uniformally giving a smoother surface, thus brighter.

Some organics from brighteners do actually form in trace amounts in the plate, but it is so minute compared to the dragout of solution when you move parts out of the tank that it is not considered in the plating reaction equasion. Some breaks down from oxygen formed at the anode, so it must be added in tiny amounts over a period of time to keep the plating bright.

Hope this helps. Not a lot of the true mechanism is known. You could do a PHd on the subject and still not know it all.

James Watts - Fl

Well, the formula is a bit unusual, but I was trying to develop a plating bath using only chemicals you might find around the house, and as near neutral as possible. Letter #064. And I don't usually keep PEG6000 in my medicine cabinet:-)

For my next (cheap) trick, I will present a Plating4Kids slide show and demonstration to folks in Minneapolis, MN from Brick, NJ using $70.00 CuSeeMe software, the internet, a browser, lots of green grease paint (I will dress up as the Statute of Liberty for the show), and will switch over to zinc plating just to keep sharp.

Tom Pullizzi platronica.com Falls Township, PA

 

The ethylene glycols are essentialy anti-freeze. Some racers still use it in this form.

It is slick -- such as the surfactant effect.

It is very toxic, even though manufactures include it in our foods, medicines and cosmetics in what they consider small enough amounts to be tolerated by our bodies. It is also absorbed though the skin into the system. So be very careful when handeling "glycols". It is poison to everyone. Some people can not tolerate it at all.

Laura Konter

I would have to disagree on the general idea that ethylene glycol is a hazardous chemical to everyone. Ethylene Glycol is the base ingredient in most antifreeze today. It is toxic when ingested (swallowed) because it is converted to Oxalic Acid in the stomach. This is why the new "safe" antifreeze is made with Propylene Glycol. This change is mostly do to the fact that the sweet taste of Ethylene Glycol is favored by dogs and cats that lick droppings from the ground. The one way to counter the toxic effects of Ethylene Glycol poisoning is to drink ethanol (name your brand) which would counter the conversion to Oxalic Acid. If handled properly, Ethylene Glycol is a valuable chemical to all of industry, just don't flavor your meal with it.

Richard Zuendt
Garfield, New Jersey

Since many people discuss its use in automobiles, the purpose was freezing point depression of water. The coolant in cars being water (because of its heat capacity), solutions of water and EG could provide freezing points below that necessary in most places of the country in winter. So...people used to change from water to glycol solutions in the winter. EG/water is fairly corrosive in the mixed metal radiator systems of cars, containing aluminum, copper, steel, and others at elevated temperatures. So EG had corrosion preventative additives to provide for corrsion protection in the system. Actually EG/water was then better from a long term corrosion standpoint. Unfortunately the scums formed on metals to protect them were often considered to be dirty and people would clean out the systems with commercial cleaners. The freshly activated surfaces would corrode at a very high rate and so it was not uncommon for radiators to begin to leak after cleaning. Water was still best alone since the purpose was for cooling, and nothing was better than water, again for its heat capacity.

Today's cars are built to run hot for better efficiency. They operate over 212 F and so are too hot for water alone except under pressure. EG then becomes a more efficient and acceptable coolant. Alone with inhibitors it then provides longer life for your car's cooling system also. Notice it is usually refered to as coolant today not antifreeze. And not many people change the system between summer and winter. In fact manufacturers recommend "coolant" only.

Animals do like it for it's sweetness however, and it is toxic on consumption so you should be careful of leaving it around pets and small children.

C.A.Smith
The Aerostructures Corp Nashville, TN

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