Electropolishing using perchloric acid
I "touch up" some stainless steel samples using the "brush electropolishing"technique using a 900ml ethanol+20ml water and 80ml perchloric acid solution. Is it safe using it as I am not using it using the conventional "Vat technology" and do not immerse it in the solution. Besides the stylii (SS) used are approx. 4 sq. inches thru which the electrolyte is pumped.Solomon Mordecai
First off, I was never a plater ... and sure don't know if your use of Perchloric is a standard in the plating industry.
My only thought is the concern of any spillage of the Perchloric (onto wood, for example) and any ventilation. This is a super oxidizer, more efficient than Sodium Chlorate ... so if, perchance, you are venting it at all, you need to take some precautions!
Anyhow, your supplier would doubtless, I hope, have given you a data sheet on it's properties and shortcomings! Hope so, anyhow!
Seems, too, that s.s. is A.OK for pumping it around but PVC would cost far less.
White Rock, British Columbia, Canada
(It is our sad duty to
advise that Freeman passed away
April 21, 2012. R.I.P. old friend).
... just above the American border
Thanks for getting back to me about the potential hazard in handling Perchloric acid. Adequate venting is provided and at any given time only 5-15 ml of the soln. is pumped through the stylus .Solomon
Perchlorate electropolishing. This is illegal in the US since the Los Angeles detonation. I probably don't have the facts exact but in general a 250 gallon tank detonated in the late 1950-early 1960. Killed 18 people and leveled 4 blocks! Is your little stylus dangerous? Probably not if kept in the "safe" window of concentration; if not, probably not more dangerous than a hand grenade without the pin in it.
- Fridley, Minnesota
What you said was very interesting ... can you get a factual update on that?
When I first got into Perchloric, all I knew was that the Industry, the mining laboratory people who are called Assayers, had had problems and ducting blowing up and a few deaths.
It's so easy to be worldly-wise now but at that time, people just didn't realize (by people I also mean the sellers of stainless fumehood systems) that an Assayer will do all his digestions in one hood & remove the organics... and then, at the end, will use Perchloric because Perchloric and Organics go BANG.
Ah, but the predigestion acids these people use are BAD NEWS to stainless, to stone, to fibreglass, even to the exotic alloys, even to Titanium ...Aqua Regia, HCl, nitric, Sulphuric (which is boiled off at around 320 °C) HF and Perchloric.
Ergo, if your ducting isn't suitable, those other nice acids will make holes in it (especially on the underside of a 90 degree bend) through which the Perchloric can drip down and, if it drips on wood, ah, it has hit an organic and in time, POOF!
Maybe the plating industry was premature in banning Perchloric.... who knows. But to-day in the Assay field one really never, ever hears of any problems, not in this continent... and I don't want to hear of them either. So far I've been fortunate and call these systems Perchloric Fail-Safe Systems ... which I sure wouldn't were they in metal!
White Rock, British Columbia, Canada
A follow up on a subject of a couple months ago on electropolish using Perchloric acid solutions. I believe I have the following correct. The Los Angeles detonation was in 1947 it was the result of a 200 gallon tank detonating. This solution was outside the "safe" zone. It killed 15 people and leveled 4 city blocks. While I have not read the article I believe more information on this and other such mishaps can be found in an article written be Pierre Jacquet and published in Metal Finishing 47 (11) (1949) 62. Should you dig it out I would be most interested in reading it.Jon Quirt
- Fridley, Minnesota
First of two simultaneous responses -- 2001
(sent via mail)
The perchloric acid explosion occurred in Los Angeles about 1953. Jon Quirt had the details correctly. It was the O'Connor Electroplating Company. I believe it was written up in Metal Finishing at the time.
The cooling pipes in the electropolishing tank stopped functioning. The staff did not live to report the conditions. Two stories survived. One was that the chemist wasn't really a chemist. The other is more romantic. The families of the chemist and the assistant would not let them marry so they went together to perchloric heaven.
I started my lab a few years later and no property owner would rent to a plating company. I wouldn't recommend any, no matter how small, usage of the perchloric electropolishing solution.
Milton "Dr. Eddy" Weiner
- California, USA
Second of two simultaneous responses -- 2001
We thank Fred Freyer of Metal Finishing magazine for making the article in question available. The following is an excerpt from "The Safe Use of Perchloric-Acetic Electropolishing Baths" by Dr. Pierre A. Jaquet, published in Metal Finishing, November 1949 --
Los Angeles Accident
This occurred on the twentieth of Feb. 1947 in an electroplating factory which was studying the polishing of aluminum on an industrial scale in 800 liters of an electrolyte containing 3 parts of 72% perchloric acid and one part of acetic anhydride. The explosion, extremely violent, completely destroyed the factory of brick construction, leaving in the place of the bath a crater 2.2. meters deep and 6 to 7 meters in diameter; 116 houses in the vicinity, some at fairly great distances, were more or less damaged. This accident cost the lives of 17 people and injured about 150. The destruction was evaluated at about 2 million dollars.
The investigating committees established the following points:
A. The pretended inventor of the process was an adventurer without technical knowledge but who did not appear, however, to ignore the danger of his electrolyte.
B. The process had been studied since the first of September, 1946. A bath of 120 liters functioned for several months without accident.
C. An automatic system of refrigeration was provided for, so that the temperature would not rise above 27° C. A short time before the accident this system stopped operation but the electrolysis was nevertheless continued.
D. The day of the accident the racks for the work, formerly of iron, were replaced by metallic pieces covered with a plastic (cellulose aceto-butyrate).
The above results allow confirmation of the fact that the explosion was a result of serious faults in the principles and conduct of the process, faults which would have been evident to a competent technician. At the moment of the accident there was in effect, a combination of three dangerous conditions:
- Very high concentration of perchloric acid (75% of HCIO, of density 1.72 when the normal electrolytes contain a maximum of 37% HCIO, of density 1.61).
- Excessive heating of the mass of the bath, and still much more in the neighborhood of the electrodes.
- Presence of organic matter in contact with a hot bath.
One of the chemists charged with the inquiry at Los Angeles had obtained an explosion in the laboratory by adding 1cc. of this plastic to 1cc. of a mixture of 2 parts of perchloric acid and 1 part of acetic anhydride and heating progressively.
Ted Mooney, P.E.
Pine Beach, New Jersey
Striving to live "Aloha"
But one asks oneself, WHY didn't they go by the warning data on Perchloric? Why blame Perchloric? Heck, for that matter, let's go and totally ban nitric and sulphuric and glycerine ... which, ah,hah, if mixed together in the right proportions gives you a mega super bang. Commonly called Nitro Glycerine!
Perchloric isn't dangerous... by itself! It's the people who misuse it who have caused the problems so that now the entire plating industry is scared witless about using it yet it is safely used daily all over the world by Assayers.
The mention of a plastic called, you said, Cellulose Aceto Butyrate (which I've never heard of) sounds suspiciously like it might have been of the cellulose nitrate family, which is commonly known as, ah, gun cotton. Those were early days for plastics.
Cellulose nitrate was a really super plastic EXCEPT for an enormous fire hazard potential. Mixed with camphor you get a good hard bounce effect and it is absolutely totally ideal for ... Ping Pong balls! ... and for the cognescenti, those balls are now not 38 but 40 mm in dia.Freeman Newton
- White Rock, B.C. Canada
Ed. note: Courtesy of Dean Ward of Haward Corporation we have also now obtained a copy of the earlier article on the accident, written by Fred A. Herr and published in the March 1947 issue of Metal Finishing magazine, pages 72, 73, and 107. 15 people were killed, and an estimated 150 injured; it completely wrecked a number of adjacent structures and damaged an estimated 300 buildings. I believe that I would agree with Milton Weiner that perchloric acid should never be used in a metal finishing shop at all.
2006 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread
I would like to know the detailed equations regarding electropolishing of Aluminium foils using perchloric acid and ethanol mixture.Is it safe?Anuradha Bhattacharya
Student - India
to John Quirt:
You seem to say electropolishing with Perchloric Acid electrolyte solutions is ILLEGAL now. If that is what you truly mean, can you point me to any official pronouncements so stating? I am currently looking at literature from an electro-polisher company which suggests a number of electrolyte solutions containing Perchloric acid. Cautions which are included only raise more questions in my mind.
Forging - Cheshire, Connecticut, U.S.
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