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topic 14847

Safe acid etching of aluminum



A discussion started in 2002 but continuing through 2017

2002

Q. I have been asked to take an 1/8" piece of aluminum and etch away much of it for an art piece. My last and only experience with acid etching was in a school environment more than a decade ago. I recall vapors and the novel approach of pouring the excess down a storm drain. Needless to say I need some help. Either I can do the line art and a professional company can etch it for me, (referral appreciated), or I need to find out how to do this in a manner that is affordable, safe and not destructive to the environment. Any Idea?

Thanks,

Sallie T [last name deleted for privacy by Editor]
studio - Santa Monica, California


2002

A. Hello Sallie.
You should probably use sodium hydroxide, not acid, to etch aluminum. This material is also known as caustic soda, and the chemical formula is NaOH. The most accessible form is probably Drano [affil. link to product info on Amazon]. I don't believe there is any necessity for significant environmental impact because this is a household drain cleaner, but there ARE safety issues.

As for the environmental aspect, after the NaOH has dissolved the aluminum, you can neutralize it with vinegar so that it is neither acid nor alkali. The precipitate will be basically aluminum hydroxide, which is a major component of the earth's crust and non toxic. Aluminum salts are used in water treatment and wastewater treatment, so I see no problem in flushing it as long as you are talking a small quantity from an artist, not an industrial quantity. The aluminum may be impure, and release some copper or other metals in the precipitate, but again I think this will be very minor -- in the same range as from scrubbing a copper bottomed pot. But considering your neighbors who clean their pipes with Drano, it seems like nothing to worry about environmentally.

But the safety issues are another matter. Sodium hydroxide can blind you from a single drop in the eye. And the heat of dissolution or neutralization can cause water to flash to steam and make the solution erupt all over you. When you neutralize it with the vinegar it will foam up more than you can believe and it must be done supper slowly to prevent excessive heat. Plus, sodium hydroxide will kill a person if they accidentally drink it. If a person has lab or chemical training, and personal protective gear on hand, I think they could handle it. In other words, this is a chemical and a process that CAN be handled without incident, if you know what you are doing and handle it with a rational fear of the possible consequences of lack of care or accident. goggles [affil. link to product info on Amazon] and Rubber Gloves [affil. link to product info on Amazon] would be the absolute minimum safety gear, and if you've been out of school for a while a local community college may have a haz-mat training course. Good luck.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


2002

A. Search for etching, photoetching or gravure in your favorite search engine. If yours is a one-time-only operation the following generic answer might do: paint your artwork on the aluminum with acid resistant commercial enamel and immerse in a solution of caustic soda 30%. A small amount of dissolved aluminum residues and the soda will not harm the environment or the drainage pipes noticeably. For large operations find local expert assistance.

Regards,

Guillermo Marrufo
Monterrey, NL, Mexico



2006

Q. I am in industry and want to do etching on aluminium by Acid. Etching on aluminium by NaOH disturbs the masked portion. So, I want any acid.

Raj Tuteja
watch hands - New Delhi, India


January 23, 2012

A. Google up copper sulfate mordant.

It's a mixture of copper sulfate, table salt, and the active ingredient in Sani Flush.

It supposedly won't burn you if you get some on your skin, and all the ingredients are routinely poured down the drain so eventual disposal is easy (although it can be reused).

If you also Google up home-built circuit boards, you'll find many people are laser printing onto paper, then ironing the toner onto an item to be engraved, and dissolving the paper off with water. The toner acts as a mask for etching and is then washed off with acetone afterwards.

Some very intricate designs can be etched this way using simple graphic programs as the design source.

Hector Peabody
- Fargo North Dakota U.S.



Safe alkaline etching of aluminum

November 14, 2015

Q. I was reading the advice given sometime back to someone who inquired about being unsure which acid to use to etch aluminum and it was recommended to him that he use an alkaline substance rather than an acid ... specifically NaOH (i.e., lye/sodium hydroxide/caustic soda)...

My question is coming from my knowledge of some chemistry and warnings about reactive contact between different substances, but very little etching experience, so forgive me if the answer seems obvious to you ...

Aren't Sodium Hydroxide and Aluminum two materials who have a fairly peaceful nature by themselves but one of explosive hyperactive violence when brought together? I was always told they react in an explosive way that causes caustic suds/droplets to be spat unpredictably into the environment surrounding their point of contact.

Have I been the victim of over protective instructors and texts? If it does have potential to react as I've been taught, why was that possibility not expressed along with the other dangers involved in the use of sodium hydroxide as a component in aluminum etching? And, has anyone heard from the gentleman who asked for the advice on aluminum etching since that advice was given?

Again I may be misinformed or victim of exaggerated cautions, and if so, please (if you have the time) school me a bit on the reality of the actual reaction that takes place under the circumstances that would occur in the aluminum etching procedure. It's always a good thing to have someone correct one's internal encyclopedia in a way that provides a clear understanding of the facts based on firsthand experience/observation. Kinda like every genuine scientist has his best days learning that his knowledge of something he knew to be true must be replaced with a newly discovered and more complicated set of facts. Knowledge is progress no matter how small.

Siacri Acidium
- mendocino county, california


November 2015

A. Hi Siacri. Caustic has the capability to completely dissolve aluminum to nothing. In fact, some complex manufacturing processes rely upon it. For example, imagine metal bellows; a common way of making them is to lathe machine a solid aluminum cylinder into such a shape that it's outside surface matches the desired inside surface of the bellows, then plate the aluminum surface with nickel, and then completely dissolve away the entire aluminum mandrel, leaving only the hollow nickel bellows.

But whether a reaction is "explosive" (which essentially means reacting almost instantaneously) depends on several factors including the concentration of the caustic, its temperature and -- very importantly -- the surface area of the aluminum. Yes, fine aluminum powder might react so rapidly as to nearly explode, but a heavy "brick" of aluminum will react much much slower. In industry, it is very common to etch aluminum sheets by immersing them for a minute or so in a vat of fairly concentrated, say 30%, caustic.

It is difficult to offer appropriate warnings, not just because everything is relative (how will we sell people on how truly dangerous hydrofluoric acid is if we've terrorized them about caustic soda and other acids?), but also because the internet is a giant one-room schoolhouse where some people will be reading an entry and find it insulting that people are talking babytalk to them, and then will ignore all warnings, while others who are not even remotely qualified to work with such things believe they'll be okay if they just follow the warnings?

Offering heedable warnings for specific circumstances necessitates skipping over the basics -- which may be more important for a neophyte than the special warnings. For example, no one should even consider doing any chemical reaction at all, ever, without wearing chemical goggles. Should that be printed on every page? If so, must we also print on every page the important differences between safety glasses and real chemical goggles? ANSI ratings? How about the circumstances when you should wear a full face shield rather than goggles? No one should ever, ever, work alone with chemistry ... do we also put that on every page too? All of this points to why hands-on haz-mat training, not notes, must inform safe lab practices and is essential for all chemical employees, and why, at school level, the science teacher must supervise everything :-)

Unfortunately it is always tricky and the general rule is simply that you shouldn't do anything with chemicals unless a qualified person has instructed you hands-on.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


June 10, 2016

A. I have successfully used NaOH for aluminum removal in semiconductors since Al is a standard metal for bond wires and bond pads. By dissolving the bond pad the underlying structures can be inspected for mechanical damage which may have resulted from excess force during bond placement. I use small amounts of it and it is a VERY SLOW process unless it is heated on a hotplate. Even then, on a small device I will usually use 85 °C and let the device soak for up to several hours, occasionally inspecting the device under low magnification to check for remaining material.

Eugen Ellefson
- Raleigh, North Carolina USA


October 23, 2017

A. Maybe use electro-etching instead of acid etch - salt instead of acid

jeremy rutman
telavivmakers.org - tel aviv, israel


A. Readers, you may wish to search the site for related topics, or review the following closely related topics:

Thread 1953, "Paint/color filling etched metals"
Thread 22035, "Need a replacement process for etching aluminum"
Thread 40756, "Laser etching of anodized aluminum"
Thread 45834, "How to print patterns onto Anodized Aluminum"

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading

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