Calling all chemists!

[pj1775]

For those MRR vets out there, I'm sure this is an old hat but I just discovered etching.   Many of you have probably forgotten more than I know about this process, but when I dipped corrogated aluminimum in it, and let it partially disolve, I get an unbelieveable result.   When I lightly airbrush it, it looks just like metal roofing or siding that has been eaten by rust after years of exposure to the elements.    

My question is, is this method used by anyone out there?   Also can you tell me what the echant has in it that causes such an aggressive reaction?   I wear a respirator, and do it in an airbrushing vent system and I wear gloves.   I got the idea from a MR article from several years ago.   I'm just amazed by the incredible results. 

PJ

[chessie!]

PJ

 

While you did not mention any brand identification, the active ingredient is almost certainly sodium hydroxide, essentially oven cleaner.  Most acids do not touch aluminum, but caustic will eat it away pretty quickly.  Sounds like you use all the common sense safety precautions, just be sure to rinse all bowls and brushes with plenty of water.

[Allegheny2-6-6-6]

 One word of caution regarding the use of corrosives, as much as you may think that water bath cleaned off everything in many cases it has not. The only true way to neutralize an acid is with a base To fully assure that you've stopped the process I would dip or wash the item your weathering in a base solution.such as baking soda and water.

If your familiar with working on cars etc.an old trick to keep your battery terminals clean is to clean them off with a baking soda and water paste. I am not a chemist by no stretch of the imagination but at my old job we used to work with a lot of harmful acid and base solutions and at every work station there was a spray bottle of baking soda and water and one of vinegar for clean ups.

Its a smart thing that you wear a respirator during this process but to be totally on the safe side you should work outside with that stuff.

 

Pure Aluminum is very prone to corrosion do to it's porosity it actually oxidizes just like iron does but unlike iron oxide which is very soft aluminum oxide is very hard and actually creates a protective coating on the bare surface looking kinda white and chalky. Most of the aluminum we see is actually an aluminum alloy for this exact reason to help prevent corrosion all that taken into account as soon as you introduce any thing that promotes corrosion such as acid the corrosion process is accelerated.

You can try things like vinegar on aluminum to also give some what the same effect.

[sfcouple]

Chessie, Aluminum does in fact react with acid, such as hydrochloric: 2Al + 6HCl --> 2AlCl3 + 3H2 The resulting hydrogen gas can be very explosive, as can be seen by watching the following video showing a less than intelligent individual performing a dangerous experiment: http://www.youtube.com/watch?v=wYS_KK_kmNY So please be careful when working with any chemicals, acids or bases they can be very dangerous. A base, such as sodium hydroxide found in Drano can destroy an eye ball in a very short period of time. Bases have a nasty ability to get under the upper layer of skin and it then becomes very difficult to wash off. Wayne

[rrebell]

I always had trouble controlling the etching, usually got to little or too much. Now if, as you say a baking soda and water will stop it and just water will slow it down, dose that mean I can dip, wash it in water, then come back every so often and then stop it with base when it gets where I want, and if so, how often should I check. I am using circuit board acid  as an enchant.

[sfcouple]

Aluminum is a very reactive metal that combines with both acids and bases. If an exact amount of a base is added to this aluminum/acid mixture then the base will neutralize the acid producing a salt and water. Such as: NaOH + HCl > NaCl (table salt) + water. However, an excess amount of a base will continue reacting with the aluminum. It would be my recommendation to neutralize the acid solution with a base such as baking soda and then remove the aluminum and thoroughly rinse it with water. So one could dip the aluminum in some kind of acid solution, remove the aluminum to a bath of baking soda to neutralize the acid reaction, and then remove the piece from the baking soda bath and rinse the heck out of it with water. But once again, these chemicals can be dangerous and should be handled carefully while wearing appropriate eye protection.

[chessie!]

Thanks SFCOUPLE, yes I will be careful working with acids and bases, I have been an industrial chemist for 28 years.  If you notice, I said most acids, I did not think too many modelers had concentrated hydrochloric acid sitting around the workshop, maybe I was wrong. 

[sfcouple]

Just one final thought: I should have mentioned that I've never etched aluminum before so there might be some special techniques and procedures used by modelers that are not familiar to me. Remember, basic solutions like baking soda (and obviously Drano) will not harm household plumbing while acid solutions should be neutralized prior to disposal.

[Arjay1969]

 Ferric Chloride (the stuff generally used to etch PC boards) works well with aluminum, and when you're done, it gives the aluminum the appearance of old rusted steel siding.  I did this for the roof on a barn that I built some years back, and people still comment on how good the roof looks.

I thought I had at least one pic of it up somewhere, but apparently not.  I'll try and track one down tonight.

[mobilman44]

Hi!

Sodium Hydroxide was (is?) the basis for LYE, which was used to clear drains way back when.  It may still be used today, but I am not certain of that.  Anyway, as I recall, the LYE had bits of aluminum in it to facilitate the reaction when mixed with water.  As previous posters alluded, this is dangerous stuff and can pop and fizz and spurt all over the place.  If you are going to mess with it, please use total eye protection (goggles, not glasses) at the very least.  Also, I would suggest removing the bits of aluminum or whatever metal particles that may be in the store bought mixture.  This would tend to calm the reaction down a bit.

Hey, be careful out there.......

Mobilman44

[7j43k]

Sodium bicarbonate is not a base; it is a salt. When mixed with EITHER an acid or a base, it acts as a "buffer" and brings the pH of both strong acids and strong bases to very approximately 9 (slightly basic).

If you use it to neutralize a reaction, you REALLY want to rinse your piece well before dipping it into another reactive solution; so as to avoid neutralizing that solution also.

Eye protection when working with "reactive" chemicals is a must. Also handy is, yes, our new friend sodium bicarbonate. You might keep handy both an open box of the stuff and also a liquid solution. It's even been known to extinguish fires.

Apologies to real chemists, it's been many, many years.......

Ed

[sfcouple]

And thank you Chessie...I too have been a chemist my entire adult life and have seen a fair number of laboratory accidents. Whenever I get on a forum somewhere and see folks talking about these chemicals it is a little alarming to me. These chemicals can be and are dangerous and with young children running around it is an accident waiting to happen. So I'm being overly cautious here and encourage anyone reading this posting to be please be careful when using these chemicals, wear eye protection and watch out for all the young future model railroaders who might be watching. Unfortunately I have seen homeowners with hydrochloric and sulfuric acid in concentrations that should only be used in laboratory conditions. I hesitate to even mention this, but if anyone has an acid that needs to be diluted one must always add a measured amount of an acid slowly and carefully into water....never, never, pour water into an acid.

[sfcouple]

Actually sodium bicarbonate is a weak base and not a salt but you do raise an interesting and important point. When transferring parts from one solution to another you have an excellent idea of rinsing these parts with water before placing them in another reactive solution.

[rrebell]

I keep the bottle in the garage, no one around when I use it and wear goggles and gloves and only use a little at a time as it doesn't take much to cover model corrugated roofing.

[pj1775]

Thank you all for all the great feedback and insight.   The results truly are amazing.   I'll be sure & post some pics of the finished products.   If any of you have pics you'd like to share, I would love to see them.   Happy modeling!

 PJ