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Forum Index : Microcontroller and PC projects : Etchant
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palcal Guru  Joined: 12/10/2011 Location: AustraliaPosts: 1805 |
I have been using Ammonium Persulphate as an etchant as I can no longer buy Ferric Chloride locally. The Ammonium Persulphate I was using was a bit old and refused to etch. As I needed something in a hurry I looked on the Web. and found many references to Hydrogen Peroxide and Hydrochloric acid. I mixed up a batch and it worked really well and as it could apparently be used over and over I bottled it. Well the following night there was a huge explosion in my workshop, I was lucky I was not there, the bottle was blown into tiny pieces and a bottle of nail polish remover (no I don't remove my nail polish with it) was also broken. Other things on the shelf were all over the floor so it was a fairly big bang. I saw nothing on the Web to suggest anything dangerous. I mixed it 2 parts Hydrogen Peroxide to one part acid. Paul. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
I have had that happen too. In my case, I was storing the USED Ammonium Persulphate solution(copper sulphate soluttion), but the used solution was pressurising the storage container, and just what happened to you, happened to me, once the pressure got to the failure point of the plastic bottle - which can actually be quite a high pressure, and the subsequent release of pressure makes a rather large bang, as you have found. I was not storing the solution to use again, just storing it till I could find a safe way to dispose of it, cos you don't tip it down the drain or sink, as it will attack anything metal. From that point on, I still bottled it, but drilled a small hole(1mm) in the top of the cap, just to let out any gas build up. Smoke makes things work. When the smoke gets out, it stops! |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2870 |
Gday Paul, You can still get Ferric Chloride from ELEMENT14 Ferric Chloride (E14) And from RS Components, although only a limitted range Ferric Chloride (RS) Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| MOBI Guru Joined: 02/12/2012 Location: AustraliaPosts: 819 |
So....The "Big Bang" is no longer a theory? David M. |
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MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
http://www.space.com/25078-universe-inflation-gravitational- waves-discovery.html Microblocks. Build with logic. |
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| palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1805 |
On closer inspection it is worse than first thought. This is only a brand new workshop I just finished building. Shards of glass were embedded it the Gyprock wall and it sprayed over part of my vintage radio collection, I now have yellow stains all over my new benches and a computer monitor and keyboard (goodbye keyboard). There are hundreds of mentions of this solution on the Web and not one warning. Paul. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1328 |
Hmmm... more chemistry! - and you're not alone Paul. I had a two-litre Winchester of electro-polishing solution blow up in cupboard at work once - all a bit sobering, but like yours, at least it was at night! Your 'bang' would have been a proper chemical explosion like mine - metal peroxide solutions are, as they say, 'unstable'  , especially if they dry out - like around a cap or drips on the bottle. Groggy's 'bang' was more likely 'just' a pressure buildup as he's noted, but they're easier to handle.
I wonder if you used a higher concentration hydrogen peroxide (or acid) than is usual. I've never used the stuff but it seems a lot cleaner alternative to ferric chloride - or used to at least. As I remember, the peroxide that hair dressers use is 2%, but you can also buy 20% or even 40%. I'd be carefully checking around the web for the correct concentrations and mixing proportions at those concentrations - same goes for the acid. I bought my last lot of ferric chloride last June, at an art supply place here in Melbourne (Fitzroy) - they use it for brass etchings (to come up to see  ). It was $44 for 1 litre, item No. E044.00, supplied at the 'full strength' 40-42%. They call the concentration '40-42% Baume' (which is not a familiar unit to me but then I'm no artist!) I picked it up personally because I was down that way but they'may ship it for you - give them a call.
Their contact details are: Melbourne Etching Supplies 33A St David St. Fitzroy, VIC, 3065 Ph: 03 9419 5666 Web: www.mes.net.au e-mail: mes@mes.net Greg |
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vasi Guru Joined: 23/03/2007 Location: RomaniaPosts: 1697 |
Paul, I'm really sorry for your workshop and vintage collection, but many thanks for the warning! Vasi Hobbit name: Togo Toadfoot of Frogmorton Elvish name: Mablung Miriel Beyound Arduino Lang |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
Wow - sorry for that. 
I guess it is only a problem IF you bottle it. Most probably mix it, use it, and discard it. When my bottle blew, it showered used etchant solution all over my 1962 Vauxhall Velox(been in the family since 1963), and unfortunately, it DID damage the paintwork.
So, yes, it can happen, but once it does, you don't ever let it happen again! Smoke makes things work. When the smoke gets out, it stops! |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2291 |
drilling a hole in the lid is a good idea, but be cautious that the gasses vented may also be corrosive. the safest solution is a 'dangerous goods' store of some kind. a storage cabinet either outside (well locked!) or if inside then sealed but vented to the outside, so that any fumes do not make their way into your work area. to dispose of acids, i'd be inclined to place a few inches of cold water into a bucket, then add a quantity of baking soda. very slowly add the acid, making sure there is always an excess of baking soda. and monitor the water temperature. if you see it rising, quickly add more cold water. as for hydrogen peroxide, i'm not sure if baking soda neutralizes it or not. perhaps someone else can comment. the situation you were in was, in fact, very dangerous, and could have resulted in death. rob. |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1328 |
Given that the peroxide/acid etchant is used a lot around the world and you don't see reports of explosions with it, I'd say it's a rare event - that doesn't mean it's safe of course. I'm inclined to think that different concentrations are normally employed than those Paul used - it'll be interesting to see if he can turn anything up on that - but of course he'll need a new keyboard first .
Different countries and different 'fields' or industries, often 'normally' source and use very different concentrations of chemicals. Consequently if they're not carefully spelled out when reported, things can go wrong when others use them - I speak from having worked in labs most of my life. I think Grog's method for the ammonia mixture is OK, but as you say, don't store it long term where you don't want ammonia fumes e.g. an internal home office is probably not a good place, but a garage/outside workshop etc is likely to be fine. The chemical explosion is a different matter and the cause should be 'ascertained'. If it can't be 'ascertained', I wouldn't use that method in future and that might be a pity because it's a lot cleaner than ferric chloride. A dangerous goods store is not a practical proposition for the hobbyist and a home storage cabinet for dangerous chemicals can itself be dangerous because of the close proximity of 'nasties' to react with each other. Keeping them ventilated and away from each other is the mantra. Disposing of acids is reasonably straight forward - just add lime and test the solution with some litmus paper or pool pH indicator as you do it - once it's neutral it can be put onto some open ground to soak in. If it's acidic ferric chloride that's done lots of etching the copper should be removed first by putting in some scrap iron - nails or whatever, first so that you don't contaminate groundwater with copper. The copper will plate out of solution onto the iron and you can then put the scrap iron in your recycling bin. Acid down drains is bad news because lots of major drain-pipes are concrete and intermittent streams of acidic solution flowing down them, even if only a thin dribble, can quickly pierce them - not good for e.g. sewerage systems. Labs and industry use acid pits (several cubic metres volume) that all drains exit through if there's a possibility of the discharge being acidic. These pits are filled with crushed limestone to neutralize acid and the pH has to be logged continuously. Hydrogen peroxide is an oxidising agent and not neutralized like an acid - and doesn't need to be. It'll pretty quickly just turn into water if left in the open - but that's not a good idea, because until it does, it can be dangerous. The quantities we use are pretty small (a litre or so) and to get rid of that I'd just pour it slowly onto open bare ground with some water running on it - not into the drain. Obviously also not onto your lawn or below the peach tree! Greg |
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| palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1805 |
I checked the chemicals I used and they were of the same strengths as found on many web sites. However on one site I did come across a warning Maybe if the mixture was left until the reaction has finished it could then be bottled, but in future I think I will mix up just enough to do the job and then discard it. I have a bag of garden lime to neutralize it, and it's cheap enough to throw away. Paul. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
I seem to recall in the days of my using Ferric Chloride, the bottle did say something like: "Do not store used etchant solution." - but did not elaborate on that statement, but perhaps that was the reason? In my current used solution storage method, I use those 20L fill-your-own spirits containers from the pub, put my used solution in there, with hole in lid, and stored outside on shady side of garage. The aforementioned hole allows any ammonia gas to get out and NOT pressurize the container, and being outside, the breeze will blow away any gas that comes from the bottle. Old spirit labels removed, but if you are stupid enough to drink a blue liquid thinking it is something worth drinkin' without checking what it is first, then I have no sympathy for you...  That or you were trespassing too and deserve what you get! Everyone in my house knows EXACTLY what it is, so we're not gonna drink it. I put all that in, cos I bet someone will comment that I should not be using a container that used to have human-consumable product in it, in case someone drinks it - well, see previous statement!
I also throw in a handful of old PCB offcuts - you know - the useless bits you cut off the wanted bit of the board/etch. This gives the uses solution something to chew on over time. However, this would not be much in the way of copper, so perhaps I should adopt the handful of nails idea too? Would that work/be safe in copper-sulphate solution? ...we seem to have a few chemists here, so I will defer to their expertise. Smoke makes things work. When the smoke gets out, it stops! |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2870 |
Hi Groggy, I am intrigued... What are these 20L `fill your own' spirit containers that the pub sells? I cant say I have ever heard of anything like that here? 20L cleaning products etc but fill your own spirits?? Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1328 |
Grogs is in NZ Mick remember Mind you, on the West coast of Tasmania you used to be able to walk into a pub (talking 60's here) and have a 20 litre 'barrel' filled up from the beer tap - didn't ever see it happen with spirits but who knows! One 'barrel' I saw come in was a perfect small stainless steel replica of a normal 'niner' and the 'bloke' had it tucked under his arm - big fella, like you  Another one I saw was the more traditional wooden barrel with a spigot on the base. How he got it home (or to the party) without it going flat I couldn't say. I should go back down and see if they still do it!
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| palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1805 |
We're getting a bit off the subject but to make it clear the Pubs buy their spirits in 20l containers and refill the bottles behind the bar. I don't know if Grogster gets the empties or buys them full and drinks the contents first. Paul "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1328 |
Not much of a warning is it Paul - it just implies that over time, after mixing, the stuff won't work as an etchant. True enough, but no mention of explosive capability. Your comment to make up small amounts 'freshly' is the way to go. You'll always know how effective it'll be as an etchant (i.e. not previously used), you're also not storing any potential nasties and small amounts are easier to dispose of. Mobi said in another thread that he's used peroxide/HCl as his etchant for some time...(without trouble). I asked him to quote his concentrations and he said: Mobi's comment that the HCl is the same as builders use for cleaning concrete is interesting. He's right there (it's also the same as you buy in a pool shop) but I don't know anyone who'd clean concrete with straight 30% HCl - normally it's diluted 10:1, which then turns the 30% into 3%, or close. That's probably what Mobi meant (i.e. for builders) but he uses it at the full 30% for his etching mixture. It highlights that you have to be specific. If you use the same concentrations and mixing ratio as Mobi you'll presumably be right, the trick is to be sure what concentration you're dealing with. The 3% peroxide 'from the supermarket' is pretty common but I've also seen 20% peroxide sold. I had a look at my pool HCl container and it quotes "30-35% m/V --- Lower Fume". The m/V means mass/volume because HCl is actually a gas (nasty stuff), but the HCl we use is that gas dissolved in water. That concentration has around 300 grams (equates to about 200 litres) of the gas dissolved into 1 litre (1000 grams) of water (it's a highly soluble gas). At that concentration it fumes a fair bit (hence the "Lower Fume") but they can go a lot higher - maybe they call that "Choking Fume". 
Greg |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9066 |
Yes, that is exactly right - they keep them on a shelf behind the bar in the bottle-store/liquor outlet, and you can take in empty bottles and have them refilled. It is generally lower-alcohol then quality brand-name spirits, but it is MUCH cheaper. I get the empties - Not into drinking spirits much these days - always makes me feel very unwell(probably cos I over do it!), and cheap spirits taste awful compared to the higher-percentage quality stuff. Anyhoo, to paraphrase palcal - I digress....... Smoke makes things work. When the smoke gets out, it stops! |
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| palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1805 |
I've done some more research into the cause of my explosion and I have found that the cheap Hydrochloric acid bought in bulk for pools and cleaning bricks etc. can contain a lot of impurities. Apparently this explains why my etchant mixture turned a bright orange when mixed when it should have stayed almost clear. Hydrochloric acid when left to evaporate should leave no residue and mine does. So if you intend to use this mixture for etching make sure you buy a good quality acid. Paul. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2870 |
Paul, I think its better to spend a few dollars/franks/crowns/shekals/dracmas/baht etc and buy a commercial etchant.. Your life is worth more than a bottle of etchant. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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