playing with acids

[sean k]

So I read up on the muriatic hydrogen peroxide mix for etching a few weeks ago and then went out and searched them out. The muriatic was really easy to buy as spirit of salts in a 27% concentration in water but the hydrogen peroxide was a bit hardy to find in higher concentrations. After ringing chemical companies, without success, I finally rang a chemist who gave me a warning about high concentration hydrogen peroxide, and then told me to go to a pool shop... where I bought 28% concentration in water.

So last night, without re-reading the info in and around this board, I got my new plastic trays out and mixed up a 1/1 solution of the two and dropped in a board with sharpie used to mark the traces. Three or four seconds later almost all the copper was gone!, including the parts I wanted to keep. Brutal stuff.

This morning I redid the experiment using 2/1 muriatic/ peroxide which slowed down the etch to about 6-8 seconds including pulling the board out after 4 seconds and dipping in water to neutralise it then drying and redoing the sharpie in places where the ink was thin.

Still too fast and too strong but I have got a usable board.

Alls well, but then I made a mistake. The first time around I chucked, after watering down, the solution with dissolved copper in it and stored the unused 1/1 solution in a capped container. There was about 100ml in a 1litre container. In the morning that container had fallen over because the bottom had rounded off which was kinda interesting but the solution when used didn't do anything so I watered it down and chucked it.

The fun started when I mixed the used solution of 2/1 muriatic/ peroxide with the unused 2/1 muriatic/ peroxide and put it in the 1 litre container and capped it for future use... opps! five miutes later I'm passing by and hear a hissing sound from the container and I know that something going down that is potentially dangerous... what do I do? Well, I didn't grab a stick and try and shove it away nor did I do the war movie thing and pick it up like it's a grenade and hurl it as far away as possible. Nope. What I did was undo the cap slowly till it blew off and sprayed all over the place including on me.

I did all the wrong things and potentially very dangerous things with some dangerous chemicals... and even after watching the movie "the darwin awards" on DVD last night.

So I doused the areas of myself uncovered by clothes with water, reasonably liberally, then came out here to read up on the Hydrochloric/ hydrogen peroxide mix for etching. After this I'm going to have a long shower as the itchs aren't completely gone but the slight shortness of breath is gone.

Good Golly, what a total idiot I was, and as usual I got by without harm by the skin of my teeth.

28% hydrogen peroxide is indeed, like the chemist warned me, pretty dangerous stuff.

Now I'm going to mix my Hydrogen peroxide with de-mineralised water to a concentration that is quick but not too quick, maybe down to 10%, and find a ratio to mix it with hydrochloric that is again quick enough for me to use, maybe 3/1

Originally I only wanted about 200ml of 28% hydrogen peroxide but could only buy that high a concentration in 5 litre container.

Go figure eh! I can buy 200-500ml of h2o2 at 3% but can only buy 28% h2o2 in 5l.

[Ronsonic]

I just use the 3% or whatever it is peroxide you can find on the druggist shelf.

No need for anything stronger. That's sorta the point of this stuff is that everything is so dilute it can be handled without special precautions and can be found easily in stores.

No need to dilute the acid you have. It isn't the problem. What you have is pretty normal and can be handled by regular guys cleaning concrete without special tools and protective gear.

It's that peroxide stuff that's scary at this point. Cut it way down.

Re-read the previous posts on the subject and know that the peroxide described is the very, very dilute solution used for bleaching hair and as a mouth rinse and such.

[sean k]

The thing is that, and I kinda think it's a nature we all share given we make our own FX pedals, is that 500ml of 3% would cost be $12 but 5l of 28% only cost me $31 and without doing the math it's pretty obviosly more efficient to make my own 3% than allow someone else to. What I realised, or remembered, was that these scales of efficiency usually come with dangers most people aren't prepared to take on board.

In my case I did learn quickly that what I got was and is dangerous but by the same token that if I read up on stuff I can make the danger go away because I'm aware of the safety precautions.

As well as this particular form of etching I've also got onto the idea of using electrolitic action using electrical power, water and salt and yet again I'll be heading into dangerous territory because I recently bought some stuff to build a small unit to create hydrogen gas for using in my car to lift the efficiency of burning the gasoline that uses the same electrical method.

The guy who put me onto it said various salts in water needed various concentrations and the most potent salt was Caustic Soda which is 98% sodium hydroxide so now I'm thinking that the electrolitic method of etching might work well and very quickly using the caustic soda as a catalyst... but this recent experience has shown me that I need a whole lot more theoretical grounding  before I pour in a spoonful of caustic soda to water, add electricity... and then throw copper into it. 

Thing is that I've been a danger monkey all my life and I really do thrive on the element of personnal risk I very often subject myself to. I like learning and I really do think that danger adds an element to learning that really does make things stick.

[Zben3129]

I wouldn't bother with the electrolysis etching. It is messy, slow, and most importantly, doesn't work. I would always get a board with nice, shiny copper traces, except instead of the rest of the board being etched away it was just corroded copper.

Zach

[darron]

i use the acid mix too.. i use regular hydochloric acid from the hardware store (AU $13 for 5L) and 3% hydrogen peroxide w/w from the chemist (AU $4 for 500ml) mixed at 1:2 hydochloric acid to peroxide w/w solution. etch is pretty fast. not in seconds like you're talking, but maybe 10 mins. i keep it oxygenated with a fish tank pump and haven't had to replenish anything yet.

[8mileshigh]

Sean,

Hydrogen peroxide will also explode if heated, not fun.  Also, get an organic respirator, latex gloves and a face sheild to protect yourself when you're working with etchant.

Chris

[mikemaddux]

This is what has kept me from taking the jump into making my own PCBs...

Maybe I need one of those glove things Homer Simpson used to work with in the Nuclear Plant.

[Ronsonic]

If you just use the standard muriatic acid they've got at the hardware store and the peroxide off the shelf at the drug store mix it sanely, like 1:3 acid:peroxide this is pretty darned safe. I'm not saying you should stir it with your finger, but don't lick your finger clean if you do. I wear rubber gloves, cleaning-lady grade. This is overkill. I have nice Rx shop goggles I wear when I handle this stuff and almost everything else. Also overkill.

I'm sure it would suck to get it in your eyes or other orifices, so don't let that happen. Don't wipe up spills with your forearm or other body parts. Don't taste it to see if you mixed it right. The used stuff with the copper in it is toxic, don't drink it.

This is not the most dangerous thing in the shop.

[Ripthorn]

At first I thought this thread was titled "Playing with acid" and I thought that this thread had degenerated some   But it is true that this stuff is pretty safe, just use some good ol' common sense when using it.

[sean k]

Good one, maybe "playing with acidheads"

So a couple of days have passed and theres no ill effects from being sprayed with the mix. I was close to the kitchen sink, just out the back door, so liberally doused myself in water and I've developed this handy mechanism from when I play with metal, grinding, cutting and welding, that my eyes close very quickly and automatically when stuff like the cap popping on the acid mix.

My brother has done lots of bronze casting and uses the lost wax technique so yesterday I got a double biler from him and I'm going to completely encase objects in wax then scratch out what I want to etch away. Though the first thing I'll do is get a capful of this etchant mix, water it down slightly, and then put some wax into it and see whether it melts. If this works we'll be able to encase his sculptures in wax then scratch out the wax as a kind of tattoo then place them in the acid mix.

I'm well glad I've done what I've done, having 28% hydro pero, as it's opened up a bunch of possibilities for the art I do as well as making the copper etching of PC bards a whole lot easier and faster. Gone are the days of sitting over the stove elements on low and swirling aluminium trays and watching the ever so slow process of Ammonium Persulphate.

My elbows would get sore as my finger tips got too hot.

[demonstar]

I etched my first board the other day and I used Ferric Chloride. Does nobody else use this anymore? Does everyone use muratic acid now?

Judging by what happened to you FeCl₃ seems a much better option as it's much slower and more controlled. It took me half an our in cold weather in the garage with what I think was 40% acid solution. I was really pleased with my board.

Just as a side point I decided to go with kitchen cleaning gloves and light eye protection and appeared to have no problems but I don't think I'd feel comfortable handling it without gloves and certainly not without eyewear. I wouldn't solder, drill cut or handle and acids without safety glasses or goggles because it's just not worth  the risk when there are such simple safety precautions.

[newfish]

Still use Ferric Chloride occasionally, as I still have some pre-mixed.  It can take a while, but you could arguably use the time to practice the guitar.

Or drink Coffee...

Recently discovered the joys of Sodium Persulphate - which is clear, so you can keep a closer eye on your boards.

+1 on the gloves and goggles by the way. 

[Ripthorn]

I use Ferric Chloride because I have some powder mix for it, but I will probably give muriatic acid a try after what I have gets all used up (it makes a lot though).