The Shop > Finishing
Anodizing
Brass_Machine:
--- Quote from: foozer on January 24, 2011, 10:45:40 PM ---...
Always and its ALWAYS, add acid to water, never the other way round.
...
--- End quote ---
Thanks for the info Robert. Now why add acid to water? Is it because if you add water to acid, the risk of acid splash back is greater?
--- Quote from: Da_Kengineer_Meister on January 24, 2011, 10:59:05 PM ---
A quick question to those in the know. I've seen mention (online) of using DI water for all of the rinse steps in between all operations. Other places just talk about rinsing with water and do not specifically mention DI water.
Do you (anyone) feel that using, specifically, DI water is necessary to get high quality finishes without blotches / variation, or is this just a bit of bad info or specific to certain dyes, etc...?
-Thanks, Kenneth
--- End quote ---
I have seen the same thing. Some mention DI others don't. Any answers?
Eric
foozer:
--- Quote from: Brass_Machine on January 24, 2011, 11:07:24 PM ---
--- Quote from: foozer on January 24, 2011, 10:45:40 PM ---...
Always and its ALWAYS, add acid to water, never the other way round.
...
--- End quote ---
Thanks for the info Robert. Now why add acid to water? Is it because if you add water to acid, the risk of acid splash back is greater?
--- End quote ---
Thats the simplest reason and probably the best one, term escapes me but acids can react with water and kinda boil back at ya. Easy way to avoid is just always add acid to water. I've played with sulphuric and hydrochloric enough to gain a bit of respect for em. There reasonable safe enough long as some care in handling is observed. Easy enough for anyone who wants to venture to do a google and read up on em.
Be safe today and no sorrow tomorrow
Robert
andyf:
I've done a few bits of ruff'n'ready anodising over the years. Being a cheapskate, I used caustic soda (lye) from the supermarket to clean and etch a satin finish on the parts, and acid decanted from dead car batteries begged from the local battery replacement place diluted 1:1 with water as the electrolyte.
I already had a 0-30v, 20A power supply; not constant current, so I had to turn up its wick every now and again over the half-hour or so that the process took. The electrical connection was via a bit of aluminium rod threaded into a hole in an inconspicuous place on the parts, and sealed in with a fillet of sealing wax.
The resulting surface, after boiling to seal the pores, looked fine and was certainly more durable than the raw aluminium.
Experiments using fabric dye for colouring all failed; I reckon the proper dyes are needed.
Andy
Brass_Machine:
--- Quote from: andyf on January 25, 2011, 04:01:10 AM ---...
Experiments using fabric dye for colouring all failed; I reckon the proper dyes are needed.
Andy
--- End quote ---
I heard the fabric dye can be sketchy. I figure when I start, I will just buy the Pro stuff and be done with it.
Eric
raynerd:
I`m no expert but having the stuff at my disposal I tried anodising last year and posted up on here.
http://madmodder.net/index.php?topic=2441.0
It worked very well - especially the second time. I used an organic dye and that was great, better than the blue dye I posted about that looked washed out. The other piece has been floating around my house for the last year and the colour has fast well. I`d certainly give it another go next time I have something to anodise. Infact, I`ll make a point of it with my next ally part.
Regarding adding acid to water:
Sulphuric acid will "protonate" water. It`ll give a H+ ions (protons) to H2O to form H3O+. This is exothermic and gives out lots of heat. By adding the acid to the water, you are making the acid the limiting reactant (the reaction is in equalibrium which favours/"likes" protonating water (and therefore giving this violent exorthermic reaction)). Adding acid to water - the excess water is almost acting as a heat sink to dissipate the energy. Adding water to the acid (which you shouldn`t do) - with acid being more viscous (as well as all the equilibrium jazz above), they have less kinetic energy and so when the reaction occurs the energy is preferentially transfered to the water (lower Mr (molecular weight) and more kinetic energy) which causes it to boil and spit everywhere...!!
..... or so I believe .... if I`m wrong, I`ll go and hide in the corner. Sounds good though doesn`t it?? :smart:
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