lchris21
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I picked up my caustic from the local garden/pet/agriculture store?
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Kram
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The EPP requiring limit is 15% for Sulphuric.
Technically I am a member of the general public as I do not have a registered business and I am currently not in employment (by choice, until the covid bs ends.. I'm not claiming unemployment), and delivery would be to a residential address.
Zoro sell it, likely wouldnt ask for EPP as I have plenty of orders with them, but its £20/L
Anyway the CuSO⁴ is ordered, so it will be made from that.
The caustic, I have plenty for now. I got a couple of 200g bottles of granules in aldi.
For testing, I could use a cheap source of acceptable dye, red, blue or black, will buy the proper stuff when I know what Im doing.
Technically I am a member of the general public as I do not have a registered business and I am currently not in employment (by choice, until the covid bs ends.. I'm not claiming unemployment), and delivery would be to a residential address.
Zoro sell it, likely wouldnt ask for EPP as I have plenty of orders with them, but its £20/L
Anyway the CuSO⁴ is ordered, so it will be made from that.
The caustic, I have plenty for now. I got a couple of 200g bottles of granules in aldi.
For testing, I could use a cheap source of acceptable dye, red, blue or black, will buy the proper stuff when I know what Im doing.
hotponyshoes
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You use the caustic soda to prep the alloy before the anno process.
It is pretty aggressive, it can be used for removing existing anodizing before redoing it as well.
When I was running some big tanks that's where I first got the acid. The local scrap yard was letting me take limitless amounts of battries away and then take them back again empty. I had a rack over a big blue barrel and just drilled holes about an inch from the bottom of the battery to drain it out.
Leave it to settle for a few days then jug it out leaving all the crud on the bottom.
Kram
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Not ready for anodising yet but I had a go at converting the CuSO4 to sulphuric. It appears to be working in that copper is being grown on the cathode, ph is 1-2, but the gas produced on carbon anode does not appear to be oxygen! Therefore I've stopped until I work out what. Carbon and copper bits filter out easily.
The gas does not noticably increase the flamability of lit paper and flame colours slightly green so it may be a copper compound. The smell is not strong or unpleasant.
Any ideas?
The gas does not noticably increase the flamability of lit paper and flame colours slightly green so it may be a copper compound. The smell is not strong or unpleasant.
Any ideas?
if you get a small pop bottle could you dip it in and fill it up, then pick it up upside down above the bottles?
it'll be full off the liquid, as the bubbles rise into it the liquid will come out the bottom, you'll have a little bottle full of the gas as pure as you'll get it?
I'm thinking just above the bubbles won't be pure enough, unless there's a hell of a lot of bubbles?
anything would work, pop bottle was just first idea :-)
it'll be full off the liquid, as the bubbles rise into it the liquid will come out the bottom, you'll have a little bottle full of the gas as pure as you'll get it?
I'm thinking just above the bubbles won't be pure enough, unless there's a hell of a lot of bubbles?
anything would work, pop bottle was just first idea :-)
Misterg
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If you've got a carbon anode, it'll probably be mostly CO2 as the oxygen reacts with it.
(I think you could save yourself all sorts of grief by just buying some sodium bisulphate - YMMV.)
Kram
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Your correct its CO2 gas and copper particles. I finished the first reaction and went well.
I may still buy some but I think this is going to work. I dont mind some effort to learn, particually as chemistry is interesting. I now have about 8% of 250ml clear, filtered H²SO⁴ and when done it will be 15-20% at 1L, which will be plenty for the smaller parts. I assume theres a good reason that sulphuric is the standard, else cheaper acids like citric would be used?!
Still need a source of dye. Anyone tried electro colouring? Copper sulphate can be used and will give a non fading red-pink-brown as the copper gets deposited in the anodise pores.
I may still buy some but I think this is going to work. I dont mind some effort to learn, particually as chemistry is interesting. I now have about 8% of 250ml clear, filtered H²SO⁴ and when done it will be 15-20% at 1L, which will be plenty for the smaller parts. I assume theres a good reason that sulphuric is the standard, else cheaper acids like citric would be used?!
Still need a source of dye. Anyone tried electro colouring? Copper sulphate can be used and will give a non fading red-pink-brown as the copper gets deposited in the anodise pores.
Electrocolouring of anodized aluminium with copper: Effect of porous and barrier oxide film thicknesses
In this work, we have investigated the effect of the thickness ofboth porous and compact films of aluminium anodized in I5/, H2SO4 on the electrocolouring process using copper sulphate and magnesium sulphate solutions. With thin layers (less than
www.academia.edu
Misterg
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Other acids can be used for different types of anodising (e.g. chromic acid, phosphoric acid, etc. ) but they affect the type of layer produced. For the common type of anodising were talking about here, the aim is to produce a relatively thick oxidised layer (~10 micron, give or take ~50%) which is well bonded to the surface and which has a whole lot of pores in it that we can later fill with dye.
It just so happens that with acidic conditions in the presence of sulphate ions, with the correct temperature and current density, the oxide layer is simultaneously deposited and dissolved in the right sort of proportion to create 'cells' something like a honeycomb structure on the surface. The holes in the middle of these cells are only about 20nm in diameter (0.02 micron), but they extend practically the full thickness of the coating.
If there wasn't this combined dissolving / depositing action, the anodising process would stop very quickly as soon as an oxide film build up, and there would be no pores no hold colour (which I what I understand happens with titanium anodising).
Any dye must be able to get down into the pores. It's kept there by sealing ends of the pores up (very hot water hydrates the aluminium oxide here which swells up and seals the pores off).
The detail of the anodising conditions affect the size of the pores and the coating thickness, both of which affect how well the surface will take dye.
I've only used commercial dyes that I got through ebay (example 1, example 2 ), but I know that people have also had success with certain brands of food colouring or ink. The trouble is that you won't know whether the dye or the anodising process is at fault if you have poor results unless one of them is known to be OK.
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We used it in my mate's mum's rubber dustbin lid to strip the coloured anodising from our Raleigh Burner stems back in the 80s.
Kram
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I made up a 20% NaOH mix (400g to 1.6L) today for that purpose and stripped some of the 5005 black anodised sheet. It gives a much nicer finish than mechanicaly stripping it and takes about 2 minutes.
One peice of the 5005 I had bent up and the anodising had cracked around the bend. Stripping still leaves this cracked texture on the metal underneath, so next time I will strip before bending. It will be a test peice so after welding I will re-anodise it to see how the 5356 welds come out.
One peice of the 5005 I had bent up and the anodising had cracked around the bend. Stripping still leaves this cracked texture on the metal underneath, so next time I will strip before bending. It will be a test peice so after welding I will re-anodise it to see how the 5356 welds come out.
Kram
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I had an attempt at this tonight. I got cold, wet and quite annoyed!
This is the dye I bought - ebay sellers were messing about so I just got the cheap one for testing. If the colour sticks and is the same as it looks I will be happy.
I got a 7kg bucket of NaHSO⁴ and weighed out 500grams to 2.5kg of condensed water (out of dehumidifier, should be adequate for this), so about 20% by weight. I mixed it a few days ago so it is currently about 11c and, if it had all originally disolved, much has crystalised out at the bottom.
Used a milk bottle with the top chopped off as my container - the cause of much of the frustration as its not really big enough.
My test part was my tig torch holder - which I'd given a reasonable 3 minute dip in 20% NaOH a couple of days ago. I gave it a good scrub with a scourer and soap to degrease. I was going to weld on some tig filler for my connection but without a working mask I cant. I tried to make a mechanical joint which wasnt much good. To rule that out I held it above the acid level after making a freshly sanded joint, also direct croc clip above the level, same results.
Using an adjustable 0-12v 30A power supply. Connected it up and it briefely had half an amp, rapidly decreasing, 10 seconds later, nothing, at 12v. Few tiny bubbles, then nothing. Power is there, if I dip the positive croc clip lots of bubbles form.
What am I doing wrong?
I was expecing a reasonably high starting current at ~3v, with the required voltage increasing as the oxide layer gets thicker.
This is the dye I bought - ebay sellers were messing about so I just got the cheap one for testing. If the colour sticks and is the same as it looks I will be happy.
I got a 7kg bucket of NaHSO⁴ and weighed out 500grams to 2.5kg of condensed water (out of dehumidifier, should be adequate for this), so about 20% by weight. I mixed it a few days ago so it is currently about 11c and, if it had all originally disolved, much has crystalised out at the bottom.
Used a milk bottle with the top chopped off as my container - the cause of much of the frustration as its not really big enough.
My test part was my tig torch holder - which I'd given a reasonable 3 minute dip in 20% NaOH a couple of days ago. I gave it a good scrub with a scourer and soap to degrease. I was going to weld on some tig filler for my connection but without a working mask I cant. I tried to make a mechanical joint which wasnt much good. To rule that out I held it above the acid level after making a freshly sanded joint, also direct croc clip above the level, same results.
Using an adjustable 0-12v 30A power supply. Connected it up and it briefely had half an amp, rapidly decreasing, 10 seconds later, nothing, at 12v. Few tiny bubbles, then nothing. Power is there, if I dip the positive croc clip lots of bubbles form.
What am I doing wrong?
I was expecing a reasonably high starting current at ~3v, with the required voltage increasing as the oxide layer gets thicker.
Misterg
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Not enough volts.
I use a constant current supply, and the voltage usually starts off at about 16V briefly and rises to 22/ 23V.
Old-school 12V battery chargers will work OK because (i) they are poorly regulated and put out ~16 or 17V off load and (ii) there's no smoothing after the rectifier, so the voltage is pulsing to over 20 volts.
I don't think it's part of your problem at the moment, but I would also give the part a fresh dip in NaOH, *immediately* before putting it into the anodising bath. Even a few minutes is enough for an oxide film to form on the surface. A 2 minute dip in 2% NaOH will take off this oxide film. I keep the parts wet after the NaOH dip and transfer them straight to anodising.
[ETA: Your NaHSO4 concentration looks right]
What are you using for the cathode? Roughly what is the surface area of your test part?
Stick at it, it does work.
Kram
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That suprises me if it needs 16v+ to sustain miliamps. I have a constant current boost circuit I can try tomorrow.
I think my part, the tig torch holder, started off as 200x70mm sheet but I havent attempted to work out the required current. Photo from last week before the drip..
Im using a lead sheet cathode roughly 200x50mm. It was used in my other sulphuric-from-CuSO4 experiment as the anode, so it has a reasonable coating of lead oxide, but I doubt that will harm it.
Is your 20% acid mixture near saturated and do you use it cold or warm?
I think my part, the tig torch holder, started off as 200x70mm sheet but I havent attempted to work out the required current. Photo from last week before the drip..
Im using a lead sheet cathode roughly 200x50mm. It was used in my other sulphuric-from-CuSO4 experiment as the anode, so it has a reasonable coating of lead oxide, but I doubt that will harm it.
Is your 20% acid mixture near saturated and do you use it cold or warm?
Impressively so in a decent concentration - used to strip solidified aluminium out of extrusion dies - dunk it in and leave a for a few days. Or dunk it in a tank with ultrasonics, the ultrasonics keep moving the crap off the surface as it reacts, exposing fresh metal to the solution - producing high volumes of hydrogen in the process - scary amount from a few thousand litre tank!
Misterg
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I think the cathode is OK.
You should be looking for about 2 amps for that part (assuming it's still roughly 200 x 70) for 90 - 120 minutes (I tend to stick to 120 minutes).
[ETA: 2 amps is based on 6A/sq ft]
I use the same concentration of NaHSO4 cold. I'm not sure if it's near saturated or not, but now you come to mention it, I do recall seeing crystals on the bottom of the bath on occasion - could well be near saturated, but I don't think that is critical.
If the bath gets warm, the anodising will suffer. If you're using a small container and 2 amps, that could well heat it up too much. I've stood my anodising bath in a bucket of cold water to keep it cool in warmer weather. I would guess it needs to be kept below mid 20s °C.
You should be looking for about 2 amps for that part (assuming it's still roughly 200 x 70) for 90 - 120 minutes (I tend to stick to 120 minutes).
[ETA: 2 amps is based on 6A/sq ft]
I use the same concentration of NaHSO4 cold. I'm not sure if it's near saturated or not, but now you come to mention it, I do recall seeing crystals on the bottom of the bath on occasion - could well be near saturated, but I don't think that is critical.
If the bath gets warm, the anodising will suffer. If you're using a small container and 2 amps, that could well heat it up too much. I've stood my anodising bath in a bucket of cold water to keep it cool in warmer weather. I would guess it needs to be kept below mid 20s °C.
Misterg
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As a side note relevant to the pre-anodising dunk in weak sodium hydroxide aka caustic soda aka NaOH:
When you first put the part in, nothing seems to happen for a while then you start getting bubbles. What happens is that the NaOH first dissolves the aluminium oxide layer without producing any visible effect, then once it gets through to the metal you start getting the hydrogen bubbles - you want the surface of the part to be completely covered in fine bubbles (meaning that the oxide film has been completely removed) before rinsing and transferring to the anodising bath.
Misterg
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I got my yellow/gold dye and made some trial coupons. I also tried my green dye cold:
All were anodised for 2 hrs at 6A / sq ft using the bisulphate solution. The green cap is one I’d made earlier and dyed at 55 C.
I think there’s a reasonable gold colour to be found, also, it looks like the green dye will work cold if given a bit longer.
After I’d done these, I gave my anodising bath a birthday and cleaned it out. No crystals in the bottom, but there was about 1/2” of what looked like ice:
I don’t know what it is, but I suspect it might be aluminium hydroxide.
I couldn’t quite get all the sodiumbisulphate to dissolve when I made up the new bath - it was about 10 degrees and there was about a teaspoon that wouldn’t dissolve, so I guess it is near a saturated solution at room temp.
All were anodised for 2 hrs at 6A / sq ft using the bisulphate solution. The green cap is one I’d made earlier and dyed at 55 C.
I think there’s a reasonable gold colour to be found, also, it looks like the green dye will work cold if given a bit longer.
After I’d done these, I gave my anodising bath a birthday and cleaned it out. No crystals in the bottom, but there was about 1/2” of what looked like ice:
I don’t know what it is, but I suspect it might be aluminium hydroxide.
I couldn’t quite get all the sodiumbisulphate to dissolve when I made up the new bath - it was about 10 degrees and there was about a teaspoon that wouldn’t dissolve, so I guess it is near a saturated solution at room temp.
