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Matchless
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I have not read every post in this thread so this may have been answered already, I need to de-rust the steel frame of my MGA bonnet and boot lid with the aluminium still attached, I can easily make up a wood framed DPM lined tank but what do you recommend for the solution, I do have citric crystals, but have not used any as yet,
Misterg
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I had a quick play with the numbers when the original post went up. The weights only seemed to make sense to me if *all* the ingredients were anhydrous.
(You would need to increase the weights to allow for the water in the hydrated components - look up the molecular weight for each variant & scale accordingly.)
Ross365
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I have a technical paper about using citric to clean up boilers. They settled on using a solution of only 0.2% of citric in water (that's by weight) but they did operate it at 60'C and said it was effective "within a short duration". In DIY use, we may not be able to operate at 60'C if working on larger items, in which case, using a more concentrated solution is probably needed. There's always the question of getting a good balance between having a sufficient concentration that it works in a reasonable period of time, but does not significantly attack the good metal. There's a rule of thumb in chemistry (it works with lots of stuff but not everything) that for each increase in temperature of 10'C, you will speed up the rate by a factor of 2. So, at 60', you could be getting a rate of 16 times faster than that which you would have at 20'C.
Re citric anhydrous and monohydrate, the latter is going to be about 10% weaker for a given concentration.
Screwdriver
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So far as I know, citric acid will not attack aluminium. It will remove aluminium oxide which includes the thin oxide layer that aluminium naturally forms on its surface. That might leave it vulnerable to any other substances that could attack the raw aluminium but it will form again when it dries out.
Ross365
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I think it's always hard to say what citric will do to any metal without factoring in what temperature it's at, what concentration you have and how long you leave it. I once had quite a nasty surprise with some ultrasonic cleaning additive which I carelessly left a bit too long and a bit too hot
.
Screwdriver
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I think it's always hard to say what citric will do to any metal without factoring in what temperature it's at, what concentration you have and how long you leave it. I once had quite a nasty surprise with some ultrasonic cleaning additive which I carelessly left a bit too long and a bit too hot
True. Should be ok unless @Matchless boils up a super high concentration and leaves it for a week.
So I guess I should say: it should be fine to use a sufficient concentration of citric to just remove the rust without harming the aluminium. Do a test first.
Better?
Which exact recipe did you use?
JMS1972
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This one as I had washing soda to hand.
"To each liter of water, I’m adding 100grams of citric acid and 40 grams of sodium carbonate, also known as washing soda."
I didn't add anything to be a surfactant as I forgot! I wouldn't use washing up liquid as that has salt in it.
Ross365
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Maybe 10 or 20 cm3 of IPA to work as surfactant?
barracuda816
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For normal Citric de rusting solution I am using (probably way too much) 50g per 1000ml water.
Ross365
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No reason why you cannot do that as long as you keep a close eye on it.
Misterg
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I tried his recipe, and I have to say I'm impressed.
Before:
After (these have been sitting for about a week since coming out of the solution):
Took about 3 days in total. I fished them out and gave them a rinse and scrub with a wire brush a couple of times a day and knocked off a few obvious rust scabs. Most of the rust had gone after day 2, but I gave it another day and it all seems to have gone. A few rust stained bolts cleaned up in a couple of hours.
The mix I used was 100g of citric acid and 30g of caustic soda per litre of tap water and a squirt of Fairy Liquid. This is way more citric acid than I'd use if I was using it on its own. Beware that when you add the caustic soda to the citric acid solution, it gets hot - REALLY hot.
The solution started off looking like water, but ended up like this.
It is definitely much, much faster than citric alone, and if the video is to believed, it doesn't attack the good metal to any appreciable extent.
I just need to find a vat big enough to submerge a complete MX-5 now...
Before:
After (these have been sitting for about a week since coming out of the solution):
Took about 3 days in total. I fished them out and gave them a rinse and scrub with a wire brush a couple of times a day and knocked off a few obvious rust scabs. Most of the rust had gone after day 2, but I gave it another day and it all seems to have gone. A few rust stained bolts cleaned up in a couple of hours.
The mix I used was 100g of citric acid and 30g of caustic soda per litre of tap water and a squirt of Fairy Liquid. This is way more citric acid than I'd use if I was using it on its own. Beware that when you add the caustic soda to the citric acid solution, it gets hot - REALLY hot.
The solution started off looking like water, but ended up like this.
It is definitely much, much faster than citric alone, and if the video is to believed, it doesn't attack the good metal to any appreciable extent.
I just need to find a vat big enough to submerge a complete MX-5 now...
Jelly_Sheffield
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Oh dear...
bigegg
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I've been contemplating a shallow tray, big enough to drive a vehicle in, then a sprinkler system using pond pumps + 20/21mm uPVC pipe.
Rather than submerging the car, just a constant spray, recirculating the same fluid out of the tray.
Maybe not even a tray big enough for the whole car - could be one corner at a time?
Jelly_Sheffield
Time is an illusion. Lunchtime doubly so.
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You will need to contend with how much quicker water evaporates when sprayed, possibly by adding make-up water every few hours.
But there's no reason that it shouldn't work if you can get a fairly constant covering of the parts with the liquid.
An airtight(ish) tent should allow humidity rise high enough to prevent evaporation, if the gasses released are a fire/explosion risk then best not.
Jelly_Sheffield
Time is an illusion. Lunchtime doubly so.
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I wouldn't expect it to create an explosive atmosphere.
Your point about the tent is a good one, airflow (or in this case the flow of droplets through air) is normally the dominant factor in rate of evaporation... But if the air is completely saturated, airflow won't have any effect on evaporation.
I guess you would need to be "on it" with managing the humidity when you moved from section to section, and with getting a protective film over the clean metal after you have finished.
It did occur to me in the past that hooking up an old dishwasher to a tank of evaporust would be a really good way to de-rust parts bigger than I could afford to do with a tank... But I gave it away to a friend before I had any cause to try it.
