Hot Citric Acid Bath

  1. Dcal

    Dcal Forum Supporter

    Messages:
    1,820
    Location:
    Antrim Northern Ireland
    Poo nah
    I agree with your thinking, butt if he doesn't put decient paint on it what's the point?
    Also leaving it longer than necessary before painting it (once and properly) seems silly.
     
  2. RaceDiagnostics Forum Supporter

    :dontknow:

    I have found that I don't want to make up a batch of epoxy every time I have derusted a few bits and bobs, prefer to get a decent number of items together before doing the painting all at once, so I just leave the parts with the citric acid residue on till I'm ready, then I normally rinse and then bake them dry ahead of priming.

    I read somewhere it was fine to do this.
     
    rtcosic and Dcal like this.
  3. Onoff Member

    Messages:
    984
    Location:
    Sevenoaks, UK
    If it works carry on. What dilution phosphoric acid?
     
  4. Dcal

    Dcal Forum Supporter

    Messages:
    1,820
    Location:
    Antrim Northern Ireland
    I came back after a week and a half away to see how the parts I had immersed in the citric acid were getting on.
    This citric acid solution was well used and was black before I put the parts in but seemed to be working OK.
    This was just left outside with a gorilla tub over the top to keep the worst of the weather off it.

    IMG_9018.JPG

    What I found was there was a thick white deposit well adhered to the upper exposed surfaces of the metal.
    The underside was coated in a black coating that would wash off (This is what I would expect and had seen before.)
    The deposit appeared to have just settled out and covered painted surfaces as well as the clean metal although it was easier to remove from the paint.

    IMG_9043.JPG

    IMG_9047.JPG

    The deposit is difficult to remove and I tried boiling it to see if the compound dissolved in water.
    This had some effect but needed to be scrapped off and an insoluble compound was left.

    I used a needle gun on some of the bigger bits and it got it off but it was not easy and the deposit had a proper grip.

    IMG_9058.JPG

    One of the small parts was damaged during dismantling and I had repaired it by welding and turning it down. The shiny bit seemed completely unaffected by the week and a half in the citric acid and the boiling and washing to remove the deposits.

    IMG_9055.JPG

    This is what was left in the container after I decanted the citric acid solution.

    IMG_9059.JPG

    IMG_9060.JPG

    Any chemists in tonight?
    Anyone know whats going on?

    Does the citric acid react with the rust and make a compound that settles out over time to coat the parts?
    Does heating keep this compound in solution for longer?
    Can the compound be removed or is it better to dump the mix and start again?
    How long should the citric acid solution last?
    If there is more rust to dissolve will the solution "wear out" sooner?

    From a search on the inter-web it might be iron citrate? Also it might not form if the solution is heated and gives off bubbles when the rusty bits are immersed in the citric acid solution.

    I accept I should have kept a closer eye on it but it's an interesting result and shows there is probably more going on here than it seems at first glance.
     
  5. Screwdriver

    Screwdriver Member

    Messages:
    5,952
    UK London
    Looks like you have brewed up a cocktail of metals. Willing to bet a lot of that is a plating (cadmium?) plus if you had any aluminium in there that will add to the weirdness. I use citric all the time and have never seen anything like that, got a thing in the tub now as it happens (will post pics in a mo) and I only ever put steel, iron or cast iron into the bucket.
     
  6. Onoff Member

    Messages:
    984
    Location:
    Sevenoaks, UK
    The new citric acid "tank" has arrived. I ditched the original (plated brass?) waste and fitted a plastic/stainless one:

    [​IMG]

    [​IMG]

    Going for 19:1 for the big bath solution for the cross member.

    Based on:

    4:1 by volume = 250g / 1L

    19:1 by volume = 250g / 4.75L

    Rough, required volume is 1200 x 400 x 350 (cross member size) so 168L thus just under 9kg at 19:1.

    It'll be unheated and just left with an old door/tarp over it.


     
  7. Chillitt Member

    Messages:
    946
    Location:
    Cirencester
    I have just found some similar 'stuff'.
    [​IMG]
     
  8. Sean Another 602 fan

    Messages:
    1,233
    Edinburgh
    It seems to be the remnants of zinc passivating.

    Ive used a strong and hot citric to de zinc bolts before TIG welding they came out white and lumpy needed wire brushing.
     
  9. Onoff Member

    Messages:
    984
    Location:
    Sevenoaks, UK
    Should have done this back when it was warmer but I finally got around to filling the old bath up with 9kg of citric acid in water. The only hot was the 3 buckets from the tap that I mixed it up with, the rest was from the garden hose. Should have blocked the overflow off too to get a deeper fill as a couple of bits of the crossmember are poking above the surface.

    Made a rough lid from a denailed / renailed pallet and a bit of siding (not quite wide enough).

    In went the MK1 Focus rear cross member (gut feel it's too far gone to be bothering) and one of the rear trailing arms (salvageable I reckon).

    No ideas what'll happen in this weather, guessing it might freeze? Assume the derusting will be really slow too with no heat?

    20191110_151810.jpg

    20191110_151837.jpg
     
  10. Ashley Burton

    Ashley Burton Member

    Messages:
    3,486
    Location:
    Northamptonhire
    @Onoff shame you couldn't of attached a coil & heated it
     
  11. Wallace

    Wallace Member

    Messages:
    6,858
    Location:
    Staines, Middlesex, England.
    If you have a pressure washer take the parts out daily and give them a thorough wash. The citric acid will not remove the paint but the pressure washer will help with that by removing the loose stuff. I had to apply a couple of coats of paint stripper in between dips to get 1965 paint off the 383 Chrysler block.
     
    Ashley Burton and Onoff like this.
  12. ronan

    ronan Forum Supporter

    Messages:
    9,437
    dublin
    Or had an old cast iron or steel bath and stick a gas burner under it.
     
    Ashley Burton likes this.
  13. Wallace

    Wallace Member

    Messages:
    6,858
    Location:
    Staines, Middlesex, England.
    My next big mix will be warm with air agitation to get some movement around the parts.
     
    slim_boy_fat and ronan like this.
  14. Onoff Member

    Messages:
    984
    Location:
    Sevenoaks, UK
    Imagine the heat loss on this weather!
     
  15. Onoff Member

    Messages:
    984
    Location:
    Sevenoaks, UK
    Tbh the only paint left pretty much is where the frame touched the rear suspension turrets!
     
  16. The_Yellow_Ardvark

    The_Yellow_Ardvark Member

    Messages:
    12,471
    Location:
    England
    I didn't go big.
    I went tiny.

    Just a small set of spanners, boiling water and 10 minutes.
    IMG_0837.JPG

    The sound of it was enough to be heard out side of the shop.

    IMG_0593.JPG

    10 minutes. From that to this.

    IMG_0891.JPG
     
    • IMG_0837.JPG
  17. Ashley Burton

    Ashley Burton Member

    Messages:
    3,486
    Location:
    Northamptonhire
    Yeah you would need a big fire to try & win the battle
     
    ronan likes this.
  18. Could ofdrilled a hole in bath and fitted an Emersion element :dontknow:
     
  19. dannyp Member

    i made a fair size barrel for electrolosys a while back, i run it off various things depending what i want to acheve, if you want to be nice to things small battery charger and a bulb in series let it pull no more than a couple of amps , if you just want the rust gone arc welder flat out 100+ amps rips the crap off fairish then might not be so sympathetic tho
     
    • IMG_0008.JPG
  20. Onoff Member

    Messages:
    984
    Location:
    Sevenoaks, UK
    Should I re title my thread COLD Citric Acid Bath?

    It's cold out there, frost on the car one morning but I'm pleased with the results so far for minimal effort! No heating etc since the initial 3 hot buckets. I will as @Wallace suggests take the jet wash to it one night to hopefully deal with any stubborn paint:

    20191113_191100.jpg 20191113_191107.jpg 20191113_191112.jpg
     
    indy4x, Turbo and Wallace like this.
Advertisements