Impressed with citric acid de-rusting.

[MattF]

I would guesstimate that at room temperature, 5-10kgs in 50gallon is a saturated solution.

Something for adding to the "Things that bug you" thread.

 

[awemawson]

It's always worth adding a bit of washing up liquid - 'squeezy' if the bits are at all oily - it lowers the surface tension allowing the solution to wet the surface better.

 

[bigegg]

24hrs in.

 

[slim_boy_fat]

24hrs in.

Not that there's a hurry, but how does the process compare to, say, electrolysis? I've never tried the citric acid method [stop sniggering at the back! ]

 

[MattF]

You want it fully immersed to prevent any wash lines. You'll never shift those once they appear.

 

[MattF]

Not that there's a hurry, but how does the process compare to, say, electrolysis? I've never tried the citric acid method [stop sniggering at the back! ]

You can never really gauge either to perfection. Some stuff will derust quickly, but some stuff you may need to leave for days. Extract, scrub, return to the vat if necessary.

 

[bigegg]

You want it fully immersed to prevent any wash lines. You'll never shift those once they appear.

not bothered.
I'm de-rusting to try to free up the slides which are rusted solid.
after that: it's a tool, not an ornament.

(he says to the curator of the Barnsley vice museum, then goes and hides)

 

[bigegg]

Not that there's a hurry, but how does the process compare to, say, electrolysis? I've never tried the citric acid method [stop sniggering at the back! ]

slower, no need for power.
no risk of hydrogen explosion (I know, not much chance any way). it seems "cleaner" - there's no scum or massively corroded anodes to dispose of.

*possibly* more chance of damage? I've never noticed any, but I tend to use it for box + angle from the scrappy which has "character" to start with.

 

[Farside]

but I tend to use it for box + angle from the scrappy which has "character" to start with.

I think I should have de-characterised with citric acid some box I had lying around for years outside. The brackets I made with it are going to be a life-long painting sequence.

 

[bigegg]

72 hours in and the slide is free. you can see about 6mm of movement on the slide in the pic.
there's about 1mm diameter difference between the rusty part, and the smooth bit.

I'll leave it over the weekend, and then get the wire brush on it.

In related news: most of the original paint +stickers are still attached, and remain undamaged by the citric acid.

 

[Screwdriver]

I would guesstimate that at room temperature, 5-10kgs in 50gallon is a saturated solution.

Citric acid is a powder at room temperature, if you dilute it with water, it is diluted!

So 1kg per litre is a 50% citric acid solution which I think is as strong as it gets. That's the easy way to remember, about 1:1. In fact you need to mix 650g citric with 650ml water to make 1litre because the citric acid will take up some of the volume as you add more of it to the water but will dissolve and take up less volume!

That's a super concentrated solution imho and unnecessary for our purposes. We want to "reduce" the iron oxide (rust) not dissolve all of the metal in strong acid. Strong citric fruit is about 8% citric acid (when dried) and that's a good percentage to aim at. So for a 10% strength acid use 100g per litre and to hell with the maths.

I wanted to make something out of the ton of rebar I leave gently rusting in the garden. Gave the dry crusty rust a very brief wire wheel. Wire wheeling rebar is horrible because it's so grippy and the protruding deformation (tread) alternates so you have to attack it from two different angles with the wheel or it tears the wheel apart.

Got a fair bit of this PVC-U soil pipe and loads of accessory joins, first time I have used the bandsaw in anger and it's BRILLIANT! Blade falls through the plastic and gives me a perfect 90 degree cut.

I stuck about a cup of citric in there (1m tube, 8 litres?)

Had a quick peek after 3 hours and to give each bar a quick wipe down.

There's no rush so I'll probably leave it overnight.

But it works fast on dried rust. All it has to do is literally "reduce" the oxide, i.e. remove the oxygen from the iron in the surface of the steel.

While that's cooking overnight, I'll have a think about how to protect the raw surface when I take it out. Probably the best bet is just to thoroughly dry it and keep it dry. I'll probably weld these and then probably paint them so I am reluctant to oil them.

PS citric acid is used to passivate (certain types of) stainless steels. Shouldn't do any harm and will leave it with a protective oxide layer (on the chromium).

<edit> PPS when you mix up a citric acid solution it becomes extremely photo-reactive and will "spoil" in sunlight. Eventually it forms a scummy mixture which is apparently some sort of nasty fungus.

 

[anto44]

Citric acid is an awesome way of removing rust. I use this container with the basket for doing lots of small bits like nuts bolts brackets etc. Every time you get a chance give everything a scrub off with a dish washing brush to help it work.

I also have 2 of these bins on castors that pubs use for collecting bottles

 

[Screwdriver]

25kg on order for my 50 gallon tank.

According to my calculations, not a bad guesstimate (sorry MattH).

50 gallons = 190 litres. Remembering the citric will take up a fair bit of the volume, 19kg would give you the 10% solution you really want. I'm gonna just guess you should start by aiming for 150 litres and 15kg and see what volume turns up. Should be close and Google the maths if you really must.

Incidentally, for that sort of cost (!) I would recommend mixing it 1:1 in warm water in batches or say 20 litres, then dilute that "saturated" (?) mixture to taste. Otherwise you'll end up with an expensive pile of undiluted powder in the bottom of the tank.

<edit> again remembering this is a very popular foodstuff, if you use distilled water, it will keep longer. Any organic material that gets in there will help develop fungus. We've all see what happens to the odd spider/fly/cat that accidentally falls in.

 

[bigegg]

drop of bleach should kill the algae?

but Costco washing up liquid seems to work?

 

[Screwdriver]

OMG! This is horrible. My maths skilz have deserted me! I *think* 6.6 litres of water + 6.6kg of citric should yield 10litres of 50% citric acid solution.

So 20 litres would be 13.2l/13.2kg, then add 180 litres of water to make 200 litres of ~10% concentration.

GCSE Bitesize Maths Q.
"Wallace wants to make a 10% dilute acid solution. 1 litre of water plus 1kg of citric makes 1.3 litres of 50% acid solution. How many kg of acid and water must Wallace mix up to make exactly 50 gallons of 10% solution?"

Yeah I know, I'm saying 200 litres is good enough for Wallace. Not that that makes it any easier!

 

[130]

So next thread on molasses?

Also if you heat steel and throw it in old engine oil you get a martensite coating or something ?
It's a cheap black finish.

 

[Wallace]

Just for starters I will try using the Deox-C ratios of 19:1 & 4:1 (5 & 20%) as a direct comparison. I will be able to do a direct comparison at some stage as I have a 383 Chrysler block identical to one I did a few years back that came out like new, that was written up for a club magazine article.

 

[MattH]

According to my calculations, not a bad guesstimate (sorry MattH).

Uh, who what eh?

 

[MattF]

Uh, who what eh?

He means me. In relation to using the word: guesstimate.

 

[Screwdriver]

Also if you heat steel and throw it in old engine oil you get a martensite coating or something ?
It's a cheap black finish.

You're more likely to get cancer to be honest...

Old engine oil is one of the worst products you can do anything with. Getting it on your skin is bad enough, getting it into your lungs: well, good luck with that!

Martensite is a phase state for hardenable (typically high carbon) steel. It is generally above red hot before steels enter that phase before you "quench" the material (often in oil depending on the grade) which locks in or freezes the crystalline structure. It is not a surface only process, case hardening is something else.

You can brush oil (or ideally wax) onto hot steel to give you a robust coating but not red hot and it's not martensite.