Strength of phosphoric acid?

[nadroj]

I want to buy some phosphoric acid for rust removal.
The local hardware has small bottles of 85% concentration.
A chemical supplier has 81%, which they say will be OK for my needs.
Is the 4% difference anything to worry about?

Jordan

[Stustoys]

Hi Jordan,
Well the rust remover I have in the shed is 35%. So assuming more is better, you're a long way in front of that.

Stuart

[Greg Ward]

4% will not be noticed for what you want to do
Gfreg

[Anorak Bob]

Hello Jordan,

When I acquired my little No. O mill it was in a fairly appalling condition as a result of exposure to water based coolant and general mistreatment. The non painted surfaces were all discoloured with rust, some of it quite heavy. My brother in law, a farmer, had encountered Corro Dip at some country show and swore by it. As a result of immersion of those parts in Corro Dip, I do too.

index.html (http://www.liquideng.com.au/corrodip.html)

BT

[nadroj]

Thanks for the advice folks.
Bob - the CorroDip looks like a quality product, and likely has phosphoric acid in it at a guess. I have some steel that I want to clean up before painting, and will give the 81% stuff a go.

Jordan

[Anorak Bob]

Whatever you use Jordan, don't spill the stuff on concrete and leave it. I have a depression the size of a cereal dowl in the shed floor where some Corro Dip bled out over a few days from a useless plastic milk bottle.:no:.

BT

[Pete F]

Hi Jordan,
Well the rust remover I have in the shed is 35%. So assuming more is better, you're a long way in front of that.

Stuart

Yes mine is pretty much the same. I was using it earlier (3M "rust dissolver") and so checked the concentration. It was 30%.

Pete

[jack620]

Jordan,
I'm not a chemist, but with acid I would not assume stronger is better. If you are going to use it for rust conversion I would dilute it to 30-35% if that's what concentration the commercial rust converting products use.

Lower concentrations will be safer for you and anything you happen to spill the stuff on.

BTW what purpose is the 85% phosphoric product sold for?

Good luck with the project.

[Mr Brush]

I've found the 30-35% "Rust Dissolver" to be fine for most purposes, especially when applied with fine steel wool.

Just keep it away from any aluminium parts; it will remove anodising colour as well !

[Stustoys]

What would you thin it down with?
Water just sounds wrong.

Stuart

[BobL]

Water is the go for dilution, plus a couple of drops of wetting agent per litre - dishwashing liquid is fine.

[Mr Brush]

The wetting agent is a good idea, as the stuff doesn't wet a surface very evenly without.

I use this stuff on machinery surfaces all the time - stinks a bit, but very effective indeed. :2tsup:

[BobL]

If it too concentrated it will not dry properly and sits on the surface absorbing water and forms a horrible gooey messy. To speed up the drying I bake the derusted objects in a BBQ oven on low for an hour and it goes a sort of grey-white colour which can be readily painted over.

[nadroj]

BTW what purpose is the 85% phosphoric product sold for?


Sorry, I didn't think to read the label, just saw it was 85%.
It was in a Home Hardware shop in Mittagong NSW.

A few good additional pieces of advice - thanks again fellas.

I bought 35kg for just under $80.

Jordan

[BobL]

I bought 35kg for just under $80.


Wow - that is a lota rust!

[nadroj]

I like to buy wholesale. Hope it sees me out!

Jordan

[issatree]

Hi All,
Hey, what is wrong with a bit of Vinegar & a bit of Steel wool to get that rust off.
A dash sight cheaper than $35.
Yes, I've used Coro Dip, & yes, it worked fine, BUT, so does Vinegar.
I use 8 to 1, being 8 of water to 1 of Vinegar & leave in a Plastic Container.
I leave mine outside & cover it with a bit of Plywood to help stop Evaporation.
I suppose I'm lucky, that I'm allowed to clean my rusty bits in the Laundry Sink. I use a fair bit of Washing Powder, in hot water,& use a Brass Brush to wash all the rubbish off, then run it under the Hot Tap & dry with an old towel.

[pmcgee]

I suppose I'm lucky, that I'm allowed to clean my rusty bits in the Laundry Sink. I use a fair bit of Washing Powder, in hot water,& use a Brass Brush to wash all the rubbish off, then run it under the Hot Tap & dry with an old towel.

Awww ... memories ... that's how my old mum used to wash me when I was little

:U

Paul McGee

[Woodwould]

Awww ... memories ... that's how my old mum used to wash me when I was little

:U

Paul McGee
Did she use vinegar and steel wool too?

[issatree]

Hi all,
Well you may laugh, Ha, Ha, but My Mum did use Vinegar on us when we were silly enough to get Sunburnt . It really took the soreness out of the burn.

So what were the words of wisdom about using Vinegar & Water on Rusty bits.

[jack620]

So what were the words of wisdom about using Vinegar & Water on Rusty bits.

As I understand it, phosphoric acid reacts with rust to form an inert substance. Vinegar reacts with olive oil to form salad dressing. :D

[Pete F]

As I understand it, phosphoric acid reacts with rust to form an inert substance. Vinegar reacts with olive oil to form salad dressing. :D

Yes that's correct Chris. I can't recall the compound that's formed, but it basically protects the steel. I haven't tried vinegar, but I've tried several other acids and the part will literally rust before your eyes once it's removed from them. I use phosphoric acid before painting if there's light rust, any heavy rust I drag out the big-guns and just wipe it down the light rust that forms with phosphoric just before painting/powder coating

Pete

[Stustoys]

So says Wiki

"The phosphoric acid converts reddish-brown iron(III) oxide, Fe2O3 (rust) to black ferric phosphate, FePO4.
"Rust converter" is sometimes a greenish liquid suitable for dipping (in the same sort of acid bath as is used for pickling metal), but it is more often formulated as a gel, commonly called naval jelly. It is sometimes sold under other names, such as "rust remover" or "rust killer". As a thick gel, it may be applied to sloping, vertical, or even overhead surfaces.
After treatment, the black ferric-phosphate coating can be scrubbed off, leaving a fresh metal surface. Multiple applications of phosphoric acid may be required to remove all rust. The black phosphate coating can also be left in place, where it will provide moderate further corrosion resistance (such protection is also provided by the superficially similar Parkerizing and blued electrochemical conversion coating processes)."

[issatree]

Hi Jack620,
As It says, put it into English, as I'm not sure what you mean.
I have a few Tools in the V/W at this time, & when I get to clean them up, I expect for them to be a Beautiful Light Grey in colour.
To stop the future rust, most of my stuff is in Wooden Draws with an old Tea Towel that was soaked in that Product that those Shoe Shiners try to sell you, which is most likely Lanolin.
No Rust in My Shed.

[pmcgee]

As I understand it, phosphoric acid reacts with rust to form an inert substance. Vinegar reacts with olive oil to form salad dressing. :D

:rofl: :rotfl: :roflmao:

[jack620]

Hi Issatree,
sorry if I sounded flippant. I was just making the point that phosphoric acid and vinegar both have their specific uses. Pete F and Stu filled in with the details. It's the compound that phosphoric acid converts rust into that makes it suitable for the job. Vinegar doesn't convert rust, so is less suitable for the job. It may well remove rust (I haven't tried it), but it doesn't convert it to an inert compound.
Cheers

[Oldneweng]

Hi All,
Hey, what is wrong with a bit of Vinegar & a bit of Steel wool to get that rust off.
A dash sight cheaper than $35.
Yes, I've used Coro Dip, & yes, it worked fine, BUT, so does Vinegar.
I use 8 to 1, being 8 of water to 1 of Vinegar & leave in a Plastic Container.
I leave mine outside & cover it with a bit of Plywood to help stop Evaporation.
I suppose I'm lucky, that I'm allowed to clean my rusty bits in the Laundry Sink. I use a fair bit of Washing Powder, in hot water,& use a Brass Brush to wash all the rubbish off, then run it under the Hot Tap & dry with an old towel.

All acids will remove rust but as stated phosphoric converts to an inert compound. Vinegar in the bottle is a solution of about 4% acetic acid so is already very dilute. I use it to clean dirty stainless kettles. Pour in about a cup full, top with water, boil. Rinse, repeat if needed.

We use 85% phosphoric at work to neutralize caustic and as a cleaning step when cleaning our centrifuges. We buy in 200l drums. When the drum is empty (almost) there is enough left for me to take home. We use a pump to empty the drum into a bucket but the pump does not get it all. Due to the danger we are not supposed to use any other method. It is much safer at home tho!

I agree that it should be diluted to about 35% or so. I have used conc acid before and had to add water to get it to remove rust. The water is needed to create H3O+ ions which do the work. I would suggest that the acid is washed off with water after use. Then wipe etc dry.

Dean

[barney2804]

Just remember to add acid to water and not the other way around.

[Oldneweng]

Just remember to add acid to water and not the other way around.

Thanks for that timely reminder. I was going to mention it but I forgot.

Dean