De-Rusting - Experiments with Citric Acid.

[Pete W.]

Hi there, all,

As the photos at the start of this thread show, I found citric acid fairly effective in removing rust from steel parts.

I recently found some DTI stand parts among a job-lot I'd acquired some time ago.  They were rusty so I decided to give them the citric acid treatment.

They were also rather greasy so I swilled them in some isopropyl alcohol first and then carefully dried them.

I put them in a plastic pot with a couple of dessert spoons of citric acid crystals and topped-up with warm water.  So far, there is no apparent action!!!

It's the same batch of citric acid as I used back in February 2014 and it's been in a sealed container all that time.  Even if there had been some ingress of atmosphere or moisture, I can't think of any chemical reaction that could have reduced its effectiveness.  So, I'm          

[awemawson]

I reckon that the parts have some lacquer or whatever on the surface. I've stored crystals of citric acid for years and not had any degradation of it's effectiveness.

[Bluechip]

I've used the electrolytic caper many times and have been baffled why that didn't work occasionally.

I have been told anything that has a phosphate, Sherardized or gun-blue finish may well fail to clean up too well. The original finish may not be apparent.

This was long after I stopped so I cannot verify it ... 

Get another bit of rusty steel and try that, I see no reason why citric acid should 'go off' as it were ..

Dave

[hermetic]

I have some apple trees at my workshop,  that is why it is called "Appletree works" and every year I try to make cider, and some is superb, and some goes wrong! I use the wrong stuff for derusting, and it works very well indeed, have also used it with electrolysis, and that works too. Anything with a bit of acidity will dissolve the rust, I was well impressed with some thread guages that, to look at, were really too far gone, but they cleaned to the point where the engraving is chrystal clear, and most of them are perfect bright metal again, and all done in bad cider, with no electrickery! Citric acid I suppose!
Phil

[howsitwork?]

probably acetic acid from the alcohol breaking down rather than citric.

Interesting thread. I have tried electrolysis on drills , someone mentioned that this causes  "hydrogen embrittlement " of the tools? They still cut OK so don't know how true , or critical for use this is.

Ian

[Arbalist]

I tried some citric acid derusting on some nuts and bolts as it would have been a fag setting up the battery charger. It worked well enough but the surface finish was terrible compared to washing soda and a battery charger. Never again unless I want to blacken the surface afterwards.

[Pete W.]

Hi there, all,

Well, I decided to leave the parts in the citric acid solution and they did eventually start to bubble but only slowly.

This morning, I decided to check what progress had been achieved.  Here's a photo of the parts straight out of the 'bath':



I then rinsed the parts in fresh water and then in methylated spirit and allowed to air dry.  That got me to here:



The parts were covered with a fine dark-coloured sediment.  I went over them with a brass bristled suede brush and they came out quite well:



I finished off by coating the parts with 3-in-1 oil.  I think that these parts are now in a good enough condition to be returned to service.

It seems that my stock of citric acid crystals hadn't 'gone off', rather that there was some coating on the parts under the rust that slowed up the reaction or made progress less apparent. 

[Eugene]

I have tried electrolysis on drills , someone mentioned that this causes  "hydrogen embrittlement " of the tools? They still cut OK so don't know how true , or critical for use this is.

There's certainly the possibility it could happen, especially given the extended times the parts are subjected to.

Hydrogen embrittlement is a potential problem with hardened and spring steels, electro-plating and it's associated cleaning processes being a prime cause; even common or garden rusting can cause it on susceptible steels. Mild steel is unaffected. The process of embrittlement can be reversed by heat treatment so within industry it's SOP to remove the hydrogen immediately after plating. The usual temp is around 200 C for two hours, so the home brew de-rusting of taps, dies and suchlike can be usefully followed by a stay in the domestic oven; it certainly won't do any harm and if it avoids a broken tap (such fun ) then why not do it?

There was a time in my life when I designed a test rig for plated parts that were safety critical and used it to check what felt like several million spring washers to establish some sort of statistical regime. It was the second most boring job I ever did. Weeks and weeks of sitting on your duff waiting for something to go "ping" .... ooh the excitement.  H & S rules forbid the publishing of my most boring job; simply reading about it can permanently shut down a complete cerebral hemisphere.

The effect of cider on rust is probably due to the tannins as much as anything else. Some commercial de-rusters are made from manipulating the lees left over from the fermentation of grapes in wine making and utilising the tannins; we imported hundreds of barrels of the stuff from Italy and sold the resulting product as "FerTan". Or was it FerroPro? Or both? I think it was under licence anyway.

Eug