Naked Science Forum
Non Life Sciences => Technology => Topic started by: Doug Saga on 24/12/2008 15:50:18
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Doug asked the Naked Scientists:
Hi,
Can you provide some comment or advice with the following.
Regards
Doug
Problem: a 5 year old radiator has been stored in a garage for a year and is obviously corroded as evidenced by spills of black liquid. To prevent contamination the Rust needs to be removed from the interior prior to re-installation in the central heating system.
What is the most effective method of removing the rust ?
Two options already identified.
Option 1: Acid Treatment
To remove rust one could either use dilute Hydrocholric acid or Phosphoric acid (available in the form of e.g. Brick Cleaner from a local DIY store). The process in each case would be:
flush several times
fill with dilute acid for a period of time
flush several times
fill with dilute solution of neutraliser for a period of time
flush several times
install in heating system and top up with inhibitor (Fernox MB1)
Questions arising:
Whereas Hydrochloric is the more powerful would it be equally effective to use Phosphoric acid to dissolve the rust. The latter is being less harmful to the environment.
What concentration of acid is appropriate?
What type of neutraliser and concentration is appropriate? Sodium Carbonate appears suitable for the Hydrochloric Acid (it would produce CO2 and yield some salts) but would it work satisfactorily with Phosphoric acid?
How long should the period of time acid treatment and neutraliser treatment be in each case?
What chemical or combination of chemicals would work equally well as alternatives to the proprietary Fernox MB1 as a corrosion inhibitor?
Any other advantages/disadvantages between using the two types of acid?
Option 2: Electrolysis followed by Phosphoric acid treatment
Electrolysis involves filling the radiator with an electrolyte [a solution of Sodium Carbonate (washing soda)], attaching a battery charger negative electrode to the radiator and the positive electrode to an iron bar immersed in the solution (making sure the iron bar does not make contact with the radiator). After a day of electrolysis (in the open air as hydrogen gas is given off) the electrolyte solution would be flushed and the Phosphoric acid treatment applied as above to remove any remaining coating of magnetite.
Matters arising: would the problem of hydrogen embrittlement cause damage to the radiator welds and paint?
Option 3: are there better methods of removing the rust ?
What do you think?
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Generally you go to a spare parts and accessories dealer and get radiator cleaner to mix with water and fill the radiator, stand it for the specified time then flush it with a water hose.
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Generally phosphoric acid is what is used to remove rust but quite honestly you would probably be better of to just go and buy a new radiator. They are not that expensive and I have a suspician that if the radiator was allowed to rust for a year that it will not last too long. In use the circulating water loses dissolved oxygen and internal corrosion takes years. But if used, then left empty for a year, the corrosion could well be severe.
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Doug asked the Naked Scientists:
Hi,
Can you provide some comment or advice with the following.
Regards
Doug
Problem: a 5 year old radiator has been stored in a garage for a year and is obviously corroded as evidenced by spills of black liquid. To prevent contamination the Rust needs to be removed from the interior prior to re-installation in the central heating system.
What is the most effective method of removing the rust ?
Two options already identified.
Option 1: Acid Treatment
To remove rust one could either use dilute Hydrocholric acid or Phosphoric acid (available in the form of e.g. Brick Cleaner from a local DIY store). The process in each case would be:
flush several times
fill with dilute acid for a period of time
flush several times
fill with dilute solution of neutraliser for a period of time
flush several times
install in heating system and top up with inhibitor (Fernox MB1)
Questions arising:
Whereas Hydrochloric is the more powerful would it be equally effective to use Phosphoric acid to dissolve the rust. The latter is being less harmful to the environment.
What concentration of acid is appropriate?
What type of neutraliser and concentration is appropriate? Sodium Carbonate appears suitable for the Hydrochloric Acid (it would produce CO2 and yield some salts) but would it work satisfactorily with Phosphoric acid?
How long should the period of time acid treatment and neutraliser treatment be in each case?
What chemical or combination of chemicals would work equally well as alternatives to the proprietary Fernox MB1 as a corrosion inhibitor?
Any other advantages/disadvantages between using the two types of acid?
Option 2: Electrolysis followed by Phosphoric acid treatment
Electrolysis involves filling the radiator with an electrolyte [a solution of Sodium Carbonate (washing soda)], attaching a battery charger negative electrode to the radiator and the positive electrode to an iron bar immersed in the solution (making sure the iron bar does not make contact with the radiator). After a day of electrolysis (in the open air as hydrogen gas is given off) the electrolyte solution would be flushed and the Phosphoric acid treatment applied as above to remove any remaining coating of magnetite.
Matters arising: would the problem of hydrogen embrittlement cause damage to the radiator welds and paint?
Option 3: are there better methods of removing the rust ?
What do you think?
If you want to accelerate the corrosion use the Hydrochloric acid...
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How much does a new radiator cost?
How much does it cost to replace an engine which has overheated suddenly, due to coolant loss?
A no brainer, as far as I can see.
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Why would hydrochloric acid accelerate corrosion?
oh you meant because it'll eat the steel as well as the rust, nevermind.
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Why would hydrochloric acid accelerate corrosion?
oh you meant because it'll eat the steel as well as the rust, nevermind.
Yes, I wouldn't use HCl for that reason. Probably, in appropriate chemical conditions (depending on exact type of material used for the radiator, type of rust, pH, ecc.), you could even use it, but it would be too risky, in my opinion. Even trying with less aggressive acids as fosforic, oxalic and acetic acid would be useful only if you were completely sure that the metal isn't attacked. One should first break a little piece of metal from the radiator, weigh it with a very sensitive scale, put it in a solution of the acid you want to use for an appropriate amount of time and then weigh it again to verify if it's been attacked and how much, and from this extrapolate the result to simulate the reaction with all the radiator...Probably very complicated.
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I work in a galvanizing plant, and before we dip the steel into zinc it goes through a treatment process to make the steel clean enough that the coating will take onto it. One of the treatments is a hydrochloric acid bath, it has something called "Iron save" in it which somehow inhibits it from eating the steel away, while still being effective on rust and whatever else is on the steel.
I've always wondered how this Iron Save stuff would work, does anyone have ideas?
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Are you sure that it is pure hydrochloric acid? There might be some hydrogen peroxide added. I'll have a look...
It has been discovered that by adding a hydrogen peroxide rinse aid solution to a hydrochloric acid rinse bath for acid pickled stainless steel the rinse bath easily removes stainless steel oxides and smutt from the surfaces of the stainless steel to produce a bright and clean finish that is comparable to the finish produced by nitric/hydrofluoric acid rinse systems.
In a most preferred embodiment to date of the present invention, a hydrogen peroxide rinse aid solution comprising about 7.7% w/w hydrogen peroxide, about 3.57% w/w phosphoric acid, about 1.66% w/w sodium 2-ethylhexyl sulfate (a preferred wetting agent), and the balance water, has been added to hydrochloric acid stainless steel rinse baths as a rinse aid to improve significantly the cleaning ability of the bath. This hydrogen peroxide rinse aid solution was then metered into a stainless steel rinse bath at the rate of about 2 times the rate of addition to the rinse bath of 32-38% w/w hydrochloric acid.
http://www.patentstorm.us/patents/5821212/description.html
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If you have time there is a very very good article about corrosion inhibitors here: http://www.surtec.com/Publikationen/InhibitorsSteelStrip.pdf
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No I don't think its pure, there's probably all kinds of stuff added, like from your example. Thanks
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No worries mate!