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Doug asked the Naked Scientists:Hi,Can you provide some comment or advice with the following.RegardsDougProblem: 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 TreatmentTo 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 timesfill with dilute acid for a period of timeflush several timesfill with dilute solution of neutraliser for a period of timeflush several timesinstall 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 treatmentElectrolysis 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?
Why would hydrochloric acid accelerate corrosion?oh you meant because it'll eat the steel as well as the rust, nevermind.
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.