Ferric chloride attacking steel

[THX-1138]

Over the last few days, I had an AP (armour-piercing) bullet in a ferric chloride etchant bath to remove the copper jacket. Which it did, but to my surprise some of the underlying penetrator was attacked as well. AFAIK, these are hardened steel, so I wouldn't have expected the iron(III) chloride to have affected it.

 

Was my expectation incorrect? Will ferric chloride attack iron and steel items as well?

 

Thanks!

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Was this a stupid question?

[John Cuthber]

Ferric chloride will attack most metals.

Most things will attack steel more readilly than copper.

The only stupid questions are the ones you don't ask and thereby leave yourself ignorant.

[THX-1138]

Most things will attack steel more readilly than copper.

 

Really! I've always thought copper was more reactive. No basis in anything except impressions gained.

 

So I'm guessing that the steel got turned into ferrous chloride in solution. Bugger. /me tries to figure out the reaction formulae. Hmm, I'm not getting it.

[Fuzzwood]

Oxidation where iron(III) reacts with iron(0) i guess.

[THX-1138]

So let's see:

[ce]

2FeCl3 + Fe -> 3FeCl2

[/ce]

[ce]

FeCl3 + Cu -> FeCl2 + CuCl

[/ce]

 

Is this probably what's happening here?

[John Cuthber]

Now with added

CuCl + FeCl3 --> FeCl2 +CuCl2

[THX-1138]

Thanks!

 

Now, it's probably difficult to remove the impurities (ferrous and cupric chlorides) from the bath, so for disposal I should probably neutralise it with NaOH until the pH is at or above 7.0, correct? What will be the result? Aqueous NaCl and precipitated elemental iron and copper?

[CharonY]

More likely iron hydroxides.

[THX-1138]

{Sigh}

 

What should I study in order to determine the probable course of reactions such as this? It's been a long time since my chemistry classes..

 

Thanks!

Edited October 1, 2009 by THX-1138

[Fuzzwood]

Doesnt have to do much with studying as with stuff just snapping into place

[THX-1138]

Well, I'm assuming that there's some sort of scale of reactivity. For instance, that as the NaOH concentration goes up, the ferrous and cupric chlorides won't give up their chlorines at equal rates..?

 

So if everything is in perfect balance, and all of each compound will participate in the reaction,

 

[ mumble ]

 

I'm thinking the end result will be NaCl, iron and copper hydroxides -- and chlorine gas. Um.

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Or maybe not

 

[ce]

7NaOH + FeCl3 + FeCl2 + CuCl2 -> Fe(OH)3 + Fe(OH)2 + Cu(OH)2 + 7NaCl

[/ce]

 

Except that ferrous hydroxide isn't particularly persistent, right? So there'll be at least one more reaction before things stabilise.

 

Too bad I can't readily remove the ferrous and cupric chlorides; I'd like to preserve as much of the etchant as possible. Oh well.

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Perhaps this is best asked in the 'practical chemistry' forum.