From: dwilkins@means.net (Don Wilkins)
Newsgroups: rec.crafts.metalworking
Subject: Re: what acid for disolving steel wire?
Date: Wed, 03 Dec 1997 15:29:22 GMT

>I have a small plastic part in which is a thin (18 gauge?) solid steel
>wire, held captive by internal barbs.  There is no way to separate the
>two without the destruction of one or the other.
>
>I wish to preserve the plastic part, so I thought I could dunk the gizmo
>in some kind of acid, and have the wire dissolved right out, without
>harming the plastic part.  What would be the best choice of (easily
>obtainable) acid?  Would ferric chloride work?

Depends on what steel.

>If anyone is in the Toronto Ontario area (preferably Downsview), can you
>recommend a place which could sell me what I need?  I have also been
>interested in doing some electroplating, and most of the etches and
>pickles are comprised of concentrated hydrochloric/sulphuric/nitric
>acids, so I need to get these anyways.


Well you didn't indicate the length to diameter ratio, what kind of
steel, and what plastic.

If you have a long wire then you are going to have a problem. It is
very difficult to dissolve a wire when you only have solution access
to the end of the wire. The problem is getting fresh solution on to
the surface of the metal and getting the dissolved material out of the
hole. 18 gauge is a little small for a glass capillary to move to move
solution in and out of a hole.

My choice would be hydrochloric acid. This would be the least likely
to cause damage to a plastic and also the least likely to do damage to
the person handling the acid.

If you can get at both ends of the wire you might try anodic
dissolution. Translation...Connect one end of the wire to the anode
(plus) of a battery and put the other end of the wire in a conducting
solution. Then connect the cathode (minus) of the battery to another
wire which is in the solution. The solution can be ordinary salt
(NaCl) with a bit of muriatic acid.  Two volts is plenty and a single
dry cell may do it. A 12 volt car battery is overkill and may generate
chlorine gas.

Wear proper eye protection and you shouldn't have any unfortunate
visits to the emergency room. If you had to ask the question then you
shouldn't even think about using nitric acid as it can give you some
painful skin burns. Contrary to the opinion of another poster I
believe you can get some serious burns from "battery acid". This is
rather concentrated sulfuric acid and you can even get into difficulty
diluting the acid.

Concentrated hydrochloric acid will not give you immediate skin
damage. You first notice an itching sensation which should send you to
the sink to flush off the acid. If you have open cuts or scratches the
reminder will come rather quickly but you will not suffer the type of
burn you can get from nitric or sulfuric.

In the USA you can get muriatic acid (commercial grade hydrochloric
acid) at most hardware stores. I would dilute with an equal amount of
water and have at it. If you don't get bubbles (hydrogen gas) then it
isn't dissolving. A good rule is to add acid to water but in this case
it won't make a difference. Keep in mind that when you dilute sulfuric
acid you better add the acid to the water or you will be sorry. I
always added the concentrated sulfuric to ice. Much safer.

I would recommend that you stay away from nitric acid until you are
much more experienced than appears from your questions. If you mix
nitric and hydrochloric acids you can generate chlorine gas. This type
of reaction is not for the inexperienced and the trip could be to the
morgue not the emergency room.

I am a retired chemist and after some 50 years in the lab have been
nicked a few times. The worst was hydrofluoric followed by nitric and
sulfuric. I have never had a burn from hydrochloric acid.