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Plating Fe-55 on a Stainless Steel Wire

June 29, 2011

Hello,

I work in a research lab where we need to have an radioactive Iron-55 source on the end of a stainless steel wire. The wire will then be silver soldered into a series of stainless steel tubes to collimate the beam of x-rays through a beryllium window. The wire is 0.004" (100 microns) in diameter and needs to have a 5 microCurie source on just the end. We bought a solution of Iron-55 in a 0.026 M ferric chloride ⇦this on eBay or Amazon [affil links] solution in 0.5M HCl with an activity of 1 milliCurie. The total volume is one drop, 0.025 mL. Our plan is to copper plate the end of the wire and then plate the iron. The thickness of the plated iron would need to be 6 microns to achieve the necessary radioactivity.

I've been practicing with non-radioactive Iron-56 for the last month and have not had much luck. Here's a summary of what I've tried.

I've sealed the wire into a glass capillary tube exposing just the end of the wire. We bought a proprietary plating solution for plating copper onto the end of the wire, that works fine. I then use a platinum anode with one drop of iron solution on it to plate the wire's end, kind of a micro bath if you will. We're using platinum because it's a neutral electrode, whereas an iron electrode would "dilute" our radioactive iron when its plating. I've made two solutions that plate iron on the wire just fine. They are:

1) ferrous sulfate ⇦this on eBay or Amazon [affil links] 0.86M (240 g/L)

2) Ferrous Chloride 1.5M (300 g/L)
Calcium Chloride 2.7M (300 g/L)

They both make a brown precipitate, which I'm guessing is Ferrous Hydroxide, I've filtered it out however and the solution stills plates the wire. The current densities I've used range from 200 to 400 A/m^2.

I've been trying to make solutions that more closely match our 0.026 M ferric chloride ⇦this on eBay or Amazon [affil links] , 0.5 M HCl solution but haven't had any luck. I've made a solution of 1.5M Ferrous Chloride and 0.5 M HCl and this will not plate the wire, but it can be plated on to a larger sheet of copper-plated stainless steel. We're planning on reducing the ferric solution to ferrous using hydroxylamine hydrochloride. I haven't been able to plate ferric solutions onto the wire, only ferrous ones. I'm also starting to suspect the low pH of the FeCl2 HCl solution is preventing it from plating the wire, but not entirely sure.

Some questions I have are:
1) How would I control the pH of the FeCl2 HCl solution without affecting the plating process?
2) Would an elevated bath temperature be useful?
3) How can I determine my plating efficiency?
4) How can ferric solutions be plated?
5) Will hydroxylamine affect the plating process?

I don't have enough intuition with respect to chemistry, as I am just a lowly physicist, to truly wrap my head around these problems. Any suggestions would be appreciated.

Thank you,

Greg Jaehnig
- Madison, Wisconsin, USA