Mu metal plating, coating, and finishing

A. Don't know of any literature for plating on Mu metal, but I did plate some a few years back.

I first tried anodic sulfuric. 6 V at room temp. Used lead as a cathode. Worked pretty well. Had some spotting and pitting at first, then learned the work had to be dry on immersion into the sulfuric. Followed this with a cyanide copper strike and then cyanide copper plate. Also plated nickel from a Watts solution. As the process evolved, I ended up using an electropolishing formulation for nickel from Electro-Glo.

Good luck

A. Dave,

As I recall, MU metal is a nickel iron alloy used for magnetic shielding. We used to etch it in a solution of 70 ml H2O, 20 ml HCl,

10 g ferric chloride ⇦ this on eBay or Amazon [affil links] hexahydrate, for 45± 5 sec. at RT. This leaves a very active surface and I suspect you could put a Woods nickel strike over it and then finish plate. Good luck.

"Electroplating Engineering Handbook"
by Larry Durney

on AbeBooks

or eBay or

Amazon

(affil links)

Does Dr. Seuss fit in somewhere in all this?

A somewhat mumentous occasion: Mumetal listed in Durney's Electroplating Engineering Handbook as 76 Ni, 16 Fe, 6 Cu, 2 Cr, 8.6 g/cu cm..

A. Mu metal is used for electromagnetic shielding, its created from a a nickel iron alloy which is then heated in a gas to about 3000 degrees then cooled in stages over about 3 days and costs about £3 per square inch. its very soft and malleable, and is damn good at screening.

A. To plate mu-metal treat it like any other nickel-iron alloy e.g. INVAR

A. Mumetal is used to realize an external Faraday Cage to protect vacuum tubes from EM noise coming from different surfaces or to realize small metallic boxes used as shielding enclosure for EMI RFI sensitive electronic components. If you need, you can also find specially designed enclosures for vacuum tube shielding.

Regards
Stefano

A. Mu (Greek symbol µ, ASCII character alt 230) metal has many formulations. It is quenched rapidly (several thousand degrees a second) to make it amorphous; there is no identifiable crystallinity. It behaves mechanically, in thin sheets, like flexible glass. Its major claim to fame is the extremely high magnetic permeabilities, which persist up to the microwave region.

A. I am sure that you have covered the magnetic properties of plated metals, but just in-case, we used the magnetic properties of electroless nickel to our advantage in 1960 for integrated circuit connection. My memory is a little fuzzy, but as I remember it, the magnetic properties only came from one bath. We had used both baths that utilized the Boron reducing agent, and hypophosphite reduction, but I don't remember which worked. Since the bath with the boron reducing agent plated much faster, I suspect that this was the bath. I would suggest trying this for magnetic shielding, even over plastic.

A. Mumetal is an unusual alloy that provides shielding from electromagnetic radiation per MIL-N-14411C and ASTM A753. It is nominally 80% nickel and 20% iron, but I found a proprietary composition Permalloy C® Mumetal® Ni77/Fe14/Cu 5/Mo 4. I suggest pretreatment per ASTM B343 and application of a Wood's nickel strike before silver plating, but anyone with experience should feel free to comment.

Silver plating specifications that might apply are QQ-S-365 [from DLA] , available from http://assist2.daps.dla.mil/quicksearch, ASTM B700, available from www.astm.org and AMS2410, AMS2411, AMS2412 & AMS2413, available from www.sae.org

Both QQ-S-365 and ASTM B700 allow chromating the silver for better corrosion resistance, as Grade A and Class S, respectively. I am unfamiliar with the AMS specs.

A. Rick, one reason I can guess at is that perhaps the MgO serves as a barrier to keep the parts from sticking together when they are annealed. Nickel iron parts are annealed after final forming / machining to give them the best soft magnetic properties, at about 2100 to 2200 °F. If you just dump parts in a hydrogen, argon, or vacuum furnace they'll stick together after a few hours at temperature, and the follow-up hammering to separate them can adversely affect dimensions.

Again, this is a guess, but a reasonable one. If you're sourcing your material from CarTech, I can attest to the competence of their customer service staff.

A. The material is coated to reduce eddy current loss in inductor application. Standard procedure in my industry.

A. MuMetal® is a registered brand of Magnetic Shield Corporation. Although historically mumetal was the generic name used for magnetic shielding material, it does have a specific chemical composition.

MuMetal can be finished with paint or plating - however certain precautions must be taken to maintain grain structure of the material so it provides maximum field attenuation.