Iron Colours in eMag Fields

[Arctic Fox]

I don't have any idea what it's called...

When iron (or metal?) is subject to an extreme magnetic field, it turns different colours. Does this happen to all metals, or just some?

I'm thinking about designing jewelry and trying to get this effect, but am wondering what causes it, and on what materials.

I'd like to get this look without having to diamond plate it:

http://www.titaniumrings.com/pix/spectrgroup2.jpg

 

[Astronuc]

In the case of titanium, it is anodized to produce different thicknesses of oxide, which have different optical behaviour (interference) depending on thickness. See - http://mrtitanium.com/interference.html

I am not sure iron changes colour in a magnetic field necessarily. What is considered an extreme magnetic field?

 

[Arctic Fox]

I am not sure iron changes colour in a magnetic field necessarily. What is considered an extreme magnetic field?

I don't know what would be considered extreme. I just remember years ago, I think on the television about how iron (or whatever metal is in a transformer) will degrade and will change colour from black to something looking like oil drops in a rain puddle. I wish I could remember the name of the effect...

 

[Gokul43201]

When iron (or metal?) is subject to an extreme magnetic field, it turns different colours.

Please find me a reference for this. Neither have I heard of this, nor can I infer it theoretically from anything I know about magnetism.

 

[Arctic Fox]

Searching... searching...

The only thing I find so far is this:

What makes this promiscuous behavior so interesting is that, every time an electron shifts from one part of the d orbital to another, the atom either takes in or gives off a little "puff of energy", often in the form of a wavelength of visible light. This makes the transition elements colorful. Note Fe (iron) is one of these, and we've already discussed that iron changes color from green or black to red or yellow when it changes from Fe2+ to Fe3+. We'll see that this and other transition elements can be present in tiny amounts in a mineral, yet give them a vivid color.

That makes no sense to me, though...

 

[Gokul43201]

That split in the energies of the d-orbitals comes from crytal fields, and is in the visible range - that's why most transition metal salts are colored. It has nothing to do with applied magnetic fields.

The energy split that does arise from an applied B-field (the Lamb Shift) is about 5 orders of magnitude (?) too small to result in transitions in the visible range.

 

[Astronuc]

. . . the atom either takes in or gives off a little "puff of energy", often in the form of a wavelength of visible light . . .

which is absorption or emission of light.

However, color for most materials is reflected light - which has mostly to do with reflection and refraction, and interference.

The color of Fe does depend on the Fe valence (2+ or 3+), which in turn determines the characteristic of the oxide Fe₂O₃, like hematite, or Fe₃O₄, like magnetite, and also whether they are hydrated or not.

Also in an aqueous environment, one can have hydroxides and oxyhydroxides, which are certainly different than anhydrous oxides.

 

[Arctic Fox]

Thanks, guys, for the additional information. :)

As I think about this, I might remember it having to do with atom smashers - something about the device not using an iron core for the electromagnets... maybe this is something? Anyone know why SCs don't use iron cores for the eMags?

 

[Gokul43201]

The way most SC magnets are used (especially in research), the place where the magnetic field is required (ie : where the sample being studied lives) is at the magnet center (ie: inside the solenoid), not outside the magnet. In fact, many SC magnets are wound with extra windings (above and below the primary windings) going in the opposite direction to the primary windings so as to minimize fields away from the magnet center.

 

[Rogue Physicist]

Examining the pictures you posted does look like industrial electroplating. Another easy way to get this would be electroplating with bismuth. This element naturally has this rainbow coloring on the surface, probably due to natural oxidation.

I reproduced similar colors when trying to get copper to turn green as per church roofs. The rainbow-like effect was not as even or well controlled, but was done simply by baking the copper plates in house oven.