Magnetic fields in molten iron

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Magnetic fields in molten iron

#1  Postby DougC » Jan 24, 2021 11:30 pm

Question.

Does the magnetic field increase, decrease or stay the same in molten iron?

(This is a genuine question. Not a start of a 'Shrinking Globe' style thread.)
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Re: Magnetic fields in molten iron

#2  Postby BlackBart » Jan 25, 2021 12:42 am

DougC wrote:Question.

Does the magnetic field increase, decrease or stay the same in molten iron?

(This is a genuine question. Not a start of a 'Shrinking Globe' style thread.)


It reduces. When iron is heated the iron atoms will stop lining up and lose their magnetism. When that happens, it's called the Curie point.

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Re: Magnetic fields in molten iron

#3  Postby Spearthrower » Jan 25, 2021 1:22 am

Brunet Bartholomew's already answered, but hey... it's so nice to see a science question on this forum (thank you!) that I am going to add unnecessarily to it! :)

Ferromagnetism comes from the the structure of the atoms in the material causing an alignment in dipoles; change that structure and the magnetic property is lost. Heat will change that structure; iron's Curie point is 770 °C, below that iron is ferromagnetic; above that, it becomes only partially magnetic - so you could say it still is magnetic, just not as strongly.
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Re: Magnetic fields in molten iron

#4  Postby Cito di Pense » Jan 25, 2021 6:39 am

The earth's magnetic field is not generated by remanent magnetism in ferromagnetic minerals in the crust of the planet below the Curie temperature. The strength of the magnetic field fluctuates over time, and reverses polarity from time to time. The location of the magnetic poles also has a secular variation on scales of years or decades.

The generation of the Earth's magnetic field is not fully understood in terms of the equations of electromagnetism. The earth's outer core is molten and convects vigorously compared with the convection rates in the mantle. The interaction of the motions of the iron in the outer core with the existing magnetic field induce electrical fields that feed back into generating magnetic fields in a process scientists call the geodynamo.

This field has been present for at least several billion years, insofar as ferromagnetic minerals appear in rocks of that age with their original magnetization. The magnetic fields in minerals below their Curie point are far too weak to be the source of the magnetic field we can measure at the surface. A good guess is that the field commenced when chemical differentiation caused the separation of the core from the rest of the planet and the outer core began convecting.

Getting Maxwell's equations and the equations of fluid flow to work together to predict the fluctuations of the magnetic field has not been a rousing success. Magnetohydrodynamics is the nerdiest.

https://en.wikipedia.org/wiki/Dynamo_theory

Jupiter, for example, also has a strong magnetic field. This field is thought to be generated by hydrogen at or near its center which is subject to enough pressure to undergo a phase transition to a metallic electronic structure. Fun! Fun! Fun!
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Re: Magnetic fields in molten iron

#5  Postby laklak » Jan 25, 2021 3:04 pm

Cito di Pense wrote:
The generation of the Earth's magnetic field is not fully understood in terms of the equations of electromagnetism.


Checkmate, atheists.
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Re: Magnetic fields in molten iron

#6  Postby The_Metatron » Jan 25, 2021 4:16 pm

Cito di Pense wrote:The earth's magnetic field is not generated by remanent magnetism in ferromagnetic minerals in the crust of the planet below the Curie temperature. The strength of the magnetic field fluctuates over time, and reverses polarity from time to time. The location of the magnetic poles also has a secular variation on scales of years or decades.

The generation of the Earth's magnetic field is not fully understood in terms of the equations of electromagnetism. The earth's outer core is molten and convects vigorously compared with the convection rates in the mantle. The interaction of the motions of the iron in the outer core with the existing magnetic field induce electrical fields that feed back into generating magnetic fields in a process scientists call the geodynamo.

This field has been present for at least several billion years, insofar as ferromagnetic minerals appear in rocks of that age with their original magnetization. The magnetic fields in minerals below their Curie point are far too weak to be the source of the magnetic field we can measure at the surface. A good guess is that the field commenced when chemical differentiation caused the separation of the core from the rest of the planet and the outer core began convecting.

Getting Maxwell's equations and the equations of fluid flow to work together to predict the fluctuations of the magnetic field has not been a rousing success. Magnetohydrodynamics is the nerdiest.

https://en.wikipedia.org/wiki/Dynamo_theory

Jupiter, for example, also has a strong magnetic field. This field is thought to be generated by hydrogen at or near its center which is subject to enough pressure to undergo a phase transition to a metallic electronic structure. Fun! Fun! Fun!

Thanks for that useful summary.

I'd sort of expect we'll find a property of metals at core pressures and temperatures we didn't expect or look for. There has to be current flow. A difference of potential, perhaps between the phase change between the core and mantle. I'm guessing that current flow, concentrated into the currents of the convection of the metal core self organize enough to generate the magnetic field. But, I'm high as fuck right now. I'll see how this looks later.
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Re: Magnetic fields in molten iron

#7  Postby The_Metatron » Jan 25, 2021 4:28 pm

I'd look for paths for that current. I wonder if iron, at core temperatures and pressures, varies a bit in conductivity with temperature. If it did, the convecting currents of cooler iron may be the path of least resistance for that electric current you need to generate a magnetic field.

If such a thing were to be spinning, that may be what organizes the iron convecting currents (also the paths of electrical current) to shape the resultant magnetic field into what we see.

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Re: Magnetic fields in molten iron

#8  Postby BlackBart » Jan 25, 2021 5:54 pm

Must be all kinds of weird shit sloshing round down there - piezo crystals the size of the Nimitz anyone? :awesome:
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Re: Magnetic fields in molten iron

#9  Postby DougC » Jan 25, 2021 7:44 pm

Thanks guys. Lots to look at.

Additional question.
If iron cools in a strong magnetic field (or electronic current) will the resulting bar/rod/ingot be more magnetic?
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Re: Magnetic fields in molten iron

#10  Postby Cito di Pense » Jan 25, 2021 10:27 pm

DougC wrote:Thanks guys. Lots to look at.

Additional question.
If iron cools in a strong magnetic field (or electronic current) will the resulting bar/rod/ingot be more magnetic?



https://en.wikipedia.org/wiki/Ferromagnetism

Just reading the introduction to that article (three paragraphs) will give you a basic orientation (no pun intended).

Wikipedia is a waste of time for discovering anything about soft subjects, but for basic science like this, you can learn enough by a little reading to make it worth your while. If you keep hitting a few links for terms that interest you, it will become obvious that you can't discover exactly what you will find most valuable or satisfy your curiosity in a single evening and that you need a professionally-trained teacher to give you the optimal executive summary. For that, you will have to pay somebody.

laklak wrote:
Cito di Pense wrote:
The generation of the Earth's magnetic field is not fully understood in terms of the equations of electromagnetism.


Checkmate, atheists.



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Re: Magnetic fields in molten iron

#11  Postby DougC » Jan 25, 2021 11:01 pm

Thanks CdP.
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Re: Magnetic fields in molten iron

#12  Postby eduardo » Jan 27, 2021 7:09 pm

laklak wrote:
Cito di Pense wrote:
The generation of the Earth's magnetic field is not fully understood in terms of the equations of electromagnetism.


Checkmate, atheists.

Eddy currents. Explained.
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