Magnetic weapons

Rivkin · 27th February 2005, 05:06 PM

Quote:

Originally Posted by Ann Feuerbach

It would not matter if magnetite was part of the smelt or crucible steel refining process. During the actual production of the crucible steel, since it is liquid and an homogenous steel, the iron particles in the ingot would have a definite alignment to magnetic north (back to Archaeomagnetism). If anyone is really interested in that I could probably give some references as I was teaching it a few weeks ago.

I'm sorry, may be I'm not getting something but:
I understand that magnetite will not make a difference, but taking in mind that iron melts at 1800K, and its Curie temperature is 1000K how it can have (in a liquid state) _any_ definite magnetization. If at 1000K the exchange can not hold these guys together, thermal energy should completely negate any infinitesmal influence that the Earth's magnetic field can possibly have on a liquid metall. Most of steels have Curie temperatures even lower than this, up to 300K and below for some non-corrosive nickel and other steels.

What do you mean by "iron particles" in the _liquid_ ? Domains ? Individual spins ? Non-uniformities of a liquid state ?

Ann Feuerbach · 27th February 2005, 06:52 PM

Perhaps the ingot does not have a magnetic alignment.

I do not know of any experiments done on the archaeomagnetism of iron objects because for archaeomagnetism to be studies, the object must be in situ since firing. Archaeomagnetism is based on the principle of Thermoremanent magnetism (TRM). When a material containing iron such as clay, is heated to above 700 C (1290 F) the iron particles in the clay align to face magnetic north. The direction and intensity of the magnetism of the kiln or hearth is measured to give the date. I assumed that the same principle would have applied to the crucible steel. All the literature I have read just refers to "iron particles". Perhaps I am wrong and the ingot would not have had a TRM. As I said, I must do some more research on this. I must point out that having TRM and being magnetic are different things. As a side not, I have noticed that many archaeological slags with high iron content and iron lumps, that one side is definitly attracted to a magnete while the other side definitly repels.
Ann

Rivkin · 27th February 2005, 08:34 PM

Neither ignot nor iron objects nor any objects would have any magnetization when heated above Curie temperature.

What TRM is, is when cooled _slowly_ the object that in general is macroscopically isotropic will be magnetized along the Earth's magnetic field (with some exceptions).
I think that magma is Fe3O4 or something like this, and it can move around without loosing its magnetization, so the TRM happens when it's actually very hot, but I'm not quite sure about it.Very primitive discussion is located here:
http://www.moorlandschool.co.uk/earth/magnetism.htm

Rivkin · 27th February 2005, 09:13 PM

Again - magnetic properties of a macroscopic iron is a tremendously complex problem, that can be approach with numerics.

I'm not a specialist (so I wish to be corrected by ones), but:

Local magnetic structure depends on the crystalline lattice (unobtainable in normal conditions "diamond" iron for example is even anti-ferromagnetic), including stress, grain size etc. There are dozens (!) of phases that correspond to basically chemically similar steels that have different crystalline structure (and btw hardening is the way to obtain a metastable crystalline structure).
These lectures notes can be of help:
http://neon.mems.cmu.edu/laughlin/pdf/252.pdf
btw austenite is paramagnetic.
It will greatly depends on local chemical decomposition.
It's going to greatly depend on how uniform and fast the cooling is (uniform cooling leads to permanent magnetization alongside the local magnetic fields)
In general there are some companies who measure conductivity and magnetic permeability in order to undestand how uniform their steel is. I don't want to refer to non-publicly available papers, so:
http://doc.tms.org/ezMerchant/prodtm...df?OpenElement

Now to the question "what happens to a sword":
1. Swords are intrinsicly anisotropic due to their shape.
2. They are usually completely non-uniform in their magnetic properties due to nonuniformities of steel they are made off, and nonuniform cooling (first of all - nonuniform quenching).

Before I've the patterns of the dagger that were shown here I believed that such patterns can be produced by a weird external field. Now I think that because they are so damn non-uniform, and most of the dagger is not magnetized at all, the structure of this dagger should be tremendously non-uniform by itself, and I believe that conductance or X-Ray tests can prove that.

Now to what happens to swords when they lie in Earth. I thought about who would've been interested in this, and realzied that mine detector peoples are.
And indeed one can read a very interesting pamphlet over here:
http://neon.mems.cmu.edu/laughlin/pdf/252.pdf]

one should keep in mind that they are interested in a dipole moment i.e. the magnetic field procuded by objects very far away from the object itself, so it's much more uniform and depends on Earth's magnetic field in a much more direct way (since those guys quetly cool down underground), but we are interested in a local magnetization - quadrupole and up moments, that create these beautiful patterns.

Ann Feuerbach · 27th February 2005, 10:18 PM

Thanks. Lots of food for thought!

Rivkin · 28th February 2005, 12:59 AM

You are welcome.

Btw, the thing I always wondered about archaeomagnetism people - do you take in mind only the total magnetization and connect it to the strength of the Earth's magnetic field at the time of making of the object, or you actually use oomf/rkmag

to see how the object with such chemistry and shape would react to the applied magnetic field of such strength ?

Jim McDougall · 28th February 2005, 02:49 AM

Hello Ann,
I would like to also welcome you to our forum, and to say what an honor it is to have you join us. I have had your outstanding work "Crucible Damascus Steel"for some time now, and it is brilliantly written!
For someone such as myself who is fascinated with history, yet lost with the complexities of physics, science and technology, it is an entirely readable and well crafted blend of history with well explained technical details.

This thread, as well as that of meteoric iron, have really become high profile and I am delighted that Jens posted them, as the knowledge and discussion has become irresistable! Aside from your extremely interesting article, most discussions on these topics can be quite dry to most of us in the lay world....but this thread keeps getting better, and your joining us is outstanding!

All the best,
Jim

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27th February 2005, 06:52 PM	#2
Ann Feuerbach Member Join Date: Feb 2005 Posts: 133	Perhaps the ingot does not have a magnetic alignment. I do not know of any experiments done on the archaeomagnetism of iron objects because for archaeomagnetism to be studies, the object must be in situ since firing. Archaeomagnetism is based on the principle of Thermoremanent magnetism (TRM). When a material containing iron such as clay, is heated to above 700 C (1290 F) the iron particles in the clay align to face magnetic north. The direction and intensity of the magnetism of the kiln or hearth is measured to give the date. I assumed that the same principle would have applied to the crucible steel. All the literature I have read just refers to "iron particles". Perhaps I am wrong and the ingot would not have had a TRM. As I said, I must do some more research on this. I must point out that having TRM and being magnetic are different things. As a side not, I have noticed that many archaeological slags with high iron content and iron lumps, that one side is definitly attracted to a magnete while the other side definitly repels. Ann

27th February 2005, 08:34 PM	#3
Rivkin Member Join Date: Dec 2004 Posts: 655	Neither ignot nor iron objects nor any objects would have any magnetization when heated above Curie temperature. What TRM is, is when cooled _slowly_ the object that in general is macroscopically isotropic will be magnetized along the Earth's magnetic field (with some exceptions). I think that magma is Fe3O4 or something like this, and it can move around without loosing its magnetization, so the TRM happens when it's actually very hot, but I'm not quite sure about it.Very primitive discussion is located here: http://www.moorlandschool.co.uk/earth/magnetism.htm

27th February 2005, 09:13 PM	#4
Rivkin Member Join Date: Dec 2004 Posts: 655	Again - magnetic properties of a macroscopic iron is a tremendously complex problem, that can be approach with numerics. I'm not a specialist (so I wish to be corrected by ones), but: Local magnetic structure depends on the crystalline lattice (unobtainable in normal conditions "diamond" iron for example is even anti-ferromagnetic), including stress, grain size etc. There are dozens (!) of phases that correspond to basically chemically similar steels that have different crystalline structure (and btw hardening is the way to obtain a metastable crystalline structure). These lectures notes can be of help: http://neon.mems.cmu.edu/laughlin/pdf/252.pdf btw austenite is paramagnetic. It will greatly depends on local chemical decomposition. It's going to greatly depend on how uniform and fast the cooling is (uniform cooling leads to permanent magnetization alongside the local magnetic fields) In general there are some companies who measure conductivity and magnetic permeability in order to undestand how uniform their steel is. I don't want to refer to non-publicly available papers, so: http://doc.tms.org/ezMerchant/prodtm...df?OpenElement Now to the question "what happens to a sword": 1. Swords are intrinsicly anisotropic due to their shape. 2. They are usually completely non-uniform in their magnetic properties due to nonuniformities of steel they are made off, and nonuniform cooling (first of all - nonuniform quenching). Before I've the patterns of the dagger that were shown here I believed that such patterns can be produced by a weird external field. Now I think that because they are so damn non-uniform, and most of the dagger is not magnetized at all, the structure of this dagger should be tremendously non-uniform by itself, and I believe that conductance or X-Ray tests can prove that. Now to what happens to swords when they lie in Earth. I thought about who would've been interested in this, and realzied that mine detector peoples are. And indeed one can read a very interesting pamphlet over here: http://neon.mems.cmu.edu/laughlin/pdf/252.pdf] one should keep in mind that they are interested in a dipole moment i.e. the magnetic field procuded by objects very far away from the object itself, so it's much more uniform and depends on Earth's magnetic field in a much more direct way (since those guys quetly cool down underground), but we are interested in a local magnetization - quadrupole and up moments, that create these beautiful patterns.

27th February 2005, 10:18 PM	#5
Ann Feuerbach Member Join Date: Feb 2005 Posts: 133	Thanks. Lots of food for thought!

28th February 2005, 12:59 AM	#6
Rivkin Member Join Date: Dec 2004 Posts: 655	You are welcome. Btw, the thing I always wondered about archaeomagnetism people - do you take in mind only the total magnetization and connect it to the strength of the Earth's magnetic field at the time of making of the object, or you actually use oomf/rkmag to see how the object with such chemistry and shape would react to the applied magnetic field of such strength ?

28th February 2005, 02:49 AM	#7
Jim McDougall Arms Historian Join Date: Dec 2004 Location: Route 66 Posts: 10,281	Hello Ann, I would like to also welcome you to our forum, and to say what an honor it is to have you join us. I have had your outstanding work "Crucible Damascus Steel"for some time now, and it is brilliantly written! For someone such as myself who is fascinated with history, yet lost with the complexities of physics, science and technology, it is an entirely readable and well crafted blend of history with well explained technical details. This thread, as well as that of meteoric iron, have really become high profile and I am delighted that Jens posted them, as the knowledge and discussion has become irresistable! Aside from your extremely interesting article, most discussions on these topics can be quite dry to most of us in the lay world....but this thread keeps getting better, and your joining us is outstanding! All the best, Jim