[HN Gopher] What Materials Are Magnetic?
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What Materials Are Magnetic?
Author : rwmj
Score : 32 points
Date : 2024-07-18 17:18 UTC (5 hours ago)
(HTM) web link (sciencenotes.org)
(TXT) w3m dump (sciencenotes.org)
| FrankWilhoit wrote:
| Their example of nickel is a U. S. five-cent coin. Nickel is
| ferromagnetic, but the coin is 75% copper and a magnet will not
| pick it up.
| barelyauser wrote:
| But they can be picked up with right kind of electromagnetic
| arrangement[0].
|
| [0]. https://youtu.be/7ZeBWJLRXqM&t=1231
| m463 wrote:
| I have a shrunken nickel from these folks:
|
| https://www.capturedlightning.com/frames/interesting1.html
|
| Don't know if the copper figures into the shrinking...
| analog31 wrote:
| Interestingly, the Canadian coins are the same dimensions, but
| are magnetic. US vending machines used to have a magnet that
| would deflect Canadian coins into the coin return slot.
|
| When I was growing up near Detroit, merchants took US and
| Canadian coins interchangeably, and gave both back out as
| change. But the Post Office was strict about it. I managed to
| collect a set of King George coins -- at least the smaller
| ones.
| eth0up wrote:
| And some Canadian coins used be actual sterling, until they
| went to 80%ag. I think US coins were always 90.
|
| A few nickels from the early 1940s were, I think, 43% Ag, due
| to wartime metal shortages.
|
| But man, if you ever find a 1943 copper wheat penny in good
| to fair condition, you can think about retiring. The 1943
| steel penny goes for about < $2.00 on average.
| bediger4000 wrote:
| Tungsten carbide is magnetic. I bought a "tungsten" cube from
| some shoddy Amazon vendor. It's a lot denser than steel, but not
| as dense as pure tungsten. It is magnetic. The density of the
| cube is in the range of tungsten carbide.
| foobarian wrote:
| I got one of those too, and it came with a manifest showing
| that there is about 5% of nickel in the composition so not too
| surprising.
|
| I would certainly be surprised if they could manufacture a pure
| cube (> 99.9%) for the price they sell it at :-)
| matsemann wrote:
| What are you using the cubes for?
| cyberax wrote:
| > Tungsten carbide is magnetic
|
| Pure tungsten carbide is not. You just got some magnetic
| contaminants in it.
|
| This has is a good test for fake "gold" that can consist of
| tungsten core with a thin film of gold on top. It's pretty much
| impossible to get pure tungsten, so such "gold" ends up being
| magnetic.
| RavingGoat wrote:
| My smile of course :)
| bsmith89 wrote:
| Most interesting sentence:
|
| > 304 stainless steel isn't normally magnetic, but it becomes
| partially ferromagnetic if it's bent at room temperature.
|
| Anyone have a lay-person explanation for this?
| koolba wrote:
| Not a physicist, but I'd guess that bending the metal causes it
| to heat up, which in turn could make it easier for electrons to
| align and respond to magnetic waves.
| Tuna-Fish wrote:
| Nope, heating would make it non-magnetic again.
|
| It's the act of physically working it that makes it change
| structure.
| Keyframe wrote:
| you're only right about not being a physicist. sorry, had to
| have a laugh. What made you draw that conclusion?
| Tuna-Fish wrote:
| Iron exists in many different crystal structures in different
| kinds of steels. Some of these forms are magnetic, others are
| not. When you work the metal, such as by bending it, you can
| cause it to change from one structure to another.
|
| 304 is an austenitic stainless steel, and austenite is non-
| magnetic. But when it's cold worked, it turns into martensite,
| which is harder and magnetic. If you anneal it by heating it
| and letting it cool, it turns back into austenite.
| riiii wrote:
| Interesting. Do you know if it affects it's anti-rust
| properties after you work it / make it martensite?
| dvh wrote:
| Liquid oxygen is magnetic too (I think para in this case)
| mankyd wrote:
| That's mentioned at the bottom: "However, liquid oxygen and
| boron fullerenes (B80) are paramagnetic."
| m463 wrote:
| Wonder if you could use that to separate gasses.
|
| I also wonder about "sorting" atoms/molecules like Maxwell's
| demon:
|
| https://en.wikipedia.org/wiki/Maxwell%27s_demon
| DoingIsLearning wrote:
| Very cool, the site's entire 'materials' archives is really
| interesting as a layman in Materials Science. [0]
|
| This kind of reminded of the sense of wonder of reading through
| Encarta entries in the late 90's and how I assumed the internet
| would look like in the future.
|
| [0] https://sciencenotes.org/category/chemistry/materials/
| SigmundA wrote:
| So aluminum and copper are listed as not magnetic yet powerful
| magnets are used to separate them from non metallic materials in
| recycling? Seems like a semantic argument.
|
| https://en.wikipedia.org/wiki/Eddy_current_separator
| wtallis wrote:
| > Seems like a semantic argument.
|
| That kind of phrasing usually indicates someone doesn't
| understand or is rejecting a meaningful and useful distinction.
| Is that what you intended to do here?
|
| The article seems to be pretty clear about how there are
| several different types of magnetism that can be exhibited by
| materials, and appropriately classifies various materials.
| Nothing about the existence or mechanism of eddy current
| separators is a counterexample to anything in the article.
| SigmundA wrote:
| "Magnetism is the class of physical attributes that occur
| through a magnetic field, which allows objects to attract or
| repel each other."
|
| Aluminum is repelled by a strong magnetic field, hence the
| use of ECS, plastic is not. Aluminum is not Ferro-magentic it
| does however seem to be magnetic depending on the definition.
|
| https://en.wikipedia.org/wiki/Magnetism
|
| The article itself on contradictory showing aluminium as
| nonmagnetic then classifying as paramagnetic, which is a type
| of magentisim, which is it?
| eth0up wrote:
| I'm not a kid, but resemble one when I get a hold of a
| copper tube and strong neodymium magnet. Probably my
| favorite toy. I'm kind of glad I have only a kid's
| understanding of it.
| csours wrote:
| https://hackaday.com/2022/09/01/iron-nitrides-powerful-magne...
|
| Iron Nitrides
| mjfl wrote:
| At the microscopic level, what determines whether a given set of
| valence elections has an excess spin, and thus an excess magnetic
| moment, is still determined by an empirical set of rules, called
| Hund's rules, instead of from first principles, iirc:
|
| https://en.wikipedia.org/wiki/Hund%27s_rules
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