pruning away
Steel (and metals, in general) have a grain structure that
changes with cold working and heat history. Spinel
(ferrite) is a ceramic material that changes grain structure
only with sustained heating well above red heat. Just
heating ferrite through its Curie temperature (where it
demagnetizes, completely) doesn't change its grain structure.
Agreed, that's what I've been taught and believe.
Then I wonder how important grain structure really is? In small
transformers (less than 5+ KVA) they talk about the importance of
grain orientation for maximum efficiency. But with larger
transformers and motors the physical strength or hardness begins to be
a consideration. I guess (never worked with big transformers) if you
have a lamination that is a few feet long, you'd worry about it
bending before you got it secure in the core - so perhaps (I really
don't know, just conjecture) the relatively high efficiency intrinsic
to big, versus little, is more important.
I did work with a small - wind the transformer to spec - company some
time ago. My boss (only 25 people) kept mentioning his claim to fame
was not taxing the iron too much - we used some grain oriented steel
with moderate cost for most stuff, and stacked the laminations at 1X1,
and our clients would rave about how cool the transformers ran. I
assumed, back then, that not everybody was using grain oriented steel.
Only if the magnetic field strength was high enough to push
it all the way to saturation. I think that the external
field from a neodymium iron magnet is not quite high enough.
You haven't re magnetized it, but you haven't proved that it
can't be re magnetized with a high enough field.
It does reverse polarity - even faster or with less effort than the
regular ceramic magnets do. It is the regular ceramic change polarity
about 1.25" from the neodymium and get sucked in, the wimpy heated
magnet changes polarity at ~2" and is still in my fingers.
Maybe partial magnetization is misleading - the heat treated one is
weakly magnetic.
That is a pretty good test. You originally said that the
heat did not eliminate all the magnetism, but only weakened
it. Does that weakened magnetism reverse when you apply the
external magnet?
Yes, it does indeed reverse, and some distance out from the strong
magnet, compared to the regular magnets.
Perhaps. But how did they make the ferrite in a kiln,
originally, without making it soft? Perhaps it was fired in
a low oxygen atmosphere (or some other gas than air), and
heating it in air has changed its chemical makeup. The
oxygen content of ferrite has a big effect on its properties.
Well, I don't know. One of the mysteries reserved for ferrite makers?
Working iron makes it hard. Perhaps there's some process that
converts iron billet or ferric oxide to powder without hammering on
it? Like spraying molten metal into an inert or hydrogen atmosphere?
Then how does one make hard versus soft ferrite? Maybe hard ferrite
is harder to make, and it has to be processed in a different way to
make ceramic magnets.
I had been assuming they took metal particles and heat and fuse them
like other sintered materials, now I'm not too sure. Why call it
ceramic? does it contain clay? An "off the wall question" is leading
to more questions.
So far Googling hasn't worked - too much commerce or the wrong search
words.
You need to do an inductance test of a coil with either the
unheated ferrite or the heated ferrite in it, as a core.
I haven't gotten any results I trusted with high frequency cores. The
place I worked had a "National Radio" (I think) impedance bridge that
worked very well - my home attempts haven't been trustworthy. I do
trust the 60 hertz power line tests, but not any from my audio signal
generator.
You may be right.
I would try heating it with a propane torch on a piece of
fire brick.
Not sure the propane torch is up to the task. I may have a spider
living in the works. Left it outside one night . . . now the flame
looks weak. The barbeque, on the other hand, will definitely exceed
1,000 degrees in the coal basket for more than enough time. Anyhow
the torch is probably OK but low on fuel so I'll use it till it dies.
I'm living very frugally (both a necessity and environmental awareness
predisposition) so I work the experiments in when they don't interfere
with life.
I don't believe in God - man makes the mistakes and man should be
fixing them, not praying.