I was thinking of getting some small rare earth magnets to keep a stubborn metal door closed. I have tried Velcro and some standard bar magnets, these kind of work but it would help if they were a bit stronger.
On mythbusters they have used rare earths several times and imply they can be very dangerous. Is this so how powerful are they really, does it depend upon size?
Any magnetic experts here? What is a rare earth magnet and how is that different than the small bar or kitchen magnets you can find anywhere.
Rare earth magnets can be dangerous, yes, but also very useful for applications like you describe (and many, many other applications).
The three main dangers:
– getting pinched – rare earth magnets can be much stronger than you expect, and even fairly small ones can give you a good bruise if you’re not careful.
– getting shrapnelled – they can be brittle, and if you let them snap together, they can break. The pieces tend to be sharp.
– swallowing them – little kids eat everything. Swallowing *one *isn’t usually dangerous, but if you swallow *two, *they will cause serious problems if they pin together bits of your innards.
Pretty much it’s just a matter of size. The big magnets that they used on Mythbusters could conceivably generate enough force to crush a hand. Also, they can chip and shatter. This isn’t an issue for any ordinary magnets however.
I got some neodynium rare earth magnets from here:
They are very strong, and the bigger ones are dangerous. I can’t pull the 1/2"x 1/2’x1/4" one straight off the fridge - I have to slide it to the edge. The 1" cube one, held in my palm, will stick my hand to my filing cabinet!
They do sell coated magnets which will reduce the risk of shrapnel.
“The term “Rare Earth” derives its name from the misconception on their discovery that some of the elements exhibit low natural abundancy. However, with the exception of the highly-unstable promethium, the rare earth elements are found in relatively high concentrations in the earth’s crust with Cerium being the 25th most abundant element in the earth’s crust at 68 parts per million.”
From Wiki: Rare-earth element - Wikipedia
Neodymium Iron Boron magnets are more fun than even grownups should be allowed to have. They are strong enough to dimple water, hold a bismuth plumb bob noticeably out of vertical, and levitate a flake of pyrolytic graphite. Kjmagnetics is a great place to order them from, and I have a total of maybe 5 lbs of their NIB magnets.
I think anybody playing with NIB magnets bigger than an acorn should be a little nervous, like you’d be when setting a mousetrap. They can shatter and get in your eyes and the fragments are kind of sharp. But, it’s not like they are too dangerous to enjoy. Just, imagine them shattering and don’t do things where that would hurt you.
Rare earths are elements in a couple of families that are oddly similar to each other in a chemical sense. The elements within a family act a little bit like they are all one element. They are mostly not very rare. For some reason, Florida beach sand is one of the few sources of them, though there seems to be a plentiful supply there. One of my favorite rare earths is Gadolinium, whose Curie point is between room temperature and body temperature. This means it is ferromagnetic, and a magnet can easily pick it up, when it is cool, but not when it is warm. It also exhibits a big magnetic cooling effect. Moving a chunk near a powerful magnet cools it. And, its salts are used as a contrast agent for MRI scans, though I don’t know exactly why. Guess it must have something to do with these magnetic properties?
All the rare earth magnets are ceramics, meaning they are metal oxide powders that have been compressed and heated (or “sintered”).
I have an enormously powerful NIB magnet that Fierra bought me sticking to my server rack - through a box and insulation. It is powerful enough that I did get a nasty pinch and did have a nail come flying at me once from a few inches away (ouch). That’s the danger they’re talking about here.
Very insightful explanation. However, you may have a mistake here as rare earth magnets are not ceramics, merely containing oxide. They are actually sort of metal compound. When get oxidized, rare earth magnets will lose their magnetic strength. So most rare earth magnets are plated with nickel or other protective coatings.
the magnetic attraction can be such that they are hard to remove from the metal or that it might shatter if placed near another rare earth magnet and allowed to smack together.
Right you are. Neodymium iron boron, and samarium cobalt, and as far as I know all the other rare earth magnets, are made entirely of metal and are not ceramics. Don’t know where I got that misinformation from. Thank you for fixing this!
The “scare 'em straight” story I was given in high-school physics class was that some kid from a previous year put one in his mouth and another on his cheek. They clamped together strongly enough that the only way to remove them was by making an incision through his cheek (presumably with a non-magnetic scalpel) to pull them through.
