Magnetic fluid

People have long tried to obtain magnetic fluids by shaking fine powders of ferromagnetic material in water, oil and other liquids. But such a magnetic fluid disintegrated, and the powder settled: it was too large and heavy. Only in the 60s. XX century the ferrite powder was ground so well that, being poured into a mixture of kerosene and oleic acid, it ceased to precipitate. Humanity has received a liquid magnet!

It turned out that the magnetic fluid has new, very interesting properties

What's the matter here? It turns out that the powder particles were already so small that the thermal (Brownian) motion of the molecules prevented them from settling, and a colloidal solution was obtained, which is known to us, for example, as egg white and stationery glue.

It turned out that the magnetic fluid has new, very interesting properties. First of all, a magnetic fluid is not a ferromagnet, but a powerful paramagnet. If you pour a magnetic fluid into a glass and bring a magnet from below, then it forms an antinode that is completely unlikely for liquids - a bump, almost solid to the touch. If you bring the magnet from the side, then the liquid will climb up the wall and can rise as high as you like behind the magnet. If it is poured over the surface of the water, then a magnet immersed in the water can quickly collect it on the pole of the magnet. It is bad, if it is a permanent magnet, it will not be so easy to "tear off" the tenacious liquid from the magnet. This seems to be a clever trick.

Where can magnetic fluid be used? Now many useful applications have been invented for it: for sealing shafts and pistons, for "eternal" lubrication, for collecting oil spilled on water, for enriching minerals, for treating and diagnosing many diseases, etc.

Let's talk about the most interesting and technically promising applications of magnetic fluid. The most widely used magnetic fluid is to seal gaps between moving parts of machines. Most often, rotating shafts need to be sealed. When the shaft is ferromagnetic (for example, steel), then a ring magnet with two washers is put on the shaft with a gap, into the gaps of which with the shaft - in one or both - magnetic fluid is poured. It immediately rushes into the gap, where the magnetic field strength is maximum, and freezes there in a thick gelatinous mass.

Magnetic fluid, especially oily fluid, can be successfully used as "eternal" lubricant, filling with it both sliding and rolling bearings, even gearboxes and gearboxes, holding it in the required place with magnets.

The question arises: can a magnetic fluid containing a suspension of magnetic particles be a lubricant? Will it play the role of emery powder? It turned out that no, and this has been proven by numerous experiments. The size of the particles is so small that they do not in any way affect the cleanliness of the surface of the rubbing parts.

The magnetic fluid can play the role of not only a lubricant, but also the bearing itself. If, during the rotation of the shaft, it is brought into rapid rotation with the help of special notches on the surface of the shaft, then even heavily loaded shafts will float up in it. Such bearings are called magnetohydrodynamic bearings.

Magnetic fluid has another amazing, truly unique property. In it, as in any liquid, bodies less dense float and bodies more dense than itself drown. But if you apply a magnetic field to it, then the drowned bodies begin to float. Moreover, the stronger the field, the heavier the bodies rise to the surface. By applying a magnetic field of varying strength, it is possible to make bodies float up with a given density. This property of the magnetic fluid is now used for ore beneficiation.

Magnetic fluid is also used to collect various petroleum products on the surface of seas, oceans, lakes. A small amount of magnetic fluid is sprayed onto the spilled slick from a helicopter, which quickly dissolves in the oil slick, then strong magnets are immersed in the water, and the slick begins to shrink to a point, and here it is pumped out by pumps.

And what a space for magnetic fluids in medicine! Let's imagine that some medicine should be used to treat a certain part of the body, without affecting the rest of the body. For example, you need it to concentrate in any organ of a person, and the blood carries it throughout the body. After mixing the medicine with a magnetic fluid, it is injected into the blood, and then a magnet is placed near the sore spot. Naturally, the magnetic fluid, and with it the medicine, will soon gather near the magnet and will act only on the diseased part of the body.

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