Long battery life. Fun chemistry experience at home

ENTERTAINING EXPERIENCES AT HOME
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Long battery life. Chemical experiments

Entertaining experiments in chemistry

Entertaining experiences at home / Chemistry experiments for children

Imagine what happened: you started an electrochemical experiment, assembled a circuit - and the battery suddenly "sat down", and there is no spare battery. How to be? But it's still half the trouble. Much worse when a flashlight goes out on a dark evening, and even in the forest. And what a shame if the batteries of a transistor receiver fail just at the minute when your favorite song is broadcast on the radio, or during the broadcast of a football match. But what can you do...

In the meantime, there are some things you can do. If there is no spare battery, do not rush to throw away the old one, but try to "revive" it.

Many modern batteries consist of elements of the manganese-zinc system. During operation, the negative electrode of these batteries - a zinc cup - gradually, but very slowly, dissolves, and the positive electrode is manganese dioxide MnO₂, is reduced to trivalent manganese hydroxide (its formula can be represented as MnOOH). It gradually covers the oxide grains, penetrates deep into the grains, and closes access to the electrolyte. Even half of the manganese oxide has not been used, and the element has already stopped working; zinc by that time remains even more, up to four-fifths! In a word, an almost good battery has to be thrown away.

But if you remove the "shell" of MnOOH, then the electrolyte will again be able to flow to the grains and the battery will come to life. But how to take it off? The easiest way is to tap the battery properly with a hammer or stone. Then the grains inside the cells will crack, and the electrolyte will again be able to penetrate into them. This method is not so hot as good, but in the forest, perhaps, the best can not be found ...

If the battery failed at home, then manganese dioxide can be activated much more efficiently. Punch a hole in the zinc cup of the battery with a nail and lower the battery into the water. The electrolyte in the cell is not liquid (that would be inconvenient), but thickened. It soaks in water, liquefies, and it is easier for it to penetrate to the grains of manganese dioxide. This simple trick allows you to increase battery life by almost a third. But it can be further simplified.

Filling the battery with water is not necessary. It is enough just to punch a hole in a zinc cup. The manganese oxide in the element is mixed with graphite powder - this is necessary in order to increase the electrical conductivity. As soon as air begins to flow in, graphite will absorb oxygen, and along with manganese dioxide, another positive electrode will appear - the so-called air electrode, on which oxygen is reduced. In a word, a simple nail turns a manganese-zinc element into an air-zinc one!

In fairness, let's say that after such a procedure, the battery will be discharged with a small current - these are the properties of a home-made zinc-air cell. But it will serve for a very long time.

And the last thing: we will make the old battery almost exactly like a new one. To do this, the battery must be charged with electric current, i.e., treat it in the same way as with a battery. The reaction in the battery is reversible, and MnOOH can turn back into MnO₂.

Note that not all batteries can be recharged, but only those in which the paste has not dried up and the case is not damaged. And it is necessary to charge not with the usual direct current, as batteries are charged. In this case, zinc will begin to deposit on the battery case in the form of branched dendrites, and very soon this will lead to a short circuit and the battery will fail. It must be charged with the so-called asymmetric current. To get it, you need to rectify the alternating current not completely, for example: include a rectifier diode in the circuit and a resistance (about 50 ohms) in parallel with it. The source voltage should be about 12 V, so you cannot use the current directly from the network, you need a step-down transformer.

Manganese-zinc cells can be charged up to three times, while their capacity drops very slightly. And small, so-called button elements (they use a mercury-zinc system) can be recharged up to ten times. But there is no point in punching them with a nail or knocking on them with a hammer - after the discharge, there are practically no active substances left in these elements.

Author: Olgin O.M.

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The problem of heat dissipation in the modern computer industry is acute: despite the reduction in the size of the transistor, the complexity of processors and graphics cores is constantly growing, and along with clock frequencies, which results in a corresponding increase in heat dissipation.

Single-slot video cards of a fairly serious level are becoming less and less common on the market, and bulky LSS have firmly taken the place of air coolers in enthusiast systems. But the "Jumping Droplets" technology (jumping droplets), as its developers promise, can significantly increase the efficiency of cooling systems, especially in the case of hot spots.

The new method works in much the same way as cicadas protect their fragile wings from getting wet. The fact is that with sufficient hydrophobicity (the ability to repel moisture) of the surface, the combination of two tiny droplets of water generates enough energy for the resulting larger drop to break away from this surface itself. The "cicada effect" has been known for quite a long time and is well described in science, but it was the first time that it was possible to apply it for cooling microelectronics. As was found out in the joint work of Intel and Duke University, this property can also be used to cool modern microchips.

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The head of the team, Professor Chen Chuanhua (Chuan-Hua Chen) is sure that soon the new technology will be standardized, and from this point to the release of the first workable cooling systems based on the new principle is one step.

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