A magnetic stirrer or magnetic mixer is a laboratory device that employs a rotating magnetic field to cause a stir bar (also called "flea") immersed in a liquid to spin very quickly, thus stirring it.
The rotating field may be created either by a rotating magnet or a set of stationary electromagnets, placed beneath the vessel with the liquid. Since glass does not affect a magnetic field appreciably (it is transparent to magnetism), and most chemical reactions take place in glass vessels, magnetic stir bars work well in glass vessels.
Magnetic stirrers are often used in chemistry and biology.
They are preferred over gear-driven motorized stirrers because they are quieter, more efficient, and have no moving external parts to break or wear out (other than the simple bar magnet itself).
Because of its small size, a stirring bar is more easily cleaned and sterilized than other stirring devices. They do not require lubricants which could contaminate the reaction vessel and the product. They can be used inside hermetically closed tools or systems, without the need for complicated rotary seals.
Magnetic stirrers may also include a hot plate or some other means for heating the liquid.
Choosing a Magnetic Stirrer
A device that can be found in almost every laboratory and is used to mix liquids and solutions in a simple way, without the need for a stir bar.
-In any laboratory in the life sciences, chemistry can be found magnetic stirrers that are used for mixing of solutions without the need for manual mixing of a laboratory worker.
-Magnetic stirrer suitable for mixing liquids in tools 4 cm to 40 cm in diameter.
In small tools such as test tubes or small vials with a diameter of 30-40 mm it will not be possible to stir.
In large tools with a diameter of over 50-60 cm it is not possible to perform an effective stirring that will stir all the liquid in the tool and not just in the center.
Considerations in choosing a magnetic stirrer
-The first consideration is, what is the volume of the solution you want to stir?
The larger the amount of liquid, the greater the need for a magnetic stirrer with a large motor and a larger work surface.
Magnetic stirrers with DC motors are designed for stirring small amounts usually up to a maximum of 1 liter or less, Changing viscosity during stirring
Will cause their speed to slow down, impair the quality of the stirrer and may cause the engine to burn out.
For stirring of quantities greater than 1 liter, it is advisable to work with a magnetic stirrer with an AC motor
Recommended magnets length:
For stirring 250 ml, a 25 mm long magnet is recommended
For stirring 600 ml, a 40 mm long magnet is recommended
For stirring 2 liters, a 60 mm long magnet is recommended
For stirring 3-10 liters, a magnet with a length of 70 mm is recommended
For stirring 10-30 liters, a magnet 80 m long is recommended
-The second consideration in choosing the magnetic stirrer is the diameter of the tool in which the liquid is located.
- The stirring speed is 100-1200rpm. In cases where slow stirring is required, a magnetic stirrer should be selected for a low speed range of 40-200rpm.
-In places where a large number of tools are mixed, multi-position stirrers of 4,6,10,16 positions are used
How a magnetic stirrer works