A Brief Introduction to What Magnetic Stir Bar is All About

What is Stirrer? This is a simple enough question one might think. Since just about any device can be used as a stirrer. Although we usually associate stirring with some we generally do in the kitchen while cooking, this simple technique of stirring has several other applications as well.

For example, a chemical laboratory often requires to stir either a combination of chemicals or some chemicals in order to have the necessary effect or prepare them for further use. However, some of these chemicals need to be stirred for more than 8 to 10 hours hence it is not practical to do it manually. That is where magnetic stirrers come in which is effectively has the same concept but is not manual. Hence the real question here is actually “What is a Magnetic Stirrer?

Introduction to Magnetic Stirrer

A magnetic stir bar is a coated magnet that can be used for the purpose of stirring liquids. One of the main advantages being that the container of liquid does not have to be open in order to stir it and the container can even be completely sealed.

The most common application of a magnetic stirrer is in a chemical or biological laboratory for the purpose of research (often in the field of medicine). In addition to which enthusiasts often use it in their home brewers too.

Working of a Magnetic Stir bar

magnetic stir bar

The way the magnetic stir bar works is that a magnet is placed inside a container. This container will usually be filled with the fluid that is to be stirred. The second magnet is placed underneath the container since both the magnets need to work together. The magnet underneath the container will be attached with a motor. Thus when this magnet spins the one inside the container will also spin along with it. The distance between the two has to be set appropriately though.

The Neodymium magnetic stir bar

The stir bars are generally made using either ceramic or Alnico magnets. Ceramic magnets are common and comparatively inexpensive. On the other hand, ceramic magnets are the strongest kind of magnets available. The Neodymium magnets are very stronger magnets compared to the Ceramic magnets which have only 8 to 10% of the pull force.

The Neodymium magnets are also stronger than the Alnico magnets which are made from Aluminium, cobalt and nickel. They have about 25% the strength of a Neodymium magnet although they but are stronger than the Alnico magnets.

The Alnico magnets are often used for magnetic stirrers. The main advantage being that they can be used for high temperatures. However, the most popular one is the Neodymium magnet for a magnetic stirrer. The main reason for this is the coercivity. The coercivity of a magnet is how easily they demagnetise and become week. The Alnico magnets have a very low coercivity, while the Neodymium magnets have a high coercivity and in addition to that are also stronger than both Ceramic and Alnico magnets.

How strong are the magnets used in a Magnetic Stirrer?

Magnetic Stirrer

The maximum torque for a magnetic stir bar is the most relevant measure of strength for the magnet. The reason being that the greater the torque the greater the stirring ability.

However, there are several other factors that affect the strength of the magnet. These factors have been listed here:

  • The size and strength of a stir bar magnet is an important factor.
  • The bigger the magnet the stronger it will be.
  • A magnet that is big in size needs a bigger space. Since it is bigger it will push more liquid when placed inside the liquid container. Thus the speed at which it will turn depends on size of magnet and size of container too.
  • The strength also depends on the configuration of the magnets underneath the container. This can be 2 magnets at the end of the stir bar or simply as single long magnet.
  • The distance between the two magnets; the one underneath the container and the one inside also plays a crucial role.
  • The viscosity of the fluid plays an important role too.
  • The RPM (rotation speed) too is relevant.

How Neuation can help?

Neuation

Neuation is firm that supplies many different laboratory equipment. The magnetic stirrer is one of them. The magnetic stir bar from Neuation is coated with PTFE material that makes them more durable. There are several types of Magnetic stirrers available depending on the application.

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