What is a Magnetic Stirrer?

A magnetic stirrer also known as magnetic mixer is a kind of laboratory equipment which is mainly used for stirring or heating stirring in low-viscosity liquid or solid-liquid mixing experiments. A rotating magnetic field is generated under the container plate, and the principle of homosexual repulsion and heterosexual attraction is used to push the magnetic stirring rod in the container to rotate rapidly, thereby achieving the purpose of stirring. The plate usually has a heating function to meet more experimental needs.

The lab magnetic stirrer is usually used in the chemical and biological fields, and it is suitable for airtight containers or closed systems. It doesn’t need a complicated rotating seal structure like an electric mixer, and there is no need to maintain the rotating motor frequently or replace easily worn parts. It is quieter, more efficient, more wear-resistant than electric stirrers, and is not easily damaged (except for the simple bar magnet itself). The magnetic stirrer is more suitable for glass containers, because glass does not significantly affect the magnetic field, and it is easy to observe the stirring.

The stir bar is magnetic, also called magneton. It provides stirring function in the liquid, and its power is provided by a rotating magnet or electromagnet assembly under the device panel. The magnet is usually coated with polytetrafluoroethylene (PTFE) or less glass coating. The coating must be chemically inert and not contaminate or react with the reaction mixture in which it is located. The glass coating is used in liquid alkali metals (except lye) and alkali metal solutions.

The stir bar is a bar magnet with a raised ring in the middle to rotate around the center. Its cross-section is usually hexagonal or octagonal (or directly jujube-shaped), and there are also various special shapes for more effective mixing. Its length varies from a few millimeters to a few centimeters. Because the stirring rod is small in size and simple in structure, it is easier to clean and disinfect. At the same time, the limited size of the bar also means that the magnetic stirrer can only be used for small experiments of 4 liters or less. The magnetic stirrer may also include a heating plate or other devices for heating the test solution. The agitator is also difficult to handle viscous liquids or suspensions. For more viscous liquids or solid-liquid mixtures, some kind of mechanical stirring is usually required.

In an ideal situation, the stir bar will rotate by magnetic force. However, within a certain range, it will enter a metastable state, making it spin irregularly in the bottom of the bottle. Its trajectory does not necessarily rotate on a circle. This phenomenon occurs when no solution is added to the flask or various low-viscosity fluids are added. It is normal. When the stirring bar and the liquid reach a certain speed and frequency at the same time, it will tend to stabilize.