Stir Bars
Magnetic stir bars, also known magnetic followers, magnetic stirrers or magnetic fleas, are small, cylindrically-shaped laboratory devices used with magnetic stirring plates to stir liquids held in suitable vessel or container such as a beaker, flask or bottle. The stir bar is introduced into the liquid, the container is placed on a magnetic stirrer, the stirrer is switched on and the bar rotates by magnetic attraction stirring the liquid. They offer the unique attraction of being able to operate inside completely sealed containers.
Stir bars typically have a magnetic Alnico (aluminium-nickel-cobalt) core coated in a protective, chemically-resistant and inert covering such as PTFE (most commonly), or glass. They are manufactured in a range of lengths and diameters to accommodate different sample sizes and vessel capacities, ranging from 1.5mm in length often up to 160mm.
Although most stir bars are smooth, round-ended cylinders, some have different cross-sectional shapes (octahedral or triangular). Others may also have a central circumferential pivot ring which helps the bar spin more effectively and to help centre it in the middle of the vessel during mixing. Other bars are shaped as ovals, crosses, cross-headed discs or spheres, all of which are designed to provide optimal turbulence and spin efficiency.
Magnetic stir bar kits offer a selection of sizes and shapes in one package to accommodate different requirements.
Magnetic stir bars have several purposes in the laboratory:
- For ensuring that solutions are well-mixed during titrations
- For dissolving solids
- For mixing miscible liquids
- For maintaining particulates in suspension