PTFE Stir Bar Laboratory Mixed Magnet with Pivot Ring Feature:
Item No. MSB-PR series
Material Polytetrafluoroethylene (PTFE)
Color White
Shape Cylindrical with Pivot Ring
Size Custom
Magnetic stirring bar set consists of 10 of the most standard bars, complete with crystal clear box.
The stirrer magnet is a bar magnet encapsulated in a material which protects the magnet and prevents contamination of the liquid medium.
The core of the stirrer magnet is usually Alnico V, a less used alternative is Samarium-Cobalt. Due to its exceptional chemical and thermal (-200 °C to +260 °C) properties, Polytetraflouroethylene is the most preferred encapsulant. It can easily be processed, is readily sterilised and satisfies FDA and USP Class IV requirements.
In principle, it is difficult to find the most effective magnetic stirring bar for a particular application, but important factors are the vessel shape and the viscosity of the stirring medium. In a petri dish, a long stirring bar at low speed will be effective, in a round bottom vessel egg-shaped (oval) magnetic stirrers will be a suitable choice. The ideal configuration is where the magnet of the stirring bar and the magnet of the drive are of equal length and with a minimum distance between them.
Why use a neodymium magnetic stir bar?
Many stir bars are made with ceramic or Alnico magnets. Ceramic magnets are inexpensive and common, but not nearly as strong as a neodymium magnet. They have only about 8-10% of the pull force.
Alnico magnets are made from aluminum, nickel and cobalt. They are stronger than ceramic magnets, about 25% of the strength of a neodymium magnet of the same size. They have been commonly used for stir bars, especially for high temperature use. The downside is that Alnico magnets have very low coercivity, meaning they are easiest to demagnetize. If exposed to a strong magnetic field, they can become weaker. They are often sold in pairs to avoid this, though they can lose strength through mishandling. PTFE Magnetic Stirring Bar
Neodymium magnets are stronger than ceramic and Alnico magnets, and have the highest coercivity of all permanent magnet types. If you keep the temperatures of these N42H grade Stir Bar Magnets below 248°F (120°C), they should retain their magnetization practically indefinitely.
Prod # Description Unit
MSB-PR-1 Stir Bar, Pivot Ring, PTFE, 15 x 4.5mm OD
MSB-PR-2 Stir Bar, Pivot Ring, PTFE, 12 x 4.5mm OD
MSB-PR-3 Stir Bar, Pivot Ring, PTFE, 20 x 6mm OD
MSB-PR-4 Stir Bar, Pivot Ring, PTFE, 25 x 6mm OD
MSB-PR-5 Stir Bar, Pivot Ring, PTFE, 35 x 6mm OD
MSB-PR-6 Stir Bar, Pivot Ring, PTFE, 45 x 8mm OD
MSB-PR-7 Stir Bar, Pivot Ring, PTFE, 40 x 8mm OD
MSB-PR-8 Stir Bar, Pivot Ring, PTFE, 60 x 9.5mm OD
MSB-PR-9 Stir Bar, Pivot Ring, PTFE, 50 x 8mm OD
MSB-PR-10 Stir Bar, Pivot Ring, PTFE, 70 x 9.5mm OD
MSB-PR-11 Stir Bar, Pivot Ring, PTFE, 30 x 6mm OD
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