HP550-S Hotplate Stirrer Ceramic Plate 550°C (Fix Speed)

A magnetic stirrer or magnetic mixer is a laboratory device which uses a rotating magnetic field to cause a stir bar to spin very quickly. The rotating field may be created either by a rotating magnet or a set of stationary electromagnets, placed beneath the vessel with the liquid. It is a very useful and convenient method of stirring liquids and suspensions and it's crucial in air-free processes.

Uses and limitations

Magnetic stirrers are often used in chemistry and biology, where they can be used to stir hermetically closed vessels or systems without the need for complicated rotary seals.

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). Magnetic stir bars work well in glass vessels commonly used for chemical reactions, as glass does not appreciably affect a magnetic field.

The limited size of the bar means that can only be used for relatively small experiments, of 4 litres or less. Stir bars also have difficulty in dealing with viscous liquids or thick suspensions.

For larger volumes or more viscous liquids, some sort of mechanical stirring (e.g., an overhead stirrer) is typically needed. In synthetic chemistry, a combined stirrer/heater, equipped with a built-in temperature control mechanism and temperature probe.

It is commonly used with a heating bath (commonly oil, sand, or low-melting metal) or cooling bath (commonly water, ice, or an organic liquid mixed with liquid nitrogen or dry ice as coolant), allowing reactions vessels placed in the bath to be maintained at temperatures between approximately –120 and 250 °C.

Which type of lab stirrer is best for you

There are several points to consider when buying the best laboratory stirrer for your needs.

Volume & capacity

Typical are rated for volumes as high as 20 liters, while the top volume of overhead stirrers often range from 2 to 80 liters and up. Maximum volumes for both types of stirrers, unless otherwise specified, are based on water.

Sample viscosity

Consider viscosity: the stirrer’s bar has no direct connection to its motor, so fluid resistance may prevent mixing of higher viscosity samples.

Mixing speed

Take desired speeds into account, as well. For very high or very low rpm settings, overheard stirrers boast a wider range (12 to 6,000 rpm). The low speeds for often start at 100 rpm. In some cases, the magnet could decouple at the stirrer’s highest speeds, leaving the stir bar bouncing around the edge of the beaker’s base instead of creating flow.