There are a variety of stirrers available for laboratory use, each having their own qualities which make them more suitable for certain applications than others. Below is an outline of the types of stirrers available and what they are more suitable for:
Magnetic stirrers use a rotating magnetic field to cause a stirrer bar (of flea), immersed within a liquid, to spin and therefore stir.
Most magnetic stirrers are suitable for small volumes of low viscosity. However there are some models which have been developed to handle large volumes and high viscosity.
The plates of magnetic stirrers are generally made of either ceramic or stainless steel.
Ceramic top hotplates have excellent chemical resistance, so are ideal if you are working with corrosive chemicals which may splash onto the plate surface, and the white surface also means they are good for titrations or other work where clear visibility of colour is essential.
A stainless steel top plate does not produce eddy currents (like aluminium) and so ensures a very powerful coupling and stirring action.
Stirrer hotplates are stirrers combined with a hot plate. Either function can be use on its own on combined with each other.
The main difference in the variety of stirrer hotplates are what material the top plates are made from:
Ceramic top plates have excellent chemical resistance, so are ideal if you are working with corrosive chemicals which may splash onto the plate surface. They can offer
higher temperatures of up to around 450°C and are easy to wipe clean.
Again, as with the magnetic stirrers, the white surface also means they are good for titrations or other work where clear visibility of colour is a must.
Ceramic plates also have cool edges, which is useful for operator safety but may not be suitable if you need heating all over the plate surface.
Ceramic hotplates must only be used to heat glassware, do not heat liquids in metal containers on a ceramic hotplate. They are also not suitable for sand baths and any vessel which will reflect heat
back onto the surface causing cracking.
Aluminium top plates are more robust and will withstand accidental knocks better than ceramic plates.
They offer a consistent temperature all over the plate and become hot right up to the edges of the plate surface.
Metal top hotplates can also be used to heat metal vessels, so if you are working with stainless steel beakers or other metal containers this is the best choice.
They are used more commonly for large volume and viscous solutions.
The variety of paddle types can be used for different applications as they create different stirring motions:
Low to medium speed, gentle mixing for minimal turbulence. Tangential flow.
Medium to high speed, used in round vessels with narrow necks. Creates axial flow.
Medium to high speeds, used for drawing the material to be mixed from above. Minimum shearing forces. Reduced risk of injury to operators when stirring elements make contact with the vessel. Creates axial flow.
Medium to high speeds. For drawing the material to be mixed from the top and the bottom. High turbulence, high shearing forces, particle reduction, radial flow.
Medium to high speeds. Flow efficient design with minimal shearing forces. Draws material from top to bottom, axial flow.
Submersible Stirrers– sealed stirrers which are suitable for submersing in water or oil and can be used with a wide temperature range. Ideal for use in water baths, ovens or incubators.
Biological Stirrers- specifically designed for stirring biological samples such as cell cultures. Provide gentle, heat free stirring and are dust and germ proof.
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