Guide to heating and stirring 

Plate Material 

Hotplates and hotplate stirring can have a number of different plate materials, the most suitable of which depends on your application and the features you require of the plate. The plate material will influence the temperature range and uniformity of the hotplate. 


Ceramic plates will heat to very high temperatures and have excellent chemical resistance. However, they have poor temperature uniformity across the plate due to cool edges and cannot be used with any kind of reflective vessel or a sandbath. Aluminium plates are very robust and strong against knocks in the lab and have much better temperature uniformity as they offer all over heating of the plate. The surface however has less good chemical resistance and can be quite difficult to clean. The plate colour is not white and this may be a factor in colour work. Aluminium plates do not heat to as high a temperature as ceramic plates.


Enter ceramic coated aluminium plates which combine the best of both worlds – they offer good temperature uniformity across the plate along with a high level of chemical resistance given by the ceramic coating. As the plate itself is composed of aluminium, they do not heat to as high a temperature as strictly ceramic plates do.


You can read more information on the comparison of the plate materials to help decide which is the most appropriate for you here. 

Plate Material Feature Comparision Table: 


Sample Properties

Magnetic stirrers and hotplate stirrers work using an internal drive magnet. The magnetic stir bar that’s placed into your sample to be stirred will couple with the internal drive magnet and spin as driven by this. It is the strength of this coupling (along with that of the motor itself) that dictates the amount and type of sample that the stirrer is capable of working with. Most magnetic stirrers are only designed to work with small volume, low viscosity samples.

Sample Volume

  • The specifications will tell you what the maximum volume is. Usually as the size of the top plate increases, the maximum volume compatible will also increase.
  • The maximum volume of most stirrers is between 10-20L. 

Sample Viscosity

  • Generally, stirrers are only validated to stir a set volume of water, or liquid with the viscosity around that of water. In practise, most stirrers will work with no issues when a sample viscosity is no higher than 100mPas. If your sample is too viscous, the stir bar will become uncoupled and break away or the motor could burn out.
  • For samples with a high viscosity, we advise that you consider using an overhead stirrer which has a much stronger stirring action. 

Heavy Duty Magnetic Stirrer Suitable For Large Volume Viscous Samples

We recommend the use of an overhead stirrer for large volumes and viscous samples. However if you wish to use magnetic stirrer, the max drive system by 2mag has a maximum stirring volume of up to 250L and can cope with viscous liquids.  

 


Analogue or Digital Controls

  • Analogue hotplates and stirrers use a dial, usually with an arbitrary numbered scale for you to set your temperature and stirring speeds. These are designed for users who have applications that don’t need to be performed to exact specifications. You may wish to immerse a thermometer into your sample to get a measure of the temperature. Some analogue hotplate stirrers are compatible with external temperature controllers allowing accurate control of your sample temperature. 
  • Digital hotplates and stirrers feature an LCD or LED display where temperature and speed values are displayed and this make control much more accurate compared with analogue counterparts. Temperature values displayed will be that of the plate surface so consider using an external temperature probe immersed into your sample to get an accurate picture of the sample temperature. 

Stir Bar Selection

Once you have selected a stirrer, the next step is to select the most appropriate stir bar (also called flea). In the specification of the stirrer, it will usually detail the maximum size stir bar that can be used to with the stirrer (this maximum is dictated by the length of the internal drive magnet). Many stirrers will actually included a stir bar to get you started, and will be suitable for general purpose operation. Choosing a stir bar which is the right size and shape for your task can make the stirring action much more effective.%MCEPASTEBIN%

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