Electrolytic preparation

About Electrolytic Preparation

A fast and efficient method.

Electrolytic preparation is a fast and efficient method for metallographic preparation providing a deformation free surface, whereas mechanical grinding and polishing tends to leave a thin deformation layer at the surface.

Using the electrolytic polishing equipment, the specimen is configured as the anode in a suitable electrolyte, and material is removed by controlled dissolution of the surface of the specimen. Electrolytic polishing can be followed by an electrolytic etching process to bring forth contrasts in the microstructure of the specimen.


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How to do electrolytic preparation

To do electrolytic preparation the right method needs to be selected, Struers’ equipment contains 10 standard methods for different materials. If these standard methods do not fit the material, a correct electrolyte can be selected from the Selection of electrolyte list. Having selected the correct electrolyte for your purpose, it is necessary to determine the polishing voltage. This is done using a scan function that is built in to the electrolytic preparation equipment.

Correct application settings

After placing a specimen on the polishing table, a pre-defined voltage range is scanned to determine the current density curve. This curve is used to define the correct polishing voltage for the polishing or thinning process. The other parameters to be determined are polishing time and the flow rate. Once the correct application settings have been determined, they can be stored in the database and recalled for subsequent polishing tasks.

Safety is key

Safety is a key word when dealing with electrolytes and all users must be familiar with the relevant safety procedures.

Selection of electrolyte

Several materials can be polished/etched with more than one of the electrolytes.
The right choice depends on the composition of the material and what it is you want to see.

Electrolyte-tabel

Troubleshooting

Problem

Surface not polished or only partly polished
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Cause: Current density insufficient
Solution:
Adjust the voltage
Cause: Electrolyte too old
Solution:
Renew electrolyte
Cause: Insufficient quantity of electrolyte
Solution:
Add electrolyte
      Reduce flow rate
Spots that have not been polished
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Cause: Gas bubbles  Solution:  Adjust flow rate 
      Check electrolyte temperature 
      Decrease voltage 
Etching of the polished surface
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Cause: Chemical attack of grain boundaries after switching off current  Solution: Remove the specimen immediately when the current is switched off 
      Choose a less corrosive electrolyte
Phases in relief
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Cause: Polishing film is inadequate  Solution: Increase voltage 
      Improve mechanical 
      preparation of the specimen 
Cause: Polishing time too long Solution: Reduce polishing time 
Pitting
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Cause: Polishing time too long  Solution: Improve mechanical preparation 
      Decrease time 
       
 Cause:  Voltage too high  Solution:  Lower voltage
Cause: Insufficient anodic layer  Solution: Reduce flow rate 
      Use a different electrolyte
Attack at the edge of the specimen
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Cause:  Film too viscous or too thin Solution:  Decrease voltage
       Increase flow rate
Centre of specimen deeply attacked or not polished at all
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Cause: Polishing film did not form in the centre of the specimen Solution: Increase voltage 
      Reduce flow rate 
      Add more electrolyte 
Deposits on the surface
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Cause: Insoluble reaction products  Solution: Renew electrolyte or try a different one 
      Increase voltage 
Wavy surface or residual deformation
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Cause: Polishing time too short  Solution: Increase time 
Cause: Flow rate too high or too low  Solution: Change flow rate 
Cause: Rough surface after grinding Solution: Improve preparation prior to electrolytic polishing 
Cause: Electrolyte too old Solution: Renew electrolyte 
Cause: Selective polishing because of potential differences in surface (heterogeneous material) Solution: Other electrolyte with other polishing data or use mechanical preparation instead 
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Knowledge leadership

Find new knowledge and inspiration by taking part in Struers training courses and e-Seminars. Gain valuable insights into the latest applications and preparation methods via knowledge sharing. Refresh your knowledge or learn new techniques together with our application experts. The choice is yours!

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