To ensure a good electrical connection between the electrode and skin, it is vital to properly prepare the electrode paste. It is especially important when recording EEG or evoked potentials, where good contact is critical to the quality. The electrode paste can also help to reduce the artifacts created by the electrodes in contact with each other and the plastic around them. We recommend that you use a conductive cream or paste (such Ten20 Conductive Paste) to improve the electrical conductivity.
To prepare carbon powder for an electrode, first remove the microcloth discs from the kit. These have a brown color and a soft velvety texture. Attach the glass plate by peeling off the adhesive backing. Next, remove a nylon disk from the polishing kit and attach to the opposite side of the plate. This will allow you to polish the electrode without wearing the supporting plastic.
Fill the open wells in the electrode block with paste. Use the end of a long glass rod to tamp it down evenly and eliminate any air pockets. The paste must be mounded a little higher than the surface.
Repeat step 2 to cover the entire electrode block. Apply a small amount alumina to a cotton-swab. Rub it on the electrode's surface. This will give your electrode a more refined finish and reduce the risk of shorting and scratching.
After applying the alumina, rinse the electrode in clean water. Continue this process until you have removed all the alumina and the electrode's surface is smoother. It may take up to 20 cycles of rinsing and flushing before the electrode is ready for abrasion.
Carbon electrode paste consists of three main components: calcined petroleum coke, coal tar pitch, and additives. Calcined petroleum, a by-product of high quality petroleum coke is the main carbonaceous material that provides electrical conductivity and strength for the carbon electrode. The coking by-product coal tar is also used to bind the carbon particles, making them stable and cohesive. Lastly, different additives are used to enhance the specific properties of an electrode like electrical conductivity or thermal stability.
During the process of polishing it is essential to keep your electrodes flushed. This will prevent any encrusted alumina or coal tar debris from being carried to the next step of polishing and interfering with its effectiveness.
After polishing the electrode with alumina, rinse it thoroughly in clean distilled methanol and then water. This cycle should be repeated until the carbon has a uniform texture and is ready to abrade. It is important to check the surface again for cracks and discontinuities after the carbon has already been polished. This will help you determine whether to continue the abrasion process or to skip ahead to the final etching step. It is generally easier to etch the electrode than to repair a carbon surface.
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