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We are often asked the question: Which method is "better", carbon rod or
carbon fiber coating?
For over twenty years, SPI Supplies has offered the carbon fiber head as standard and the carbon rod head as an optional accessory item. And for this period of time that has spanned many years and many customers, for those who have available in their laboratories both heads, almost always, the carbon fiber head is the preferred method of coating. So the question then becomes "why". |
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Very high through-put of samples: Carbon fiber coating involves much more of a "flash evaporation" of the carbon fiber, in a matter of a second or so, the fiber heats up, flashes off carbon and breaks. Carbon gets deposited before the head actually gets a chance to heat up. Carbon rod evaporation, on the other hand, involves a slower evaporative process, stretching over a period of a number of seconds, perhaps 5-15 seconds. And during this time, the head gets a change to really heat up, so hot in fact, that it does take some amount of time for the head to "cool down" so that the rods can be replaced for another run. A waiting time of 15-20 minutes would not be unusual. And this is not something unique to the SPI coaters, this would be true of any coater using carbon rods., even a vacuum evaporator. But for carbon fiber evaporation, one can start the process of changing/replacing the carbon fiber almost immediately since the head has never really had a change to get that hot. Customers in busy laboratories, understandably, don't want to waste the time needed for their carbon rod head to cool down and consequently, for those who have both, and could use either, the carbon rod head tends to "sit on the shelf" and it is the carbon fiber head that does the work. What about coating quality? A side-by-side comparison of the grain size that results from carbon rod vs. carbon fiber coating would suggest that the grain size is slightly larger for carbon fiber coating. There does not seem to be any conductivity differences and the only users who might find the slightly larger grain size to be a disadvantage would be someone looking at sub-micrometer size particles on a polycarbonate track etch membrane filter. When the grain size becomes approximately the of the particles to be characterized, there is always the potential for some confusion. But this kind of situation does not arise very often and therefore, the carbon fiber approach is the preferred approach in laboratories that have the choice. |
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