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Don Grant & Debra Carrieri, CT Associated, Inc., Eden Prairie, Minnesota, USA  

ABSTRACT 

Metal and ceramic parts in components used in high purity liquid delivery systems are susceptible to attack by concentrated acids. If these parts are exposed to the acids they can be corroded and may result in premature failure of the part or contamination of the acid. An example of parts that are susceptible to acid attack are the magnets in the impellers in magnetically-levitated centrifugal pumps manufactured by Levitronix. In order to prevent attack, the magnets are encapsulated with a perfluoroalkoxy (PFA) coating to protect them from attack. However, if the acid gases permeate through the coating they can still attack the magnet in the impeller thereby causing premature failure of the pump and contamination of the acid. This study was undertaken to measure the permeation rate of HCl through the PFA used to encapsulate the magnets in Levitronix pump impellers as a function of the temperature and the concentration of hydrochloric acid to which the impeller is exposed.