Suppression of particle generation in a modified clean room corona air ionizer

We describe a very simple modification to a standard bipolar DC corona ionizer which eliminates the ammonium nitrate buildup on the negative corona points, and also eliminates the bursts of submicron particles (tentatively identified as ammonium nitrate) which seem to be the last major source of microcontamination associated with the best modern corona ionizers. The modification consists of a cover which seals to the front of the ionizer, forming a channel, which is supplied with clean, dry nitrogen via a perforated hose. The cover has perforations in front of the corona points to allow the partially ionized nitrogen gas to escape and mix with the ambient air. With water vapour excluded, there is no hydrogen source from which to make ammonia, and so the particle generation ceases. We present data which demonstrates the effectiveness of this method. © 1990.