Corona positive

The positive column is a region in which atoms, electrons, and ions are all present together in similar numbers, and it is referred to as a plasma. Again, as with the corona discharge, in mass spectrometry, plasmas are usually operated in gases at or near atmospheric pressure. 

All three types of discharge involve the formation of ions as part of the process. For various reasons, most of the ions are positive. The ions can be examined by mass spectrometry. If small amounts of a sample substance are introduced into a corona or plasma or arc, ions are formed by the electrons present in the discharge or by collision with ions of the discharge gas. 

There are, however, also similarities between the two discharge types. Positive ions drifting toward the opposite electrode form a space charge that affects the electric field and the corona current principally in the same way as in a negative corona discharge. Also, the charging of particles takes place almost in the same way for both types of corona discharge. 

Back corona is caused by the electrical breakdown of gas in the dust layer. This breakdown produces positive ions, which drift toward the negative discharge electrode. The presence of ions with opposite polarity causes a reduction in the particle-charge and -collection efficiency. To avoid this problem, several methods are used. These include... 

Particles become positively charged by a corona discharge and travel out of the charging chamber and collect on a substrate such as a microscope slide. Thus, the method is useful for particles which are to be examined by optical or electron microscopy. 

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