Difference Between Cold Corona And Hot Spark?

The primary difference is the voltage gradient. In ambient air at sea level and 25C, cold corona occurs as a light visible glow at a voltage gradient of approximately 20 kVrms/cm. Brush corona would appear at about 25 kV rms/cm and positive polarity plumes at 30 kVrms/cm. The last two would be considered spark corona. Those gradients are AC in air at standard temperature and pressure. Different electrode geometry, dielectrics, voltage waveforms, pressures and temperatures would result in different critical gradients.

A description of ozone generation is given here:

http://www.inspiredliving.com/airpurification/airpurifier-comparisons.htm

Basically, if you have a high potential (voltage) applied to something with sharp points, at some voltage a corona will form, due to ions being formed. (Actually corona formation is somewhat complex, but I won't go into details here.) Ozone and small amounts of other compounds such as NOx are formed by the interaction of O2 and N2 and their ions. Only a small amount of current flows.

If the voltage is increased, eventually the breakdown voltage of the air is reached, the air becomes conductive, and a spark is the result. The breakdown voltage varies with the distance between electrodes, RH and other factors.

Once you have a spark, lots of current can flow. Sparks generate much more heat, light etc. than coronas. Sparks are likely to produce more NOx, and to erode electrodes much quicker. .

Because of this, I doubt that there ozone generators that use a true spark discharge. They would use too much current and produce too much unwanted byproducts. However, I will stand corrected if you can give a reference.

Hope this helps.

Tad

Thanks for the info. I am thinking of using pure oxygen for my project and maybe a voltage somewhere between hot and cold spark in cylindrical electrodes. Will there still be unwanted by-products?

Sorry, I had assumed air. Since you are using pure O2, ozone should be the only product.

Tad