Ionization and corona discharge electrodes, and possible air pollution - Page 1
Forum section: electronics / projects

author: DavisLV
author_rank: Newbie
timestamp: April 15, 2020, 03:41:45 am
content: I have a question about materials (and soldering) to use for air ionization and corona discharge ozone generation electrodes (two separate projects).It is well known that electrodes themselves will corrode over time, however I haven't been able to find information on whether the electrodes will "dissolve in the air" (whether the air will be polluted with particles of the electrodes).In the air ionization project around 10 kV DC will be applied to sharp "needle type" electrodes and expected current will be microamps.In the corona discharge ozone generation project a ready-to-use Chinese ozone generation module (something like this:https://www.aliexpress.com/item/32977809317.html) will be used.It is planned to use air ionizer in the living room and bedroom, and use the ozone generator for package (including food!) disinfection.My main concern is possibility of lead (or other metal pollution). Do the electrodes "dissolve in the air"?How important it is to use high quality stainless steel electrode, and should only lead-free solder be used in for the high voltage (as some ionization and corona discharge will happen also in unintended places)?And are there any reason not to use Chinese ozone generation module for food package/food surface (pizza box with holes and pizza inside, open bag with vegetables etc.) disinfection?

author: jpanhalt
author_rank: Super Contributor
timestamp: April 15, 2020, 05:53:20 am
content: Pure and alloyed metals have very low vapor pressures at room temperature (ca. 293°K). You can calculate it with the equation here:https://pubs.acs.org/doi/abs/10.1021/ja01286a001Even mercury ( bp = 357°C), which has a very high vapor pressure compared to other metals at room temperature is about 2X10^-4 kPa (https://www.govinfo.gov/content/pkg/GOVPUB-C13-66a1ade54071892930184393b1802e69/pdf/GOVPUB-C13-66a1ade54071892930184393b1802e69.pdf). That is about 1.8 mm Hg or 0.0024 atmospheres.Organometallics and compounds such as UF6 (uranium hexafluoride) are very different stories. I suspect you will not be dealing with them.Isn't ozone considered a pollutant? Why are you making that?

author: helius
author_rank: Super Contributor
timestamp: April 15, 2020, 07:24:50 am
content: The vapor pressure is, of course, not the whole story, as it only describes an equilibrium fraction of the gaseous phase of a substance in air. Even the "very low" 2.4 mbar of Hg is far above the long-term exposure limits if that was evenly mixed in a breathable airstream: precisely the reason that experiments with mercury require fume hoods. I understood the OP question to be about all routes of contamination, including solid dusts, and at the surface of a corona electrode, which is far from room temperature.My suggestion would be to use stainless steel needles, since they are good at resisting corrosion, and corrosion products are mechanically weak and would be the most likely form to enter the air as dust during the ultrasonic and temperature shock of corona discharge. Stainless steel can only be soldered using highly active fluxes such as phosphoric acid. The solder joints themselves will be far from the arc points and experience negligible deterioration or fragmentation into the air. Therefore, lead in the solder will not be a problem, however, lead-free solders with silver are mechanically stronger and would be preferred if they can be used with low failure rates. You can use high-dielectric varnishes or paints to seal the circuit beneath the needles to prevent undesired corona in that area.Ozone is a very widely-used and non-toxic method for disinfection and odor neutralization. Its corrosive properties are what kills microbes, and likewise irritates the mucus membranes and the lung alveoli. It quickly dissipates after use and there is no residue with articles treated in this way.