Weird Science

Corona discharge

Polish ver­sion is here

What Is Corona Discharge?

Corona discharge is an elec­tri­cal discharge cau­sed by the ioni­za­tion of the gas sur­ro­un­ding a con­duc­tor. It occurs when the poten­tial gra­dient exce­eds a cer­tain thre­shold but rema­ins insuf­fi­cient for die­lec­tric bre­ak­down or the for­ma­tion of an elec­tric arc. This phe­no­me­non is also known as elec­tri­cal corona or par­tial discharge. It is clo­sely rela­ted to elec­tro­sta­tic wind and can be obse­rved in devi­ces such as the elec­tro­sta­tic motor.

Par­tial discharge is a pro­cess in which an elec­tric cur­rent begins to flow thro­ugh a neu­tral gas from a high-vol­tage elec­trode, often refer­red to as the corona elec­trode. This move­ment of charge occurs due to the ioni­za­tion of the sur­ro­un­ding medium. The gene­ra­ted ions tran­s­port elec­tri­cal charge to regions of lower poten­tial aro­und the elec­trode or recom­bine, retur­ning to a neu­tral ato­mic state.

If the corona elec­trode is sha­ped like a sharp point, a strong poten­tial gra­dient forms aro­und it. If the applied vol­tage is too low to cre­ate a full pla­sma chan­nel but high eno­ugh to par­tially ionize the medium, a corona discharge appe­ars.

Corona dischar­ges can be either posi­tive or nega­tive. While they appear simi­la­r—both emit­ting a blue or vio­let glow aro­und the corona elec­tro­de­—their beha­vior dif­fers in one impor­tant aspect: ozone pro­duc­tion. A nega­tive corona gene­ra­tes signi­fi­can­tly more ozone than a posi­tive one.

For­tu­na­tely, corona dischar­ges are not just the­o­re­ti­ca­l—they can be obse­rved with rela­ti­vely sim­ple equ­ip­ment.

To do this, you will need a high-vol­tage power source. A ZVS dri­ver is a sui­ta­ble cho­ice for this expe­ri­ment. One ter­mi­nal sho­uld be gro­un­ded, while the other is con­nec­ted to a shar­pe­ned elec­trode. The poin­ted elec­trode sho­uld be posi­tio­ned oppo­site a col­lec­tor elec­trode in the form of a wire ring (which must also be gro­un­ded):

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War­ning: The use of a ZVS dri­ver is not recom­men­ded for begin­ners without prior expe­rience in han­dling high vol­tage. The out­put vol­tage of this device can reach seve­ral tho­u­sand volts (poten­tially tens of tho­u­sands). Mishan­dling can result in serious elec­tric shock! Addi­tio­nally, ozone pro­du­ced during this expe­ri­ment is toxic. The author assu­mes no respon­si­bi­lity for any damage or inju­ries that may result. Use cau­tion and pro­ceed at your own risk.

When power is applied, a corona discharge will form aro­und the sharp elec­trode. The glow is espe­cially visi­ble in dark­ness. Below are some pho­to­gra­phs of the emit­ted light taken during my expe­ri­ments:

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In addi­tion to the visi­ble glow, a distinct ozone smell is also noti­ce­a­ble.

Bey­ond being a fasci­na­ting phe­no­me­non, corona discharge has nume­rous indu­strial appli­ca­tions, inc­lu­ding:

Corona dischar­ges are par­ti­cu­larly use­ful for air puri­fi­ca­tion, as they charge air­borne par­tic­les, which are then attrac­ted to an oppo­si­tely char­ged elec­trode. Addi­tio­nally, the free radi­cals and ions gene­ra­ted during the discharge can help break down toxic che­mi­cal com­po­unds.

Enjoy your expe­ri­ments, and have fun!

Fur­ther rea­dings:

Marek Ples

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