What Causes Plasma Formation in Microwave Ovens?

[Sam G]

Hello, I've been watching some videos on youtube of people putting a lit flame into a microwave oven. After a few seconds the flame bursts into a bright ball of plasma, why is this?

Is there anywhere online that I can research the science that causes this?

https://www.youtube.com/watch?v=MTznh5uK6Oo

 

[Astronuc]

Ah - that's a candle, and that would produce a weakly ionized gas, primarily due to combustion - a very weak plasma, and certainly not fully ionized.

So what is happening?


Well, how does a candle work? The flame is produced by the combustion of the paraffin (a hydrocarbon) in the air. The heat of the flame melts the paraffin and volatilizes it. The vapor of hydrocarbon combines with the air and 'burns'.

Now what happens when the burning candle is placed in the microwave oven, which is then turned on? The microwaves heat the candle and that energy volatilizes the melted paraffin and facilitates the dipersion of the paraffin vapor - which burns in the air.

If one were to replace air with an inert gas like Ar, then the flame would extinguish, and there would be no glowing gas.


If one puts a stick of frozen butter in a microwave and turns it on, one will note that the butter heats and then melts. It could also boil and volatilize.

 

[Sam G]

A fellow Satriani fan I see, cool!

Okay, thanks for the response. Only thing is -it's not a candle. Note around frame no.0:34 the text states that it's a piece of burning wood.

I think I still understand how you explained it tho

Thanks

 

[Astronuc]

Ah - I see that it is a wood splint. When the turn the microwave on, the split seems to burn much better, and there appear flames below the glowing area in the inverted bowl.

The microwaves would also interact with the steam (a combustion product) and perhaps some of the unburned wood. Part of the wood also volatilizes as it burns, and that seems to be enhanced with the microwaves. It would be an interesting experiment to do, but I'm sure my wife would object, espeically since we just replaced the microwave (2 weeks ago) after the old one died.

I once put a foil lined bag of frazen vegetables in the microwave oven. When I turned it on, it made a pretty spectacular light show.