PowerLabs Potassium Permanganate Hypergols

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Introduction:

  Due to their spontaneous nature, hypergolic reactions can be amongst some of the most interesting to watch in chemistry. Although there are exceptions to this, in general if two substances are reactive enough ignite spontaneously on contact chances are that the reaction will also proceed at a very high rate. Fluorine/metal powders, Alkali metals/water, Fuming Nitric Acid/Fuels, and others will all explode on contact due to the extremely high reaction rate and heat produced during the reaction. This classic high school chemistry demo shows one particularly interesting (although not very violent) hypergolic reaction, and also demonstrates that not all self initiating chemical reactions happen spontaneously:
 

Materials:

Reactants:

 Materials:

Potassium Permanganate (KMnO4(s))

Hourglass

Ethylene Glycol (C2H6O2(l))

Eyedropper

Propylene Glycol (C3H8O2(l))

 

Glycerin (Glycerol, C3H8O3(l))

 

 

Procedures:

  On the topic of potassium permanganate, it should also be mentioned that the reaction with hydrogen peroxide, particularly at high concentrations (50%+), is EXTREMELY violent and has been used to power turbopumps and rocket engines as the KMnO4 decomposes into O2 and Mn3O4, which then goes on to decompose the H2O2 into O2 and H2O, with the evolution of enough heat to turn the entire batch into a blast of steam. PowerLabs hopes to develop one such engine some day, should time and machining facilities permit.
  For this demo a teaspoon of potassium permanganate (a black/purple powder) oxidizer is placed in the middle of an hourglass with a small depression on it and a few drops of a liquid fuel are placed in the depression.
 

Results:

Potassium Permanganate ignites with Glycerine.  Depending on the ambient temperature, the water content of the fuel, the amounts used, the degree of mixing and the grain size of the fuel the reaction may take place any time between instantly or after several minutes. With coarse grains and low ambient temperatures (this reaction is VERY temperature dependant) the reaction may refuse to take place at all until warmed up. Ethylene Glycol (caution: this is a poison) is the fastest reagent, igniting on the tested samples within 10 - 20 seconds. Glycerin takes longer, at 20 - 30 seconds. Propylene Glycol took the longest, averaging over 40 seconds prior to ignition. Once the reaction starts some smoke develops and a purple flame (emission typical of excited potassium ions) erupts with the evolution of some smoke. Clicking the image will download a video showing Glycerin reacting.
 3.2MB, 25seconds, .mpg.
 

Relevant Links:

Sodium Peroxide Deflagration; another fine example of hypergolic reactions!
PowerLabs Deflagrants overview; examples of similar reactions to the one on this page.

 
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