Mica - reactivity with water?

[hitower1275]

Dear all,

 

I am currently confronted to a problem involving mica and its potential reactivity with water / humidity. Let me first explain the phenomenon.

 

Phenomenon description

A piece of mica-loaden Nomex® 818 (formerly referenced as type 418) insulating paper (datasheet here: www.dupont.com/content/dam/assets/products.../418_419.pdf‎) is sharply folded, then placed into a glass containing distilled water. Shortly after, small bubbles start to form at the location of the fold and raise to the surface.

If a piece of Nomex® 410 - a Nomex® type NOT containing mica - is prepared the exact same way, no such bubbles appear.

If a piece of Nomex® is placed in a glass of distilled water without being folded beforehand, no such bubbles appear.

 

Why does it matter?

Nomex® is used as insulating paper in electrical appliances, such as motors and transformers. The mica-loaden Nomex® types are required in case the voltage exceeds the partial discharge inception voltage (PDIV). Once all wires and insulation materials are readily assembled, the whole component (rotor, stator, winding) is then impregnated using a resin such as Elantas Epoxylite®. This resin has a tendency to absorb a sertain quantity of water from ambient humidity and will also contain reactive -OH groups.

Consequently, when a component containing Nomex® 818 is impregnated, the bubbling will occur and, due to the viscosity of the resin, these bubbles will remain inside the resin. Once the resin hardened, the bubbles still present in the resin will constitute initiation points for partial discharge and ultimately cause a premature failure of the equipment.

 

And the question is...

Assuming the chemical nature of the mica platelets is muscovite (KAl₂(AlSi₃O₁₀)(F,OH)₂) , what is the reaction occurring between this material and water?

I would speculate that some metallic (Al? Li?, Mg?) inclusions are present inside the mica platelets. Sharply folding the paper sample would also break the platelets, suddenly exposing these inclusions to the "outside world", triggering a reaction like M° + H₂O -> M-OH + ½ H₂.

 

Again, the above paragraph is pure speculation, as I don't have the equipment to identify the nature of the gas formed. Also, I could not collect solid evidence that metallic or other water-reactive substances are included in mica platelets. So, my questions to you are:

 

- What is causing the reaction that forms a gaseous substance in the described set-up?

- How could this reaction be inhibated?

 

Your advice would be greatly appreciated!

 

With kind regards,

Hendric

 

[John Cuthber]

Have you considered that it might not be a reaction at all?

The sharp edges of the broken mica are acting as nucleation sites for air coming out of solution.

[hitower1275]

Well, I cannot totally exclude this possibility. But given of the rather large amount of gas formed, I would still tend to believe there is a reaction.

Anyway, I will have to repeat the experiment with de-gassed water.

 

Thank you so far!

Hendric

[Sensei]

Again, the above paragraph is pure speculation, as I don't have the equipment to identify the nature of the gas formed.

 

You don't have fire.. ?

 

If there is substantial amount of gas then place above it up side down beaker, filled with water first, so it'll be filled by gas going up.

Then try to fire it. If there is explosion, it's Hydrogen, the most likely.

In presence of not flamable gas, such as Carbon dioxide, fire will shut down.

In presence of Oxygen, fire will start burning more intense.

 

How about placing it in other liquid, that has no water.. ?

If it's caused by reaction with water, there will be no gas, or reaction will be different.

If it's what John said, gas bubbles will appear also.

Edited August 22, 2015 by Sensei

[hitower1275]

Dear user Sensei,

 

Thank you for your reply.

Of course, I know about the flammability of hydrogen. Unfortunately, the gas quantities are too small to burn. The size of the bubbles formed are comparable to what you would see after pouring a nice cold Lager beer into a glass.

I might try to add some dishwasher liquid, so the bubbles would form a foam, which could be burned.

 

I will keep you posted about any progress.

 

Hendric