Highest dielectric strength known: Pyrolytic Boron Nitride (PBN)

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winterhaven
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Highest dielectric strength known: Pyrolytic Boron Nitride (PBN)

Post by winterhaven » Tue Aug 02, 2005 4:28 am

I just found this, it's made by GE and others and is supposed to have the "highest dielectric strength known" which they cite being 200,000 volts / mm
Since some of the ideas flying around here tend to be limited by the current technology of insulator materials I thought I'd just say "ok, this is your limit as it stands at this point in time" of course it must be noted that with all insulators the volt / thickness rating GOES DOWN with greater thickness because you have more impurities and defects with greater thickness. I would assume that this figure of 200,000 v / mm was done with the standardized test of 1/8" thick material.

Here's a little of what it says and a link

Pyrolytic Boron Nitride (PBN) is an anisotropic, high-temperature ceramic which exhibits a unique combination of high electrical resistance and good thermal conductivity. This non-toxic, non-porous compound is exceptionally pure by virtue of the synthesis process (high temperature/low pressure chemical vapor deposition). It can be deposited or easily machined into a limitless number of shapes, including......

http://www.advceramics.com/geac/products/pyrolytic_bn/

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Richard Hull
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Re: Highest dielectric strength known: Pyrolytic Boron Nitride (PBN)

Post by Richard Hull » Tue Aug 02, 2005 1:44 pm

It should be remembered that some nasty electrostatic energy storage effects are attendant with such materials. Surface effects could be unsuspected with materials of this high a K factor.

It would be interesting to play with. I would imagine this stuff might make some fearsome minature HV capacitors.

Richard Hull
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Re: Highest dielectric strength known: Pyrolytic Boron Nitride (PBN)

Post by DaveC » Tue Aug 02, 2005 7:10 pm

Todd -

Thanks for that. I had seen some mention of it a while ago. Seems like it would be great for feed through insulation, where you anw high temperature, low ouotgassing , reasonably low dielectric constant, and high dielectric strength in the ground plane region to avoid puncture.

Need to look out for who will be producing them. I will try to get some more information from GE and will post.

Dave Cooper

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Re: Highest dielectric strength known: Pyrolytic Boron Nitride (PBN)

Post by Richard Hull » Wed Aug 03, 2005 3:10 pm

OPPS!! Boy is my face red. I saw dielectric constant (k) in my mind instead of dielectric strength as mentioned in Todd's post. I only caught myself in Dave's response. I was tempted to just delete my post, but hey..........more proof of my humanity, if to err is human.

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Re: Highest dielectric strength known: Pyrolytic Boron Nitride (PBN)

Post by MARK-HARRISS » Thu Aug 04, 2005 12:33 pm

If pure water can be used for cooling anodes in ~10KV valve circuitry and
it has a dielectric constant of 100 or so why not use it for HV caps?. I
suppose on reflection the cooling system would have a fair length in it's
cooling lines which would make breakdown less of a problem.

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Re: Highest dielectric strength known: Pyrolytic Boron Nitride (PBN)

Post by Richard Hull » Thu Aug 04, 2005 2:44 pm

Water is one of the most amazing substances on earth. It is equally enigmatic.

Water is not used in caps as it is a highly polar molecule and very reactive as a nearly universal slovent. In most any environment it will start getting conductive quickly unless physically deionized and stored in totally inert containers.

In a capacitor you have two conductive plates with water in between and electricity constantly coming and going. A water based dielectric capacitor with de-ionized water would last about .03 seconds before it would begin becoming a highly efficient electrolyic cell, plating enigne, and resistor. Unless you used 999999 pure platinum for the plates, the plates with their impurities would turn your dielectric into an ionic carrier of current as the water under the influence of electrical force on the plates slowly took up anions or cations from those plates or walls of the container.

Hope this helped show why water is never even considered as a capacitor dielectric.

We had trouble batch to batch in our water arc experiments as the de-ionized water we used gave inconsistent results based on the length of time between introduction of the water into the gun barrel and the firing of it. Water doesn't like to be pure. It likes to have stuff enter into solution with it and does a great snatch-and-grab on every ionic carrier it sees.

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Fusion is the energy of the future....and it always will be
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Re: Highest dielectric strength known: Pyrolytic Boron Nitride (PBN)

Post by Richard Hester » Thu Aug 04, 2005 4:56 pm

Water has been used as a dielectric to build huge low impedance transmission line energy storage systems. There was one at NRL. The water is carefully deionized, and a pulse charging system is used to reduce leakage effects. It also makes a nice spark gap filler, if the same precautions are observed.

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Re: Highest dielectric strength known: Pyrolytic Boron Nitride (PBN)

Post by UG! » Thu Aug 04, 2005 5:01 pm

this is an interesting point though. though water may be useless, but Methanol has a dielectric constant of 33, and is not nearly such a good solvent. methanol is cheep, and any remaining water could be removed with Richards copper sulphate method :) the cap would have to be sealed to prevent uptake of water, but that shouldn't be a huge problem.

flamibality would be a problem. or a feature :)

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Re: Highest dielectric strength known: Pyrolytic Boron Nitride (PBN)

Post by Starfire » Thu Aug 04, 2005 7:38 pm

Any alcohol will dissolve water and makes a great drying agent - I have used it { as Vodka } in the past to dry-out flowmeters which had been totally emerged in water. The alcohol is allowed to evaporate and takes the water with it. I don't the dielectric strength of the solvent mix.

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Re: Highest dielectric strength known: Pyrolytic Boron Nitride (PBN)

Post by DaveC » Fri Aug 05, 2005 1:11 am

Water although it has a DC dielectric constant of 81, has a high conductivity (high, that is, for DC capacitors). Fully de-ionized water at room temperature is only 18 Meg ohm -cm resistivity. Compare this to almost any plastic which has a resistivity of some 10^14 -10^16 ohm cm., about 8 to 10 orders of magnitude larger. That said, water resistivity can be increased to about 100 Meg Ohm cm by cooling it to about 4 C. Since liquid conductivities are influenced by ion mobilitiy, you can see how by cooling water to the point of max. density, the viscosity is highest and ion current is lowest.

But water capacitors CAN be used for high voltage pulsed operation. Usually the water treatment system is an ion-exchange polishing unit and chiller that runs continuously.. to keep dissolved ions at low concentration.

For other High K liquid dielectrics, there is the Nitrobenziene, with an SIC of 324, also O-Dichlorobenzene and Benzaldhyde in the 80's if I remember correctly. But these materials are very hygroscopic and need really careful handling to purify them. Over the years, fast electro-optical HV switches usually used Nitrobenzine because of sub nsec response and high Kerr coefficient. But these liquids are rather nasty and carcinogenic. Probably not good choices for just hacking around.


Dave Cooper

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