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Highest dielectric strength known: Pyrolytic Boron Nitride (PBN)

Posted: Tue Aug 02, 2005 12:28 am
by Todd Massure
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/

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

Posted: Tue Aug 02, 2005 9:44 am
by Richard Hull
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

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

Posted: Tue Aug 02, 2005 3:10 pm
by DaveC
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

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

Posted: Wed Aug 03, 2005 11:10 am
by Richard Hull
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.

Richard Hull

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

Posted: Thu Aug 04, 2005 8:33 am
by MARK-HARRISS
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.

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

Posted: Thu Aug 04, 2005 10:44 am
by Richard Hull
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.

Richard Hull

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

Posted: Thu Aug 04, 2005 12:56 pm
by Richard Hester
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.

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

Posted: Thu Aug 04, 2005 1:01 pm
by UG!
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 :)

Oliver

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

Posted: Thu Aug 04, 2005 3:38 pm
by Starfire
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.

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

Posted: Thu Aug 04, 2005 9:11 pm
by DaveC
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

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

Posted: Fri Aug 05, 2005 4:55 am
by MARK-HARRISS
I remember some experiments dissolving powdered glass into distilled
water to show how good a solvent it is. I can't help but speculate if there's
some additives for water along with say carbon or graphite plates and as
Dave mentioned, a chiller and deioniser..........Hang on, when I used to
test deionised water for a certain type of autoclave with a conductivity
meter, one of the best performing waters turned out to be carbon
filtered tapwater from the local battery shop. Hmm I could have a
frozen cap in the freezer with graphite and activated carbon plates!.

Hmmm and with the massive surface area of activated carbon, I should get some decent plate area.....possibly.

Regards
Mark

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

Posted: Fri Aug 05, 2005 3:26 pm
by DaveC
I think the activated carbon filter is a great way to remove volatiles, organics and ions from water.

Incidentally, activated carbon is also used to purify silicone dielectric fluids, and either this or activated alumina, silica gel, or the molecular sieve desiccant materials will greatly purify, dehydrate and lower conductivity of transformer oils.

You can get an order of magnitude estimate of the surface area increase by measuring the capacitance, (AC is probably better here than DC which has galvanic issues.). Then calcuate the capacitance using the surface determined from the dimensions, and permitivity of water (81). The ratio of measured to calculated is roughly the surface area enhancement factor.

The one important unknown in this is the degree to which gas films occur. A gas layer could be nearly any thickness at all. Since it is in series with the water dielectric, a Maxwell-Wagner two capacitance layer capacitor forms. The water has a high dielectric constant but large thickness, the dielectric constant of the gas film (Er ~1.00) is low, but the thickness could be very small, so results might be all over the place... unless the water is first degassed.

Ahh... the joys of experimental science.

Dave Cooper

Re: Dieletrics and Townsend Brown's "bentonite"

Posted: Sat Aug 06, 2005 9:48 am
by Paul_Schatzkin
Hey guys, remember me?

I'm just going to chime in here with one quick note re: dielectrics.

Townsend Brown was apparently preoccuppied with a substance called "bentonite" which as a very high "k" factor. Anybody ever heard of Bentonite?

Speaking of Brown... I have been off on a very long and arduous journey trying to make sense of his life, which is more or less why I have not been contributing much in this space. I have been monitoring some of the discussions and, as always, am pleased to see a rich dialog taking place.

But I have to tell you, on some level, trying to understand Townsend Brown's life/work has pretty much challenged everything I've ever believed about anything, and it's going to take some time to digest. I'm no closer now to writing an actual book than I was when I first heard about the guy, which is now more than three years ago.

Hopefully soon I'll wrap my head around enough of what I've been through -- particularly in the past year -- to make a meaningful post here somewhere.

Mostly I just wanted to let y'all know I'm still alive, and just coming up for a gulp of fresh air...

--PS

Re: Dieletrics and Townsend Brown's "bentonite"

Posted: Sat Aug 06, 2005 4:09 pm
by JohnCuthbert
Bentonite is a clay-like mineral, used among other things for fining wines. This means that you can get it from home-brew shops if you want to experiment.
The other thing I wanted to pint out is tht even totally pure water conducts fairly well and so you can only use it for capacitors that get charged and emptied quickly. How you purify it, and with what doesn't matter.
BTW, liquid hydrogen cyanide has a higher dielectric constant than water, but it isn't nice to work with. Acetonitrile (methyl cyanide) might be interesting to try.

Re: Dieletrics and Townsend Brown's "bentonite"

Posted: Sat Aug 06, 2005 6:06 pm
by Richard Hester
In addition to its endearing poisonous qualities, HCN poses the same explosion hazard as acetylene. Acetylene is prone to explosive polymerization due to its labile triple C-C bond. Acetylene tanks do not contain the pure compressed gas - instead, it is dissolved in acetone entrained in diatomaceous earth. HCN is shipped in liquid form with an inhibitor agent added to prevent explosive polymerization. The inhibitor is suppoedly good for only 90 days or so, then you have to ship the remaining HCN back to the manufacturer, where they burn it to dispose of it.

Re: Dieletrics and Townsend Brown's "bentonite"

Posted: Sat Aug 06, 2005 9:11 pm
by MARK-HARRISS
Hi Paul, Good to hear from you. Sounds like you may have quite a story to tell once you sift through all the information.

Regards
Mark H

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

Posted: Sat Aug 06, 2005 9:26 pm
by MARK-HARRISS
I found a reference to a activated carbon "supercap" in the RadioShack
Science Projects notebook cat. No. 62-5018 by Forrest M Mims on page
13. I knew I'd seen the idea before somewhere: Forrest gets 1.2V breakdown
per sheet of activated carbon aquarium filter with lemon juice
electrolyte and a stack of 6 sheets to form His cap.

I'll have to give this idea a try sometime and report back the results.
Then maybe try some bentonite as well.

That's a great idea to add some dessicant to transformer oils, Dave
I'll try a packet in some of my HV projects as well, sealed and tied
down out of the way though silica would be better than carbon for
this application.

Regards
Mark H

Pyrolytic Boron Nitride thread and note on insulating oil maintenance

Posted: Sat Aug 06, 2005 9:56 pm
by Verp
As far as getting better performance out of oil through routine maintenance, I recommend this web site; http://www.wapa.gov/rm/psmmCHAP-10.pdf . (If you need a source of DBPC, also known as BHT, there is http://www.generalwax.com/p___P0295086.html .)

Re: Pyrolytic Boron Nitride thread and note on insulating oil maintenance

Posted: Sun Aug 07, 2005 3:49 am
by MARK-HARRISS
Thanks rod, I have a copy now in my library. I recall someone also posted
a similar document about adding preservatives to oil also. I'll have to see
if I can find a copy of that too.

Mark H

Re: Pyrolytic Boron Nitride thread and note on insulating oil maintenance

Posted: Mon Aug 08, 2005 10:01 am
by Richard Hull
Bentonite clays are the primary ingredient in many kitty litter products and is naturally, mildly radioactive depending on the source. I have measured merely statistically arrived at levels of additional radiation in our brand of cat litter. Though I hear some are double background.

Man! I hope you guys don't injure yourselves or put out a lot of money and effort looking for the super exotic capacitor dielectric in a world that has already identified them and found them wanting or worthless on a useful scale.

Richard Hull

Re: Pyrolytic Boron Nitride thread and note on insulating oil maintenance

Posted: Sat Aug 13, 2005 6:53 pm
by Verp
I forgot to mention earlier that the antioxidant DBPC talked about in the PDF at http://www.wapa.gov/rm/psmmCHAP-10.pdf is also known as BHT, the candle ( http://www.generalwax.com/p___P0295086.html ) (and once common food) additive, so it is not a dangerous chemical, when handled with common sense, as the MSDS indicates; http://www.mindfully.org/Plastic/BHT-Bu ... e-DBPC.htm .

Rod

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

Posted: Wed May 08, 2019 5:40 am
by Maria Higgins
As far as getting better performance out of Pyrolytic Boron Nitride (PBN), I recommend this web site: http://www.samaterials.com/boron-nitrid ... tubes.html