Σldritch
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Sulfur/Selenium/Tellurium High-K dielectric
I came across the first attatched paper looking to verify some of my thoughts and ideas about/for dielectrics. It describes a 1:1 atomic ratio
Sulfur-Selenium alloy produced by melting together the components in an inert athmosphere. It supposedly has a dielectric constant of 74 and low loss
factor even at MHz frequencies, a breakdown voltage of about 40kV/mm and desireable mechanical properties. It struck me as something very amateur
friendly. It has a very simple composition, half of which is the very readily available element Sulfur. It can potentially be recycled very easily by
remelting, even in an amateur setting, and has excellent properties.
Naturally, my first thought was if the Sulfur-Tellurium variant would'nt be better as Tellurium is far more polarizeable than Selenium. However, it
turns out Sulfur and Tellurium in a 1:1 atomic ratio phase separate on fusion! Seems there is another way though as the second paper I have attatched
describes the formation of a black precipitate in the elemental ratio 1:2-Te:S forming when tellurous acid reacts with Hydrogen Sulfide. When dried it
is a soft solid fusing into a grey, somewhat lustrous mass. I don't like the sound that lustrousness (conductive?) but it sounds pretty promising,
too.
Now, I've been recommended not to try to build my own capacitors for Tesla coils and such but for devices like (spiral) vector inversion generators
(which actually have an old thread on the forum) and such I think this could be really useful.
Attachment: High-K_dielectric_sulfur-selenium_alloys.pdf (1.4MB)
This file has been downloaded 313 times
Attachment: snelling1912.pdf (654kB)
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Twospoons
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Pity they didn't show K vs electric field strength. That would have been interesting to compare against barium titanate based dielectrics.
Helicopter: "helico" -> spiral, "pter" -> with wings
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Σldritch
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Be that as it may Barium Titanate is not an elastomer. Quite difficult to make a capacitor out of for the amateur, don't you think? PTFE or
polypropylene would be more comparable I think.
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Twospoons
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Well if I were to build my own capacitors I'd be using paper-in-oil for the dielectric, because i'd only be interested in making large , high voltage
pulse caps. I was curious to see how this sulfur/selenium dielectric compared to other high K dielectrics, of which Barium Titanate and distilled
water are the first which come to mind. I thought the high low-frequency loss factor to be a rather large drawback. I use a lot of ceramic
capacitors in my day job, and the loss of capacitance under DC bias is a well known issue that needs to be accounted for in design.
Helicopter: "helico" -> spiral, "pter" -> with wings
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Mateo_swe
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Nikola Tesla used oil based capacitors so they must be at least usable at HV and high frequency.
For a tesla coil cap, easiest is to build a MMC from small pulse caps, lots of info on it on the web.
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Mateo_swe
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Onyxmet has Barium Titanate if a smaller amount is needed, but its quite expensive.
I think for making capacitors a large grain variant is best, someone told me so long ago.
Once i had the idea to make a DIY Barium titanate capacitor but i never finalized the idea.
If i remember correctly tesla used metal sheets submerged in oil for his capacitors, but he used not only high voltage but also lots of current to his
tower sized tesla transformer.
He was not trying to make huge sparks, rather to put out as much energy without it starting to arc.
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blogfast25
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It's perfectly possible to load some elastomer, like EPDM, with BaTiO3 and mould or shape it into any shape (then cure it). With typically
about 30% of the barium titanate in the moulding...
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Mateo_swe
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You are probably correct, but will the mixed compound still have the high dielectric K-factor that BaTiO3 has when used alone?
Maybe you can make some experiments, it would be interesting.
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blogfast25
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Quote: Originally posted by Mateo_swe  | You are probably correct, but will the mixed compound still have the high dielectric K-factor that BaTiO3 has when used alone?
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Such high K-value compounds are certainly used for the manufacture of high voltage cables.
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Σldritch
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Seems like something that would give inconsistent results, especially in an amateur setting, while being the obvious method industrially. Also
wouldn't you get vastly lower breakdown voltage by using a biphasic dielectric? Ceramic isolator components are often curved to maximise the distance
a surface discharge would have to travel after all. Of course S/Se is not much better there with some DC conductivity though the result may be less
destructive. I suppose you shouldn't really push capacitors that far anyway.
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blogfast25
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| Quote: Originally posted by Σldritch | | Seems like something that would give inconsistent results, especially in an amateur setting, while being the obvious method industrially. Also
wouldn't you get vastly lower breakdown voltage by using a biphasic dielectric? Ceramic isolator components are often curved to maximise the distance
a surface discharge would have to travel after all. Of course S/Se is not much better there with some DC conductivity though the result may be less
destructive. I suppose you shouldn't really push capacitors that far anyway. |
Formulations of EPDM/EPM are used for transmission cables up to 150 kV and higher.
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Texium
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Thread Moved
30-11-2023 at 10:54 |
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