dielectric constant for glycerin - Page 1
Forum section: electronics / beginners

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: March 21, 2019, 04:50:31 am
content: Going to make a high voltage capacitor with glycerin as the insulator.Its dielectric constant is ~40 and it says nothing about its dissipation in AC circuits (Spark Gap TC) which is what this capacitor is intended for.Plates are 0.6mm pcbscappcb platesCap will have ceramic washers to space the plates at the corners. There will be more plates in the capacitor than in the assembly image.

author: BravoV
author_rank: Super Contributor
timestamp: March 21, 2019, 04:57:01 am
content: As glycerin is very hygroscopic subtance, curious how do you plan to dry it ?

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: March 21, 2019, 04:58:33 am
content: Quote from: BravoV on March 21, 2019, 04:57:01 amDo you mean glycerin needs drying before it assumes its dielectric constant?The cap will be airtight and nearly entirely filled to the top with the oil.Was going to use this for something else but the capacitor will fit in it much betterhttps://www.mouser.com/ProductDetail/546-1591USGY

author: BravoV
author_rank: Super Contributor
timestamp: March 21, 2019, 05:06:45 am
content: Quote from: LaserTazerPhaser on March 21, 2019, 04:58:33 amHow do you know your newly purchased glycerin is dry ? As its so hygroscopic, when exposed to open air, it will start to absorb water vapour from the air.As you mentioned it your self, this will be for HV stuff, and surely doesn't play well with water or absorbed humidity between that two HV plates isn't it ? Not sure, I'm not the expert.

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: March 21, 2019, 05:12:46 am
content: Quote from: BravoV on March 21, 2019, 05:06:45 amLab grade glycerin can used to ensure no vapor was absorbed.Im mainly concerned for its RF power losses. Im also considering deionized water for dielectric.

author: 0culus
author_rank: Super Contributor
timestamp: March 21, 2019, 07:06:31 am
content: ...and as soon as you expose it to air it's going to start absorbing water.Seems to me that very pure water is a better bet. OR something exotic like fluorinert...but that's a rabbit hole unto itself...

author: DC1MC
author_rank: Super Contributor
timestamp: March 21, 2019, 07:10:57 am
content: Word of advice: there is NOTHING a hobbyist can do to prevent contaminating the water and have the capacitor turned into a "hydrogen bomb".Been there, done that, the scars are mostly gone now after 30 yrs.DC1MC

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: March 21, 2019, 07:26:13 am
content: Quote from: DC1MC on March 21, 2019, 07:10:57 amDidnt know electrolysis could occur, Im not using water due to it. You must have used it for long durations for electrolysis to have built up enough gasses to destroy the device.Glycerin seems ideal for high frequencies. I might mix the glycerin with TiO2 powder to make a dense mixture.

author: Marco
author_rank: Super Contributor
timestamp: March 21, 2019, 10:23:20 am
content: Just use EVO.

author: gbaddeley
author_rank: Regular Contributor
timestamp: March 21, 2019, 10:33:21 am
content: DIY HV caps often use mineral oil, aka baby oil (with no added fragrance)

author: Zero999
author_rank: Super Contributor
timestamp: March 21, 2019, 10:38:25 am
content: Is the water a problem? As long as the glycerine doesn't contain any ionic salts, then I don't see the problem. It can soak up water from the air, but as long as the air isn't polluted with sulphur or nitrogen dioxide, then I don't see how it can be a problem.How about adding silica gel to soak up the water?

author: Bud
author_rank: Super Contributor
timestamp: March 21, 2019, 11:00:45 am
content: What is wrong with mineral oil? I just filled a dried 50 Ohm dummy load with it.

author: Zero999
author_rank: Super Contributor
timestamp: March 21, 2019, 11:19:49 am
content: Quote from: Bud on March 21, 2019, 11:00:45 amBecause glycerol has a higher dielectric constant, than mineral oil?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 21, 2019, 12:27:36 pm
content: Dielectric constant doesn't mean much by itself, unfortunately.Pure metals have a dielectric constant in the thousands. That doesn't mean you can use them as a capacitor -- the phase of that displacement current is almost perfectly imaginary, which is to say, resistive rather than capacitive current flow.Polyalcohols tend to have labile protons. More simply, glycerin is chemically "wet": despite not itself being H2O, it can participate in many interactions the way H2O can.Besides having huge affinity for water, it can also dissolve ionic salts. Offhand, it looks that NaCl is soluble to the tune of 10%wt, so it is an effective ionic solvent.I don't even know how you dry it -- can you dry it? Concentrated sulfuric acid or P2O5 certainly isn't going to do (dehydration, condensation reactions), and anhydrous salts will simply dissolve in it (ruling out usual suspects like CaCl2).Not only will you need to ensure it is very dry, but it will need to be free of ions, just as you'd use deionized water for an application like this. The apparatus needs to be extremely clean, for the same reason; even then, ions simply dissolve from everything, everywhere, somehow or another, and the water needs to be cycled fairly often through an ion exchange resin, or replaced with fresh.The biggest problem though is that alcohols tend to have strong dielectric losses to begin with, and I think glycerin will be one such case. Typically, there is a relaxation time constant in the mere ~kHz, where the k goes from large to small, and while it's dropping off, it's very lossy (tan delta ~ 1).Here's a study of PVA:http://www.ufrgs.br/lapol/insulating_characteristics.pdfPVA is alternating CH2s and CHOHs, while glycerin is HOH2C-CHOH-CH2OH (three CHOHs plus two H end caps, no CH2s), and it's also liquid (which means the OH protons are moving around constantly). I would expect PVA to perform better, and clearly it doesn't perform all that well (depending on whatever they're doing there, different temperatures, and heat treatment I think?). I believe water has a similar response?Likewise, you can infer based on chemistry, what might perform actually well -- if those protons are locked down in bonds instead, say in esters, amides or hydrocarbons -- the dielectric constant will be a lot lower, true, but it will be a lot flatter with respect to frequency, and that's the important part.PET (a polyester) for example, has a modest k, and reasonable enough losses (and various other features: stability, cost of raw materials, ease of manufacture..) that it's commercially important as a capacitor type already.Still pretty lossy, enough that you can't use it for, say, resonant power supplies (or radio transmitters, CW Tesla coils, induction heaters..), but it can be okay for pulsed applications when the internal heating isn't enough to burn a hole through the thing. (It may be hard to find caps that are constructed for pulsed application too, though -- heavy metallization, thicker leads, noninductive build.)Downside of course being... interesting and all, but there aren't any esters in liquid form that are also cheap. Well, except for esters of glycerin, oddly enough -- fats are triglycerides (three fatty acids stuck onto a glycerin backbone). Not much k, they're mostly hydrocarbon -- but it satisfies everything else.Tim

author: Jwillis
author_rank: Super Contributor
timestamp: March 21, 2019, 06:22:48 pm
content: Would you be opposed to using something other than glycerin.Titanium Dioxide - Titania has much better dielectric strength at around 4kV /nano meter and a greater electron absorption or dielectric constant of around 85.It has a much better resistance to water absorption than glycerin/glycerol.You could significantly reduce the size of your construction with the same results.What are your parameters for voltage and charge?Purification/distillation of glycerin/glycerol can't be done simply by boiling it at atmospheric pressure because it will reabsorb as much water as it releases.It was a long time ago but I believe it needs a much lower atmospheric pressure then frozen to allow the crystals to precipitate.Then the crystals require washing with acetone.Seems a bit much for the kitchen.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: March 21, 2019, 09:18:25 pm
content: I would probably make a capacitor like this from glass plates and 2 pieces of auminimum or copper foil.You can fold one piece of foil zig-zag from left to right and the other from top to bottom.For higher pulse capacity use loose sheets of foil and connect them all together.Use glass plates that are a few cm wider than the foils to crate gaps and maybe put the whole thing in some liquid to isolate the edges further."Regular" glass has a relative permitivity of 6 to 8, so you'll need more layers, but you'll have to mess a lot less with liquids.It might be worth putting dabs of silicone or whatever on only the corners of the glass plates, for extra isolation.

author: coppercone2
author_rank: Super Contributor
timestamp: March 21, 2019, 09:43:46 pm
content: why can't you dry glycerin over phosphorus oxide or oleum?I think you can in a vacuum desiccator.Intensity and capacity of common desiccantsDrying agents can conveniently be grouped into three classes, depending on whether they combine with water reversibly, they react chemically (irreversibly) with water, or they are molecular sieves. The first group vary in their drying intensity with the temperature at which theya re used, depending on the vapour pressure of the hydrate that is formed. This is why, for example, drying agents such as anhydrous sodium sulphate, magnesium sulphate or calcium chloride should be filtered off from the liquids before the latter are heated. The intensities of drying agents belonging to this group fall in the sequence:P2O5 >> BaO > Mg(ClO4)2, CaO, MgO, KOH (fused), conc H2SO4, CaSO4, Al2O3 > KOH (sticks),silica gel, Mg(ClO4)2·3 H2O > NaOH (fused), 95% H2SO4, CaBr2, CaCl2 (fused) > NaOH (sticks),Ba(ClO4)2, ZnCl2 (sticks), ZnBr2 > CaCl2 (technical) > CuSO4 > Na2SO4, K2CO3Where large amounts of water have to be removed, a preliminary drying of liquids is often possible by shaking with concentrated solutions of calcium chloride or potassium carbonated, or by adding sodium chloride to salt out the organic phase (for example, in the drying of lower alcohols).Drying agents that combine irreversibly with water include the alkali metals, the metal hydrides, and calcium carbide.

author: Marco
author_rank: Super Contributor
timestamp: March 21, 2019, 09:46:28 pm
content: Quote from: Doctorandus_P on March 21, 2019, 09:18:25 pmWeight or volume wise you're going to be way over an oil solution. The oil can be dimensioned much less conservatively, one dielectric failure with oil and the oil is a slightly less good insulator ... one dielectric failure with glass and it's gone. Oil is generally the one to beat, the way to beat it is better dielectric constant (ultrapure water or high K ceramics) or better dielectric strength (BOPET, BOPP).

author: bson
author_rank: Unknown
timestamp: March 21, 2019, 10:36:58 pm
content: How about experimenting with epoxy resins? Coat the boards in a plain protective layer first, then pot the whole assembly with a mix of ferrite dust and resin... That should give you a sky high relative permittivity! Maybe use a vacuum chamber to eliminate air bubbles or pockets?Just thinking out loud here.Edit: maybe confine the high-µrmix to the center so it can't conduct fields around the plates...

author: Marco
author_rank: Super Contributor
timestamp: March 21, 2019, 10:43:00 pm
content: If there were easier ways than the complex ceramics to make high k dielectrics, the capacitor manufacturers would be using it ... you're not going to beat just using the same dielectric strength of mylar, infact you will likely lose by a lot.

author: David Hess
author_rank: Super Contributor
timestamp: March 22, 2019, 01:05:37 am
content: Quote from: LaserTazerPhaser on March 21, 2019, 05:12:46 amI have tested materials for low dielectric loss by measuring their temperature rise in a microwave oven.Quote from: T3sl4co1l on March 21, 2019, 12:27:36 pmApply a vacuum after assembly?Quote from: Doctorandus_P on March 21, 2019, 09:18:25 pmThat is how I have done it. A wide margin around the edges of the glass plates prevents flash-over between the two sides. Corona discharge was significant with the rough cut aluminum foil but gave the capacitor a nice eery blue glow at night. The aluminum foil was attached with spray adhesive.I spaced the plates apart and used one spring connection for each pair of facing sides. The added space aids air cooling.

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: March 22, 2019, 02:27:02 am
content: Glycerin is not going to workhttps://www.pupman.com/listarchives/1997/november/msg00362.htmlQuote from: Marco on March 21, 2019, 10:23:20 amWhats the k value?Quote from: bson on March 21, 2019, 10:36:58 pmSeller repliedhttps://www.ebay.com/itm/332870578714/has 3.11 K value and I can add up to 10% TiO2 thus 10% of Tio2 + that compound is 14.11, still quite low.Quote from: T3sl4co1l on March 21, 2019, 12:27:36 pmMany polymers dielectric strength decreases with increasing thickness.Quote from: gbaddeley on March 21, 2019, 10:33:21 amIm considering saturating mineral oil with loads of TiO2 in a blender then removing any dissolved air with a vacuum then pouring it in the capacitor. This combination seems the most ideal, BaTiO₃ would be much better but its cost far greater.

author: bson
author_rank: Unknown
timestamp: March 22, 2019, 04:18:48 am
content: Calcium copper titanate seems to be the material of choice. It appears to have µron the order of 10k-250k, depending on source, grade (presumably), and temperature. TiO2 seems to have µraround 100 at room temp.With a bit of digging...https://www.alibaba.com/product-detail/Calcium-Copper-Titanate-CCTO_60682595594.html?spm=a2700.7724857.normalList.32.7ae030a12ep29OI'd see if I could find 1-2kg affordably, and go with that.

author: bson
author_rank: Unknown
timestamp: March 22, 2019, 04:28:49 am
content: I'd also mix it with a resin, and determine the maximum ratio empirically. It doesn't need to retain epoxy-like adhesion or strength, just keep together reliably as a solid block under normal use. A liquid such as oil always presents a potential problem with particulate matter settling...