You may wonder where post named “Hydrogen generator Mk. VII” went, when there my last update on the this topic is “Hydrogen generator Mk. VI“. Well, there was that update on Aluminium corrosion – which practically is another update in that direction so it didn’t fell well not to count it. Even more when there were too many things happening meanwhile.
So just a tiny recap on where we’ve been couple months ago. After the debacle with Aluminium lid, Serge designed a new one, made out of Formica (Bakelite). I did a quick run and all went well so prepared everything for a major run (24hrs). Commencing an over-night run a nasty surprise came following morning, not even Formica can withstand harsh environment of KOH and ~80C for too long.
Not just that beautiful bend, but also all bottom of that was lid was covered by “juicy blisters”.
And because it would be too easy to fix the lid on its own, I’ve noticed that electrolyte started somehow leaking into the cooling basin. After scratching my head for a while and failing to explain how that would be happening without an actual hole in the tray, I removed all remaining electrolyte just to find this:
In my naivety I haven’t accounted for a material corrosion on that stainless steel tray – caused by that try being actually grounded! So it is very likely that all the time I was generating hydrogen in this stainless steel tray – it was generating it also around all its surface – and not on the cathode as intended!
Being unable to accept such a straightforward failure I made a quick trip to Nisbets and got whole the same set, but in poly-carbonate. Serge came instantly and ran whole cutting procedure again.
Based on pictures above – I hope you agree – Serge is getting damn good at it! It all starts looking seriously serious. 😀
Anyway, using that new narrow container, as shown on picture 4, caused instantly another problem – overheating. All that poly-carbonate tray together with a limited space for circulation made electrolyte boil in few minutes. Instant solution came to me to replace that hydrogen-capturing container with a bigger one and as we are now getting “seriously serious” I’ve picked “Holman 125mm x 1m PVC DWV Pipe + lid” and converted it to the shape needed.
Another run. Couple minutes later into another run, I’ve noticed a new electrolyte leak in to the cooling basin. Counting to ten, I’ve extracted remaining electrolyte into a container and checked that poly-carbonate trey. It broke!
This is actually becoming a museum of Jan’s failures! It really took me couple weeks to digest it and think it through. I’ve been discussing options with many smart brains including Serge, Richard and Greg. Out of the options available I started to incline to get another stainless-steel tray and paint it from inside with Bitumen.
Using bitumen will provide insulation between the electrolyte and a surface of that tray and that’s what’s needed. Problem here is that bitumen seems to be sensitive to a heat and melts in higher temperatures. Also I really need to have a good heat exchange between the electrolyte and the cooling basin to remove all that excessive heat (~30% of energy input). While having couple beers with my friend Vilda, I run him through all that story and he suddenly came with an idea of Teflon!
So, what it is Teflon? Teflon is that black non-sticking part of practically every pan in the kitchen these days.
Reading about it – it actually comes with an interesting story.
Teflon was accidentally discovered in 1938 by Roy J. Plunkett while he was working in New Jersey for DuPont. As Plunkett attempted to make a new chlorofluorocarbon refrigerant, the tetrafluoroethylene gas in its pressure bottle stopped flowing before the bottle’s weight had dropped to the point signalling “empty.” Since Plunkett was measuring the amount of gas used by weighing the bottle, he became curious as to the source of the weight, and finally resorted to sawing the bottle apart. He found the bottle’s interior coated with a waxy white material that was oddly slippery. Analysis showed that it was polymerized perfluoroethylene, with the iron from the inside of the container having acted as a catalyst at high pressure.[3] Kinetic Chemicals patented the new fluorinated plastic (analogous to the already known polyethylene) in 1941,[4] and registered the Teflon trademark in 1945.
Wikipedia
There is also a great in-depth description of “Polytetrafluoroethylene” coming from https://omnexus.specialchem.com/ – clearly worth reading for an even more in-depth understanding of Teflon.
Anyway, even more interesting from my perspective are its characteristics:
| Property | Value |
|---|---|
| Density | 2200 kg/m3 |
| Glass temperature | 114.85 °C (238.73 °F; 388.00 K)[19] |
| Melting point | 326.85 °C (620.33 °F; 600.00 K) |
| Thermal expansion | 112–125×10−6 K−1[20] |
| Thermal diffusivity | 0.124 mm2/s[21] |
| Young’s modulus | 0.5 GPa |
| Yield strength | 23 MPa |
| Bulk resistivity | 1018 Ω·cm[22] |
| Coefficient of friction | 0.05–0.10 |
| Dielectric constant | ε = 2.1, tan(δ) < 5×10−4 |
| Dielectric constant (60 Hz) | ε = 2.1, tan(δ) < 2×10−4 |
| Dielectric strength (1 MHz) | 60 MV/m |
| Magnetic susceptibility (SI, 22 °C) | −10.28×10−6[23] |
From the table above, you can see that Teflon’s melting point is 326C – that is way above what’s needed in our case. Another important parameter is Dielectric constant – which, in simple words, describes material’s resistance to conduct electric current. For example vacuum has this constant equal to 1 (this constant actually uses vacuum as a part of its definition), pure water 80 and copper > 250.000. So our Teflon is actually doing an excellent job here.
Last interesting parameter here is the Thermal diffusivity, which measures the rate of transfer of heat of a material from the hot end to the cold end. With the value of 0.124 mm2/s, our Teflon is not actually our champion at all (gold having 127, while wood 0.082), but if it can be used for cooking, it has to do for us as well.
In comparison with Bitumen – Teflon is clearly our best choice here. Now getting practical – Bitumen can be bought in a nearest Bunnings as a common gutter paint. Unlike Teflon – that actually needs to be sprayed on a surface as a dust and burned onto it in autoclave! Asking Mr. Google where it can be done in Australia, practically the only single place appeared – DECO Australia located in Minto NSW.
I’ve carefully sent them (safe) description of what needs to be done, asking for a quote and they came promptly with not-that-crazy $140 quote. Packaging was fun – our new stainless steel tray made it nicely in one of our used-to-be-welder boxes.
Payment managed by Veronika.
.. and in a couple days our improved tray arrived!
Our next hydrogen run awaits, but that is for another day 😉
Update 2022/12/21:
Received an email from Mr. Paul Martin, coming with a more comprehensive in-depth guide about “Polytetrafluoroethylene” (Teflon), having far more detailed explanation than Wikipedia. I thought it would be a great complement here – relevant section above updated.