Sciencemadness Discussion Board - The Diaphragm Chronicles

The Diaphragm Chronicles

Zandins - 31-7-2016 at 09:32

Greetings Sciencemadness community,

Introduction
During the last month, I have done quite a lot of tinkering on different chloro-alkali electrolysis setups. One of the main caveats in its implementation can be the diaphragm, which separates the anolyte from the catholyte. I have gone through several different materials and would like to share my findings and conclusions.
Chapter 0:The Cell
The electrolysis cell is an empty plastic ice-cream box. The diaphragm separates the container into 2 unequal partitions. The cathode component(where NaOH is generated) is approx. 3 times larger than the anode component, to provide more room for the product and reduce the amount of chlorine-saturated water(in case of diaphragm failure).
Chapter I:Filter Paper
A diaphragm can be made from filter paper. If no sheet of sufficient size is avaliable, cardboard can be substituted with, with a cut square holding the filter paper of available size.
Pros: Cheap, readily available and easily workable, low resistance.
Cons:Fails quickly in hot or corrosive conditions.
Conclusion: The simplest option in case of mundane, noncaustic chemicals.
Chapter II:Glasswool
Using epoxy resin, a patch of glasswool can be glued in the container.
Pros:Cheap, easily available
Cons:Irritant, can be a pain to adhere to the cell body, tends to fail after ~12h of use at the point of most mechanical stress(slightly above the bottom adhesive)
Conclusion:More reliable than filter paper, though still not stable enough for bulk purposes.
Chapter III:Asbestos
In those countries where it is available, asbestos mattings can be used as diaphragms. However, safety precautions have to be observed, as asbestos is harmful to the lungs.
Pros:Inert, durable
Cons:Hard to acquire, toxic.
Conclusion:Asbestos can be used effectively, however, its limited availability decreases its usefulness.
Chapter IV:Battey plate pockets
In some lead-acid battery, each plate is contained in a "pocket",which prevents badly adhering paste from falling off and shorting between plates. I don't know the material they are made of, but it is durable,as they are made to resist 35 % sulfuric acid. The diaphragm must be soaked thoroughly before it starts conducting ions.
Pros:Durable, does not fail
Cons: Must destroy a car battery, must be soaked in electrolyte for at least 30 minutes to start conducting current.
Conclusion:The best option taken so far.
To be continued...

----
In a few days' time, I plan to test each material's electrical resistance as well as add some pictures of my setups. This data will gradually appear in the thread. Meanwhile, what are your preferred materials? Feel free to add any I am unaware of.

Zandins

Sulaiman - 31-7-2016 at 09:43

for some primary cell voltaic cell experiments I have been using these
http://www.edulab.com/prod/daniel-cell-porous-pot-150x50mm

BromicAcid - 31-7-2016 at 09:50

As I recall I have seen people using Tyvek and Gortex to various efficacies. An unglazed ceramic pot was always the go-to in college but it's my understanding that it severely limits the current of your cell.

Fulmen - 31-7-2016 at 13:46

Something like Tyvek sounds promising. It's made from polyethylene, so it should be fairly resistant to chemical attacks. If needed you should be able to heat-weld it to a larger support structure.

MrHomeScientist - 1-8-2016 at 07:01

I've used ceramic pots for cells before and they definitely work, but the real question is how do you seal the hole at the bottom? Everything I've tried hasn't fared well in the harsh environment of the cell.

Magpie - 1-8-2016 at 07:34

If you have access to a kiln for ceramics you could slip cast ceramic tubes, closed one end. These could be made to any desired composition and wall thickness.

Pottery

Zandins - 1-8-2016 at 11:21

I have heard many people dismissing pottery as having too high electrical resistance, is there any quantitative data to confirm it?

careysub - 1-8-2016 at 16:31

This study tested Tyvek and found it had very high resistivity:

http://journals.plos.org/plosone/article?id=10.1371/journal....

But it is cheap and readily available and otherwise attractive (chemically resistant, tough), so if anyone has a mind to do any testing give it a go.

Any opinion on whether reverse osmosis membranes might be suitable?

http://www.ebay.com/itm/Osmosis-Membrane-Only-/112022860681?...

[Edited on 2-8-2016 by careysub]

PHILOU Zrealone - 2-8-2016 at 09:25

Quote: Originally posted by careysub

Any opinion on whether reverse osmosis membranes might be suitable?

http://www.ebay.com/itm/Osmosis-Membrane-Only-/112022860681?...

[Edited on 2-8-2016 by careysub]

Reverse osmosis membrane theorically will be of no use since it is only permeable to water...thus not to ions except maybe the ones from water autoprotolysis (H(+) or H3O(+) and OH(-)); and if this happens, then you will have dramatic pH change from one side to the other...very fast leading to reverse migration of the H(+) and OH(-) ions to neutralize.

[Edited on 2-8-2016 by PHILOU Zrealone]

Sulaiman - 2-8-2016 at 11:22

MrHomeScientist
i have read but not verified that candle wax is a suitable sealant for 'flower pot' holes.
Daniell's original cell used ox gullet ....

PHILOU Zrealone - 2-8-2016 at 12:31

Quote: Originally posted by Sulaiman

MrHomeScientist
i have read but not verified that candle wax is a suitable sealant for 'flower pot' holes.
Daniell's original cell used ox gullet ....

Should be OK because wax is alcanic in nature --> hydrophobic, impermeable like polyethylen but with a much lower melting point...so don't go too high or it will soften, lose integrity and melt.
Otherwise use silicone alone or PolyEthylen or PolyPropylen and glue (or silicone as a glue).

[Edited on 2-8-2016 by PHILOU Zrealone]

Romain - 17-9-2016 at 03:14

Very interested in this topic, I'm looking to make a chlor-alkali cell too. Regarding flower pots:

I can say that I used one in a permanganate cell (see last post in permanganate thread for details) and it worked pretty well (alkaline sodium permanganate up to 0.4 M on the anode side and KOH 1M on the cathode side). The pot was left untouched after electrolysis so it should withstand the caustic environment in a chlor-alkali cell without too much trouble. Definitely not expensive to replace in any case.

As far as the electrical resistance is concerned, it worked surprisingly well (at 5 V and room temp. for a 7 cm diameter pot, a current of 500 mA could pass through the cell).

And regarding sealing the bottom of the flower pot:
- I used a rubber stopper for the permanganate cell and it worked well.
- I tried candle wax for a very quick chlor-alkali test and it seemed to work too. Note that the wax tends to wick up in the ceramic and block the pores so you loose some conductive surface on the sides if you use too much wax and heat for too long. It may not be an issue with bigger pots.

careysub - 17-9-2016 at 05:39

You might also consider sodium silicate/ground vermiculite cement for sealing. It is usually used as a high temperature cement, but should be an inert ceramic material when hardened.

On-line guidance also suggests: "Adding a small amount of Portland cement or plaster to an aggregate mix of sodium silicate and vermiculite will cause the mixture to set in just a few minutes."

Although I know it is not typical for electrolysis cells to operate "hot", be aware that candle wax can start to melt around 120 F, and the widely available GulfWax melts at 128-133 F. The silicate cement can take any temperature.

[Edited on 17-9-2016 by careysub]

MrHomeScientist - 19-9-2016 at 07:48

All interesting options! I'll have to try those next time I make a cell.

I've tried various types of caulk but those all fail relatively quickly. Candle wax sounds quick and easy.

alive&kickin - 21-9-2016 at 04:51

MrHomeScientist & Zandins, no need to seal a hole in ceramic pots when you can find them without holes. Found these at Walmart, (also saw them at Michael's craft store, I'm sure others carry them) for $3.00 and they hold approx 500ml. Of course the outside pot would have to be fairly large, but should work.

[Edited on 21-9-2016 by alive&kickin]

Deathunter88 - 21-9-2016 at 04:55

Quote: Originally posted by alive&kickin

MrHomeScientist & Zandins, no need to seal a hole in ceramic pots when you can find them without holes. Found these at Walmart, (also saw them at Michael's craft store, I'm sure others carry them) for $3.00 and they hold approx 500ml. Of course the outside pot would have to be fairly large, but should work.

The glaze on the inside of the pot would pose a problem right?

alive&kickin - 21-9-2016 at 05:00

sorry Deathhunter88, wrong picture, picked up both at the store glazed and unglazed. Wasn't sure what I was going to use them for at the time, but thought ought to grab them while I could.

MrHomeScientist - 21-9-2016 at 05:35

Wow nice! In the gardening section? I will definitely get some of those.

careysub - 21-9-2016 at 06:52

Quote: Originally posted by alive&kickin

I wonder if these are a regional item. I have looked at both stores in the past and have never seen them (SoCal) and they do not appear on either stores website from what I can tell. I know that not everything in these stores is a national item.

When searching on-line for ceramic electrolysis cells I have found the terms of art are "porous cup" and "porous pot" is you want to find purpose-made ones. They are rather hard to source even so.

In the UK you have "porous pot" at http://education.scichem.com/
In the US "porous cup" here:
http://crscientific.com/electricity.html
http://products.unbeatablesale.com/ginsberg_scientific_7_182...
In India:
http://japson.com/product/porous-pot-_280_4.html
In Australia:
http://www.haines.com.au/index.php/lab-equipment/porous-pot-...

Ginsberg Scientific makes these for school use (and Googling "Ginsberg cup" or variations is useful), and are available cheap in quantity here:
http://www.teachersupplysource.com/product/64163/ginsberg-po...

Anyone want to do a group order? They are only $1.75, but the minimum order is $40 (they have other school supplies though, so you could piggy-back).

This same Ginsberg cup is available on Amazon for the preposterous price of $22 each:
https://www.amazon.com/Ginsberg-Porous-Cup-Voltaic-Cell/dp/B...

I think you can order these from Fischer since it runs an educational supply operation, and is not just a B2B outfit:
https://www.fishersci.com/shop/products//s13612

[Edited on 21-9-2016 by careysub]

yobbo II - 28-9-2016 at 14:25

The Nafion store

http://www.nafionstore.com/

Nafion tubes

http://www.permapure.com/products/nafion-tubing/

[Edited on 28-9-2016 by yobbo II]

careysub - 28-9-2016 at 16:07

Quote:

Quote: Originally posted by yobbo II

The Nafion store

http://www.nafionstore.com/

The store at least lists prices and has an actual store front purchasing system in place. But the cheapest membrane listed is $140 per square foot.

Not impossibly expensive, just very, very expensive:
http://www.nafionstore.com/store/p/40-Nafion-Membrane-NR-211...

Quote: Originally posted by yobbo II

Nafion tubes

http://www.permapure.com/products/nafion-tubing/

[Edited on 28-9-2016 by yobbo II]

Like most industrial suppliers, there are no prices listed, nor any way to buy on-line. You have to contact them for a quote, and submit a purchase order. Nearly all such places have no interest in dealing with hobbyists (I occasionally try to contact such places, but rarely do I get a response, and never a helpful one thus far.)

yobbo II - 29-9-2016 at 03:05

Agreed on all fronts.

One way to get some product that sometimes works is to request a sample. You can suggest you are a student or somesuch.

If two people were to purchase the square foot it would get more manageable but still expensive.

These guys sell smaller amounts but the price is the same for a square foot

http://fuelcellsetc.com/store/Nafion/N212?gclid=CPK19tfAtM8C...

Lots to choose from here but the prices are still high

http://fuelcellstore.com/fuel-cell-components/membranes

The 'resin' beads that (I don't know exactly what these things are) are in water softeners were obtained, places onto a flat surface (say a glass sheet) in a one bead layer and they some substance (say polyester resin (no relation the the 'resin' mentioned above) or wax) was pored onto this layer so that a sheet of 'resin beads in a solid matrix' was formed. This could be used as a membrane (or could it). The beads would perhaps be too thick. What are the beads made from?
You sometimes see domestic water softeners dumped with the beads still inside.

http://www.softenerparts.com/Resin_Replacement_s/54.htm

Resin for sale
http://www.softenerparts.com/High_Capacity_Cation_Softening_...

About 120 dollars for a cubic foot of stuff. That would make a lot of one bead think membrane assuming the half crazy idea is sensible.

Water softening manual attached.

[Edited on 29-9-2016 by yobbo II]

Attachment: 0901b80380885879.pdf (2.8MB)
This file has been downloaded 551 times

Melgar - 30-9-2016 at 07:11

Doesn't anyone else use glue guns to quickly assemble prototypes? The glue sticks that they use are basically low-melting-point polyethylene. At least the white translucent ones are. And in my experience, as long as you attach it to a clean, dry surface, it has the same chemical properties as polyethylene, in that it's inert to just about everything as long as it stays below its melting point, which is hot enough to burn your skin, so probably 80-90C. You could just put the pot on an upside-down beaker or some other piece of glass, then use a glue gun to fill in the hole with glue, or use any other heat source for that matter. Or just glue a piece of polyethylene to the top or the bottom of the hole.

edit: yobbo, you want ion exchange MEMBRANES, not resin.

[Edited on 9/30/16 by Melgar]