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Author: Subject: DIY - Diaphragms
BASF
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smile.gif posted on 25-3-2005 at 03:36
DIY - Diaphragms


I know that historic chloralkali-electrolysis also used cement, gipsum, ceramics as porous seperator between the cells before the plastic-fibre-reinforced asbestous diaphragm came to use.

Eventually it would be possible to concentrate nitric acid for example, using a CaSO4-diaphragm.
(i refer to http://67.15.145.24/~sciencem/talk/viewthread.php?action=attachment&tid=1716&pid=40180 brought on by chemoleo).




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[*] posted on 25-3-2005 at 05:39


I used to make copper sulpahte / copper wire and zinc sulphate / zinc batteries in small containers, the two cells being seperated by gypsum and they worked wonderfully. The gypsum thickness I used to make was about 1cm and it was still conductive.

Besides concentrating nitric acid, I found the document useful for hydroxylamine synthesis. I must get myself some mercury.




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[*] posted on 25-3-2005 at 06:14


Maybe it would be possible to make N2O5? - Can´t get these expensive nafion ion-exchange membranes(PTFE).

I wonder how stable the gypsum-barrier would be using 99+% HNO3.
(I fear the barrier would get brittle)
Of course a big-surface platinated Al/Fe-sheet would have to be used?

(platinated platinum should be beyond my financial abilities)

BTW: i would rather use zinc alone.
The yield of hydroxylamin is still acceptable, no mercury-trouble.

If you still stick to the mercury: mercury-salt solution on zinc to make the amalgamated electrode.
For the question of the mercury-salt i see only thermometers, mercury pigments (HgS) or the HgO in batteries as source.
Then dissolving in warm 70%HNO3 (NOx evolving reaction, similar to Pb(NO3)2) for HgO and Hg, depending on the source.

[Edited on 25-3-2005 by BASF]

[Edited on 25-3-2005 by BASF]




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[*] posted on 25-3-2005 at 12:27


Gypsum is soluble in strong acids..

Anyone used the car battery membranes in any experiment? I saved some just in case and now it's been a year they're lying without any use..
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[*] posted on 25-3-2005 at 13:13


Calcium sulfate in based on the strongest acid, no? Or is it just that all the other strong acids can be distilled out, pushing the equilibrium in favor of sulfates (ex: NaNO3 > HNO3(g) + NaSO4).

Tim
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[*] posted on 25-3-2005 at 22:46


Yeah, but HSO4- isn't that strong acid.. So following happenns: CaSO4 + H+ --> Ca++ + HSO4-
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[*] posted on 25-3-2005 at 23:12


Ah, like how bicarbonate is more soluble. :)

Tim
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[*] posted on 26-3-2005 at 09:41


The thieme lexicon states that hydrogen sulfates are only known as MHSO4 not
M2(HSO4)2.
(I believe the soluble species generated is some SO4x- complex-anion.)

Furthermore, the Jander Blasius "Lehrbuch der anal. u. präp. anorg. Chemie" states that CaSO4 is soluble in conc. H2SO4, conc. HCl and conc. (NH4)2SO4 solution. - So what happens in the case of 100% nitric acid?

Quote:

Anyone used the car battery membranes in any experiment?

What do these car-battery membranes consist of?

[Edited on 26-3-2005 by BASF]




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[*] posted on 9-4-2005 at 02:55


The car battery bags work great and can be spliced together or glued on a removable frame. Polypropylene is most common and the high quality larger maintenance free batteries have much heavier bags.

They stand up to most anything for quite a while although they get a little brittle using strong oxidizers. Chem resistance charts of plastics are readily available.

Never used more than dilute Nitric so can't say on this. In "Dirty" type cells the membranes need to be cleaned once in a while as deposits build up causing
excessive ohmic losses.
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[*] posted on 15-4-2005 at 09:22


Would asbestos used as a membrane, as in the cloralkali industry, resist the corrosive environment of two compartments of a cell one containing sulfuric acid and the other a mixture of sulfuric and nitric acids, all of which are at a 50% concentration? Apart from resisting the harshish conditions, can it be applied to such a type of electrolysis for the production of hydroxylamine? Would it be effective in seperating the two compartments? Thanks for the help.



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[*] posted on 17-4-2005 at 10:27


I'm sorry for my previous post. I was in a lack of information about asbestos. I didn't know is was composed of a magnesium silicate, and couldn't find any information on the net. Well now I know, and knowing that I suppose asbestos cannot be used in a strongly acidic medium. Do you have suggestions for any other types of diaphragms?

I suppose this is a little bit out of topic, but should a salt bridge filled with 50% sulfuric acid be sufficient to connect the type of electrolytic cell mentioned previously for the synthesis of hydroxylamine? Thanks for the help.




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[*] posted on 11-5-2005 at 22:37


..........mixture of sulfuric and nitric acids, all of which are at a 50% concentration?...............

The battery bags (PP or PE) will stand up fine as long as temp isn't over about 50deg or so.
They won't last forever but they were free anyway,or get a roll of Nafion. Best grade Nafion is only about $500 by the square foot with the cheap shit only say $250!

You might also try Tyvek! It's liquid shedding, gas permeable, teflon coated and would let ions thru. Maybe double it up if needed. Just get some USPS big envelopes or at the stationary store. It's PE use Typar for PP.
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[*] posted on 12-5-2005 at 03:10


About 5 to 10 mm fine glasswool (or more) for insulation covered in glasswool fabric for automotive repairs works too. The yellow insulation glasswool has to be heated to remove the binders until it turns grey/white. This gives a nive heat and acid resistant diaphragm.

/ORG




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