2phat
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Molten salt electrolyte
First of all, Hello everyone, and sorry for bad english (google translate). I am not a chemist, so I need help. Seeking the melted salt, which serves
as the electrolyte (as in zebra batteries), which has the following characteristics:
- The highest possible breakdown (decomposition) voltage, at least 3,5 volts (how to calculate the decomposition voltage?),
- Low melting point, <270 C,
- Cheap and easy to find,
- Non-toxic, non-flammable, etc.
- Non-corrosive to carbon.
These are the main requirements.
It is desirable to have good conductivity, low viscosity, and is not corrosive to aluminum (the best), Inox (OK), copper (OK), titanium, nickel and
other (expensive).
For now, I have in mind the following salts:
1st sodium tetrachloraluminate (AlCl3 + NaCl):
- Mp 155 C, used in zebra batteries, but the aluminum chloride is a dangerous and difficult to find (expensive?)
2nd mixture CaNO3, KNO3, NaNO3:
- Mp about 130 C, but I do not know the other characteristics,
3rd FeCl3 + NaCl:
- Mp155 C, fairly inexpensive and available, I know that FeCl3 is very corrosive, it is in liquid form as well?
I found the forum link for Tohoku Molten Salt Database, but is now unavailable. Can someone provide a link that works?
I'm also interested in how the impurities could affect the above characteristics?
Thank you very much!
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aaparatuss
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The second mixture is a stable melt. Above 400 degrees the nitrates will decompose to nitrogen gas slowly.
Nitrate salt baths are useful for many things.
but what will be reduced what will be oxidized in your system if you are useing it for a type of battery.
The nitrate salt baths are known for their heat holding ability and a good sink of latent energy.
step up to stainless for these baths..
[Edited on 26-7-2011 by aaparatuss]
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2phat
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Thank you for your response. But I read somewhere (google books) that melted salts with cations such as S03, NO3, CO3 are not as good as the
electrolyte, presumably due to the low breakdown voltage, but I'm not sure.
Actually I think a little experiment with double layer capacitors in which you can use 3 types of electrolytes:
1st water-based, simple, inexpensive, but a small max. voltage of 1V, (electrolysis of water begins)
2.organic electrolyte + salt, toxic, hard to find, smaller capacity, but the max. voltage is 2.7v,
3rd ionic liquids, there are generally means room-temperature ionic liquids, and these are quite expensive, very low conductivity and high viscosity,
non-toxic and max. voltage up to 4V, but the capacity is even smaller due to large ions. But because the stored energy in the capacitor is
proportional to the square of voltage, these capacitors have the highest energy density. Still have not seen them in commercial capacitors, I read
that there are some problems.
But I have not seen the capacitor with molten inorganic salts, probably due to the need for high temperatures. But with good insulation, it should not
be a problem.
As you can see, since there is no chemical reaction, the composition of salt is not essential, it is important that the liquid has ions, and that the
breakdown voltage as large as possible to maximize energy density.
So I first need a formula to calculate the breakdown voltage of melted salts (eg sodium chloride, FeCl3 + NaCl) at a particular temperature, and thus
eliminate the ones that are too low breakdown voltage.
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watson.fawkes
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Quote: Originally posted by 2phat  | | 2.organic electrolyte + salt, toxic, hard to find, smaller capacity, but the max. voltage is 2.7v |
"Smaller"?
This is the class of electrolytes that Maxwell uses for their Boostcap line. They're rated in the few kF for a capacitor about the size of a soda can.
The surplus ones I've got are 2.6 kF @ 2.7 V. These are two generations back. The current generation is 3.0 V. The product sheet states they use
tetraethylammonium tetraflouroborate and acetonitrile.
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2phat
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Yes, a smaller capacity compared to the aqueous electrolyte. This same capacitor could have a 50% - 100% more capacity if the electrolyte for example
aqueous KOH, but because the max. voltage was 1V, would have a lower energy density.
I can not find the Maxwell capacitor with 3.0V operating voltage, can you provide a link?
I have a couple of questions:
1st On the following link:
http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch20/fa...
stated that the minimum voltage needed for electrolysis of melted sodium chloride 4.07 V, which is calculated using tables of standard potentials. Is
that right, given that the temperature of> 800C, and that NaCl is not in the water?
In the paper the following link:
http://www.re-journal.com/download.asp?ID=2851
Figure 1 shows the Theoretical decomposition voltage of some molten metallic
cations salts, and what is strange that the breakdown voltage greater than what is written in the table of standard potentials?
That is why I am confused.
2nd The standard potential for SO4 (2 -) is-2.05V:
SO42-2 ----> S2O82-+ 2 e- Eoox = -2.05 V
I can not find Eo (ox) for nitrate, carbonate, phosphate, OH (-) anions?
Why are they not in the table of standard potentials?
In electrolysis of NaCl (molten), occurring sodium and chlorine. What is obtained by electrolysis melted NaOH, Na2CO3, NaNO3, etc.? Sodium on one
electrode, but what emerges on the other electrode?
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watson.fawkes
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I was confusing
generations. Their previous operating voltage was 2.5V. They have a 3 kF can out, which is, I'm guessing, where the '3' came from.
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sakshaug007
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| Quote: Originally posted by 2phat |
In electrolysis of NaCl (molten), occurring sodium and chlorine. What is obtained by electrolysis melted NaOH, Na2CO3, NaNO3, etc.? Sodium on one
electrode, but what emerges on the other electrode? |
I've had the same question before. If my electrochemistry knowledge serves me right you would likely get for NaOH: OH- => O2 + H2O + e- for NaNO3:
NO3- => NO2 + O2 + e-, and for Na2CO3: (CO3)2- => CO2 + O2 + e-. It's possible you may end up with other polyatomic oxides along the way (as is
the case with sulfate).
This is a very good article article concerning the electrochemical oxidation of nitrate ion: http://curtin.academia.edu/DebbieSilvester/Papers/234602/The...
"If everyone knew everything what would be the point?"
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