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watson.fawkes
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Quote: Originally posted by merrlin  | | At what point in an electrolytic reduction reaction can the cathode donated electron and an unpaired cation electron be considered a coupled electron
pair? I don't know the answer to this, but I believe that if the applied DC magnetic field and the microwave pumping intensity are large enough and
the other magnetic influences are minimized, that spin correlation could be achieved between an electron at the cathode surface and a cation that is
some distance away. |
My guess is that it's when they're within reaction distance, not farther. The whole
point is to suppress reaction by putting the electrons in a state that forbids reaction. So if they're not close enough to react, the reaction is
forbidden because of distance and spin coupling is irrelevant.
The problem you've got is that you need the cathode-donated electron to be bound into an orbital state with angular momentum (that is, not an 's'
state) so that it's got the possibility of forming triplets. I may be wrong on this, but I don't see how an unbound electron form a triplet. Electrons
inside the metallic electrode are bound, but they're not in orbital states (at least not the conduction electrons) because of the crystal lattice. So
you need to rely upon whatever is adsorbed onto the electrode surface to bind the electron. Ideally, that adsorbed material should completely coat the
cathode to prevent direct reduction of the metal ions.
In your proposed reaction, you've got sulfate, metal ions, a metallic cathode, and water. The negatively charge species, sulfate and
OH<sup>(-)</sup> will flee away from the cathode because of the electric field. The only adsorbed species are ions,
H<sub>3</sub>O<sup>(+)</sup>, and neutral water. In this setup, I don't see a situation that will lead to forbidden triplets.
On the other hand, you report this:
| Quote: | | Zinc and iron are attractive since fractionation by electrodeposition has already been reported for them |
Could you post these papers? I'd be interested in seeing the details of their apparatus and electrolyte. Either I'm missing
something, got something wrong, or don't know some details about what the situation is.
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merrlin
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| Quote: Originally posted by watson.fawkes | | Quote: Originally posted by merrlin | | With regard to fluorine, the important thing is that notwithstanding the nuclear spin state of the fluorine atom, the nucleus has a magnetic moment
that can influence the spin of nearby electrons. |
I don't know the relevant magnitude of the energies
involved. That does matter. I think I was assuming it was small, but I'm likely wrong there.
It would require a second oscillator, but since the gyromagnetic ratio of the nucleus is fixed, and since you know what your magnetic field is, the
resonant frequency for pumping is determined. |
You've anticipated one of the approaches that are available for pumping. For efficiency's sake, I am planning to tune the physical circuit structure
to the resonant frequency being used for magnetic pumping. A single frequency and two entirely different resonant phenomena! However, a wideband
structure could be simultaneously pumped at more than one frequency. Buchachenko has referred to the desirability of simultaneously pumping magnetic
and non-magnetic species, assuming that their resonance frequencies are sufficiently separated.
I contacted an expert in spin chemistry last June and he said in brief that it was interesting and would require more thought. Since he was out of the
country and also working on a textbook about spin chemistry, I had not heard from him since August, until today. He has doubts about overcoming the
relaxation effects I've referred to in my previous posts:
"The idea you propose is interesting but I think you will always be fighting some rather efficient electron spin relaxation processes that can
eliminate the coherence that you need on a very fast time scale, perhaps as fast as 100 ps."
The encouraging thing is that he has not rejected it out of hand, nor has he cited a fundamental flaw that dooms the approach. He has also indicated
that in spite of his busy schedule he is open to further discussion. The upper bound he cites for relaxation processes (100 ps) equates to 10 GHz and
is quite daunting, but by periodic cathode masking to avoid standing wave nodes and/or replacing the transmission line short by a matched termination,
I think the operating frequency could be extended to several GHz for research purposes. Solute and solvent selection offer a lot of potential for
shifting the relaxation times towards the microsecond end of the relaxation timescale.
I stumbled on to this approach in part because of my employment background involving microwave missile components and research and development in
electrochemical energy storage devices (ultracapacitors) for implantable defibrillators. I've come up with an apparently novel approach, but there are
a lot of people more capable than I am of carrying it forward. I am also sure that there are people on this board that possess knowledge and abilities
that I do not. Electrochemically, this is a vast unexplored territory that I believe is within the means of the individual explorer. I used to do
sideline research on high pressures and temperatures using a 10kV 200 microfarad capacitor that sits in my garage. This is a lot less dangerous.
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merrlin
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| Quote: | Originally posted by watson.fawkes
Could you post these papers? I'd be interested in seeing the details of their apparatus and electrolyte. |
The two papers concerning iron and zinc fractionation during electrodeposition are below. From what little I know about spintronics, it seems that the
spin of free electrons in solid conductors can be manipulated by external fields, so I guess that the task at hand is to induce the same spin state in
the free electron and unpaired electron. In simplest (too simple?) terms it would seem to be a matter of keeping them both "up" or both "down" by
appropriate magnetic pumping in an applied DC field.
Attachment: Redox-driven stable isotope fractionation in transition metals--Application to Zn electroplating.pdf (375kB)
This file has been downloaded 584 times
Attachment: The isotopic effects of electron transfer-An explanation for Fe isotope fractionation in nature.pdf (355kB)
This file has been downloaded 569 times
[Edited on 8-4-2009 by merrlin]
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watson.fawkes
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| Quote: Originally posted by merrlin | | The upper bound he cites for relaxation processes (100 ps) equates to 10 GHz and is quite daunting [...] Solute and solvent selection offer a lot of
potential for shifting the relaxation times towards the microsecond end of the relaxation timescale. |
That
100 ps time shouldn't be taken as corresponding specific frequency. You're looking at population dynamics. Essentially, you've got two competing
rates. One is a decay rate going from a target state to a non-target one; this is the relaxation rate. The other is going from non-target to target;
this is your pumping rate. Since these are species conversions, the underlying math starts off similar to radioactive decay. In this case, however,
you've got one species decaying to the other, and vice-versa. It's pretty straightforward to compute, given the two figures for half-life, what the
steady-state populations are.
I'd recommend doing this computation, because it will give you some good intuition about the effect of these manipulating these rates. I would not
assume, though, that these rates have the same mathematical form. The pumping rate can be assumed to be random, so that one's an exponential. I can't
say offhand, though, whether the decay process looks like a similar exponential or whether it can be assumed to be a roughly constant-time process (or
something else).
The principal means that you can decrease the pumping half-life is to increase the intensity of the pumping radiation. After that, I don't see
immediately how to increase the absorption cross-section, although that might be possible. radiation. Perhaps some modulation of the magnetic field
would make the species to be pumped appear "blacker".
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merrlin
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@watson.fawkes: You're right about looking at this as a problem in statistics. In spin chemistry there two relaxation times T1 and T2 that are
associated with spin-spin relaxation and spin-lattice relaxation respectively. Quoting Buchachenko's book:
"It is worth remembering that the transitions between electron spin states (and, consequently, between Zeeman sublevels) are responsible for electron
spin resonance (ESR), while the transitions between the nuclear spin states for the basis for nuclear magnetic resonance (NMR). These transitions are
induced by a microwave magnetic field at the frequency of electron or nuclear precession and are accompanied by spin projection changes. The magnetic
field may be applied externally, as in ESR or NMR, or be produced by the lattice stochastic molecular motion, which produces the fluctuating, noisy
magnetic fields of different frequencies and amplitudes. The spectral component of this noise at the frequency of electron or nuclear precession
induces the spin-lattice or spin-spin relaxation (i.e., transitions between spin states)."
Increasing the intensity of the magnetic field is definitely an advantage. This is one of the reasons that I believe radiationless pumping will be an
improvement. When working with a solution containing charged particles or dipoles, interactions with the electric field component of an
electromagnetic wave is going to increase the noise level without contributing to the magnetic pumping. Heating alone can prevent CW operation. By
using the magnetic field induced by a microwave current in a single-turn solenoid or short transmission line segment, a locally intense magnetic field
can be produced without an appreciable electric field being produced in the electrolyte. Because of skin depth losses at higher frequencies, there is
probably some kind of trade-off between high frequency/low intensity pumping and low frequency/high intensity pumping.
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