Summer School 2010.7: Quantum Physics

Our lessons are coming to a close, but that also means they are approaching the modern view of quantum mechanics. This week, we go Down the Rabbit Hole.

10 replies on “Summer School 2010.7: Quantum Physics”

  1. TarlNeustaedter says:

    Thank you. The explanation of electron orbitals matching x+1/2 wavelength being because of self-interference had never sunk in before. It will stick this time.

  2. jtriley says:

    Quantum Physics is about to change the world (again)

    A small Texas start-up company called EEStor has build a factory to build EEStor Electrical Energy Storage Unit (EESU) for all electric cars. The 300 pound units will power a sports or economy car for 300 miles on a charge and are rated at 1,000,000 charge/discharge cycles. The first production units are due out this fall.

    Everybody wants to know how they work. Technical people want to know now! EEStor has been very secretive for the last two years but there is a long trail of breadcrumbs we can follow.

    One thing is clear. This baby works on quantum physics.

    Here is my best guess on how it works:

    • jtriley says:

      Visualizing How Barium Titanate Super Caps Work

      The heart of the EESU is a super-cap made from to thin aluminum plates with a layer of especially prepared barium titanate between them. This structure forms a super-cap and the EESU is just a box full of several thousand of these caps in parallel. The only real technical question is what is so special about the barium titanate layer that enables the super-cap to hold so much power.

      The barium titanate crystal structure includes one titanium ion (Ti4+) boxed in by six oxygen atoms. You can think of it as ionized titanium atom at the center of a game die with an oxygen atom in the middle of each face.

      If an external electric field is applied, the Ti4+ ion is drawn off center in the direction of the negative charge. Then the fun starts. Barium titanate is a member of group of compounds described as Ferroelectric which have a very unusual property. In normal materials when the external field is removed, all the atoms are forced back to their low energy positions by internal electrostatic forces. In ferroelectric materials some displaced ions, here Ti4+, can fall into a dip in the energy curve and not return all the way to their lowest state.

      This is like having a marble in a round bottomed metal bowl. External forces can push the marble up the side of the bowl temporarily but when the forces are removed the marble will return to the low point in the center. The ferroelectric bowl has a special configuration. Around the side of the bowl are dimples like a Jell-O mold in which the marble can settle and remain indefinitely unless disturbed by another external force.

      When Ti4+ ion is in this displaced but stable state, the crystal becomes highly polarized with each crystalline cell having a positive end and a negative end. It is as if the crystal contained many millions of tiny permanent electric fields, all aligned. This arrangement is somewhat like a permanent magnet and has been know in the lab for about a 100 years.
      To make a capacitor, this material is formed between two metal plates. Excess electrons are forced on one plate by an external voltage and the same number of electrons are withdrawn from the other leaving holes. This establishes an electric field between the two plates.

      The electrons can be seen as small clouds of probability under the Heisenberg Uncertainty Principle. If a measurement were made, the probability field defines the chances of finding the electron at any particular spot.

      Electrons are affected by the electro-magnetic force and carry a negative charge. When the probability cloud of one electron overlaps with another’s, then they exchange virtual photons and are strongly repelled from each other. This force is inversely proportional to the distance between the particles. The more excess electrons your force onto the plates, the harder they push back.
      If an electron’s probability cloud overlaps a particle with a positive charge, like a proton, the particle exchange virtual photons and are attracted. The spaces where electrons have been forcibly removed, called holes, act much like an electrons would if it had a positive charge.
      If an system of electrons is in a low energy configuration and balanced with positive particles as they are in the complete shells of an atom, then the probability clouds of all the particles in the system blend together and have little effect on outside particles.

      When the barium titanate is polarized it is not in this balanced state. It has stored energy which is distorting the crystal structure so that the overall probability cloud favors negative charges at one end and positive at the other.
      When many extra electrons are pushed onto one plate, their probability fields overlap and they feel each other’s electric fields. They are strongly repelled. These electrons also feel the holes on the opposite plate and are attracted to them, but the holes are distant. The balance of these forces sets how much energy can be stored in the capacitor for a given voltage.

      The presence of the polarized barium titanate lets the excess electrons feel the holes on the far plate much more clearly. It is as if the polarized crystal cells are passing the influence of the holes along like a daisy chain. The final result is that an enormously larger number of electrons can be forced onto the plate by a given voltage. EEStor is claiming an improvement of 19,600.
      In the manufacturing process the whole assembly is heated up above the Curie Point of Barium Titanate (120 C). This erases any past memory. The assembly is then cooled while under an external electric charge which programs a large numbers of titanium ions to be out of position in support of the external field as the temperature drops back beneath the Curie Point.

      At these temperatures the plastic matrix material is also quite liquid. This allows the rounded barium titanate particles to rotate somewhat to align with the external field. They are then frozen in place when the plastic matrix material cools.

      Barium titanate has strong piezoelectric properties. The shape of the crystal changes significantly under the influence of the external electric field. The distances moved are not great but the effect can create enormous internal stresses. By dividing the barium titanate into small particles, we can insure that internal stress will not be so large that the material breakdowns. This does mean that any dimensional changes of the particles will have to be taken up by the slightly rubbery plastic matrix. The small size of the particles also insures that each particle is one electric filed domain and domain boundaries do not move.

      The amount of power that can be stored in a capacitor is proportional to the square of the voltage on its plates. Most ultra-caps operate at relatively low voltages from 3.0 to 120 Volts. The EEStor EESU works at a very high voltage of 3750 Volts. The ability to handle this voltage is an absolute key to its success.
      Although the ceramic, barium titanate, is a good insulator, in the ferroelectric state and at the achievable level of purity, it is not a good enough insulator for use in a high voltage capacitor. This mean that additional insulation is needed to provide the needed voltage rating. This layer should be as thin as possible and is provided here by an alumina coating (think sparkplugs) on the particles which is farther supported by the plastic matrix. This alumina layer also provides a protective skin around the particles.

      Unfortunately the whole process is easily poisoned by impurities in the barium titanate. Any crystal cell with an impurity not only does not participate in the polarization, but it shades others that do and may provide movable charges. Fortunately modern manufacturing techniques developed for microchips and hard drives make the needed purity possible, even if they make manufacture difficult and slow to set up. The claimed purity is 30 parts per billion.

      Although the ferroelectric materials have been known for nearly a hundred years (1921), it is only within the last few decades that we have been able to mass manufacture major consumer devices based on them. Such product include liquid crystal displays, piezoelectric actuators, electret microphones, and now energy storage units for electric cars.

      ________________-

      This explanation seems a bit weak. Can anybody in this course use quantum physics arguments to show where most of the power is actually stored.

  3. TarlNeustaedter says:

    A couple of rules of thumb:
    1) If a small company makes extraordinary scientific claims but is secretive, odds are overwhelmingly in favor of it being a scam rather than new science.
    2) When the ratings are specified in terms of “miles of sports car” rather than kWh or joules per volume or mass, the imprecision is deliberate.

    The advertising tract you posted doesn’t have enough information to start worrying about quantum physics; capacitors in general are expressions of QM, but the above has enough techno-babble that it’s hard to separate babble from ordinary description of capacitors from what might be different about their product.

    • JD DeLuzio says:

      I was wondering about my poor returns on that money I sent to Fleischmann and Pons.

    • jtriley says:

      They are backed by big time venture capitalists and Lockheed has put in a million for the military rights. Their Texas factory is built and the Zenn Motors of Canada has bet their 1.2 billion dollar company on getting the product.

      A good project history is available on Wikipedia under “EEStor”.

      The most important technical information is in their patents that are available through the Wikipedia article.

      A out-and-out hoax this is not. But, that does not meant that it is too late to fail.

      If they are not shipping product by the end of the year they are dead.

      • TarlNeustaedter says:

        Supercaps in general are big business these days; my employer ships computers with capacitors instead of batteries to keep disk-cache memory alive through a power-failure. It turns out the energy density of these capacitors is so high we have to remove them from systems before air-shipping them – they are in effect little bombs. And their capacity is increasing more and more as we get better materials.

        Supercaps will eventually replace rechargeable batteries in most applications, likely with many more charge/discharge cycle before having to be replaced. I just can’t tell whether the company you are referring to has anything new – too much advertisingspeak and technobabble.

  4. jtriley says:

    Neutrino flux from the sun may affect half-lifes on Earth

    The measured half-lifes of rapidly decaying isotopes manufactured on Earth for medical purposes may show timing changes due to activity deep inside the sun.

    http://news.stanford.edu/news/2010/august/sun-082310.html

    This could affect the age estimated made with carbon-14 and make it difficult for doctors to set the correct dosage for cancer killers.

    This is a concern in that a particle that is not suppose to interact with anything much, the neutrino, is changing something that is not suppose to change, half-lifes.

    Earlier work has also shown that the two inner electrons are close enough to the nucleus the have some effect on half-lives.

  5. jtriley says:

    Thanks for the summer course. I enjoyed it immensely.

    It seems to end at the point where the explanations are not simple any more. In keeping things simple it got a lot farther then I though possible at the start.

    I guess it has to be a bit of a cliff hanger so that your students will go on to other studies.

    You might want to note that Lawrence M. Krauss has a new biography of Richard Feynman out soon called “Quantum Man”.

    Thanks again,
    Tom Riley

    • Thanks for the feedback. There are other topics I could have covered, but one of my goals was to restrict things to theories that likely aren’t going anywhere. I’ve been toying with a followup course to cover the topics not covered here for some future summer (after assessment in 2011, entirely written, and relativity in 2012, which I started in earnest this weekend) but it wouldn’t have the coherence of the series, as it’s entirely made of the paths not taken. Instead, I may just do a series of unrelated one off articles.
      Either that, or follow up on the forthcoming “Math From Scratch” project (covering all of the math I know, starting January 1, 2011 in triweekly articles; the first five are done) with a “Physics From Scratch” project that covers everything I know in that field, but that would be quite a bit longer. (I actually have degrees in physics. Math is a hobby.)

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