# Does a Centrifuge distort atomic geometry?

1. Apr 10, 2006

### pallidin

Greetings. I know that a centrifuge can "seperate" different elements by virtue of centrifugal force, but what effect does a centrifuge have on the atomic geometry of individual atoms?
That is, since the nucleus of an atom is generally more massive than the collective orbiting electrons, does a centrifuge "distort" an otherwise "balanced" geometry of the atom?
Is is possible to "rip" the nucleus out of an atom by extreme centrifugal force?

2. Apr 10, 2006

### Integral

Staff Emeritus
Think about the material you would have to use to accomplish this? Would not the atoms of the centrifuge disinagrate? I believe that the answer to this is no, at least with materials known to us today.

3. Apr 10, 2006

### pervect

Staff Emeritus
A centrifuge essentially creates pressure, according to the relation a*x, where a is the acceleration of the centrifuge, and x is the position. This is equivalent to the formula P = g*d for hydrodynamics, where d is the depth.

[clarification]This is imagining a liquid or gasseous sample, in a test-tube in a centrifuge, being spun around. The liquid will be under pressure - the greater the depth, the higher the pressure. The rotor of the centrifuge on the other hand, will be in tension.

You can replace a*x by $\int a(x) dx$ in the case where the acceleration variews with position.

There will probably be some very small effects on the orbits of the electrons as the pressure increases. I haven't worked out the equations, but intuition suggests that they will become oval rather than circular.

As a practical matter, you can't rip atoms apart in a centrifuge because the rotor is built of atoms. The bonds between atoms will fail before the atoms themselves do, causing the rotor of the centrifuge to fail. But you can look at what happens to matter under high pressure by looking at high gravity situations, like the interior of Jupiter and the surface and interior of stars.

Atoms do not exactly "rip apart" in these circumstances, but given enough pressure, normal matter will turn into electron degnerate matter, white dwarf star material.

What basically happens in this case is that rather than have electrons orbiting individual nucleii, you have a "sea" of electrons, not associated with any particular nucleus, with the nucleii scattered throughout the "sea" of electrons.

To create this state of affairs requires enormous pressures, but it will happen under extreme conditions such as the interior of a white dwarf. (Further reading suggests that metallic hydrogen, thought to be found at the core of Jupiter, may also be a form of electron degenerate matter, though I'm not terribly familiar with it or its properties. Corrections on this point are welcome.)

http://en.wikipedia.org/wiki/Degenerate_matter

As Wiki mentions, it is the Pauli exclusion principle that keeps electrons normally form intermingling with the nucleii of any atom other than "their own". When the pressure becomes high enough the Pauli force is not large enough to exclude electrons from inter-penetrating, and we get degenerate matter.

Last edited: Apr 10, 2006
4. Apr 10, 2006

### pallidin

With a mechanical centrifuge, yes. There would be significant, catastrophic issues with centrifuge motion as covalent bonds are ripped apart during the event.
But prior to this catastrophic event, does the atomic geometry alter, with electron shells "shifting" to assymetry?
Does this electron assymetrical shell nature force, or assist, covalent bond-breaking?

5. Apr 10, 2006

### Staff: Mentor

A centrifuge produces a centrifugal force on atoms (or molecules). At a given radius from the center, the heavier atoms (molecules) will experience a proportionally greater force m$\omega^2$r - note force is proportional to mass. This is primarily how U238 is separated from U235 (both in form of UF6 molecules)- the heavier molecules diffuse toward the outside of the centrifuge and displace the lighter molecules which move inward.

The energies required to ionize atoms are on the order of eV (see first ionization potential), and atoms have Z electrons surrounding them. One can convert eV (or equivalent temperature T) to kinetic energy from which one could compute the speed of molecules or atoms. The centrifuge velocities are well below that, IIRC.

If the contents of a centrifuge could be disassembled, then the centrifuge itself would ostensibly disintegrate.

Besides - atoms are ionized by collisions (with atoms, nuclei or electrons) or EM radiation, and unless energy is dumped into them, the atoms recombine. The collisions usually require high temperatures - as in a plasma.

Last edited: Apr 10, 2006
6. Apr 10, 2006

### pallidin

I thus assume that covalent bond-breaking in a mechanical centrifuge is partially the result of catastrophic covalent orbital alteration from circular to obloid; rendering stable covalent bonding difficult.

7. Apr 10, 2006

### Staff: Mentor

In the centrifuge, the mass of the centrifuge trying to move outward puts the structure under tensile stress in the hoop or circumferential direction. That is what breaks the bonds, which normally happens near the grain boundaries in a polycrystalline material.

Materials most often fail in tension or shear.

IIRC - the bond between electron and its parent atom is much stronger than the bond between atoms, at least for covalent bonds. Maybe Gokul or ZapperZ can elucidate upon this matter.

8. Apr 10, 2006

### pervect

Staff Emeritus
The potential energy correction for an isolated atom in an accelerating frame of reference is just mgh. This potential term is the term that one would have to add to Schrodinger's equation in addition to the electrostatic potential term to solve for the effect of the acceleration on the shape of the electrons orbit.

To get an idea of the effect, let's look at hydrogen in a 1 g field, where we would calculate the energy by the following formula

mass of electron * 9.8 m/s^2 * bohr radius

Google gives this as 4.7e-40 joules, which is 3*10^-21 electron volts.

We can see that this is totally negligible compared to the electrostatic binding energy, which is on the order of 14 ev - by over 20 orders of magnitude.

While this is an extremely rough calculation only for one particular atom, it illustrates why the effect is not very important on the atomic scale at reasonable accelerations.

9. Apr 11, 2006

### pallidin

Thanks, pervect and all. I actually learned more than I previously knew!
PF rocks!

10. Apr 11, 2006

### DaveC426913

I'm hoping he really means either
a] he learned something, or
b] he now knows more than he previously knew,
because if, literally, he learned more than he previously knew, then his sum total knowledge has more than doubled during the course of this thread (which, I suppose if we confine it strictly to the context of the topic - as opposed to his overall knowledge - is not entirely outside the realm of possibility...)