On Jan 10, 2006, at 11:47 AM, [EMAIL PROTECTED] wrote:
Thanks! Good food must be digested slowly. But, one question, you
said single protons or deuterons don't fit in the Pd lattice. The
Pd lattice is fcc with a unit cell dimension of 389.1 pm.
Interesting. I have a bond length for Pd of 275.11 pm. This is not
consistent with a cell size of 389.1 pm. If you have better lattice
data for the table below I would very much like to see it.
Pd atomic radius is 137 pm.
I have 179 pm atomic radius, and 128 pm covalent radius in my Sargent-
Welch periodic table. I'm pretty sure I used the covalent radius in
the calculations for the size ball that would fit in the face hole
and tetrahedral space, so this gives more space (a smaller intruding
bulge) than your numbers, and your unit cell dimension implies a
longer bond length than I used, so that implies more space as well.
It would indeed be nice to get the best available data for all this.
With a Bohr radius of 0.529 pm, the hydrogen atom
My periodic table shows the H covalent radius to be 0.32 angstroms,
i.e. 32 pm, and the H radius to be 0.79 angstroms, 79 pm. Even 0.529
angstroms sounds way off, unless the H is in partial orbital state.
certainly squeezes in interstitially; or, am I missing something?
Forgive me if the answer is in the paper cited.
For some reason we have very different data. Mine could certainly be
wrong. I did not use the most reliable and current source.
Unfortunately I don't recall offhand where I got the bond length data
I used in the AEH paper. I'll have to dig around and don't have the
time at the moment. Unfortunately I threw out the drawing and
original paper and pencil calculations, and have upgraded computers
since. Below is the table I computed, as cut and pasted from the AEH
article.
Elem. Bond Covalent Atomic Face Hole Tetrahedral
Length Radius Radius Radius Space Radius
(A) (A) (A) (A) (A)
Ge 2.4498 1.22 1.52 0.1944 0.5123
Pt 2.7460 1.30 1.83 0.2854 0.6417
Ni 2.4916 1.15 1.62 0.2885 0.6118
Cu 2.5560 1.17 1.57 0.3057 0.6373
Pd 2.7511 1.28 1.79 0.3083 0.6653
Au 2.8841 1.34 1.79 0.3251 0.6993
Ag 2.8894 1.34 1.75 0.3282 0.7031
Al 2.8630 1.25 1.82 0.4030 0.7744
Ce 3.6500 1.65 2.70 0.4573 0.9309
Yb 3.8800 1.74 2.40 0.5001 1.0035
Ca 3.9470 1.74 2.23 0.5388 1.0509
Pb 3.5003 1.47 1.81 0.5509 1.0051
Sr 4.3020 1.91 2.45 0.5738 1.1319
I simply looked at the geometry as if the atoms were little balls.
I believe I've read a fairly recent article somewhere where neutron
scattering data confirmed the partial orbital state of single
hydrogen atoms in a loaded Pd lattice. I don't recall where. My
memory is just not very good.
It does seem to me that if your data shown above is assumed then
there is no way to account for the lattice swelling that occurs prior
to full loading, and it would be difficult to account for diffusion
rate observations. The hydrogen would go through the lattice like
food through a goose.
It would be good to find some reliable data.
Horace Heffner
