At 04:42 PM 9/29/00 +0200, you wrote:
>Jim wrote:
>
> >The hydrostatic stress level is inversely
> > proportional to the radius of curvature of the particles. Therefore, the
>
>Exactly, how did you determine the trend? Have you measured the cell
>parameters for different granulometries?
This view of the matter came from consideration of surface tension effects
on droplets. The hydrostatic compressive stress on a droplet due to
surface tension is inversely proportional it's size. There is
circumstantial evidence in the literature on the observance of a reduction
in lattice parameter with a reduction in crystallite size. But I don't
know that anyone has actually set out to due a systematics study of this
effect. It does, however, follow that this purely geometric effect will
operate in reverse, i.e., surface compression for surface tension and
hydrostatic tension for hydrostatic compression.
>Last curiosity. The old SRM 640b was having a certified cell parameter
>slightly smaller than the crystal used for 640c. Do you think that in this
>case it was not measured correctly the "absolute value" or it "was"
>different?
Interesting question: The certification methods for the two SRMs were
completely different (this is why SRM 640c has been so long in
arrival). Therefore, it is difficult to say why the two certified cell
parameters are different. I may look into this in the future. I am
building a new diffractometer for certification of SRMs and this is a
problem to which it will be well suited.
>Sorry for the question, but I personally and philosophically don't think we
>can measure absolute values......
I disagree; and I enjoy my job too!
Regards,
Jim
James P. Cline [EMAIL PROTECTED]
Ceramics Division Voice (301) 975 5793
National Institute of Standards and Technology FAX (301) 975 5334
100 Bureau Dr. stop 8523
Gaithersburg, MD 20899-8523 USA
