Jim wrote:
>At 11:32 AM 9/28/00 +0200, you wrote:
>>Hi Jim,
>>
>>i) this is what the NIST web site shows under X-ray constants for the
>>Silicon lattice parameter: "Concise form 543.102 088(16) x 10-12 m"
>>ii) this is shown in your SRM 640c Certificate of Silicon Powder:
>>"0.54311946 nm +-0.00000092 nm"
>>
>>I can see no overlap of the estimated standard deviations.
>>Any comment?
>
>The single crystal lattice parameter value listed on the web site under
>X-ray constants is the result of a compilation of measurements from three
>laboratories (PTB, NRLM, and IMGC) using combined X-ray and optical
>interferometry. The value listed is for an "ideal" silicon of a specific
>........
This explain a lot. I made some computations for curiosity (we also
encountered some cases where similar idrostatic stresses change the lattice
parameters) and for the case of the oxide using a particle size of 5
microns (mean from the certificate) the expansion can be caused by an oxide
of 2.5 nm with a tensile stress of 5 GPa (or higher thickness and lower
stress).
For the other case of the vacuum/no vacuum the change in cell parameters
requires a change in pressure of around 7.15 bars that is a little bit more
than 1 atm.....
>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?
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?
Sorry for the question, but I personally and philosophically don't think we
can measure absolute values......
Best regards,
Luca Lutterotti
-----------------------Luca Lutterotti----------------------------
Dipartimento di Ingegneria dei Materiali, Universita' di Trento,
via Mesiano 77, 38050 Trento, Italy
e-mail address : [EMAIL PROTECTED]
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