Criticality safety assessment of tank 241-C-106 remediation Page: 45 of 83
This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
WHC-SD-W320-CSA-001 REV 0
/ broad when the crystal size is up to nearly 0.1 pm (Hsu 1977, p 108). Hence,
care must be taken when reviewing literature to discern whether the author is
calling a mineral completely amorphous (based on absolutely no diffraction
patterns above a background noise such as particles below 0.003 to 0.004 pm
would give) or whether the author is calling very broad peaks amorphous.
An author with this perspective might call such very broad spectra of
particles that are as large as 0.1 pm as amorphous. A quantitative equation
to estimate the crystallite size is known as the Scherrer-equation and is
defined as follows (Smith 1989):
D = (K "A)/[b * cos(0)]
where
D = Crystallite size in (A)
K = A shape constant (usually =0.9)
A = The wavelength of the incident X-ray in (A)
b = The half-width of the diffraction profile due to the sample
(measured breadth minus instrumental blank breadth at wavelength)
0 = Diffraction angle
A = Angstroms (10 pm).
This equation cannot be used to estimate the size of a crystal when the
sample gives no peak distinguishable from the instrument background (where b
becomes zero) but experts on X-ray diffraction have used the value quoted
above, 0.003 to 0.004 pm, as an estimate.
Thus, if the initial precipitates formed by the fast neutralization of
the Hanford acidic waste streams with sodium hydroxide are actually forming
very small Pu oxide and/or neutron absorbers crystalline particles with a size
less than 0.003 to 0.004 pm, they would appear amorphous to the traditional
instrumentation (powder X-ray diffraction) used to identify solids.
As described in various articles (e.g., Schwertmann and Cornell 1991,
Stumm and Morgan 1981, Hsu 1977, and Cornell and Schwertmann 1979) many common
oxides (such as Al, Fe, Cu and Zn) appear to form very small crystallites that
have been interpreted as being amorphous at first but that grow in size and
become "crystalline" with time. Schwertmann and Hsu prefer to conclude that
the crystallites were essentially crystalline from the start but the
individual particles were just too small to yield X-ray diffraction patterns
that could be measured. Because small particles exhibit very large surface
energy (Stumm and Morgan 1981), they are thermodynamically less stable than
larger particles of the same mineral. Thus, there is a driving force for the
small particles to agglomerate into more stable larger particles. Once the
particles reach a size above =0.003 pm, they start looking "crystalline" to
X-ray diffraction analyzers. In nature and in the laboratory, crystalline
ferric oxides and aluminum oxides often are found as discrete particles with
0.1 to 10 pm sizes.
Schwertmann and Cornell (1991) show that pure ferric oxides follow the
stated trends and transform into several larger-sized crystalline forms in a
matter of days to a few weeks, depending on chemical and thermal conditions.3-22
Upcoming Pages
Here’s what’s next.
Search Inside
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
Waltar, A. E. Criticality safety assessment of tank 241-C-106 remediation, report, July 19, 1996; Richland, Washington. (https://digital.library.unt.edu/ark:/67531/metadc702698/m1/45/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.