Hanford Tank 241-C-106: Impact of Cement Reactions on Release of Contaminants from Residual Waste Page: 28 of 177
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collodion solution and associated effects on relative peak intensities also influence the overall pattern
intensity. The combined effect of these factors could have some effect on the characteristic mineral peak
intensities, which precluded quantitative comparisons of peak intensities for equivalent reflections in
background-subtracted XRD patterns for different sludge samples.
3.4 SEM/EDS Analysis
The morphologies, sizes, surface textures, and compositions of phases present in the 1-month and
Stage 6 sequential samples of residual waste from tank C-106 leached with Ca(OH)2 and Ca(OH)2/CaCO3
were studied by SEM/EDS and EDS element mapping. Two or three mounts were prepared of each
sample to compensate for the possibility that one or more less-than-optimum mounts of a sample might
occur, thus improving the likelihood of obtaining representative SEM images of each sample. The
mounts used for SEM/EDS consisted of double-sided carbon tape attached to standard aluminum
mounting stubs. For each mount, small aliquots of each sludge sample were placed on the exposed upper
surface of the carbon tape using a micro spatula. Each mount was then coated with carbon using a
vacuum sputter-coater to improve the conductivity of the samples and thus the quality of the SEM images
and EDS signals.
A JEOL JSM-840 SEM was used for high-resolution imaging of micrometer/submicrometer-size
particles from the sludge samples. The SEM system is equipped with an Oxford"a) INCA EDS software
system that was used for semi-qualitative element analysis. As noted in Deutsch et al. (2005b), the JEOL
JSM-840 SEM was upgraded in late calendar year 2005 to the Oxford INCA software to automate the
collection of EDS spectra over multi-micrometer-size areas of an SEM-imaged sample. This upgrade
permits the mapping of the spatial distributions over user-selected areas and/or lines of the relative
concentrations of any user-specified element detectable by EDS. Operating conditions for the SEM/EDS
analyses consisted of 10 to 20 keV for SEM imaging, and 20-30 keV, 100 live seconds) for the EDS
analyses.
The EDS analyses of particles are limited to elements with atomic weights heavier than boron.
Photomicrographs of high-resolution secondary electron (SE) images and backscattered electron (BSE)
images were obtained as digital images and stored in electronic format. To help identify particles that
contain elements with large atomic numbers, such as uranium, the SEM was typically operated in the BSE
mode. Secondary electrons are low-energy electrons ejected from the probed specimen as a result of
inelastic collisions with beam electrons, whereas backscattered electrons are primary electrons emitted as
a result of elastic collisions. Backscattered electron emission intensity is a function of the element's
atomic number - the larger the atomic number, the brighter the signal. Backscattered electron images are
obtained in exactly the same way as secondary electron images.
The SEM micrographs included in the main body of this report (Section 4.3) were selected because
they show typical morphologies, sizes, and surface textures of particles in the sludge subsample mounts.
All of the SEM micrographs and EDS spectra determined for samples of 1-month and Stage 6 sequential
(a) Oxford Instruments, Concord, Massachusetts.
(b) Live time is when (real time less dead time) the EDS system is available to detect incoming x-ray photons.
Dead time is the portion of the total analyzing time that is actually spent processing or measuring x-rays. While
each x-ray pulse is being measured, the system cannot measure another x-ray that may enter the detector and is,
therefore, said to be "dead."3.9
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Deutsch, William J.; Krupka, Kenneth M.; Lindberg, Michael J.; Cantrell, Kirk J.; Brown, Christopher F. & Schaef, Herbert T. Hanford Tank 241-C-106: Impact of Cement Reactions on Release of Contaminants from Residual Waste, report, September 1, 2006; Richland, Washington. (https://digital.library.unt.edu/ark:/67531/metadc887933/m1/28/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.