Chemically bonded phosphate ceramics for radioactive and mixed waste solidification and stabilization Page: 7 of 22
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60wt% of the zeolites in the starter powder could be incorporated and the
samples set wcll.
Chemical and Physical Characterization of MAP Ceramics
To identify the reacted paste, X - ray diffraction analysis of the samples
was done. The XRD output is shown in Figure 2. The peaks are identical to
those reported by Connaway-Wagner et al., for magnesium orthophosphate
cement [11] and are also very similar to those reported by Sugama and
Kukacka [5]. Detailed identification of the major peaks shows that this is a
polyphosphate cement, which includes both struvite (MgNH4PO4.6H20) and
magnesium phosphate hydrate (Mg3(PO4)2.4H20). The strong peaks of MgO
suggest that considerable unreacted MgO remains in the material. Sugama
and Kukacka [5] have shown that, except for the release of free water, this
material is stable at high temperatures. With this temperature stability and
the high density, MAP may form a suitable containment matrix for
contaminants.
Figure 3 shows the microstructure of a MAP specimen with 11% porosity.
When compared with the microstructure from Figure 1, one may see that
porosity is considerably less in Figure 3. In addition, content of MAP cement in
this Figure is much more than that in Figure 1 and MgO grains are less visible
now. This implies that the reaction of grains of MgO from the pores with
ammonium phosphate has resulted in the densification during the soaking.
The physical properties of MAP ceramics are listed in Table 2. The
submicron pore sizes may make this material leach-resistant. In addition, the
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Wagh, A. S.; Cunnane, J. C.; Singh, D.; Reed, D. T.; Armstrong, S.; Subhan, W. et al. Chemically bonded phosphate ceramics for radioactive and mixed waste solidification and stabilization, article, January 1, 1993; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc1313838/m1/7/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.