Stabilization with open porosity

Wagh et al. [45] demonstrated stabilization of Cr, along with Cd, Pb, and Hg from contaminated soil and wastewater in the Ceramicrete waste form. Table 16.8 shows the contaminant levels in the waste and the wastewater, and the corresponding TCLP result for the stabilized waste. The wastewater in the Ceramicrete slurry was equal in amount to the stoichiometric water needed for the stabihzation process. Including this wastewater, the total waste loading was 77 wt%. The waste forms had open porosity of 2.7 vol% and a density of 2.17 g/cm. Compression strength was 34 MPa (4910 psi). 

Parts with an open coherent porosity of >20% are used in vacuum tubes and aeronautics because of refractoriness, shape stability, and chemical resistance. Examples are porous cathodes impregnated with alkaline earth oxides as electron-emitting sources in special tubes, thermoionic converters heated by nuclear energy, and ionic propulsion units with porous tungsten plates as ionic sources for Cs vapor of high temperature. Those emitter plates are made of globular tungsten powder (7 pm) density 75-85%, pore size 2-30 pm, and pore number 1.4 x 10 -8 x 10 cm . ... 

The fabrication of encapsulated metal hydride involves 3 main steps 1) break the metal hydride to fine particles and stabilize the fines for handling in open air 2) encapsulate the metal hydride particles in silica with the sol-gel method 3) treat the composite with heat to obtain desired strength and porosity. Micrographs of a typical encapsulated sample are shown in Figure 1. 

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