Manufacturing of porous niobium phosphate glasses

Niobium phosphate glasses with composition 33P(2)O(5)center dot 27K(2)O center dot 40Nb(2)O(5) are usually very stable with regard to crystallization resistance, with a relatively high glass transition temperature (T-g 750 degrees C), and are potentially suitable for nuclear waste immobilization. Porous niobium phosphate glasses were prepared by the replication method. The porous glasses were produced via the dip-coating of an aqueous slurry containing 20 wt% powdered glass into commercial polyurethane foams. The infiltrated foams were oxidized at 600 degrees C for 30 min to decompose the polymeric chains and to burn out the carbon, leading to a fragile glass skeleton. Subsequent heating above the glass transition temperature in the range of 780-790 degrees C for 1 h, finally resulted in mechanically stable glass foams, which maintained the original interconnected pore structure of the polyurethane foam. The struts showed the neck formation between particles, evidencing the initial stage of sintering. The open and interconnected porosity of the glassy foams lies in the range of 85-90 vol.%. It was concluded that porous niobium phosphate glasses are potential candidates for immobilizing liquid nuclear waste. (c) 2006 Elsevier B.V. All rights reserved.