Condensed silica fume, a by-product from the production of silicon all
oys, was sintered by (i) conventional heating in a dilatometric furnac
e, both at constant heating rate and isothermal heating, and (ii) by t
he microwave heating. The dense products with relative density up to 9
5% of theoretical can be obtained only by short runs at high heating r
ates, preferentially accomplished by the microwave treatment. Prolonge
d heating leads to the devitrification of the original glassy phase to
cristobalite, accompanied by an arrest of densification.