Sandro Hreglich

Vitrification of industrial and natural wastes with production of glass fibres

Abstract Solid wastes coming from the municipal incinerator of Reggio Emilia, Italy, and sludge excavated from the lagoon of Venice were successfully vitrified at 1350–1500°C. Glass cullet, coming from a community glass recycling program, was introduced in some of the batches as a melting aid. Several analyses performed on the glasses showed that the glass transition and devitrification temperatures shift to higher values with increasing amount of waste in the raw materials. The glasses obtained display a good durability. Two kinds of wastes tested in the experiments could be vitrified by themselves, with no addition of external raw materials. Glass fibres were drawn from the obtained glasses at various temperatures. Mechanical tests showed that the elastic modulus increases with the waste content, while it does not depend on the drawing temperature. The fibres possess a good tensile strength (a maximum value of 1.6 GPa was obtained).

Mechanical properties of metal-particulate lead-silicate glass matrix composites obtained by means of powder technology

The great quantity of waste glasses leads to the need for new applications. The realization of matrices for innovative and cost-effective materials is one possible use. In the present work, lead silicate glasses, recovered from cathode ray tubes (CRTs) are investigated. A low cost powder processing route is proposed for the manufacture of particulate aluminium reinforced glass matrix composites. These composites exhibit an anomalous mechanical behaviour which is thought to be due to a complex metal/glass interaction. In the case of limited metal/glass interaction, good bending strength and fracture toughness are achieved. The obtained KIC level of about 1.20 MPa m0,5, together with the observed crack control behaviour, appears promising.

Inertization of hazardous dredging spoils

Vitrification and production of ceramics materials starting from sediment excavated from Venice lagoon is described. This sediment is classified as toxic waste because contains several heavy metal ions and organic pollutants and was successfully vitrified at 1200-1350 degrees C. Twenty weight percentage of glass cullet, coming from a community glass recycling program, was added to the raw materials, previously calcined at 900 degrees C, as a way of adjusting the variations of composition of the individual sediment batches. Chemical durability (leaching) tests showed that the optimized glass compositions are inert, and thus not only volume reduction but also inertization of the waste was obtained by this process. Moreover, the economics of the entire process was analysed. The valorization of the waste was accomplished by the subsequent processing of the glass derived from the inertization. Glass ceramic materials were produced by viscous phase sintering of pressed glass powders which crystallized during the densification process. Sintered glass ceramic products had good mechanical characteristics (HV = 7.5 GPa, bending strength 150 +/- 8 MPa), making them suitable for applications in the building industry.

Monolithic and Cellular Sintered Glass-Ceramics from Wastes

Several kinds of wastes have been converted into glasses, successively powdered and sintered with simultaneous crystallisation. The employed “sinter-crystallisation” process was useful to obtain glass-ceramics with particular crystal phases (sometimes un-accessible from traditional nucleation/crystal growth treatments, like feldspar crystals). Conventional pressing of fine glass powders led to monoliths, after sintering, with remarkable mechanical properties (for example bending strength exceeding 100 MPa), useful for tile applications; replication processes, by employing sacrificial polymeric materials, after the same thermal treatment employed for the monoliths, led to open-celled glass-ceramic foams, useful for filtering applications. The enhanced specific surface due to porosity was found to have a positive effect on crystallisation.