Use of hydrothermal reactions for slag/glass recycling to fabricate porous materials

• Porous glass fabrication was conducted by hydrothermal reaction to silicate glass.
• After hydrothermal reaction, the silicate glass contained a lot of H2O.
• By reheating, the glass containing H2O expanded to form porous glass structure.
• SiO2–Na2O–B2O3 glass after hydrothermal reaction exhibits low temperature foaming.
• Porous glass with hydrate crystals was made by hydrothermal reaction to slag/glass mixture.

As one of approaches for slag and glass recycling, the authors have applied hydrothermal reactions to create value-added porous materials. Under hydrothermal conditions such as 473–573 K and 30–40 MPa with a high pressurized H2O, slag and glass powders are sintered to make solidified ceramic materials containing plenty of H2O. When the glass containing H2O is reheated, the glass expands with releasing H2O and porous material can be obtained. Hydrothermal process takes advantages of energy costs, because it is operated at lower temperatures than those used for conventional sintering processes. Moreover, hydrothermal reactions use H2O as a solvent to fabricate ceramic materials, therefore it can be regarded as energy-saving, environmental-friendly, and spontaneous processing.