Effect of hydrothermal treatment on the structure and foaming of waste glass

This study explores the potential of hydrothermally treated waste glass for producing foamed glass using a carbonaceous foaming agent (glycerol) in an air atmosphere. The objective was to assess the feasibility of this alternative route for producing sustainable, lightweight materials with reduced energy and material inputs by repurposing cathode ray tube panels (CRT), flint glass (FG), and mixed-color container glass (MCG). Investigated glass powders were treated in a saturated steam atmosphere inside a pressure vessel and characterized using Xray diffraction and Fourier-transform spectroscopy to identify structural changes. The foaming behavior of hydrothermally treated waste was analyzed through heating stage microscopy and thermogravimetric analysis coupled with mass spectrometry. The foamed glass samples were further assessed for density and thermal conductivity. The results demonstrate that hydrothermal treatment significantly influences the foaming process. Glass powders with higher content of structurally bonded water exhibit lower sintering temperature and pronounced expansion after the hydrothermal treatment. A higher hydration level reduced the onset foaming temperature and facilitated higher expansion. Additionally, combining hydrothermally treated powders with glycerol as a foaming agent enabled effective expansion, even in an air atmosphere, achieving density as low as 108 kg m-3. The results of this study suggest that hydrothermal treatment of waste glasses enables the implementation of carbonaceous foaming agents in the air atmosphere and could thus offer an alternative route for the foaming of glass.