Mechanical behaviour and thermal and electrical properties of foam glass

Cellular glasses were synthesised by heat treatment (750–850 °C for 60–120 min) of waste cathode-ray tube (CRT) glasses (funnel and panel) with a SiC or TiN reducing agent. Macro-size pores with a single distribution were formed after reduction with SiC, whereas a double distribution was observed for TiN. The intrinsic properties of these materials were investigated. We found that the flexural strengths of the samples varied from 4 to 68 MPa depending on their porosity, and that the compressive strengths varied from 4 to 267 MPa. Our analysis shows that Ashby's model is more appropriate for these porous materials because their Poisson ratios are porosity-independent. The thermal conductivities of the materials were determined from their thermal diffusivities at room temperature, obtained by means of laser flash experiments. We also determined the variation of the conductivity with the porosity of the cellular glasses. The samples were found to have thermal conductivities in the range 0.08–0.43 W m−1 K−1. The dielectric constants of the materials were determined by impedance spectroscopy, and indicated that the materials are insulators. The samples were found to have permittivities in the range 2.6–3.1 S cm−1. These values varied with sample thickness, and appeared to tend towards a limiting value determined by the porosity of the material, or more particularly, by the relationship between the volumes of air and matter in the sample.