Influence of the glass particle size on the foaming process and physical characteristics of foam glasses

•Influence of the particle size on the foaming process•Analysis of the foaming process•Preparation of low-density foams•Improved thermal insulation properties•Great potential for further improvements

We have prepared low-density foam glasses from cathode-ray-tube panel glass using carbon and MnO2 as the foaming agents. The effect of the glass particle size on the foaming process, the apparent density and the pore morphology is revealed. The results show that the foaming is mainly caused by the reduction of manganese. Foam glasses with a density of < 150 kg m− 3 are obtained when the particle size is ≤ 33 μm (D50). The foams have a homogeneous pore distribution and a major fraction of the pores are smaller than 0.5 mm. Only when using the smallest particles (13 μm) does the pore size increase to 1–3 mm due to a faster coalescence process. However, by quenching the sample from the foaming to the annealing temperature the pore size is reduced by a factor of 5–10. The foams with an apparent density of < 200 kg m− 3 are predominantly open-porous. The foams exhibit a thermal conductivity as low as 38.1 mW m− 1 K− 1 at a density of 116 kg m− 3. For the investigated foam glasses, there exists a great potential to further decrease their thermal conductivity by increasing the closed porosity and by changing the trapped gas to CO2.