Applicability of water glass for the transfer of the glass-foaming process from controlled to air atmosphere

Abstract

For thermal insulation to be sustainable, its performance and production efficiency must be considered. Foamed glass prepared from the mixture of waste cathode ray tube panel glass (CRT), Mn3O4 and carbon could become such a material assuming that its production efficiency could be improved. In light of this, the aim of the study was to engineer the transfer of the foaming process from inert to air atmosphere without drastically disturbing the primary mechanism of expansion. Foaming of carbon-containing mixtures in air atmosphere is normally a challenge due to premature oxidation of carbon by the oxygen from the air. Here, we systematically investigate how the addition of water glass (WG) affects the process by thermogravimetry coupled with mass spectrometry (TG/MS) and heating-stage microscopy analysis. Further, we propose an explanation about how WG protects the carbon and show that the addition of WG allows for the process to be successfully performed in air atmosphere. Two direct sources of expansion were identified (carbon-Mn3O4 reaction and WG) and quantitatively evaluated, allowing determination of an optimal addition of WG, 12 wt %, for the foaming temperature of 800 °C. The obtained foamed glass samples have a relatively low density and degree of open porosity, which reflects in their low thermal conductivity (λ). The lowest λ obtained was 39 mW m−1 K−1 at a density of 145 kg m−3, which is comparable to the samples prepared in inert atmosphere and best commercial products.