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Abstract: Foam glasses are usually prepared through a chemical approach, that is, by mixing glass powder with foaming agents, and heating the mixture to a temperature above the softening point (106.6 Pa s) of the glass. The foaming agents release gas, enabling expansion of the sintered glass. Here, we use a physical foaming approach to prepare foam glass. First, closed pores filled with inert gases (He, Ar, or N2) are physically introduced into a glass body by sintering cathode ray tube (CRT) panel glass powder at high gas pressure (5‐25 MPa) at 640°C and, then cooled to room temperature. The sintered bodies are subjected to a second heat treatment above the glass transition temperature at atmospheric pressure. This heat treatment causes expansion of the pores due to high internal gas pressure. We found that the foaming ability strongly depends on the gas pressure applied during sintering, and on the kinetic diameters of the gases. The pressure for attaining maximum expansion, that is, lowest density and highest porosity, is found to be around 20 MPa. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the kinetics and dynamics of the reaction between Na2CO3 and the cathode ray tube panel glass powder at 923–1173K. The reaction causes foaming of the glass melt. After the reaction, the T g decreases with increasing Na2CO3 content and reaches a minimum value of T g. However, this T g value is even lower than that of the homogeneous bulk glass with the same chemical composition. The lower T g of the foam glass could be attributed to inhomogeneous incorporation of Na in the glass, leading to Na-rich domains that cause an overall decrease of T g. Remarkably, after 5min treatment at 1073K, the T g drops by 120K, indicating that the reaction between Na2CO3 and glass is very fast. Increasing treatment duration causes a slight increase of T g likely due to both a more homogeneous Na distribution and the compositional change of the glass as a result of Na2SrSi2O6 crystal formation. [Copyright &y& Elsevier]

Phosphates play a role in different foaming processes. In slag foaming, the phosphate can lower the surface tension and increase the foam life time. In the sintering–foaming process, sodium phosphates are added as “foam stabilizers”. Though, phosphates show documented effect in slag foaming, the effect of phosphate in the sintering–foaming process still needs to be clarified. In this work, we investigate the influence of alkali phosphates (Li 3 PO 4 , Na 3 PO 4 , and K 3 PO 4 ) on the glass foaming process, foam density, and glass transition temperature ( T g ) of waste silicate glasses. The results show that the T g of foam glasses decreases with increasing the alkali phosphate content, and with decreasing the alkali ion radius. The results, therefore, indicate that alkali phosphates can be used to decrease the heat-treatment temperature, however, only K 3 PO 4 and Na 3 PO 4 prove to be promising candidates to obtain low density foam glasses. [ABSTRACT FROM AUTHOR]