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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]

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]

We prepare foam glass from cathode ray tube (CRT) panels using MnO 2 as foaming agent at different temperatures for various durations. The reduction of MnO 2 to Mn 2 O 3 leads to formation of O 2 gas, and hence, causes initial foaming. The Mn 2 O 3 particles dissolve into the glass melt and subsequently reduce, causing further formation of O 2 gas and foaming of the glass melt. Increasing the treatment temperature and time enhances foam expansion, Mn 2 O 3 dissolution, and lowers the closed porosity. Once the foam reaches a percolated stage, the foam continues to grow. This is caused by nucleation of new bubbles and subsequent growth. We discuss evolution of pore morphology in terms of pore number density, pore size and closed porosity. The thermal conductivity of the foam glasses is linearly dependent on density. The heat transfer mechanism is revealed by comparing the experimental data with structural data and analytical models. We show that the effect of pore size, presence of crystal inclusions and degree of closed porosity do not affect the overall thermal conductivity. [ABSTRACT FROM AUTHOR]

• Development of low-density open- and closed-porous foamed glasses. • Homogeneous pore structure with >90% of open or closed pores. • Open porosity achieved by partial crystallization of the glass. • Low thermal conductivity (37.5–65.6 mW m−1 K−1) measured using heat-flow meter. • Analysis of the difference in the thermal conductivity. Future developments in foamed glass should focus on improving the thermal insulation properties, controlling the foamed structure and the type of porosity. In this study, we report on the synthesis and properties of foamed glasses with open-porous and closed-porous structures prepared from waste cathode-ray-tube (CRT) panel and soda-lime-silica glasses with the addition of carbon black, and manganese or iron oxides. The samples exhibit a homogeneous structure with an average pore size in the range 0.5–1.35 mm and open porosity above 91% or closed porosity above 92%. The open porosity was obtained by partial crystallization of the glass during the foaming process. The thermal conductivity, measured using a heat flow meter at 10 °C, is 57.2–65.6 mW m−1 K−1 at 116–143 kg m−3 for the open-porous samples and 37.5–56.2 mW m−1 K−1 at 107–245 kg m−3 for the closed-porous samples. The conduction in the solid phase contributes the major part to the effective thermal conductivity (52–72%). The conduction in the gaseous and solid phases, respectively, is higher in the open-porous foamed glass due to the different gas composition (air) and the different solid composition (glass composition and crystalline content). The developed foamed glasses also have high mechanical strength, making them suitable for load-bearing applications. [ABSTRACT FROM AUTHOR]