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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 have prepared low-density foam glasses from cathode-ray-tube panel glass using carbon and MnO 2 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 CO 2 . [ABSTRACT FROM AUTHOR]

Abstract: We prepared foam glasses from cathode-ray-tube panel glass and CaCO3 as a foaming agent. We investigated the influences of powder preparation, CaCO3 concentration and foaming temperature and time on the density, porosity and homogeneity of the foam glasses. The results show that the decomposition kinetics of CaCO3 has a strong influence on the foaming process. The decomposition temperature can be modified by varying the milling time of the glass–CaCO3 mixture and thus for a specific CaCO3 concentration an optimum milling time exists, at which a minimum in density and a homogeneous closed porosity are obtained. Under the optimum preparation conditions the samples exhibit a density of 260kg/m3. The thermal conductivity of the foam glass was measured to be 50–53mW/(mK). The observed dependence of the foaming process on the decomposition kinetics of the foaming agent can be applied as a universal rule for foaming processes based on thermal decomposition. [Copyright &y& Elsevier]

The recycling of glass from obsolete cathode ray tubes (CRT) has hitherto only occurred to a very limited extent, but the production of foam glass used as an insulation material component has recently been proposed as a promising recycling method. CRT panel glass has high recycling potential due to its non-hazardous composition. Here we report on the foaming of CRT panel glass using Na2CO3 as the foaming agent. We explore how heat treatment temperature and concentration of Na2CO3 affect the density and porosity of the foam glasses, and whether Na2O is incorporated in the glass network. The optimum foaming temperature for minimising density and maximising closed porosity is found to be between 1023 and 1123 K. The pore structure depends on the amount of added Na2CO3, viz, the pores generally become more open with increasing Na2CO3 content. A minimum density of 0 ⋅ 28 g/cm³ is found when 14 wt% Na2CO3 is added and the heat treatment temperature is 1023 K. Interestingly, the glass transition temperature (Tg) of the final foam glass decreases linearly with increasing [Na2CO3], indicating that the Na2O is incorporated into the glass network. [ABSTRACT FROM AUTHOR]

• Foaming couples for foaming CRT panel glass in air and argon atmosphere. • Best foaming effect in air achieved with MnO 2 , open-porous foam. • Beneficiary role of oxidizing agent on foaming in oxygen-free atmosphere revealed. • Best foaming effect in argon with carbon black and Mn 3 O 4 , closed-porous foam. • Pore-gas analyzed as in major part CO 2. We report on the use of foaming agent couples to foam cathode-ray-tube panel glass and uncover the influence of the carbon type, Mn x O y and furnace atmosphere on the foaming effect and physical properties of the foams. In oxidizing atmosphere, carbon burns out before the foaming starts and the best foaming effect is achieved with MnO 2. The samples are open porous and thermal conductivity is 47 mW m–1 K–1 at 161 kg m–3. In oxygen-free atmosphere, oxidation of carbon is facilitated by Mn 3 O 4 as an oxidizing agent. Activated carbon with a high reactivity leads to the formation of CO and open porosity. Thermal conductivity of the closed-porous sample with CO 2 in the pores, produced with carbon black and Mn 3 O 4 , reaches 50 mW m–1 K–1 at 204 kg m–3 and exhibits the highest potential for improving the thermal insulation further by decreasing the density. [ABSTRACT FROM AUTHOR]

Glass foams are attractive thermal insulation materials, thus, the thermal conductivity (λ) is crucial for their insulating performance. Understanding the foaming process is critical for process optimization. Here, we applied high-speed synchrotron X-ray tomography to investigate the change in pore structure during the foaming process, quantifying the foam structures and porosity dynamically. The results can provide guidance for the manufacturing of glass foams. The 3D pore structures were also used to computationally determine λ of glass foams using image-based modelling. We then used the simulated λ to develop a new analytical model to predict the porosity dependence of λ. The λ values of the glass foams when the porosity is within 40% to 95% predicted by the new model are in excellent agreement with the experimental data collected from the literature, with an average error of only 0.7%, which performs better than previously proposed models. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Low density open-porous-type foamed glass was prepared. • Nucleation agent TiO 2 secured low content of closed pores. • Contributions to the effective thermal conductivity were evaluated. • Solid thermal conductivity contributes 50% to the effective thermal conductivity. Sustainable development focused on energy and material savings is driving attempts to decrease the thermal conductivity of heat insulation materials. Foamed glass is one of the most sustainable thermal insulation materials and has unique, load-bearing properties. In this study, contributions to the effective thermal conductivity were quantified for an open-porous-type foamed glass. Foamed samples were prepared by heating a mixture of waste flat glass, the foaming additives carbon and Mn 3 O 4 , and the nucleation agent TiO 2. The density of the foamed glass was 117 kg m−3 (total porosity 95.8 vol%) with a closed porosity of only 5.8 vol%. The latter was minimized by promoting partial crystallization. The thermal conductivity was 54.3 mW m−1 K−1 at atmospheric pressure. Fitting the pressure dependence of the thermal conductivity gave a base thermal conductivity of 26.7 ± 0.4 mW m−1 K−1, and a gaseous contribution of 27.7 ± 0.5 mW m−1 K−1 with a pore size of 0.77 ± 0.07 mm. Thus, the base thermal conductivity, which is attributed mainly to the thermal conduction in the solid phase, is much higher than in the case of fibrous glass insulation products. [ABSTRACT FROM AUTHOR]