Production and characterization of foam glass from container glass waste

Abstract

Foam glass with excellent properties was produced from container glass waste. The processing technique depended on the powder sintering approach using sodium silicate solution as a foaming agent. The morphology, density and compressive strength were studied in relation to different processing parameters: sintering temperature, amount of foaming agent, soaking time, powder particle size and glass powder color. Foam glass was sintered in the range (750-900 oC) for 30 minutes with the incorporation of 12 and 19 wt. % sodium silicate solution. At lower sintering temperature (750-800 oC), the foam has denser structure (bulk density ranged from 0.37-0.61 g/cm3) along with high compressive strength (ranged from 2.29-18.68 MPa). As the sintering temperature increased, higher levels of porosity were achieved. At 850 oC with 12 wt. % sodium silicate solution, lightweight (bulk density = 0.25 g/cm3), highly porous (% of porosity = 90 %) foam glass was achieved. It had relatively high compressive strength (1.62 MPa), compared to other insulating foams, along with low thermal conductivity (0.078 W/m.oC) and the most homogeneous pore morphology. Significant change in foam glass properties took place with changing the amount of foaming agent. As the amount of foaming agent increased, the density of the foam decreased till it reached a minimum of (0.25 g/cm3) that corresponded to 12 wt. % sodium silicate solution. Further addition of foaming agent caused the density to re-increase and the pore morphology to coarsen. Sintering foam for different soaking times had a slight effect on changing the foam glass properties. The morphology of all the foam glass produced at different soaking times was comparatively homogeneous. The compressive strength of the produced foam was relatively high (1.6 MPa at 40 min and 3.13 MPa at 10 min). The powder particle size had a major effect on foam glass properties. As the particle size increased, the bulk density of the the foam increased and the morphology became less homogenuous. Increasing the sintering temperature for the larger particle size did not succeed in increasing the foam structure homogeneity. The glass color also had an effect on the foam glass properties. The properties and the morphology of the green and brown glass samples were approximately the same (bulk density = 0.38, 0.37 MPa and compressive strength = 2.05, 1.97 MPa respectively). However, they differed from the morphology and properties of the white glass (bulk density = 0.25 g/cm3 and compressive strength = 1.62 MPa). The specific compressive strength of the white glass foam (6.48*10-3 MPa m3/Kg) was higher than that of green and brown glass (5.39*10-3, 5.32*10-3 MPa m3/Kg respectively). EDX analysis was performed for the white, green and brown powder. It showed that they had more or less the same compositions (except the presence of chromium element in green glass and titanium in brown glass which are coloring additives). They had the same main elements but with different weight percentages. The optimum processing parameters for producing foam glass for thermal insulation was to use sintering temperature 850 oC, amount of foaming agent 12 wt. %, soaking time 30 min and glass powder particle size 75 µm.