Effects of molding pressure and sintering temperature on properties of foamed glass without blowing agent

A process of fabricating the foamed glass that has closed pores with 8 ~ 580 µm sizes without a blowing agent by sintering 10 µm boron-free glass powder composed of CaO, MgO, SO₃, Al₂O₃–83 wt% SiO₂ at a molding pressure of 0 ~ 120 MPa and a sintering temperature of 750 ~ 1000^oC was investigated. To analyze the glass transition temperature of glass powder, thermogravimetric analysis–differential thermal analysis (TGA-DTA) method were used. The microstructure and pore size of foamed glass were examined using the optical microscopy and field emission scanning electron microscopy (FE-SEM). For the thermal diffusivity and color of the fabricated samples, a heat flow meter and ultraviolet–visible–near-infrared (UV–VIS–NIR)-colormetry were used, respectively. In the TGA-DTA result, the glass transition temperature of glass powder was confirmed to be 626^oC. In the microstructure result, closed pores of 7 ~ 20 µm were formed at 750 ~ 900^oC, and they were not affected by the molding pressure and sintering temperature. However, at 1,000^oC, when there was 0 MPa molding pressure, closed pores of 580 µm were confirmed, and the pore size decreased as the molding pressure increased. Moreover, at a molding pressure of 30 MPa or higher, closed pores of approximately 400 µm were formed. The porosity showed an increasing trend of smaller molding pressure and larger sintering temperature, and it was controllable in the range of 5.69 ~ 68.45%. In the thermal diffusivity result, there was no change according to the molding pressure, and, by increasing the sintering temperature, up to 0.115 W/m·K could be obtained. The Lab color index (CIE-Lab) results all showed a similar translucent white color regardless of molding pressure and sintering temperature. Therefore, based on the foamed glass without boron and blowing agent, it was confirmed that white foamed glass, which has closed pores of 8 ~ 580 µm and a thermal diffusivity characteristic of 0.115 W/m·K, can be fabricated by changing the molding pressure and sintering temperature.