The foaming mechanism of glass foams prepared from the mixture of Mn₃O₄, carbon and CRT panel glass

Cathode ray tube (CRT) panel glass is processed into glass foams by using carbon and Mn₃O₄ as foaming agents. We investigate the foaming ability and foaming mechanism of the mixture by varying the composition and the temperature. Carbon load of 5 wt% inhibits the sintering of the glass powder, while 2 wt% carbon promotes the coalescence of pores during foaming. Carbon load of ≤0.4 wt% is suitable for achieving low density foams (0.15–0.23 g cm^-3) with closed pores (75–100%). Foaming is initiated by the reaction between carbon and Mn₃O₄ and this is the main source of melt expansion. Reduction of cations in the glass melt, including Mn³⁺ dissolved from Mn₃O₄, makes an important contribution to the melt foaming at >800 °C. The main gaseous product is CO₂ (67–95 vol%). CO appears above 800 °C and the concentration increases with temperature.