Effect of time and furnace atmosphere on the sintering of glasses from dismantled cathode ray tubes

The dismantling of cathode ray tubes (CRTs) represents a pressing environmental problem. CRTs consist of three distinguished glass parts. The front part is a barium-strontium glass, while the parts hidden inside the TV sets consist of lead silicate glasses. The high quality standards in manufacturing new CRTs impose a very limited amount of glasses to be recycled in the production of the original components. In addition, the presence of easily reducible oxides (like PbO) in the chemical composition of CRT glasses causes the risk of dispersing poisonous substances during remelting. Sintering of powdered glass could be a profitable way to produce new dense glass based materials without remelting. CRT glasses were found to be strongly susceptible to both the duration of the firing at the sintering temperature and the furnace atmosphere (oxygen, air, nitrogen). The evolution of the relatively large amount of dissolved oxygen, typical of CRT glasses, is found to contrast densification. Very short firing times (up to 15 min) are found to limit gas evolution. In addition, oxidative atmospheres lead to high quality sintered materials, capable of optical transparency comparable to that of pristine glasses.