Use of colemanite and borax penta-hydrate in soda lime silicate glass melting-A strategy to reduce energy consumption and improve glass properties

In view of recent energy crisis and environmental considerations, reductions of melting temperature and CO2 emissions during the production of commercial soda lime silicate (SLS) glass at industrial scale are major intentions. Here we show that this goal can be achieved by using carbonate-free borate minerals such as colemanite (Ca2B6O11.5H2O) and borax penta-hydrate (BPH, Na2B4O7.5H2O) as alternative sources for CaO and Na2O, respectively. The SLS glass melting temperature has decreased successively by the incorporation of B2O3 with substitution of equivalent wt% SiO2 resulting from gradual utilization of colemanite and BPH. Hot Stage Microscopy (HSM) revealed that the melting temperature was decreased from 1650 degrees C, for the parent commercial SLS glass, to 1528 degrees C on use of colemanite and further down to 1072 degrees C on utilization of both colemanite and appropriate quantity of BPH up to which the properties of the pristine glass can be retained. Thus, energy consumption equivalent to reduction in melting temperature could be minimized during the glass production. Another important environmental benefit achieved by using carbonate free minerals is significant reduction (12%) of CO2 emissions during thermal decomposition in glass melting which could minimize greenhouse gas to the atmosphere at a great extent. Further, the addition of colemanite improved micro-hardness, elastic modulus and thermal properties of the pristine glass through polymerization of glass network structure. In contrast to the use of BPH as a source of more than 8 wt% Na2O deteriorated glass properties with the formation of non-bridging oxygens into the glass network.

Automated summary

The study demonstrates that using carbonate-free borate minerals as alternatives in glass production can reduce melting temperature and CO2 emissions. This can not only save energy consumption, but also improve the mechanical and thermal properties of the glass.