Mechanisms of boron coordination change between borosilicate glasses and melts

International audience; The structure of two borosilicate glasses and melts has been investigated by neutron diffraction coupled with Reverse Monte Carlo (RMC) simulation. For both compositions (10B2O3 ⋅ 30Na2O ⋅ 60SiO2 and 10B2O3 ⋅ 15Na2O ⋅ 15CaO ⋅ 60SiO2), the fraction of tetrahedral boron ([4]B) drops from 0.7 to 0.3 from the glass to the melt. The change from a modifying to a charge compensating role of cations during quench is related to the boron coordination change. These molecular scalemodifications explain the low viscosity of alkali/alkaline-earth borosilicate melts relative to alkali/alkaline-earth silicate melts, as the viscous flow is enhanced with the proportion of [3]B. RMC simulations of soda borosilicate glass and melt show a preferential interbonding between B and Si polyhedra. Such medium range order interbonding is unfavored in the soda-lime borosilicate glass showing a nearly random network. The effect of Ca enhancing the proportion of B-B pairs is here highlighted.