Fig. 5: BA5 1250 °C glass coupon after the 49-day VHT.

a The post-reaction coupon suspended from the stainless-steel apparatus at the end of the reaction (inset shows pre-reaction coupon), (b) optical micrograph of a polished cross section, (c) and (d) BSE-SEM cross sections at different magnifications (the red box is the area associated with (d)).