Borate glass

Borate glasses have a more complex action of alkali (or other modifier) ions than silicate glasses.^[1] In silicates, depolymerisation occurs due to the oxygen added alongside the alkali or modifier ions introducing non-bridging oxygen, whereas in borate glasses it can also lead to the conversion of trigonal planar BO3 units into singly charged BO4 tetrahedra,^[2] thereby increasing, rather than decreasing the network connectivity and polymerisation. Borate glasses also have major differences in their optical and other properties.^[3]

The single largest use of boron compounds in the world (accounting for half of total global use) is the production of certain types of boron-treated glass fiber for insulating and structural fiberglass.^[4] In these uses the boron may be present as borax or boron oxide, and adds to the structural strength of the glass as borosilicate, or is added as a fluxing agent to decrease the melting temperature of pure silica, which is difficult to extrude as fibers and work with in pure form, due to the high temperatures involved.