The normal form of boric acid is the orthoboric form (H3BO3) which
is hydrated boric oxide( B203) . When ortho boric acid is heated
slowly it loses water and becomes the metaboric form (HBO2). Borax is
the sodium salt of boric acid and is the primary natural ore. It
is not formed by heating boric acid . These materials are very
hydroscopic and the crystalline forms have various amounts of
water of crystallization. They are all glass formers which can
act as a flux to dissolve other oxides . Metalurgical fluxes
are generally borates , silicates , and could include phosphates.
All are glass formers. The more active flux mixtures will usually
contain a fluoride and or chloride salt. The proprietary fluxes
are all sort of “witches brew” mixtures . They are not a single
compound and there is no real “magic” right composition although
some maybe better than others.
The main use for these borates,silicates and phosphates is as
cleaning agents a their use as fluxes in glass making and in
metallurgy is relatively small in comparison . jesse