Hardening of glass bodies having optical surfaces - using molten potassium nitrate with addn of potassium dihydrogen phosphate to prevent damaging of optical surfaces during ion exchange

摘要

Spectacles, magnifying glasses, lenses for optical instruments, etc., are hardened by replacement of ions having small radii, by K ions in a fused KNO3 bath contg. 0.1-2.0 wt.% of KH2PO4, or a corresp. amt. of P2O5, an acid (poly)phosphate or polyphosphoric acid. The temp. of the fused salt bath is below the transformation temp., pref. in the range 380 degrees-460 degrees C.