Some Phase Relationships within the System Na2O/B2O3/Nb2O5

Phase behaviour over regions of the ternary system Na2O/B2O3/Nb2O5 has been explored. Liquidus temperatures and the stability regions of primary phases have been determined over selected composition ranges by high temperature microscopy. Crystallisation processes in melts and corresponding glasses have been followed using both conventional methods' of thermal analysis and newly developed micro techniques combined with hot stage microscopy. An electron microscope has been employed to follow changes in the microstructure of quenched glasses after controlled heat treatments. It has been shown that the system contains a liquid immiscibility gap, and some attention is given in the discussions to the influence that can be assigned to cations in determining the extent of such gaps and general structural relationships in borate/oxide systems.