Preparation and studies of some thermal, mechanical and optical properties ofxAl2O3(1 −x)NaPO3 glass system

Sodium aluminophosphate glasses having compositions of xAl2O3(1-x)NaPO3 (x = 0.05-0.2) were prepared using conventional melt-quench technique. Density, glass transition temperature, microhardness (MH), thermal expansion coefficient (TEC) and transmission characteristics were measured as a function of alumina content for different samples. They were found to depend on O/P ratio with pronounced changes taking place for O/P ratio ≥3.5. Density, glass transition temperature and microhardness were found to increase up to 15 mol% of alumina and then they showed a decreasing trend. Thermal expansion coefficient decreased continuously with alumina content. Optical gaps for different glass samples as measured from transmission characteristics were found to be in the range 3.13–3.51 eV. It initially decreased with alumina content up to 15 mol% and then increased. The behaviour was explained on the basis of change in the average aluminum coordination number from six Al(6) to four Al(4) (i.e. Al(OP)6/Al(OP)4 ratio) along with the changes in polyhedra linkages in the glass network due to change in O/P ratio.