Thermochemistry of Charge‐Coupled Substitutions in Silicate Glasses: The Systems M_l/nⁿ⁺ AlO₂‐SiO₂ (M = Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Pb)

Enthalpies of solution of framework aluminosilicate glasses xM_l/nⁿ⁺ AlO₂‐(1‐x)SiO₂ (M = Cs, Rb, K, Na, Li, Ba, Pb, Sr, Ca, Mg) in molten 2PbO.B₂O₃ near 973 K were measured. The sequence above represents increasing ability of the nonframework cation M to bond to the bridging oxygen. In that sequence, the enthalpy of the substitution Si⁴⁺→+ Al³⁺+ 1/nMⁿ⁺ in the glass becomes less exothermic, the enthalpy of vitrification increases, and the tendency toward glass‐glass immiscibility becomes more pronounced. These parameters correlate smoothly with the ionic potential, z/r, of the substituting cation.