Use of Interdiffusion to Determine Crystalline Solubility in Alkali Halide Systems

Measurement of the discontinuities in the concentration‐distance graphs describing interdiffusion of the components in the binary systems NaF‐LiF and NaCl‐RbCl gave the crystalline solubility limits just below the eutectic temperatures. These are 8 mole % LiF in NaF and 1.5 mole % NaF in LiF at 625° C and 6 mole % NaCl in RbCl and 0.8 mole % RbCl in NaCl at 515°C. Experiments in the complex systems NaCl‐Kl and NaF‐LiF‐MgF2 showed that the method was inapplicable to nonbinary systems where the phase compositions at intermediate stages in the interdiffusion do not correspond to those of the final equilibrium assemblage.