Solid-liquid equilibrium, crystal type, solid solubility and thermal stability studies of potassium ammonium chloride solid solution

Solid-liquid equilibria of (KCl + NH4Cl + H2O) ternary system were investigated and it was found that there were five crystalline regions in the course of crystallization (respectively pure NH4Cl, mNH4Cl·KCl solid solution, NH4Cl·nKCl solid solution, mixed mNH4Cl·KCl and NH4Cl·nKCl solid solution and pure KCl). The type of two solid solutions was determined by analysis of X-ray diffraction (XRD), Fourier transform infra-red (FTIR), lattice constant and density of solid solution crystals. It could conclude that they were limited substitutional solid solutions. Solid solubility (substitutional impurity in solvent) was measured at 25 °C and its variation was in accordance with Vergard's law. Moreover, thermal stability of two solid solutions was compared by TG-DTA. Results showed that both mNH4Cl·KCl and NH4Cl·nKCl shared the property of their mother phase and maintained its individual characteristics.