Crystallization process of ZnCl₂·2NH₄Cl and its thermal decomposition behavior

The ammonium zinc chloride (AZC, II type, ZnCl₂·2NH₄Cl) crystals were prepared by using zinc chloride and ammonium chloride in water solvent. The effects of the mole fraction of zinc chloride and ammonium chloride on the type of AZC crystals were investigated by the X-ray diffraction techniques. The thermogravimetry analysis and the non-isothermal experiments were carried out for the crystal's thermal decomposition behavior. The TG curve showed that the decomposition process of AZC (II) crystal is consisted of two main steps-the decomposition of ammonium chloride and that of zinc chloride. However, TG-DTG curves showed that the decomposition of ammonium chloride could be refined into four sub-steps. The apparent activation energy (E) of the two main steps are 91.25 kJ·mol^-1 and 104.76 kJ·mol^-1, and the pre-exponential constant (A) are 10^5.94 s^-1 and 10^4.51 s^-1, respectively. The results indicate that AZC (II) has high thermal stability and the as-synthesized AZC (II) can meet the requirements of chemical transport agent in CVT growth of ZnSe single crystals.