THERMAL DEHYDRATION AND DECOMPOSITION OF NICKEL CHLORIDE HYDRATE (NICL2.XH2O)

Abstract

The dehydration and decomposition characteristics of an undried and a partly dried sample of NiCl2.xH2O have been investigated by isothermal and non-isothermal (TG and DTA) methods in static air as well as flowing nitrogen environment. While the isothermal weight loss method fails to distinguish between different steps of reaction, TG curves upto 800-degrees-C reveal as many as five steps in static air and four steps in nitrogen atmosphere. However, both methods indicate that NiCl2 is stable upto 400-degrees-C above which dehydrochlorination takes place in presence of water vapour. The intermediate products of dehydration and decomposition at different temperatures have been characterized by chemical analysis, X-ray diffraction, infrared and diffuse reflectance spectroscopy. All these methods reveal the presence of water in samples calcined at even 400-600-degrees-C. Thermodynamic functions for different steps of dehydration have been calculated and discussed in the light of the possible structural changes occurring in the partially dehydrated products.