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  • Author or Editor: K. S. Rejitha x
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Abstract  

Thermogravimetric techniques have been used to study the kinetics of thermal deamination of tris(ethylenediamine)nickel(II) sulphate. The complex was synthesized and characterized by various chemical and spectral techniques. Thermal decomposition studies were carried at different heating rates (5, 10, 15 and 20°C min−1) in dynamic air. The complex undergoes a four-stage decomposition pattern. The stages are not well resolved. Decomposition path can be interpreted as a two-stage deamination, and a two-stage decomposition. Reaction products at each stage were separated and identified by means of IR and XRD. The morphology of the complex and the residue were studied by means of SEM. Final residue of the decomposition was found to be crystalline NiO. The deamination kinetics was studied using model-free isoconversional methods viz., Friedman, Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods. It is observed that the activation energy varies with the extent of conversion; indicating the complex nature of the deamination reaction.

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Abstract

Investigations on the thermal behaviour of [Ni(en)3]C2O4·2H2O and [Ni(en)3]SO4 have been carried out in air and helium atmosphere. Simultaneous TG/DTA coupled online with mass spectroscopy (MS) in helium atmosphere detected the presence of H2, O, CO, N2/CH2=CH2 and CO2 fragments during the decomposition of tris(ethylenediamine)nickel(II) oxalate and H2, O, NH, NH2, NH3 and N2/CH2=CH2 fragments for tris(ethylenediamine)nickel(II) sulphate complex. The thermal events during the decomposition were monitored by temperature-resolved X-ray diffraction. In air, both the complexes give nickel oxide as the final product of the decomposition. In helium atmosphere, tris(ethylenediamine)nickel(II) oxalate gives nickel as the residue, whereas tris(ethylenediamine)nickel(II) sulphate gives a mixture of nickel and nickel sulphide phases as the final residue. Kinetic analyses of these complexes by isoconversional methods are discussed and compared.

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Abstract

Thermal behaviour of nickel amine complexes containing SO4 2−, NO3 , Cl and Br as counter ions and ammonia and ethylenediamine as ligands have been investigated using simultaneous TG/DTA coupled with mass spectroscopy (TG/DTA–MS). Evolved gas analyses detected various transient intermediates during thermal decomposition. The nickel ammonium sulphate complex produces NH, N, S, O and N2 species. The nickel ammonium nitrate complex generated fragments like N, N2, NO, O2, N2O, NH2 and NH. The halide complexes produce NH2, NH, N2 and H2 species during decomposition. The ligand ethylenediamine is fragmented as N2/C2H4, NH3 and H2. The residue hexaamminenickel(II) sulphate produces NiO with crystallite size 50 nm. Hexaammine and tris(ethylenediamine)nickel(II) nitrate produce NiO in the range 25.5 nm and 23 nm, respectively. The halide complexes produce nano sized metallic nickel (20 nm) as the residue. Among the complexes studied, the nitrate containing complexes undergo simultaneous oxidation and reduction.

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Abstract

Thermal behaviour of hexaamminenickel(II) nitrate and tris(ethylenediamine)nickel(II) nitrate have been investigated by means of simultaneous thermogravimetry/DTA coupled online with mass spectral (MS) studies and temperature resolved X-ray diffraction (TR-XRD) techniques under inert atmospheric condition. Both the complexes produce highly exothermic reactions during heating due to the oxidation of the evolved ammonia or ethylenediamine by the decomposition products of Ni(NO3)2. Evolved gas analysis by MS studies detected fragments like NH2 and NH ions with weak intensity. The decomposition of nitrate group generates N, N2, NO, O2 and N2O species. Ethylenediamine (m/z 60) is fragmented to H2 (m/z 2), N (m/z 14), NH3 (m/z 17) and CH2=CH2/N2 (m/z 28) species. The formation of the intermediates was monitored by in situ TR-XRD. The residue of thermal decomposition for both the complexes was found to be crystalline NiO in the nano range.

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Abstract

Detailed investigation on the thermal behaviour of hexaamminenickel(II) chloride and hexaamminenickel(II) bromide has been carried out by means of simultaneous TG/DTA coupled online with mass spectroscopy (TG-MS) and temperature-resolved X-ray diffraction (TR-XRD). Evolved gas analyses by TG-MS revealed the presence of NH2, NH, N2 and H2 fragments in addition to ammonia during the deamination process. These transient species resulted due to the fragmentation of the evolved ammonia during pyrolysis. The intermediates formed during the thermal deamination stages were monitored by in situ TR-XRD. The final product of the decomposition was found to be nano size metallic nickel in both cases. Morphology of the complexes, intermediates and the residue formed at various decomposition stages was analysed by scanning electron microscope (SEM). Kinetic analyses using isoconversional method for deamination and dehalogenation reaction show that the activation energies vary with the extent of conversion, indicating the multi-step nature of these solid state decomposition reactions.

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