The isothermal crystallization of amorphous alloys of the type (Pd100−xNix)83Si17 has been investigated by DSC. The character of the transformation depends upon the content of Ni. Ifx>30, material crystallizes probably without nucleation in a very narrow temperature range. Ifx⩽30, the crystallization process is controlled by a nucleationgrowth mechanism. The initial stages of transformation are characterized by a relatively short incubation period with an Arrhenius temperature-dependence. Afterwards, the time-dependence of the degree of conversion is sigmoidal. Ifα<0.1, thenp∼1 characterizes a homogeneous nucleation. If 0.1<α<0.9 than the Avrami exponent isp(α)∼3–4. Atα>0.9 so-called tails are observed.
Authors:H. Langfelderová, F. Foret, P. Ambrovič, and J. Gažo
The thermal decomposition of the complexes M2ICu(SO4)2 · 6 H2O and M2Ni(SO4)2 · · 6 H2O (MI=NH4, K, Rb, Tl) containing the complex cation MII(H2O)62+ (MIl = =Cu, Ni) was studied. The values of the experimental activation energyE obtained for the dehydration reactions of both complex cations were found to be influenced in different ways by the outer-sphere cations present. It was therefore concluded that the activation energy of the decomposition of Cu(H2O)62+ depends on the degree of tetragonal distortion of this cation, which increases with the ionic radius of cation MI. TheΔH values of the studied reactions depend less on the structures of the coordination polyhedra.
Authors:H. Langfelderová, M. Hvasiijová, J. Kohout, P. Ambrovič, and K. Csomorová
The paper presents the results of a study of the course of thermal decomposition of complexes Cu(NCO)2L2 and Cu(LNCO)2, withL=pyrazole, 3,5-dimethylpyrazole, 3,4,5-trimethylpyrazole and indazole. The DTA curves of Cu(NCO)2L2 show exothermic excursions somewhat below the decomposition temperatures, corresponding to an inner complex nucleophilic addition of a carbon atom (from an NCO group) to the imine nitrogen atom of a pyrazole ligand. In this reaction the carbamoylpyrazolate anion is formed, coordinated to Cu(II). For these reactions the DSC method yielded the followingΔH values: −12.80 kJ mol−1 (L=pyrazole), −8.15 kJ mol−1 (L=3,5-dimethylpyrazole), −19.49 kJ mol−1 (L=3,4,5-trimethylpyrazole) and −11.59 kJ mol−1 (L=indazole). The course of thermal decomposition for Cu(NCO)2L2 after the nucleophilic addition is the same as for Cu(LNCO)2. The structure differences between the distortion isomers of Cu(NCO)2L2 and Cu(LNCO)2 were manifested in the decomposition temperatures and, in some cases, also in the stoichiometry of the decomposition reactions.