The special position occupied by glasses amongst solids is again underlined by their thermal behaviour. This feature was studied using As2Se3 as model glass. The range of transformation characteristic of glass is less sharply defined than the freezing point. In the thermal characterization of glass the former is highly dependent on the rate of heating and the thermal history of the glass. The recrystallization and melting temperatures are subject to corresponding modifications.
GeX2 glass (X=O, S, Se) of defined grain was investigated at constant heating rateq by applying the DTA. From the DTA-curves measured at differentq the kinetic parameters of crystallization were determined according to the Kissinger method. Under these conditions, the effective activation energies for the oxide, sulfide and selenide were found to be 179, 219 and 298 kJ·mol−1, respectively. If bulk GeS2 glass is used as starting material, the shape of the DTA-curves is different from the curves obtained from grainy material and they cannot be evaluated by the Kissinger procedure.
Based on DTA measurements made at increasing and decreasing temperatures, an empirical value
is defined for the glass-forming tendency. Similar to the parameterKg1 of Hruby, this value is based on the position of the crystallization temperature in the temperature range of the undercooled melt, but the method applied fits in better with the process of glass formation. The result is a better differentiation of the glassforming ability of the melts in the Pb- Se- Ge system.
Samples of sediments taken from the River Saale at different locations were investigated by thermogravimetry, differential thermal analysis, mass spectrometry and FTIR spectroscopy.The thermal behaviour of these sediments varied significantly depending on contents of organic and inorganic compounds. The variable organic loading resulted from the different degrees of treatment of communal or industrial waste water. Mass spectrometric investigations in the lower temperature ranges demonstrated humic substances as essential components.The mineral components in the river sections of the slate mountains differed significantly from those of the shell limestone. The results of FTIR analysis of these samples confirmed well with the findings of thermoanalytical investigations.
The Na/Tl exchange is investigated in two silicate glasses (Na2O·2SiO2 and crown-flint “KF3”) by estimation of concentration or refractive index profiles, resp. (cTl(x) orn(x)). The forms of the profiles are discussed in connection with changes of the glass transition temperature Tg owing to an increase of Tl2O contents, determined by DTA on homogeneous glass samples. During the Na/Tl exchange the local and temporal enlargement of the Tl2O content causes a drastic decrease ofTg(x, t) values and of the viscosity η(x, t), which yields a remarkable acceleration of the Na/Tl interdiffusion.
The thermal behaviour of complexes of the type M(HIm)2ac2 (HIm=imidazole,ac=acetate,M=Co, Ni, Cu) is different. Comparable to the thermal degradation of Ni(acac)2(HIm)2  the Ni(HIm)2ac2 loss acetic acid by formation of Ni(Im)2. All nitrogen ligands are splitt off from the copper complex by formation of stable basic copper acetate. The cobalt compound
eliminated acetic acid partially while acetate and imidazolate bridging species are obtained.
The thermal behaviour of the acetate complexes of pyrazole and the bulky 3,5-dimethylpyrazole is quite similar. In a first
step pyrazoliumacetate is removed.
The crystal structure of Ni(HPz)4ac2 is determined by X-ray diffraction: monocline, space group C 2/c.
The water molecule represents the centre of two N−H...O−H...O-bridges. The system of H-bridges in the compound relieves the
proton transfer, indicated by the elimination of pyrazolium acetate.
Authors:M. Döring, J. Wuckelt, W. Ludwig and H. Görls
Complexes of the type M(Pa)2(HAz)2 and M(QA)2(HAz)2 (M=cobalt(II) and nickel(II); HPa=picolinic acid, HQa=quinaldic acid; HAz=azoles like imidazole (Him), pyrazole (HPz), benzimidazole
(HBzIm) etc.) show a similar thermal behaviour. In the first step of decomposition the corresponding azolinium picolinates
or quinaldinates (H2AzPa, H2AzQa) are split off with formation of polymeric mixed ligand complexes M(Pa)(Az) or M(Qa)(Az). X-ray analysis of Co(Qa)2(HBzIm)2 XIIIa illustrates a proton transfer and a subsequent thermal removal of benzimidazolinium quinaldinate (H2BzImQa): Hydrogen bridges from pyrrole nitrogen of the benzimidazole to the non-coordinated oxygen of the quinaldinate predetermine
the thermal initiated proton transfer. The high volatility of the heterocyclic acids and the nitrogen coordination are responsible
for the formation of the mixed ligand complex Co(Qa)(BzIm) XIVa.
Exceptions are the complexes M(Pa)2(HPz)2 XIa-b and M(Qa)2(HIm)2 XVIIa-b. Pyrazole is eliminated from the complexes XIa-b with formation of the solvent-free inner complex M(Pa)2 XIIa-b. From compounds XVIIIa-b quinaldic acid or their decomposition products are split off and a high temperature modification
of M(Im)2 XVIIIa-b is formed at elevated temperature. XVIIIa-b are decomposed to the cyanides M(CN)2 similarly to the thermal behaviour of Cu(Im).
In the first step the thermal degradation of imidazole and pyrazole adducts of copper(II) picolinates and quinaldinates is
characterized by the elimination of azoles. The reason for this thermal behaviour is the weaker coordination of the azole
heterocycles in copper chelate compounds.