Kinetic parameters from thermogravimetric study of used rubber granulates–polyurethane composites

From the TG data of rubber granulates, different polyurethane and composites it can be seen that the thermal decomposition for the rubber granulate and all of the composites start above 520 K. Two major mass losses for the rubber granulates and majority of the composites were observed and thermal decomposition is essentially complete by ~820 K. The changes of activation energies of lower and higher temperature decomposition, calculated according to the different equations were observed for a priori assumed first-order reaction for devolatilisation. Differences between determined and calculated results could suggest a possible reaction between polyurethane agents and rubber granulate during the composites formations.     

The use of redox reactions in the analysis of dyes and dye intermediates: XIV. Direct current polarography of 4,4′-disubstituted azobenzenes in acetonitrile

The polarographic reduction of some 4,4′-disubstituted azobenzenes in an acetonitrile medium was studied. The diffusion character of the observed limiting currents was confirmed and a mechansim of polarographic reduction proposed. The possibility of analytical application is briefly discussed.     

Influence of cooling rate on crystallisation kinetics on microstructure of cast zinc alloys

In this study, the change of the cooling rate in the range of about 0.1–1 °C s^?1 and the addition of Sr on the crystallization kinetics of the cast zinc alloys of the ZnAlCu type, as well as its relation to the microstructure were also investigated. Therefore, the aim of the rapid crystallisation is the achievement of materials with better properties, which can be obtained by refinement of the dendritic or eutectic microstructure, elimination of segregation, or creation of metastable phases and their morphology changes. In the investigated alloys, the change of cooling rate of 1 °C s^?1 has caused microstructure’s refinement as well as increase in hardness. Increase in the cooling rate causes also morphology changes of the η + α eutectic, and makes generally a global overcooling of the alloy as well as change in the temperatures at the beginning of crystallization T _DN and of the alloy crystallization T _S. The presented investigations concerning the electron microscopy methods, including transmission electron microscopy, allow revealing the crystallographic structure, based on the d-spacing changes, as well as the diffraction method used for phase determination, which is a helpful tool for the explanation of the important points in the thermo-derivative analysis curve, where the relation between the amount of phase and the occurrence of new phases can be determined.     

Diaquadichloridobis(1H‐imidazole)manganese(II) at 100 K

The mononuclear title complex, [MnCl₂(C₃H₄N₂)₂(H₂O)₂], is located on a crystallographic inversion center. The Mn^II ion is coordinated by two imidazole ligands [Mn—N = 2.2080 (9) Å], two Cl atoms [Mn—Cl = 2.5747 (3) Å] and two water molecules [Mn—O = 2.2064 (8) Å]. These six monodentate ligands define an octahedron with almost ideal angles: the adjacent N—Mn—O, N—Mn—Cl and O—Mn—Cl angles are 90.56 (3), 92.04 (2) and 90.21 (2)°, respectively. Hydrogen bonds between the coordinated water molecules and Cl atoms form a two‐dimensional network parallel to (100) involving R₄²(8) rings. The two‐dimensional networks link into a three‐dimensional framework through weaker N—H...Cl interactions. Thermogravimetric analysis results are in accordance with the water‐coordinated character of the substance and its dehydration in two successive steps.     

The influence of the plasticization on free volume in polyvinyl chloride

Positron lifetime measurements in polyvinyl chloride (PVC), plasticized with the aid of dibutyl phthalate and tricresyl phosphate have been made. The plasticizers, the first range plasticizers, are an organic and an inorganic ester, respectively. The influence of the different concentration of the plasticizer in the PVC on positron lifetimes in the polymer have been investigated. A conventional fast-slow coincidence lifetime spectrometer with plastic scintillators has been used for the lifetime measurements. All the measurements have been performed in air, at room temperature. Mean free volumes radii have been calculated from the lifetime data.     

The use of redox reactions in the analysis of dyes and dye intermediates : VII. The reductometric and polarographic determination of N,N-dimethyl-4-amino-4′-hydroxyazobenzene

The chemical reduction of N,N-dimethyl-4-amino-4′-hydroxyazobenzene with titanium(III) chloride and chromium(II) sulfate was studied, as was the polarographic reduction of this substance. Optimal conditions for the analytical application of these reactions were found.     

The oxidation of organic substances with compounds of trivalent manganese: XXVII. The oxidation of 4,4′-dihydroxyazobenzene with the diphosphate complex of trivalent manganese

The oxidation of 4,4′-dihydroxyazobenzene with the diphosphate complex of trivalent manganese was studied. The reaction stoichiometry was found and a procedure for a direct potentiometric titration of the test substance has been proposed.     

The use of redox reactions in analysis of dyes and dye intermediates: X. Polarographic and constant-potential coulometric determination of 4,4′-dihydroxyazobenzene and 4-nitro-4′-hydroxyazobenzene

Conditions have been found for a polarographic and constant-potential coulometric determination of 4.4′-dihydroxyazobenzene and 4-nitro-4′-hydroxyazobenzene in buffered media.