Felix Baitalow

Main-Group and Transition-Element IRMOF Homologues

A simple two-component procedure was developed to synthesize not only classical zinc-based IRMOFs represented by MOF-5 but also the cobalt and beryllium homologues of this most prominent MOF. The procedure is the first manifestation of mirroring the IRMOF series with other metal centers taken from main-group as well as transition-metal elements. Because of the existence of many suitable precursors, the procedure promises the generation of a large number of IRMOF homologues. Since the IRMOF series together with the MIL series is the MOF group with the largest number of representatives, the possibility of choosing the metal centers of the secondary building units from an extended set will tremendously expand the number of obtainable structures in a predictive, crystal-engineering-type way. Use of metal centers other than zinc will allow the addition of new features to the existing IRMOF structures, such as magnetic properties in the example of cobalt.

Formal kinetic analysis of processes in the solid state

Abstract The applicability of an unconventional approach in the formal kinetic analysis of solid-state reactions is discussed. This approach is based on the joint use of so-called isoconversional methods and of the non-linear regression analysis. By means of this approach reliable kinetic parameters for the phase transitions between three polymorphic modifications of calcium carbonate were obtained. The influence of the conditions of sample preparation on the transition kinetics has been studied. Two different transition mechanisms are compared using the calculated kinetic data. The isoconversional method, proposed by Friedman, delivers activation energy values, which deviates from data, obtained by means of the Flynn–Wall–Ozawa method. Additionally, the calculated apparent activation energy is dependent on the degree of conversion. The influence of some model deviations on the accuracy of the isoconversional methods is discussed. It is shown that the robustness of these methods towards model deviations may be tested by an analysis of theoretical plots.

Thermochemical Investigations of Calcium Carbonate Phase Transitions I. Thermal activated vaterite—calcite transition

The vaterite—calcite transition above 630 K has been studied by isothermal and non-isothermal differential scanning calorimetry. Vaterite samples prepared under different conditions were investigated. The transition temperature is strongly dependent on the sample preparation. The observed transition enthalpy ΔHtr is nearly equal for different samples and experimental conditions. From 28 measurements a value of ΔHtr−(3.12±0.11) kJ mol−1 was obtained. The activation energy for the polymorphic transition was calculated from the Arrhenius plot and by use of isoconversional methods, as a function of the degree of conversion. The influence of the kinetic model distortion and experimental uncertainties on the obtained data was discussed. The actual value of the activation energy was assessed at Ea=(250±10) kJ mol−1 for nearly all examined samples. Functions, corresponded to the model mechanism of nuclei formation and growth, provide the unambiguous consideration of the transition kinetic for the investigated vaterite samples. Differences in the dynamic behaviour of several samples at the transition are established.