THERMOPROGRAMMING DESSORPTION MASS SPECTROMETRY AS A METHOD FOR DETERMINING CORRELATIONS BETWEEN DYNAMICS OF THERMAL DESTRUCTION AND MORPHOLOGICAL HYMYMYCHYMYRAM

Abstract

The correlation between the dynamics of thermal destruction and morphological parameters of biogenic calcites based on the TPD-MS method using eggshells of different species of poultry to develop a convenient model system for assessing the state of complex multicomponent bioceramic structures of the eggshell. For this purpose, different spectra of thermal desorption of biogenic calcites were studied: limestone, eggshell of different species of birds, mollusk shells and calcite nanoparticles. It is proved that the spectrum correlates with morphological parameters and depends on the degree of dispersion of biogenic calcites. The increase in the content of microdisperse, ultrafine and nanodisperse components in a biocomposite based on calcite leads to a significant change in the type of thermodesorption spectrum, which is manifested in the appearance of additional temperature regions of desorption (peaks) and their displacement in the region of temperature decrease. The spectrum of thermodesorption (thermogram) of chalk samples and non-incubated eggs of agricultural poultry was determined experimentally. It was found that the release of carbon dioxide CO 2 as a result of the reaction CaCO 3 (s) → CaO (s) + CO 2 (g), 178 kJ/mol begins at a temperature of 440-450°C and ends at 720-750°C. This indicates the nonlinear nature of the dependence of the partial pressure of CO 2 in the quartz cell on the temperature with two distinct peaks 550-560 and 640-660°C, and the peak in the low temperature region is significantly higher. It is proved that when maintaining for all heterogeneous samples of biogenic calcite the interval on the temperature scale 440-750°C of intensive CO 2 release, the intensity and width of individual peaks corresponding to the specified selection are extremely variable. The working hypothesis to explain this phenomenon was the assumption that the coordinates of the peaks on the temperature scale correspond to the dispersion levels of calcite crystals and their location in the biomaterial. Indeed, almost all of the studied samples give similar diffraction patterns corresponding to calcium carbonate. The next assumption was that the heterogeneity of the micro- and macrostructure of calcite-based biocomposites was responsible for expanding the temperature range of destruction and increasing the number of peaks of intensive release of chalk samples and bird eggs. In this case, the preliminary grinding of the belemnite sample should lead to a change in the type of thermogram, namely, to a narrowing of the destruction interval for fine-grained (> 5-10 μm) and to a corresponding expansion of this interval in the case of combining coarse and fine-grained calcite fractions in one sample.