Pritzel, Christian
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Pritzel, Christian
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Publication Access status: Open Access , Synthesis and characterization of methylammonium phosphates as crystalline approximants for anhydrous, low melting phosphate glasses(2019); ; ; Low-melting methylammonium phosphate glasses are synthesized from crystalline starting agents. To this end crystalline tris(methylammonium) cyclotriphosphate [CH3NH3]3P3O9, was synthesized by a novel and simple synthesis route from P4O10 and N-methylformamide. It, undergoes an irreversible phase transition to methylammonium catena-polyphosphate [CH3NH3]PO3. The crystal structure of the catena-polyphosphate was solved and refined from X-ray powder diffraction data by the Rietveld method using constraints obtained by solid-state 31P and 1H NMR spectroscopy. This compound crystallizes in a triclinic space group with a = 13.2236(9), b = 7.8924(6), c = 4.6553(2) Å, α = 91.068(4), β = 87.840(5) and γ = 106.550(3)°. Quantum chemical calculations confirm that the obtained structure lies at an energetic minimum. Finally the reaction of tris(methylammonium) cyclotriphosphate and P4O10 into methylammonium phosphate glass is presented. The synthesized, water-free phosphate glass shows a very low glass transition temperature Tg of 33 °C, which was verified by dynamic scanning calorimetry and NMR. The chain-like crystal structure of the high-temperature methylammoniumphosphate [CH3NH3]PO3 serves as an approximation for the short-range order of the glass.Source Type:Article1 6 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , The mechanism of the first hydration-dehydration cycle of pure α- and β-CaSO4•0.5H2OThe objective of this research was to understand the dehydration mechanism of technical dihydrate and the variation of the physical properties of β-hemihydrate after the first hydration-dehydration process. In this study, the recycling mechanism of different hemihydrate types as raw material was investigated. The influence of the first hydration-dehydration process on the hydration rate, microstructure, and mechanical properties of recycled hemihydrate were characterized by differential calorimetric analysis (DCA), calcium ion-selective electrode (Ca2+-ISE), conductivity, particle size distribution (PSD), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results showed that the formed hemihydrate after the first hydration-dehydration process differs in its properties than the unrecycled hemihydrate in some characteristics such as the morphological structure, number of surface, and side defects due to the grinding process after the first hydration step. In addition to the grinding step, the calcination process was responsible for increasing the number of defects on the crystal surface, which leads to a change in setting time and the microstructure of the recycled hemihydrate. Therefore, after the 1st reaction cycle of β-HH, the compressive strength decreases due to a decrease in the hemihydrate crystal size, an increase in the surface area, and an increase in the amount of water required to perform the hydration reaction. The obtained hemihydrate after the first hydration-dehydration process was in β form due to the applied calcination process after the first cycle.Source Type:Article7 15
