Thermodynamic and kinetic examinations of inorganic materials formation

Abstract

Inorganic materials formation is the result of a complicated interplay between thermodynamics and kinetics. Improved understanding of such factors can aid the synthesis of target materials and the discovery of new materials. Here, techniques for carrying out time-resolved studies were developed and demonstrated for the investigation of solvothermal and solid state reactions. Detailed kinetic reaction progress maps were constructed, showing quantitative information on the kinetic development of the quantity of each constituent phase during chemical reactions. The approach deployed has little restriction on the reaction conditions, and therefore can be used as a protocol for other kinetic studies of the demonstrated reaction types: solvothermal and solid state. It is shown that detailed and thorough reaction kinetics can be retrieved reliably by combining X-ray diffraction (XRD) with supplementary characterization methods without reliance on synchrotron-based facilities, allowing for high-throughout screening of different reactions. Synchrotron-based in situ XRD was also tested and developed, which can provide more insight for those selected systems that require higher- fidelity data collection. In this dissertation, it is shown that valuable mechanistic knowledge on materials syntheses can be learned from such types of thermodynamic and kinetic investigations, which can be effectively employed for the discovery of new material structures. Comprehensive quantitative information was obtained on phase evolution during the solvothermal synthesis of Cu4O3 based on time-resolved ex situ investigations. Combined with the observation of phase correlations, it was realized that the transition through Cu2(NO3)(OH)3 and a proper redox environment is critical to form Cu4O3. With the use of in situ energy-dispersive X-ray diffraction carried out at 6-BM-B in Advanced Photon Source, it was verified that all copper oxide forms CuO, Cu2O, and Cu4O3 were made at the solvothermal temperature. It was also shown that at the local scale, no apparent transformation between Cu4O3 and CuO / Cu2O took place, but the transformation between CuO and Cu2O was evident, supporting the reaction mechanism proposed from the ex situ study. Through changes in the solvothermal chemistry, it was shown that direct transformation of Cu2(NO3)(OH)3 to Cu4O3 could not be achieved with a simple mixture of ethanol and dimethylformamide. Some species generated in the original Cu4O3 synthesis scheme are required in order for such transformation to take place, which are yet to be confirmed in identity. After testing with several solvothermal solvents, it was discovered that solvent chemistry has a huge impact on the phase stability of Cu-containing inorganic materials, and four new crystalline phases were suggested based on unmatched diffraction patterns. Among these new structures, one is a coordination compound, which possesses a unique coordination stereochemistry. In this structure, Cu is coordinated to two chelating ethylenediamine ligands and one monodentate ethylenediamine ligand, which is unprecedented. Solid state synthesis of Fe2SiS4 was investigated using in situ X-ray diffraction. Important factors that affect Fe2SiS4 formation kinetics are identified to be a peritectic transition, intermetallic formation, and particle size reduction. These factors were explored for the discovery of new ternary chalcogenide materials. Realizing the effectiveness of burst formation of superheated liquid on materials formation kinetics, we explored flux-crystallization of Ba-Fe-S materials utilizing BaS3 as a reactive flux. Both lab and synchrotron in situ X-ray diffraction verified that novel crystalline phases formed when the system was in the flux state. Through the analysis of a particular set of synchrotron in situ X-ray diffraction patterns, we give suggestions on the diffraction profiles of five new flux-grown Ba-Fe-S phases. Materials discovery was also carried out with solid state synthesis for ternary sulfide and selenides systems with the help of ball milling reagents for kinetic enhancement. Based on the X-ray diffraction results of the products, the existence of three new materials are shown in the ternary systems of Sr-V-S, Sr-Cr-S, and Sr-Ni-S