New directions in time-resolved neutron diffraction: probing high power microwave materials synthesis in situ

QD Chemistry

Boscaino, Annalisa ; Gregory, Duncan

University:University of Glasgow

Department:School of Chemistry

关键词: Microwave synthesis, in situ powder neutron diffraction, ceramics, solid state synthesis;   

Others  :  http://theses.gla.ac.uk/5699/1/2014boscainophd.pdf

来源: University of Glasgow

【 摘 要 】

This thesis aims to describe the design, implementation and use of a novel instrumental set-up which, by providing in situ ultra-rapid synthesis of transition metal carbides, is capable of investigating their reaction mechanisms, thus developing new procedures to reduce energy demanding industrial processes.Ultra-rapid synthesis of titanium carbide, TiC - the main binary system studied - has been achieved through the development of a reproducible experimental technique and an investigation into crucial reaction variables, microwave applicators and applied power. Specifically in the case of the single mode cavity, this resulted in the completion of the majority of reactions within 60 s. TiC formation started from its elemental precursors (titanium and graphite). An attempt to produce TiC by using a domestic microwave oven successfully lead to the synthesis of the product after ca. 15 minutes. A further achievement was made by exploiting the linear relationship between the expansion of graphite (increase of c parameter) with temperature, which allowed for in situ bulk temperature measurements crystallographically. This method of measurement represents a more reliable alternative to traditional techniques (i.e., pyrometery or use of thermocouples).The majority of this work was performed on the D20 beam line at the ILL neutron source facility, in Grenoble. The choice of this beam line, capable of collecting diffractograms at high speed rate was crucial for revealing the reaction pathways of TiC MW-promoted synthesis, for the first time. Raman spectroscopy and scanning electron microscopy techniques were used in an effort to establish the presence of any amorphous phases in the system. The same methodology was applied in preliminary experiments to other ternary transition metal-carbon systems. In particular, tungsten (W) and tantalum (Ta) compounds were investigated, starting from both the elements and respective oxides, WO2 and Ta2O5.