25 research outputs found
Optimisation and characterisation of durable microelectrodes for electroanalysis in molten salt
This work presents microfabricated microelectrodes, capable of quantitative analysis in
molten salt (MS). MSs are an electrolytic medium of growing interest, especially in the
area of nuclear reprocessing. However, designing sensors for a MS-based nuclear reprocessing
system is a challenge, owing to the usually corrosive nature and high operating
temperatures (typically 450 - 500â—¦C) of MS.
Microelectrodes are well placed as sensors, with numerous advantages over macro-scale
electrodes. As a consequence, there have been previous attempts to utilise microelectrodes
inMS. However, these have not been successful and all have suffered disadvantages
inherent in traditional microelectrode manufacturing.
The microelectrodes presented in this work were produced using standard microfabrication
techniques and characterised in MS. An analysis of failure mechanisms guided a
systematic study of material combinations. This resulted in a sensor, which is capable
of delivering quantifiable electrochemistry in MS. However, the lifetime and yield of the
sensor were determined to only be 46% and 1.4 hours respectively.
Further investigation of the microelectrode failure mechanisms guided several layout
changes to the microelectrode design. By reducing critical area, where defects or pinholes
could form, these resulted in improvements in performance. This increased the yield to
65%, while the average lifetime increased up to 45 hours.
Test structures were designed to investigate the causes of the continued microelectrode
failures and identified shorting between the electrode metal and silicon substrate. This
suggests the existence of defects in the underlying insulator are the cause of the 35%
of microelectrodes which never functioned. Separate test structures suggested the lifetimes
of the microelectrodes could also be improved by removing the need for a metal
adhesion layer. Tantalum has been suggested as a replacement electrode metal and a
proof of concept study demonstrated the feasibility of employing thin film tantalum as
an electrode metal in LKE.
Using this technology as a platform, several proof-of-concept microelectrode designs
are also presented: liquid microelectrodes, microelectrode arrays, and a nanoelectrode.
These are targeted at specific sensing applications, and provide an expanded spectrum
of measurements in MS
A study of the non-stoichiometry in U<SUB>3</SUB>O<SUB>8</SUB>
Measurements of the oxygen-to-uranium ratio in U3O8 were performed using two independent methods, namely thermogravimetry and wet chemical analysis by cerimetry. The O/U variations in U3O8 were delineated as a function of temperature in the range 450-900°C. The experimental conditions for the attainment of the stoichiometric state were also examined