Massey Documents by Type

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Mathematical model of the forced cooling of anodes used in the aluminium industry : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Mathematics at Massey University
(Massey University, 1994) Palliser, Christopher Charles
The aluminium industry consumes large amounts of electrodes, especially anodes, to operate the smelters. These anodes must be baked at high temperatures in order to give them certain mechanical and electrical properties, after which they are cooled. Baking is done in large furnaces made up of pits inside which the anodes are placed in layers and surrounded by packing coke. The furnaces are of two types - open and closed. In a closed furnace, the pits are lined with refractory bricks inside which flues run vertically and large covers are used to close over parts of the furnace. This thesis presents a mathematical model of part of a forced cooling section of a closed furnace, where air is being sucked or blown through the flues by fans, so that the anodes cool more rapidly. Both one- and two-dimensional models are developed in order to calculate the transient temperature distribution in the anodes, packing coke and side flue wall. For the two-dimensional model, the transient temperature and pressure distributions of the air in the side wall flues and fire shafts are also calculated. After exploring an analytical method for the one-dimensional case, numerical techniques are used thereafter. Given initial block and air temperatures, the two-dimensional model allows calculation of the appropriate temperature and pressure distributions for various mass flows of air in the side wall flues and fire shafts. The results show that for a sufficiently high mass flow, the anodes can be cooled enough so that they can be safely removed from the pits after three fire cycles (the length of time the anodes are exposed to forced cooling).
The electrochemical deposition of mercury on glassy carbon electrodes : a thesis in partial fulfilment of the requirements for the degree of Masters in Science in Chemistry at Massey University, Palmerston North, New Zealand
(Massey University, 2000) Moretto, Giovanna Lucia
The mechanism for the reduction of Hg2+ on glassy carbon in aqueous acetate and nitrate electrolyte was studied. This deposition process is of interest due to the wide electroanalytical applications of mercury thin film electrodes. It was found in the early stages of this work that even though the use of these electrodes is wide spread, there has been little investigation into how the deposition stage occurs. The electrochemical techniques used were cyclic voltammetry and chronoamperometry. A range of experiments were undertaken including concentration dependence, rotation dependence, scan rate dependence, electrochemical-cleaning, and the dependence of the length of time left at open potential. The acetate experiments were carried out at a constant pH of 5.0 and all experiments were carried out at a constant temperature of 20°C. Significant dependence was established in the cyclic voltammetry work for all the experimental conditions. In acetate electrolyte the development of peaks C1 and C2 were seen after cycling of the electrode without mechanical-cleaning. A shift in the reduction potential from a mechanically-cleaned electrode cycle to the next cycle without intervening cleaning was also observed. Two new anodic peaks, A2 and A3, were also seen in acetate electrolyte. At high concentrations cathodic current spikes were observed at the extreme cathodic limits of the voltammograms. The response that was observed in nitrate electrolyte was dissimilar to that in acetate. The shift in reduction potential, current spikes, peaks C1, C2, A2, and A3, were never observed for the deposition of Hg2+ in nitrate electrolyte. The chronoamperometry work on microelectrodes led to a number of new phenomena. Transients that were obtained from these experiments lead to the development of a quantitative nucleation and growth model for the growth of hemispherical mercury droplets. At the onset of reduction the transients follow a t2 function which is in accordance with surface area dependence growth of the droplet. However, after a short length of time, the transients start to follow a function of t 1/2, which is suggestive of perimeter growth control. This is assumed to be due to the formation of a semi-passivating Hg2(OAc)2 film over the mercury droplet where Hg2+2 forms as a result of a disproportionation reaction. A qualitative model was also developed to account for the observations of both the microelectrode results and most of the features seen in the cyclic voltammetry work.
Laser ablation assisted micropattern screen printed transduction electrodes for sensing applications
(Nature Publishing Group, 28/04/2022) Rehmani MAA; Lal K; Shaukat A; Arif K
In this work we present a facile method for the fabrication of several capacitive transduction electrodes for sensing applications. To prepare the electrodes, line widths up to 300 μm were produced on polymethyl methacrylate (PMMA) substrate using a common workshop laser engraving machine. The geometries prepared with the laser ablation process were characterised by optical microscopy for consistency and accuracy. Later, the geometries were coated with functional polymer porous cellulose decorated sensing layer for humidity sensing. The resulting sensors were tested at various relative humidity (RH) levels. In general, good sensing response was produced by the sensors with sensitivities ranging from 0.13 to 2.37 pF/%RH. In ambient conditions the response time of 10 s was noticed for all the fabricated sensors. Moreover, experimental results show that the sensitivity of the fabricated sensors depends highly on the geometry and by changing the electrode geometry sensitivity increases up to 5 times can be achieved with the same sensing layer. The simplicity of the fabrication process and higher sensitivity resulting from the electrode designs is expected to enable the application of the proposed electrodes not only in air quality sensors but also in many other areas such as touch or tactile sensors.

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