Browsing by Author "Hutchings, Ron"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Open Access
    Degradation of the beta-alumina electrolyte in a zebra cell
    (1988) Van Heerden, D P; Hutchings, Ron; Ball, Anthony
    Beta-alumina solid electrolytes studied were subjected to charge and discharge cycles in a secondary, high energy density Na/beta-alumina/NaAlCl₄/FeCl₂ cell (known as the Zebra cell) at 250⁰ C. These electrolytes were studied by means of optical microscopy, as well as SEM and EDS analyses to est ablish possible failure modes. After cycling little discolouration, or impurity pickup was found to have occurred in the electrolyte. The forms of degradation of the beta-alumina electrolyte identified appeared to be a result of inherent flaws in the beta-alumina electrolyte tube, problems due to protracted storage of the tubes, or an apparent interfacial film on the cathode/electrolyte interface. A lead wetting agent was used in the cells to enhance the wetting of the beta-alumina electrolyte by the liquid Na. A study of the coating after cycling of the cell showed that the coating was adherent irrespective of the number of cycles completed. The coating did not appear to influence cracking of the electrolyte during cycling. Cracking of the beta-alumina electrolyte was found to have initiated from the Na/electrolyte interface. No evidence of crack initiation nor internal damage was found on the cathode/electrolyte interface. The cracks through the beta-alumina electrolyte wall were found to have sealed by the formation of a plug consisting largely of Na and Cl. On the basis of EDS analyses of the fracture surface of the sealed crack possible sealing mechanisms are proposed.
  • No Thumbnail Available
    Item
    Open Access
    Degradation of the beta-alumina electrolyte in a zebra cell
    (1988) Van Heerden, D P; Hutchings, Ron; Ball, Anthony
    Beta-alumina solid electrolytes studied were subjected to charge and discharge cycles in a secondary, high energy density Na/beta-al~mina/NaA1Cl 4/FeC1 2 cell (known as the Zebra cell) at 250 c. These electrolytes were studied by means of optical microscopy, as well as SEM and EDS analyses to establish possible failure modes. After cycling little discolouration, or impurity pickup was found to have occurred in the electrolyte. The forms of degradation of the beta-alumina electrolyte identified appeared to be a result of inherent flaws in the betaalumina electrolyte tube, problems due to protracted storage of the tubes, or an apparent interfacial film on the cathode/electrolyte interface. A lead wetting agent was used in the cells to enhance the wetting of the beta-alumina electrolyte by the liquid Na. A study of the this coating after cycling of the cell showed that the coating was adherent irrespective of the number of cycles completed. The coating did not appear to influence cracking of the electrolyte during cycling. Cracking of the beta-alumina electrolyte was found to have initiated from the Na/electrolyte interface. No evidence of crack initiation nor internal damage was found on the cathode/electrolyte interfac~. The cracks through the beta-alumina electrolyte wall were found to have sealed by the formation of a plug consisting largely of Na and Cl. on the basis of EDS analyses of the fracture surface of the sealed crack possible sealing mechanisms are proposed.
  • Thumbnail Image
    Item
    Open Access
    The solid particle erosion of WC-Co alloys
    (1986) Pennefather, RC; Hutchings, Ron
    An investigation involving the erosion of WC-Co alloys by solid particle impact erosion was undertaken to determine the mechanism by which material is removed. For this purpose a simple particle-gas stream erosion apparatus was employed. The nineteen different WC-Co alloys studied were initially characterised according to mi crostructural and mechanical properties. An investigation of the influence of various parameters on erosion was conducted to establish the manner by which the WC-Co alloys were eroded. A limit in erosion rate occurred with increasing particle size for all samples, which is associated with ductile erosion. The variation of erosion rate with the angle of impact was found to be dependent on the binder content. A maximum in erosion occurred at a 90u angle of incidence for the low cobalt content alloys and in the region of a SOU angle of incidence for high cobalt content alloys. Thus suggesting a predominantly brittle mode of erosion, with a ductile mode becoming more important with increasing binder content. The erosion rate was found to increase with decreasing hardness. For impact angles of 45u and greater, the hardness effect was masked by microstructural influences. Examination of the steady state eroded surface and the single particle impact event, using the scanning electron microscope revealed three modes of material removal. These may occur simultaneously, the predominant mode, however, changes with binder content. For WC-Co alloys containing less than 10 wt-% cobalt, cobalt extrusion was observed as being the controlling mode of material removal. Maximum carbide grain cracking was associated with a cobalt content of 10 wt-%. Above this binder level ductile cutting of the matrix became an increasingly important mode of material removal.