The industrial viability and characterization of WC-Co alloys produced by acid leaching and recycling techniques
Date
2016
Authors
Freemantle, Christopher Stuart
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Abstract
In the current study, the well-established zinc recycling process and a prototype acetic acid recycling plant were successfully employed to recycle cemented tungsten carbide scrap material for re-use as production powders. The recycled materials were studied and compared to new materials at each stage along the cemented carbide manufacturing route, in a production environment. Analysis of by-product materials from the zinc recycling process revealed that while some by-product material can be readily converted into powder using the supplementary acetic acid method, the rest is most efficiently recovered by using a second zinc recycling run and by controlling the size and purity of the scrap material introduced into the process. Various analytical techniques, including the novel use of proton induced x-ray emission studies were used to characterize the materials in both the powder and sintered form. The analyses revealed that the recycled materials possessed superior microstructural homogeneity than new materials, and greater than 99% purity. Studies of milling behavior and slurry rheology revealed no adverse effects of using recycled materials, provided that the slurry properties prior to powder spray drying were appropriately controlled. Polymer binder integrity remained intact despite the longer milling times associated with the use of recycled materials, and the superior slurry stability of recycled materials was demonstrated. The flow behavior and powder rheology of the spray dried powders was found to depend on the precursor slurry rheology and particle grain size. This was controlled predominantly by the formation of a sufficient yield stress to produce ideal, dense granules for greater ease of manufacturing, in both new and recycled powders. The acetic acid recycling technique can be used as a complimentary recycling process to the existing zinc recycling process, and can
produce useable recycled material at low cost.
Description
A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy in Engineerin to the Faculty of Engineering and the Built Environment, School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, 2016
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Citation
Freemantle, Christopher Stuart (2016) The industrial viability and characterization of WC-Co alloys produced by acid leaching and recycling techniques, University of the Witwatersrand, Johannesburg, <http://hdl.handle.net/10539/35300>