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Title: Surface behaviour for materials processing
Author: Owens, C.
Awarding Body: University of Exeter
Current Institution: University of Exeter
Date of Award: 2019
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The surface behaviour of minerals containing rare earth elements was investigated using zeta potential measurements. The rare earth fluorcarbonate mineral, parisite and a rare earth enriched phosphate mineral, apatite were measured under water and collector aqueous conditions, which are similar to those found under froth flotation. Firstly, the iso electric point of parisite was measured at pH 5.6 in water, this is within the range of reported IEP values of another rare earth fluorcarbonate mineral, bastnäsite. Bastnäsite currently sources over half of the world's rare earth elements and has well studied surface behaviour. The surface behaviour of parisite under collector and supernatant conditions was similar to bastnäsite, indicating that parisite could be processed using the same froth flotation regimes as bastnäsite. Secondly, the iso electric point of rare earth enriched apatite was measured at pH 3.8, which is consistent with the values of apatite non-rare earth enriched apatite in the literature. The surface behaviour of non-rare earth enriched apatite from the literature and the enriched apatite measured here is similar under common reagent conditions. This suggests apatite processing could be applied to rare earth enriched apatite deposits. The first evidence of nanobubbles at the surface of the carbonate mineral, dolomite and rare earth fluorcarbonate mineral, synchysite were also reported. The nanobubbles were measured using non-contact atomic force microscopy, and produced using the gas oversaturation method of heating the liquid. Nanobubble density on dolomite was increased by collector conditions with 0.656 bubbles per µm2, compared to 0.342 nanobubbles per µm2 under water conditions. Investigating the contact angle of the nanobubbles on dolomite indicated that the reagents effected the pinning of the nanobubbles and not their surface tension. Nanobubbles on the synchysite sample in collector conditions had an average contact angle of 24 degrees, in line with previous studies. The presence of nanobubbles on synchysite under collector conditions demonstrates that the surface is hydrophobic. Finally, nanobubbles at the surface of patterned and unpatterned chemical vapour deposition monolayer graphene were investigated. High-speed atomic force microscopy was used to image nanobubbles produced using solvent exchange. Nanobubbles were found on patterned graphene, not on the underlying SiO2 substrate. This links to the increased hydrophobicity of graphene compared to SiO2. The patterning of the graphene reduced the nanobubbles' lateral size and increased the contact angle, consistent with previous results of nanobubbles on patterning. These are the first reported results of nanobubbles constrained by chemically patterned graphene.
Supervisor: Nash, G. ; Ghita, O. Sponsor: Natural Environment Research Council (NERC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available