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Calcium carbonate growth and dissolution to the nanoscale
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Bindley, Lucy Ann (2005) Calcium carbonate growth and dissolution to the nanoscale. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b2072773
Abstract
This thesis describes three examples of how the functionality of a growth surface affects the crystallisation of CaC03; investigates the dissolution of calcium carbonates and phosphates on the microscale; and describes a new atomic force microscopy (AFM) method which has been used to investigate the reactivity of the (104) surface of single calcite microcrystals.
Growth surfaces bearing carboxylic acid- functionalised nanoparticles were prepared by deposition onto glass using a layer-by-layer method with poly(allylamine) hydrochloride as the cross linker. These surfaces were found to influence the extent of CaC03 crystallisation, which increased with nanoparticle surface coverage. For these nucleation experiments, two crystal growth techniques were used: the Kitano method, in which the supersaturation of the growth solution slowly increased with time; and a jet crystallisation method, incorporating the mixing of two undersaturated solutions to create a supersaturated solution which was jetted onto the surface of interest via a specially designed cell. Calcite was the predominant CaCC>3 polymorph formed on these surfaces, with a high proportion of the crystals nucleating on the (015) plane rather than on tire stable (104) plane, thus showing that nanoparticles have an orientational effect on CaCOj crystallisation.
Functionalisation of gold surfaces was achieved via the deposition of self-assembled monolayers (SAMs) and the effect of an applied potential on CaCC>3 nucleation was investigated. Application of a potential more negative than the potential of zero charge to any of the functionalised SAM surfaces resulted in the inhibition of CaC(>3 nucleation, whereas at more positive potentials, extensive vaterite growth was evident These studies showed that the extent of CaCC>3 nucleation could be tuned readily via the applied potential.
K coli bacterial biofilms served as substrates for experiments with direct implications on household care. The biofilms dramatically affected the crystallisation of CaCC>3, first by acting as nucleation centres for growth, and, secondly, causing significant surface and structural damage to the crystals formed. Stabilisation of crystals from unusual nucleating planes, (012) and (015), was also evident.
As a new approach for investigating proton-promoted dissolution, an ultramicroelectrode was used to direct a flux of protons towards a calcite surface, by the oxidation of water. Etch pit analysis revealed that the pit volumes increased with increasing proton flux, in a linear fashion. Modelling this process using the finite element method allowed the rate constant for dissolution to be calculated. Dissolution of more complex calcium carbonate and phosphate simulated limescale pellets was also addressed using this technique, allowing the reactivity of a range of materials to be ranked.
AFM, combined with an inverted optical microscope, was used to study the growth of individual surfaces of calcite (104) microcrystals, which were shown to exhibit a single spiral growth hillock. Growth rates of the individual spirals were found to be dependent on solution supersaturation and controlled by diffusion of species to the crystal from bulk solution. The step patterns formed were shown to depend strongly on the supersaturation. This methodology also allowed the effects of maleic acid, as a crystal growth inhibitor, to be monitored.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QD Chemistry | ||||
Library of Congress Subject Headings (LCSH): | Calcium carbonate, Crystallization, Crystal growth, Atomic force microscopy, Biofilms | ||||
Official Date: | September 2005 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Chemistry | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Unwin, Patrick R.; Macpherson, Julie | ||||
Format of File: | |||||
Extent: | vii, 249 leaves : illustrations | ||||
Language: | eng |
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