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Title: Single crystal depositions of portlandite
Author: Griffiths, Graham L.
ISNI:       0000 0004 2724 3571
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2012
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This thesis has developed a method for generating single crystals of the mineral port- landite. These crystals were formed on a silicon wafer substrate by drying a filtered solution of calcium hydroxide under nitrogen, using a specially developed glass cell. The resulting precipitate was confirmed to be calcium hydroxide using a combination of Raman spec- troscopy, SAED and XRD. The specimens were characterised using SEM, TEM and FIB and were seen to be hexagonal and prismatic with an aspect ratio 1:2. Additional facets, of the (1011) index, were also seen. In addition, nucleation sites were generated by rapidly drying the calcium hydroxide solution on a heated silicon wafer substrate. The resulting sites produced partially orientated growth of subsequent depositions of portlandite, with the (0001) facets parallel to the substrate. Forced carbonation - in pure CO2 with 97% relative humidity - of these portlandite crystals yielded a solid state reaction, without the necessity of excess water to act as a solvent. Evidence of an hydrated and amorphous form of calcium carbonate was seen, with an increase in volume of approximately 4.3 times in the first hour of carbonation. This was characterised using SEM, TEM and SAED and confirmed to be calcium carbonate using Raman, with a characteristic peak of shift between 1081cm-1 and 1085cm-1. The presence of calcite in the reaction products was also confirmed using XRD. Using the same drying cell, a filtered calcium hydroxide solution was applied to the exterior and interior surfaces of three varieties of brick. Additional fine, acicular features were seen and conglomerations of which were cross-sectioned using the focussed ion beam, showing a thickness of approximately O.lp,m. Additional high surface area, floret-type precipitate features were characterised on the surface of brick substrates, following calcium- hydroxide deposition. This was achieved using SEM, and additionally using EDX. Such features were seen to consist primarily of calcium.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available