Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310573
Title: Calcium silicate hydrate : crystallisation and alkali sorption
Author: Hong, Sung-Yoon
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2000
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Abstract:
Homogeneous single C-S-H gels have been prepared for the investigation of alkali binding potential and crystallisation. A distribution coefficient, Rd, was introduced to express the partition of alkali between solid and aqueous phases at 25°C. Rd is independent of alkali hydroxide concentration and depends only on Ca:Si ratio over wide ranges of alkali concentration. The trend of numerical values of Rd indicates that alkali bonding into the solid improves as its Ca:Si ratio decreases. Reversibility is demonstrated, indicating a possibility of constant Rd value of the material. Al has been introduced to form C-A-S-H gels and their alkali sorption properties also determined. Al substituted into C-S-H markedly increases Rd, indicating enhancement of alkali binding. However, the dependence of Rd on alkali concentration is non-ideal with composition. A two-site model for bonding is presented. Crystallisation both under saturated steam and 1 bar vapour pressure has been investigated. It has been shown that heat treatment by saturated steam causes crystallisation of gels. The principal minerals obtained were (i) C-S-H gel and Ca(OH)2 at ~55°C, (ii) 1.1 nm tobermorite, jennite and afwillite at 85-130°C, and (iii) xonotlite, foshagite and hillebrandite at 150-180°C. Properties of crystalline C-S-H were also reported for reversible phase transformation, pH conditioning ability, seeding effect and solubility. At 1 bar pressure, crystallisation is slower than in saturated steam due to lower water activity. Tobermorite-like nanodomains develop during reaction at low Ca/Si ratios. In some Ca-rich compositions, Ca(OH)2 is exsolved and occurs as nano-sized crystallites.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.310573  DOI: Not available
Keywords: GELS; CALCIUM SILICATES; HYDRATES; CRYSTALLIZATION; CHEMICAL REACTION KINETICS; DISTRIBUTION FUNCTIONS; PH VALUE; CHEMICAL PREPARATION Chemistry, Physical and theoretical Radioactive wastes Radioactive wastes
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