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The synthesis of cementitious compounds in molten salts

Sheikh, RA; (2016) The synthesis of cementitious compounds in molten salts. Doctoral thesis , UCL (University College London). Green open access

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Abstract

This thesis describes an investigation into the synthesis of cementitious compounds in molten salts. These compounds are produced in energy-intensive industries (EIIs), such as the cement process, and are responsible for emitting significant quantities of carbon dioxide (CO2) emissions. Molten salt synthesis (MSS) involves dissolving compounds in a molten salt and reacting in solution. If the MSS of cementitious compounds can occur at lower temperatures than EIIs, this could lead to fewer quantities of CO2 emissions. The cementitious compounds selected for this investigation were dicalcium silicate (β-Ca2SiO4), tricalcium silicate (Ca3SiO5), disodium metasilicate (α-Na2SiO3), tetrasodium orthosilicate (β-Na4SiO4) and the salt selected was sodium chloride (NaCl). Initally, the dissolution behaviour of the reactants; silicon dioxide (SiO2), calcium carbonate (CaCO3) and sodium carbonate (Na2CO3) were investigated in NaCl, using calorimetry, potentiometry, X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The XRD and SEM data suggested Na2CO3 and CaCO3 decomposed to CO2, calcium oxide (CaO) and sodium oxide (Na2O), and SiO2 only dissolved with a limited solubility. The calorimetric data suggested the heat of mixing (Hmix) for Na2CO3 in molten NaCl illustrated a maximum positive contribution of ~2 kJ mol-1, and its phase diagram illustrated a eutectic point at 638C, 47 mol% Na2CO3. The potentiometric data suggested the solubility products (Ksp) for Na2O and CaO in NaCl were -log 1.58 and -log 1.1, demonstrating reasonably high solubilities in comparison to other melts. This information suggests the MSS of cementitious compounds could be possible in industry. Then, the MSS of cementitious compounds were investigated using SEM and XRD and were depicted on predominance diagrams. The XRD and SEM data suggested β-Ca2SiO4 and α-Na2SiO3 can be produced, however Ca3SiO5 requires higher temperatures (>1100ºC). This suggests other cementitious compounds can be produced in this manner, thus paving the way for producing complete products, such as cement.

Type: Thesis (Doctoral)
Title: The synthesis of cementitious compounds in molten salts
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering
URI: https://discovery.ucl.ac.uk/id/eprint/1474690
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