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Title: Precipitated silicates of group II cations
Author: Lawrence, F. W.
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1983
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The compositions of alkaline earth silicate precipitates made from the double decomposition of sodium silicate with group II metal (Mg, ca, Sr or Ba) nitrates are dependent upon the mole ratio (Na20/SiO2) of the sodium silicate, the metal and the ratio of the metal to silica used in the reaction. Magnesium silicate precipitates contain the largest amount of metal, followed by calcium, strontium and barium in that order. The mole ratio of the precipitates (AO/SiO2), can be related to the charge per silicon in the original sodium silicate solution. The structure of the silicate network becomes less condensed upon moving down group II and as the amount of metal incorporated in it increases. Magnesium silicate precipitates form sheet silicate networks. Calcium silicate precipitates form *C-S-H type hydrates (when CaO/SiO2 >0.8) composed principally of dimeric andpolymeric silicate units. An analagous strontium hydrate forms above 65°C. A pentameric silicate species has been identified in both the semi-crystalline calcium and strontium hydrates. Crystalline barium silicate hydrates are precipitated directly from solution provided the reactant ratios Na2O/SiO2 and BaO/SiO2 are greater than 3 and 2 respectively. Magnesium silicate precipitates develop high surface areas (500-600 m2g 1) upon ageing at increased temperatures (65-90°C). This is attributed to microporosity development. Where C-S-H or its strontium analogue forms, the freeze dried precipitates have low bulk densities and high surface areas compared to the amorphous materials. Barium silicate precipitates and amorphous strontium silicate precipitates have low surface areas (<20 m2g-1). Addition of acids to precipitates in their mother liquors leaches the A2+ ions from the silicates in the order (from lowest to highest pH) Ba'Sr>Ca>Mg. Rapid acidification leads to a complete breakdown of the silicate network, but less silica is solubilised if the acid is added slowly. Cement chemistry nomenclature; C = CaO, S = SiO2, H = H2O
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Inorganic chemistry Chemistry, Inorganic