The stability of formed CaF₂ and its influence on the thermal behavior of C–S–H in CaO–silica gel waste-H₂O system

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• 作者：Aliona Iljina ; Kestutis Baltakys…
• 关键词：Calcium fluoride ; Calcium silicate hydrate ; Fluoride ions ; Instrumental analysis ; Hydrothermal synthesis
• 刊名：Journal of Thermal Analysis and Calorimetry
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：127
• 期：1
• 页码：221-228
• 全文大小：
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Physical Chemistry; Analytical Chemistry; Polymer Sciences; Inorganic Chemistry; Measurement Science and Instrumentation;
• 出版者：Springer Netherlands
• ISSN：1588-2926
• 卷排序：127

文摘

In this work, the stability of formed CaF₂ and its influence on the thermal behavior of C–S–H in CaO–silica gel waste-H₂O system were investigated. The hydrothermal synthesis of calcium silicate hydrates was performed at 200 °C, when the duration of synthesis and the molar ratios of the primary CaO/SiO₂ mixtures were 0.55 (16 h), 0.66 (48 h), 0.83 (48 h), and 1.0 (48 h). Later on, synthesized products were calcined in a 600–1000 °C temperature range for 30 min. It was determined that fluoride ions, from silica gel waste, participated not only for the formation of CaF₂, but also intercalated into the structure of products during hydrothermal synthesis and, also, exchanged the formation sequence of new compounds. It was found that, during calcination, the chemical composition of synthesized C–S–H affects the stability of formed CaF₂, because it remained stable in the system with C/S molar ratio of 0.55 and 0.66. Meanwhile, in the system with higher C/S molar ratio of 0.83 and 1.0, CaF₂ fully recrystallized into cuspidine. Moreover, it was estimated that the recrystallization processes and the formation of new compounds influenced the morphology of calcined products. In addition, EDX analysis showed that 9.05 mass% of fluorine are present in the crystal structure of calcination products. The obtained results were confirmed by the XRD, STA, FT-IR, and SEM/EDX analysis data.