In this study, the effect of Na 2 O on the sintering and melting behavior of representative CaO-SiO 2 -CaF 2 slag were synthetically investigated by TG-DSC, DIL, XRD, SEM, XPS, and BET. As expected, most shrinkage of CaO-SiO 2 -CaF 2 slags with and without Na 2 O during the sintering process originated from solid-phase sintering, and the formation temperature of cuspidine as the sintering phase was reduced by Na 2 O to 550 °C. While Na 2 O also transformed Ca 4 Si 2 O 7 F 2 to Ca 2 NaSiO 4 F at 650 °C–880 °C and caused unexpected volume expansion, owing to increased cell volume and corresponding pore expansion. Moreover, Na 2 O reduced the melting point of CaO-SiO 2 -CaF 2 slag and promoted the volatilization of fluoride by changing the final phase before melting.
Yanhui Zhang,Yun Yang,Xifa Long,Hualing Tian,Xiaofeng Gu,Zhi Su
A new alkali/alkali-earth metal pyrophosphate fluoride Na 2 Mg 2 P 2 O 7 F 2 without the structural disorder in the cuspidine family has been successfully prepared in the sealed system. Na 2 Mg 2 P 2 O 7 F 2 crystallizes in the space group P 2 1 / c (No. 14) of the monoclinic crystal system . The structure of Na 2 Mg 2 P 2 O 7 F 2 is shown to be an intricate three-dimensional (3D) framework that consists of the 2D layers [Mg 4 O 12 F 2 ] ∞ and the 1D chain [Na 2 O 8 F 3 ] ∞ interlinked by isolated P 2 O 7 groups, which demonstrates the precise coordination environment of cations and the framework in inorganic alkali/alkaline earth metal pyrophosphate fluoride. By comparing with other phosphate structures, we found that the introduction of F is conducive to the consistent arrangement of anionic group P 2 O 7 and enriches the diversity of cationic polyhedra. In addition, first-principle theoretical studies were also carried out to aid the understanding of microstructures, and Na 2 Mg 2 P 2 O 7 F 2 possesses a large band gap (7.1 eV) and has potential applications in the deep ultraviolet region.
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