Structural evolution and synthesis mechanism of ytterbium disilicate powders prepared by cocurrent chemical coprecipitation method

Abstract

Ytterbium disilicate powders were synthesized by cocurrent chemical coprecipitation method. The in uence of Si/Yb molar ratio and calcination temperature on compositions and structures of Yb 2 Si 2 O 7 products were investigated. The formation mechanism and thermal behavior of precursor as well as the phase evolution of Yb 2 Si 2 O 7 were also discussed in depth. Results show that pure β-Yb 2 Si 2 O 7 powders with nanoscale size can be obtained from the precursor with Si/Yb molar ratio of 1.1 after being calcinated at temperatures above 1200 ℃. The Yb 2 Si 2 O 7 precursor is an amorphous polymer crosslinked with -[Si-O-Yb]-chain segments which are formed though Yb atoms embedding in the -[Si-O-Si]network. After a continuous dihydroxylation and structural ordering, the amorphous precursor transformed to α-Yb 2 Si 2 O 7 crystals by atomic rearrangement. Elevated calcination temperature can induce to the coordination structures and environment evolutions of structural units and then converted to stable (Si 2 O 7 ) groups and (YbO 6 ) polyhedrons, which results in the formation of β-Yb 2 Si 2 O 7 .

Chemical co‐precipitation synthesis of high‐entropy rare‐earth silicate nanopowders

“…Below 773 K, the precursor underwent a significant weight loss (∼16%), accompanied by a broad exothermic peak shown in the DSC curve. The weight loss and exothermic phenomenon of the precursors should be attributed to the evaporation of adsorbed water and residual solvents, as well as the dehydration of bound water 32 . Subsequently, at 1311 K, a small exothermic peak is present, mainly induced by the phase transition of HEREMs.…”

“…It is worth mentioning that the generated H 2 SiO 3 precipitation in Equation () does not dissolve in the dilute ammonia, which is the prerequisite of the reaction occurring between RE(OH) 3 and H 2 SiO 3 41 . Due to the influence of the RE/Si molar ratios and the pH values on the electric charge and ion coordination in solution, the proceeding of the reaction between RE(OH) 3 and H 2 SiO 3 was mainly dependent on these two factors 32 . The corresponding reactions to form precursors in this system are as follows: $$$$\begin{eqnarray}&& 1/2{\mathrm{Er}}{\left( {{\mathrm{OH}}} \right)_3} + 1/2{\mathrm{Tm}}{\left( {{\mathrm{OH}}} \right)_3} + 1/2{\mathrm{Yb}}{\left( {{\mathrm{OH}}} \right)_3} + 1/2{\mathrm{Lu}}\nonumber\\ &&{\left( {{\mathrm{OH}}} \right)_3} + {{\mathrm{H}}_2}{\mathrm{Si}}{{\mathrm{O}}_3} \to {\mathrm{amorphous - }}{\left( {{\mathrm{E}}{{\mathrm{r}}_{1/4}}{\mathrm{T}}{{\mathrm{m}}_{1/4}}{\mathrm{Y}}{{\mathrm{b}}_{1/4}}{\mathrm{L}}{{\mathrm{u}}_{1/4}}} \right)_2}\nonumber\\ &&{\mathrm{Si}}{{\mathrm{O}}_5}\left( {{\mathrm{amorphous - HEREM}}} \right) + 4{{\mathrm{H}}_2}{\mathrm{O}} \end{eqnarray}$$$$…”

“…It should be noted that amorphous‐HEREM refers to the amorphous network structure formed in the precursors 32,42 . During the formation process of the precursors, some Si–O–Si bonds in H 2 SiO 3 molecules could be broken by RE 3+ cations and connect with RE 3+ to form Si–O–RE bonds.…”

Construction of Shape‐Controlled MgO Microstructures by Natural Bischofite for Cost‐Efficient Dye Adsorption

“…Chemical coprecipitation method can provide good crystallinity and extremely uniform particle size and also it has good repeatability, uninvolved harmful organic solvents, short synthesis cycle and low cost advantages, and reaction is easily controlled. [22] Qaidam Basin has an abundance of Salt Lake resources, situated in northwest China's Qinghai Province. Some of the most well-known ones are Qarhan Salt Lake, Chaka Salt Lake, East Taijinar Salt Lake and West Taijinar Salt Lake.…”

“…Commonly, the reported methods for the preparation of MgO structures include sol‐gel, [17] chemical coprecipitation, [18] combustion, [19] hydrothermal [20] and microwave‐assisted [21] synthesis methods, etc. Chemical coprecipitation method can provide good crystallinity and extremely uniform particle size and also it has good repeatability, uninvolved harmful organic solvents, short synthesis cycle and low cost advantages, and reaction is easily controlled [22] …”