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SOL-GEL SYNTHESIS OF ORTHOSILICATES
The objective of the research is the sol-gel preparation of the crystalline or amorphous orthosilicates of some bivalent metals, namely, copper orthosilicate (Cu2SiO4), which seems to be a quite efficient catalyst, although it has not been synthesized yet. The main obstacles that prevent the sol-gel synthesis of orthosilicates include high metal/silica molar ratios in precursor mixtures. They cause (i) formation of the crystalline of metal oxides at intermediate stages of synthesis and (ii) a substantial difference between intermediate and final anion structures because of the polycondensation of silicate anions at the stages of gelation and drying. This can result in a double-stage character of synthesis, involving formation of metal polysilicates and a metal oxide as intermediates. The synthesis pattern employed by the authors was based on a combination of "anti-polycondensation" actions that had three components involved: a) 3-aminopropylsilanetriol, a water-soluble silica precursor that demonstrates low polymerizability and high stability in any ambience; b) triethanolamine, a high-boiling chemically active agent that prevents metal hydroxide precipitation and inhibits polycondensation at initial stages of heat treatment; c) methyl triethylammonium hydroxide, a strong component that inhibits polycondensation processes at the stage of the solution drying. Metal nitrates M(NO3)2 (M=Cu, Mg, Zn, Cd) were employed as metal oxide precursors, while water was the solvent. Coating solutions were applied to glass, silica glass or silicon substrates and heated to 300, 500, 700 and 900 °C. The resulting silicate fi lms were studied using UV-VIS spectroscopy, FTIR, XPS and XRD methods. Molecular mass distribution of silicate anions in the films was measured using the molybdate method. As a result, the synthesis pattern proved efficient in the synthesis of orthosilicates of bivalent metals. Amorphous copper silicates with the anion structures close to the orthosilicate (basicities up to 1.96), were prepared in the form of thin films after heating up to 500 °C. At 700…900 °C, they decomposed with the formation of CuO. Only in the case of CuZnSiO4 the polymerization grade of silicate anions was suffi ciently low, if the ternary samples are taken into consideration (the anion basicity was about 1.7).
SOL-GEL SYNTHESIS OF ORTHOSILICATES
The objective of the research is the sol-gel preparation of the crystalline or amorphous orthosilicates of some bivalent metals, namely, copper orthosilicate (Cu2SiO4), which seems to be a quite efficient catalyst, although it has not been synthesized yet. The main obstacles that prevent the sol-gel synthesis of orthosilicates include high metal/silica molar ratios in precursor mixtures. They cause (i) formation of the crystalline of metal oxides at intermediate stages of synthesis and (ii) a substantial difference between intermediate and final anion structures because of the polycondensation of silicate anions at the stages of gelation and drying. This can result in a double-stage character of synthesis, involving formation of metal polysilicates and a metal oxide as intermediates. The synthesis pattern employed by the authors was based on a combination of "anti-polycondensation" actions that had three components involved: a) 3-aminopropylsilanetriol, a water-soluble silica precursor that demonstrates low polymerizability and high stability in any ambience; b) triethanolamine, a high-boiling chemically active agent that prevents metal hydroxide precipitation and inhibits polycondensation at initial stages of heat treatment; c) methyl triethylammonium hydroxide, a strong component that inhibits polycondensation processes at the stage of the solution drying. Metal nitrates M(NO3)2 (M=Cu, Mg, Zn, Cd) were employed as metal oxide precursors, while water was the solvent. Coating solutions were applied to glass, silica glass or silicon substrates and heated to 300, 500, 700 and 900 °C. The resulting silicate fi lms were studied using UV-VIS spectroscopy, FTIR, XPS and XRD methods. Molecular mass distribution of silicate anions in the films was measured using the molybdate method. As a result, the synthesis pattern proved efficient in the synthesis of orthosilicates of bivalent metals. Amorphous copper silicates with the anion structures close to the orthosilicate (basicities up to 1.96), were prepared in the form of thin films after heating up to 500 °C. At 700…900 °C, they decomposed with the formation of CuO. Only in the case of CuZnSiO4 the polymerization grade of silicate anions was suffi ciently low, if the ternary samples are taken into consideration (the anion basicity was about 1.7).
SOL-GEL SYNTHESIS OF ORTHOSILICATES
Malyavskiy Nikolay Ivanovich (author) / Pokidko Boris Vladimirovich (author)
2012
Article (Journal)
Electronic Resource
Unknown
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