In this chapter authors present basic principles of process control of sol – gel synthesis of new class of organic-inorganic nanostructured materials on basis of tetraethoxysilane and polyionenes doped by orthophosphoric acid with improved functional properties. The chemical compositions improvement results from complex investigation of morphology, physical and chemical properties. Polyionenes are shown to increase the rate of hydrolytical polycondensation reaction of tetraethoxysilane. Raise of the polyionene molecular weight leads to increasing rate of gel formation process. The polyionenes in silicophosphate sols are stated to prevent crystallization processes occurred in silicophosphate xerogels with silica phosphates and pyrophosphates.
TopBackground
Sol – gel technology allow incorporating organic molecules into an inorganic network, so that they can be combined virtually at any ratio on the molecular level with the formation of hybrid organic–inorganic nanocomposite materials (Brinker & Scherer, 1990). The mechanical properties of such materials can vary from brittle and hard to rubbery depending on the content of organic modifiers in the inorganic network.
In our earlier works we studied the influence of the introduction of small amounts of organic modifiers into silicophosphate matrix which improved the ionic conductivity and operating characteristics of membranes (Sukhyy et al., 2015). For this purpose, we used oligomeric alkylaromatic quaternary ammonium salts, i.e., polyionenes (Brinker & Scherer, 1990), (Yu et al. 2022). These compounds are appeared to be appropriate for the use in sol–gel processes, because they dissolved in water without breaking the homogeneity of the sol–gel system. These modifiers favor the formation of a xerogel that can be subsequently compacted.
The solution of an important practical problem of introduction into production of scientific developments is promoted by creation of scientific bases of formation of multipurpose hybrid organo-inorganic materials by means of the controlled and directed sol-gel synthesis. To achieve this goal, it was necessary to solve a number of specific problems that arose directly from the practical needs of industry:
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Formation of sol-gel by the method of new effective catalytic coatings for metal oxide humidity sensors,
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Creation of proton-conducting membranes that can be operated at temperatures above 100 ºC,
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Creation of highly efficient heat-accumulating materials of sorption type with energy storage density in the range of 1.5-1.7 MJ / kg.
To do this, it was necessary to ensure a favorable course of the hydrolytic polycondensation of tetraethoxysilane in the presence of organic dopants. The introduction of the latter ensures the achievement of the required parameters of the formed materials. It was necessary to optimize the conditions of hydrolysis and polycondensation, both at the stage of sol formation and at the stage of formation of prototypes. An important condition for the preparation of dispersions (sol - metal oxide) are methods of homogenization of the starting components. An obligatory part of the study is the optimization of heat treatment regimes.
To predict the parameters of the created materials it was necessary:
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To study the optimal conditions of hydrolytic polycondensation of Si (OEt)4, H3PO4 precursors in the presence of organic modifiers. This allowed to create new organo-inorganic nanostructured coatings on the surface of semiconductor and dispersed ceramic materials, thin-layer glass-ceramic coatings on metal surfaces and solid electrolyte proton-conducting membranes with a given composition, structure and required technical characteristics,
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To formalize the procedure for selecting components, optimizing their ratio in ash and conditions of sol-gel synthesis systems based on tetraethoxysilane using organic dopants,
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To study the influence of anions and cations of organic modifiers as template agents in sol-gel synthesis of nanoscale coatings on their morphology,
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To establish the relationship between the composition of the sol, the structure of the formed xerogel and the proton conductivity of silicophosphate nanocomposites.