Raman spectroscopy during formation of silica gel

Different nanostructured materials are used for a variety of applications in modern civil engineering. There are two practical techniques of nanoscale structuring of construction materials. The nanostructured materials can be produced by introducing pre-synthesized nanoobjects (nanoparticles, nanotubes etc.) directly into the composition. However, this approach has several disadvantages: the extensive treatment should be applied to provide the homogeneous distribution of nanoobjects over the composition and the constructional material; nanoparticles as independent objects may have negative impact on human health and cause environmental problems. As an alternative, the nanoscale objects can be synthesized in the bulk material during the structure forming process. Such approach can be considered as preferable, as it resolves almost each of the process-related and environmental problems of nanotechnology in construction material science. The essence of this approach is to use reagents (called precursors) that are capable of undergoing physical and chemical transformations and synthesizing nanoscale structures engaged in the structure formation of a construction material. The well-known sol-gel process is the most prominent way to produce both nanocomposites and precursors. In construction material science, one of the most promising application of nanotechnology is to manufacture special-purpose coatings — hydro- and oleophobic, self-cleaning, biocidal, photochromic. The coating usually includes both continuous and functionally active dispersed phases. The continuous phase (matrix) can be made of organic (either thermoplastic or thermoset polymer) or inorganic compound, such as silica-based composition. There are many ways to produce matrices based on nano-silica. One of these ways is to use catalytic hydrolysis of tetraethyl orthosilicate Si(OC 2H 5) 4 (TEOS) dissolved in ethanol. Depending on the substrate and desired operational properties, the appropriate state of the matrix can be either crystalline or amorphous. The transition between states can be controlled by proper selection of thermal treatment. In the present work the Raman spectroscopy is used both to examine the transition and to observe the presence of sediment of solvent. It is shown that for the mentioned production strategy the transition from amorphous to crystalline state corresponds to the temperatures higher than 500°C. Therefore this temperature can be recommended as an acceptable temperature of thermal treatment.