Structural and Morphological Features of Polycrystalline Aluminum Oxide Surface after Nanocoating with Titanium Oxide of
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ctural and Morphological Features of Polycrystalline Aluminum Oxide Surface after Nanocoating with Titanium Oxide of Different Thickness N. V. Zakharovaa,*, K. T. Akkulevaa, and A. A. Malygina a St.
Petersburg State Institute of Technology (Technical University), St. Petersburg, 190013 Russia *e-mail: [email protected] Received May 18, 2020; revised May 24, 2020; accepted May 27, 2020
Abstract—Using the molecular layering method, titanium oxide coatings were synthesized on the surface of polycrystalline aluminum oxide plates by alternating treatment with titanium tetrachloride and water vapors. It was shown by means of diffuse reflection electron spectroscopy that at different nanocoating thickness, surface complexes differing in structure are formed: distorted octahedral (alumotitanate), those with tetrahedral titanium coordination, and polyhedra with anatase-like environment of the central atom. The surface morphology changes during the synthesis and after 600 layering cycles the titanium oxide coating covers the entire surface of the initial substrate. Keywords: nanocoating, polycrystalline aluminum oxide, molecular layering, diffuse reflection electron spectroscopy, surface structure and morphology
DOI: 10.1134/S1070363220090133 Aluminum oxide samples of different crystal structure and geometric shape (porous particles, fibers, plates, finished products) are widely used as sorbents, carriers in heterogeneous catalysis, including membrane catalysis, fillers for composite materials, matrices in sensor devices, etc. [1–3]. One of the promising directions for regulating properties of products based on aluminum oxide is the modification of its surface [3–6]. To create solid-phase materials with new properties, chemical nanotechnology based on the molecular layering method is widely used, which makes it possible to perform chemical assembling of surface nanostructures with a strictly specified composition and structure [6–7]. Among widely used modifiers there are titanium oxide nanocoatings on the surface of various solid-phase matrices [7–9]. Compositions based on the known characteristics of bulk titanium dioxide (high dielectric permeability, semiconducting, optical, chemical, etc. properties) are used to create shell pigments and fillers, sorbents, catalysts, protective and optical coatings, semiconductor structures, and also to develop resistive chemical sensors [10–14]. To optimize the preparation of such compositions, it is important to identify the relationship between the structural-chemical, quantitative, and morphological characteristics of the
applied coating and the functional properties of the composite. For example, titanium dioxide in the anatase modification is an active catalyst for dehydration, in the rutile modification it is a dehydrogenation catalyst, and in the case of the simultaneous presence of amorphous, anatase, and rutile modifications, it exhibits increased photocatalytic activity [15]. In gas sensors, TiO2 with the brookite structure has an increased sensitivity to hydrogen as comp
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