Modifying chemical composition of the fine Ni 4 Nb 2 O 9 powders using chloride melts as reaction medium
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Research Letter
Modifying chemical composition of the fine Ni4Nb2O9 powders using chloride melts as reaction medium V. Khokhlov and I. Zakir’yanova, Institute of High-Temperature Electrochemistry, 20 Akademicheskaya Str., 620990 Ekaterinburg, Russia; Ural Federal University, 19 Mira Str., 620002 Ekaterinburg, Russia V. Dokutovich, G. Shekhtman, B. Antonov, I. Korzun, S. Korotkov, A. Pankratov, and N. Moskalenko, Institute of High-Temperature Electrochemistry, 20 Akademicheskaya Str., 620990 Ekaterinburg, Russia Address all correspondence to V. Khokhlov at [email protected] (Received 14 June 2019; accepted 4 September 2019)
Abstract Thermal stable chloride melts were used as the reaction medium for modifying the chemical composition of complex oxides ensuring a marked improvement of their working properties. This paper discusses the original results of the direct effect of molten KCl–CoCl2 mixtures on the fine Ni4Nb2O9 powders under argon- and oxygen-containing gaseous atmospheres at 500 °C. The initial Ni4Nb2O9 powder and the reaction products were studied in detail using the differential scanning calorimetry, thermogravimetry, x-ray diffractometry, Raman and IR spectroscopies, scanning electron microscopy, energy-dispersive x-ray spectroscopy, chemical analysis, and conductometry which demonstrated clearly the formation of the thermal stable single-phase Ni–Co niobates.
Introduction
Experimental
The A4Nb2O9 compounds, where A = Ni, Co, Mg, Mn, and Fe, and their mixtures possess a wide range of dielectric, magnetoelectric, and physicochemical properties due to the peculiarities of crystalline structure of the corundum-type compounds which can be described as a network of edge- and corner-sharing [AO6] and [NbO6] octahedral units.[1–3] The nickel diniobate-based ceramics already has a variety of applications as the catalysts for oxidative dehydrogenation of hydrocarbons,[4–7] as the electrical gas sensors[8] and electrochemical ion-selective sensors for the analysis of technological solutions,[9] as the capacitors and varistors.[10] New mixed nickel niobates (Ni–Nb–M–O, where M = Co, Mo, V, W, Cr, Mn, and REM) are considered as promising materials for wireless communication technologies.[3,11,12] The mixed nickel niobate-based functional products mentioned in the above papers were synthesized by the conventional solid-state reaction method from the proper metal oxides at the temperatures above 1000 °C. Molten salts are the promising reaction media to synthesize the nanosized complex metal oxides and to modify a chemical composition of both powder products and sintered ceramics at the temperature range of 400–700 °C.[13–15] The aim of this study is to investigate and demonstrate a new way of changing the chemical composition of nickel niobate powders in the thermal stable chloride melt containing Co2+-modifying ions as a typical example of the molten salt reaction medium.
In this section, we discuss in detail the synthesis ways of the main test subject and salt reaction medium as well as the peculiarities of
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