CC BY
27iSHS 2019
Moscow, Russia
SYNTHESIS OF NEW MIXED NIOBIUM-TUNGSTEN OXIDE BRONZES
M. K. Kotvanova*" and I. A. Sologubova"
aYugra State University, Khanty-Mansiysk, 628012 Russia
*e-mail: kotvanova@mail.ru
DOI: 10.24411/9999-0014A-2019-10070
One of the promising areas in chemistry is the synthesis of materials with a given set of properties. The basis of such materials are various mixed metal oxides including oxide bronzes containing transition metal in different oxidation states. The structures of simplest tungsten bronzes are studied and well-known. These are octahedral structures with octahedra WO6 sharing corners to form a 3D framework with tunnels. Some of the tunnels can be occupied by alkali metal.
The great interest of researchers in oxide bronzes is due to the correct combination of mechanical, physical, and chemical properties. They have unusual electronic properties, chemical and thermal stability, and extreme corrosion resistance [1]. In addition, they are cheap and non-toxic. Recent studies have shown that oxide bronzes exhibit photothermal properties [2], and mixed tungsten bronzes are also promising thermoelectric materials which can play an important role in future power management [3].
At the same time, the practical application of these compounds is hampered by the problems of their synthesis. All currently known synthesis methods are extremely energy-intensive and time-consuming.
It is known SHS are distinguished by economics, simplicity of operation, and low energy requirements. In recent years, we have shown the possibility of producing oxide bronzes of titanium, molybdenum, and tungsten in the SHS mode using various exothermic additives, particularly copper oxide (II).
This work is devoted to the synthesis of mixed oxide bronzes in the K-Nb-W-O system. Oxide bronze K0.5(NbW)5O14 was prepared by SHS of stoichiometric mixture 2WO3:Nb2O5:KI: 0.5CuO (Fig. 1). The initial substances were ground in an agate mortar until smooth and thoroughly mixed. The tablets measuring 1.5 cm were formed using ethanol as a binder. The SHS product was a dark blue substance. X-ray powder diffraction pattern for orthorhombic K0.5(NbW)5O14 is shown in Fig. 2 in comparison with our data for the hexagonal tungsten bronze K0.2WO3 (Fig. 3) that we prepared earlier by SHS [4].
It is interesting that the similar phases (hexagonal bronze Cs0.32WO3 and orthorhombic bronze Cs0.5Nb2.5W2.5O14) were obtained by the authors [5] as a result of hydrothermal synthesis.
Fig. 1. Synthesis of K0.5(NbW>O14. M. K. Kotvanova and I. A. Sologubova 193
XV International Symposium on Self-Propagating High-Temperature Synthesis
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Fig. 2. X-Ray diffraction pattern of the sample Fig. 3. X-Ray diffraction pattern of the K0.2WO3 (SHS). • - K0.2WO3 - - W03 samPle Ko.5(NbW)5Oi4 (SHS).
• - K0.5(NbW)Oi4 WO3
Thus, new mixed niobium-tungsten oxide bronze was obtained. The addition of niobium leads to the structure transformation from hexagonal to orthorhombic.
1. M.K. Kotvanova, S.S. Pavlova, N.N. Efremova, Nanocrystals of oxide bronzes of titanium, molybdenum, tungsten as components of anti-corrosion coatings, Rus. J. Chem. Chem. Technol., 2013, vol. 56, no. 9, pp.111-116.
2. P.Yu. Gulyaev, M.K. Kotvanova, A.I. Omel'chenko, Nanotechnologies of the treatment and production of complex transition metal oxides with high photothermal effect, Inorg. Mater. Appl. Res., 2018, vol. 9, no. 3, pp. 540-545.
3. M.K. Kotvanova, S.S. Pavlova, E.N. Sobol, A.I. Omelchenko, P.Y. Gulyaev, Photothermal effects of laser heating iron oxide and oxide bronze nanoparticles in cartilaginous tissues, Nanotechnol. Russ, 2012, vol. 7, nos. 3-4, pp. 127-131.
4. M. Kotvanova, N. Blinova, P. Gulyaev, A. Dolmatov, S. Pavlova, Evaluation of combustion temperature and combustion speed of the process of SH-synthesis of titanium oxide bronze, In Book Int. Symp. on Self-Propag. High-Temp. synth. SHS XIII, 2015, pp. 160-161.
5. M.D. Soriano, E. Garcia-Gonzalez, P. Concepción, C.B. Rodella, J.M. L. Nieto, Self-organized transformation from hexagonal to orthorhombic bronze of Cs-Nb-W-O mixed oxides prepared hydrothermally, Cryst. Growth Des., 2017, vol. 17, no. 12, pp. 6320-6331.
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M. K. Kotvanova and I. A. Sologubova
