Chemistry and Chemical Engineering / 7. Inorganic Chemistry

Usoltseva N.V., D.Sc. Korobochkin V.V.

Tomsk Polytechnic University, Tomsk, Russia

The Environmental Influence of Substances Obtained by Nonequilibrium Electrochemical Copper and Aluminium Oxidation on Liquid-Phase Carbonization

It is known that the heightened reactivity of nanomaterials given by high specific surface area and uncompensated texture defects is the reason of intensive interaction of nanomaterials with compounds contained in the environment. In some cases, steps should be taken to prevent adverse effect of environment on nanomaterial [1]. However, there may be positive effect on material properties from interaction of nanomaterials with such compounds.

At present nanosized oxides and oxide systems are the focus of attention of scientists. Nonequilibrium electrochemical oxidation is one of the promising methods of metal oxide synthesis [2]. This method was used by us for copper-aluminium oxide system synthesis [3].

Copper-aluminium oxide system created by electrolysis interacts with dissolved carbon oxide during ageing under solution forming basic carbonates [4]. As it was established earlier there are not any adverse effects of basic carbonates on characteristics of obtained oxide system [5]. On the contrary, the pore structure characteristics of oxide system obtained from basic carbonates are better than those of system created without carbonization. At the same time uncontrolled variations of pressure, humidity of the air, content of carbon oxide are the reason of fluctuation of composition of electrochemical copper and aluminium oxidation product. XRD patterns of the interaction product of copper-aluminium oxide system with compounds contained in the atmosphere at the different atmospheric conditions are shown in the fig. 1.

At increased humidity and carbon (IV) oxide content basic copper-aluminium carbonate (Cu-Al/LDH), basic copper carbonate (Cu₂(OH)₂CO₃) and boehmite (AlOOH) are formed. The only basic copper-containing carbonate is formed under conditions of decreased humidity and carbon oxide content. Meanwhile a part of copper (I) oxide is oxidized to copper (II) oxide in the solution. At present it is difficult to describe boundary conditions that ensure the formation of basic copper carbonate. These conditions depend on correlation of the above-mentioned characteristics of environment.

Fig. 1. XRD pattern of products of electrochemical copper and aluminium oxidation formed under conditions of comparative increased (1) and decreased (2) values of air humidity and carbon (IV) oxide content

It seems that not so mild conditions are necessary for basic copper carbonate formation in comparison with basic copper-aluminium carbonate. Interaction of semiproducts and products of metal oxidation in conditions of electrolysis is believed to be the reason of existence of basic copper carbonate or copper (II) oxide along with boehmite according to air conditions. As a result there are two forms of copper (I) oxide in the product of electrolysis that are more and less intensively associated with boehmite.

Porosity of material and its heat resistance strongly depend on crystalline structure. Hence dependence of composition of oxide system precursor on atmospheric conditions may be the reason of uncontrolled variation of pore structure characteristics of oxide system.

Actually, mixed metal oxides with high heat resistance, big specific surface area and mesoporosity are formed by heat treatment of Cu‑Al/LDH. Such textural characteristics are favorable for the catalytic and sorption materials [6]. Basic copper carbonate also has a positive affect on properties of oxides obtained from it. However it is not obvious.

Thus, we believe that there is sufficient reason for further research aimed at support of permanency of atmospheric conditions that is in contact with product of electrochemical oxidation. It should be mentioned that heightened reactivity of nanosized product of electrochemical copper and alumunuim oxidation may be the reason of product pollution by various compounds contained in the ambient air.

The above-mentioned restrictions allow talking about suitability of creation of induced environment that has advantage of natural one (contain carbon oxide) and does not have disadvantage (contain extraneous substances). Change in humidity and pressure of air, content of carbon oxide gives an opportunity to select conditions that are more suitable for basic carbonate formation than those in natural environment.

In spite of the conclusion that it is necessary to avoid an interaction between product of electrolysis and environment this study is very useful. It is due to the opportunity expanding of property change by gas process. The fact that gas carbonization takes place in the mild conditions allows believing that this method of improvement of electrolysis product is more promising.

Literature:

1. Fedorov S. G., Guseinov Sh. L., Storozhenko P. A. Nanodispersed Metal Powders in High-Energy Condensed Systems // Nanotechnologies in Russia. – 2010. – Vol. 5. – Nos. 9–10. – Pp. 565–582.

2. Korobochkin V.V. Processes of Nanodispersed Oxide Obtaining Using Alternating Current Electrochemical Oxidation of Metals: diss. … doctor of engineering science. – Tomsk, 2004. – 273 p.

3. Usoltseva N.V., Korobochkin V.V. Alternating Current Electrolysis as a Method of Copper-Aluminium Oxide System Synthesis // Materials of the I^st International Russian-Kazakhstan Conference on Chemistry and Chemical Engineering. – April 26‑29, 2011. – Tomsk: TPU Press, 2011. – Pp. 205–207.

4. Usoltseva N.V. Investigation of Cu–Al–O System Carbonization in Air // Abstracts of the VI^th National Conference of Young Scientists, PhD and Students with the International Participation “Mendeleev–2012”. Inorganic chemistry. – April 3–6, 2012. – SPb.: Solo press, 2012. – Pp. 330–332.

5. Usoltseva N.V., Korobochkin V.V. Thermal stability of copper-aluminium oxide system precursors obtained by electrochemical synthesis // Materials of the II^nd International Kazakhstan-Russian Conference on Chemistry and Chemical Engineering dedicated to the 40^th Anniversary of academician E.A. Buketov KarSU. – Vol. I. – February 28 – March 2, 2012. – Karaganda: Publishing House of KSU, 2012. – Pp. 259-261.

6. Handbook of Layered Materials. Edited by Scott M. Auerbach, Kathleen A. Carrado, Prabir K. Dutta. – N. Y.: Marcel Dekker, Inc., 2004. – 646 p.