On the Plasma-Electrolytic Formation of Porous Films of Titanium Oxide
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Plasma-Electrolytic Formation of Porous Films of Titanium Oxide M. Yu. Makhmud-Akhunovа, * and A. A. Adamovichа аUlyanovsk
State University, Ulyanovsk, 432017 Russia *e-mail: [email protected]
Received November 25, 2019; revised December 22, 2019; accepted December 26, 2019
Abstract—In this work, the features of the formation of electrolyte plasma and its influence on the structure of the surface of Ti are investigated. It is revealed that the formation of plasma in the process of the anodic polarization of Ti in an aqueous solution of sulfuric acid leads to the formation of a porous oxide on the surface. It is shown that the porous nature of the formed oxide layers predetermine the specific behavior of the plasma. The topology of the surface of the formed porous titanium-oxide film is studied by scanning-electron- and atomic-force microscopy. It is established that the distribution of pores on the surface is of a complex stochastic nature and their maximum sizes did not are around 200–300 nm. Keywords: titanium, anodic oxidation, porous oxide, mechanism of pore formation, nanostructuring, electrolyte plasma, thin films DOI: 10.1134/S1027451020030349
INTRODUCTION A method for the electrochemical anodic processing of metals and semiconductors is actively developed in terms of simplicity, low cost and ability to control the parameters of the formed layers and structures [1]. For example, a feature of the anodic treatment of valve metals, including Ti, in acidic electrolytes is the growth of a porous oxide layer [2]. Compared with other nanostructures, one-dimensional dioxide nanotubes with an average diameter of 50 to 200 nm [3] are formed on the surface of titanium, which have a number of advantages: a higher specific surface area, high mechanical strength, high adsorption capacity, photoelectric-conversion efficiency, and photocatalytic activity [4–7], and also have good biocompatibility [8–10]. Nevertheless, despite the wide range of practical applications of porous films, the driving force and the mechanism of pore formation and ordering are still not clear, which may be due to the simultaneous influence of many factors on the growth of the oxide film, as well as a lack of suitable research methods for studying the quantitative-ordering process. It is also characteristic that most of the works are devoted to the preparation of porous titanium-oxide layers in electrolytes containing fluoride ions [11–15]. In this paper, we describe the features of the formation of porous titanium oxide from the point of view of the uneven redistribution of field force lines over the sur-
face, as well as the excitation and formation of electrolyte plasma. EXPERIMENTAL Titanium of the VT1-00 grade (99.7% purity) of cylindrical shape (∅ 5.7 mm) was used to study the features of plasma electrolytic oxidation (PEO). Prior to the PEO process, the samples were subjected to mechanical grinding and polishing to a mirror state. In this work, we studied titanium processing in a 1-M aqueous solution of sulfuric acid under various modes of
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