Elsevier

Journal of Alloys and Compounds

Volume 735, 25 February 2018, Pages 1943-1948
Journal of Alloys and Compounds

Electrochemical deposition regimes and critical influence of organic additives on the structure of Bi films

https://doi.org/10.1016/j.jallcom.2017.11.329Get rights and content

Highlights

  • Determined optimal parameters for production high quality Bi films.

  • Established critical influence of organic additives on Bi films structure.

  • Developed technology for high-speed growth Bi films for practical applications.

Abstract

The electrodeposition of Bi films from an acid perchlorate electrolyte was examined. The influence of various factors on the process of bismuth electrodeposition was investigated. It was determined that electrolyte mixing, temperature, organic additives exert a noticeable influence on the electrode process of the discharge of Bi3+ions in acid perchlorate electrolyte. X-ray diffraction patterns for all samples were indexed to rhombohedral Bi. Coatings with a signified texture (012) are formed in electrolyte without additives. This texture is retained by adding into the electrolyte the organic additives such as cresol, resorcinol, synthanol. With coloring agents (acridine yellow and safranin violet), the growth texture changes and the most intense reflex becomes (110). SEM investigations of coatings surface morphology showed that films electrodeposited without additives, as well as with safranin coloring agent, eventually form crystalline films with a block size of tens of microns, but with different texture growth. The additional presence of such organic additives as syntanol and resorcinol in the electrolyte guarantees flat, dense, close grained and uniform coatings with a thickness of 600 μm at room temperature and the highest cathode current density.

Introduction

Nowadays, the problem Bi deposition has attracted attention of the scientific community because of bismuth's unique electrical, chemical and physical properties. Bismuth has found application in electroanalytical chemistry as a new promising environmentally safe electrode for the heavy metals analysis in place of a poisonous mercury dropping electrode [1], [2], [3], [4]. Bismuth deposited on various metals is used as protective and antifriction coatings due to chemical resistance and mechanical properties [5]. Bismuth sub-monolayers on some noble metal surfaces have shown enhanced catalytic activity, particularly the two-electron reduction of H2O2 to H2O, the reduction of O2 in aqueous fuel cells [6], [7], as well as the oxidation of formic on Pt [8], [9], [10], [11], [12]. The coatings based on bismuth have shown thermoelectric efficiency [13], [14], large magnetoresistance [14], [15], [16], [17] and interesting quantum effects [18]. Bismuth is also used like perspective electrochromic material for electronic devices [19], [20], [21], for resistance and rectifying contacts producing on semiconductors [22] and for films with a giant magnetoresistive effect for magnetic field sensors [23], [24]. Owing to its long charge carrier mean-free paths, bismuth has shown excellent magnetoresistance (150–350%) even at room temperature [25]. Uses of bismuth contents composites offer a very attractive alternative to lead protection from gamma irradiation due to the much more environmentally friendly bismuth [26]. Also bismuth thin films have evinced great interest recently owing to a number of its attractive properties such as highly anisotropic Fermi surface, Dirac valley degeneracy [27], small energy overlap between its valence and conduction bands, small effective charge carrier mass, long charge carrier mean-free path [28]. Much attention of the bismuth deposition literature has focused onto noble metals and growth onto non-metallic substrates, such as glassy carbon [29] and semiconductors [30], [31], [32]. There is a limited number of authors dealing with continuous bismuth films onto metallic substrates by electrodeposition [33], [34]. The main goal of this paper is to investigate high-speed electrolyte that would obtain thick-layer Bi films. Our purpose is the Bi films production by the electrochemical deposition method, because this method has significant number of advantages. First of all, it is high growth rate and the possibility of thick films producing; for another thing, it is good adhesion to the substrate; thirdly, it is the possibility of a controlled microstructure changing (the grain size, film texture and coating density) due to technological parameters variation; finally it is electrolyte composition changing owing to the adding of various organic additives. The technological factors changing (mixing and electrolyte temperature) can critically change the deposition processes parameters with the Bi films formation of different structures and microstructures. This can lead to changes in the physical properties of the obtained bismuth films samples. The organic additives adding of various nature (donors and acceptors of electron density) into the bismuth perchlorate electrolyte can drastically change the electrochemical deposition parameters. It should be emphasized that there are no information or systematic data about the various organic additives influence on deposition technological regimes, crystal structure, microstructure and physical properties of Bi films changing. This paper is dedicated to the study of the technological parameters and organic additives of various nature influence on the structure and microstructure of bismuth films.

Section snippets

Experimental

Samples of Bi films were electrodeposited from an acid perchlorate electrolyte which was prepared from bismuth (III) hydroxide and concentrated perchloric acid solution (concentration – 65%, density – 1.569 g/cm−3) with rapid mixing. Bismuth deposition was produced in galvanostatic regime at the 23–60 °C temperature range onto aluminum substrates 0.4 mm thickness. Bismuth rods were used as anodes. The electrochemical experiments were carried out using a power source B5-78/6 as a stabilized

Results and discussion

Polarization measurements were realized in a perchlorate electrolyte containing 0.174 mol/L Bi(ClO4)3 and 3 mol/L HClO4 at 23, 40 and 60 °C temperature with mixing and without for the purpose of bismuth electrodeposition conditions optimizing. It can be seen that the bismuth deposition begins at ∼30 mV potential (relative to a saturated chloride-silver reference electrode) from the current-voltage curves presented in Fig. 1. These values are close to the bismuth electrode equilibrium potential

Conclusions

The influence of various factors on the process of bismuth electrodeposition was examined. It was established that electrolyte mixing, deposition temperature, organic additives adding exert a noticeable influence on the electrode process of the discharge of Bi3+ ions in acid perchlorate electrolyte. The temperature rise from 23 to 60 °C makes it possible to expand the range of the cathode current density from 23 to 80 mA/cm2, the intensive mixing (600–800 rpm) – up to 100 mA/cm2. Bismuth

Acknowledgment

The work was carried out with financial support of Belarusian Republican Foundation for Fundamental Research (Grant No. T17M-046) and in part from the Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST «MISiS» (№ К4-2017-041 and № К3-2017-059). The work was supported by Act 211 Government of the Russian Federation, contract № 02.A03.21.0011. Additionally the work was partially supported by the Ministry of Education and

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